The End of the Road… For Now

This is the last day of Build Blitz. We’ve learned a lot about Rover Ruckus this week, some of which will lead to new products down the road! We hope that there are at least a few things you can take away from Build Blitz.

Yesterday, we started (and finished) the CAD for a robot taking into account some of the lessons learned from our prototype robot. We also went ahead and made some parts that you can download and 3D print to use on your own robot. Those parts include:

As for the robot, here’s what the final product looks like

We made some other general improvements to the robot such as bringing the intake wheels back inside the frame. We also opened up the area between the wheels to make it harder to rake objects out of the Crater, added a legal FTC control system and added guides to keep Minerals in the conveyor.


You can download the full robot CAD assembly here. Note, that there are still some improvements you can make on your own.

For example, we only use 4 of our allotted 8 motors. You can certainly upgrade the 393 Motors to the AndyMark NeveRest, Rev HD Hex or Tetrix TORQUEnado to get a little extra performance out of these mechanisms. Who knows, we might even talk about some of these upgrade during the fall.

Lastly, keep an eye out this Fall for the return of our ‘Tip Tuesday’ series where we’ll talk about tips and cool applications for different VEX products. If you have ideas for a video, or want to know more about a particular product, be sure to share them with us through our Twitter and Facebook channels. We can’t wait to hear from you!  

A Robot In 14.5 Hours

In the engineering design process, it is important to get a fully functioning robot as soon as you can. This allows you to test your strategy, iterate on mechanisms and improve functionality for a longer period of time. Our goal from the start was to develop a robot as fast as we could, and then spending the rest of our time making small tweaks to improve the robot’s appearance and functionality.

We achieved this by combining all our prototypes and making some minor tweaks to improve system integration. The result is below:


We’re still using the same control system we’ve been using since it works as-is, and also wouldn’t require us to do a bunch of rewiring. We will transition this to a legal FTC control system for the final version.

First we wanted to test the intake:

Next we wanted to test our climber. This was the first time we tried this with an actual robot attached to the climber:

16 seconds to deploy, climb and lift isn’t bad for a first attempt. Obviously, there’s lot of room for improvement, but we’re comfortable with this as a starting point. Here’s some more pictures of the climber:




Next we wanted to do a cycle test. Keep in mind, that we literally took prototypes and bolted them together. There’s lots of optimization that was left out for the sake of getting a robot running:

 

Now that we’ve hit this milestone in the process, lets recap our list of goals:


Drivetrain

  • 4-6 wheel drive (Check)
  • Geared between 16:1 and 20:1 (Check)
  • Can easily drive into and out of Crater (Check)


Intake

  • “Touch It, Own It” (Check)
  • Can pick up both Gold and Silver Minerals (Check)
  • Can hold at least 2 Minerals at a time (Check)




Mineral Scoring

  • Depot-only (Check)
  • Scores from the opposite side of intake (Check)


End Game

  • Can attach and lift robot off ground in less than 30 seconds (Check)



Autonomous

  • Can start on Lander (Check)
  • Can lower robot from Lander (Check)
  • Ability to achieve multiple autonomous tasks (Check)
  • Capable of delivering team marker to Depot (Check)


Misc.

  • Short enough to drive under Lander (Check)
  • Ideally between 20-30 lbs (Check)
  • Can be built with one expansion hub (Check)


Some of these goals, such as “capable of delivering team marker to Depot” hasn’t been done in autonomous yet, but the robot is capable of doing this. Our plan for the Team Marker is to make one that is able to fit inside our intake. So to deliver the Team Marker to the Depot, we just drive up and reverse our intake.

Regarding the robot’s weight, we actually are doing pretty well. This prototype is at about 17 lbs, which is below where we wanted to be. This gives us lots of room to strengthen parts of the robot without worrying about exceeding our desired weight.

The top gear of the climber is right at the bottom of the Lander. We actually fit under the Lander, but the pivot point of the arm is a little high, so we can probably lower that pivot point and give us more clearance under the Lander.

Again, remember this is more of a proof of concept robot than the final product. We’re going to go back and CAD then build a final robot that has better system integration and some more general improvements. Here’s a list of things we still need to improve:

 

1.“Raking” objects out of the Crater when we drive in/out.

Right now we have an issue where the drive motors and gearboxes trap objects under the robot. We think we can fix this by doing some more creative motor/gearbox placement


2. Intake wheels making it hard to drive over the Crater

Right now the intake wheels are too far forward. When we try to drive into the Crater those hit first. While it might look like we can climb into the Crater pretty easily, it actually takes a fair amount of work to do it.


3. Arm placement on the robot

You’ll notice when we’re off the ground that the robot lists to one side pretty heavily. That’s fine, but we can make this a little cleaner and easier on the arm if we try to center the arm on the robot so it balances the CG better.


4.Retaining Objects In the Conveyor Belt

You’ll notice in a couple of the videos that we can lose game objects pretty easily. There’s nothing actually retaining these objects on the conveyor. We figured this would be a problem, but we were aiming to get the robot running quickly. This should be an easy fix.

That’s our 14.5 hour robot. We’re now starting to work on the CAD of the final robot. We’re also going to spend some time implementing some of these minor improvements so we can learn as much as we can about them before we finalize them in CAD.

Design: Hanging In There

Robots waiting for the match to start be like…

As we discussed in our Game Analysis post, a robot is that is capable of lowering from the Lander in autonomous and reattaching during the end game is capable of scoring a lot of points in not a lot of time. If done by both robots on an alliance, these actions alone can secure an alliance an additional 160 points. (Or the equivalent of 80 Minerals in the Depot, or 32 in the Cargo Hold)

So, what’s the best way for our MCC robot to negate at least some of this potential point swing in the opposing alliance’s favor? It’s simple, we should be able to perform both of these actions also!

Looking back at our robot feature list, the only requirements for this mechanism are:

  • Can start on Lander
  • Can lower robot from Lander
  • Can attach and lift robot off ground in less than 30 seconds

And remember, we want to be able to accomplish both of these actions with the same mechanism to optimize the robot, and save weight. We know we’re going to have to lift the robot off the ground. However, there are a few approaches we can take to get ourselves off the lander at the start of the match:

1.) Use a dedicated mechanism, such as a claw or latch that opens and drops us off the lander. We would not recommend this with traditional wheels, but the suspension we gain by using Flex Wheels on our drivetrain allows us to get away with this. Regardless this is going to be pretty violent on the robot, so it’s not exactly ideal.

2.) Reuse the mechanism that lifts the robot off the ground. Re-using the same mechanism to achieve multiple tasks is actually a common trick in competitive robotics, and has a lot of benefits. For one, it’ll be much less violent to lower ourselves off the lander instead of dropping entirely. Secondly, we’re reusing a mechanism we know we already have to have. This means we don’t have to add additional infrastructure (motors, structure, etc) to add a dedicated mechanism to get off the climber. Less additional infrastructure also means less weight.  One popular example of this in FRC is teams using their drivetrains, arms and elevators to power their climbing devices.

As far as climbing back up on the Lander goes, there are a number of different ways to do so. We didn’t feel we could easily achieve a climber powered by our drivetrain, so we didn’t go down that path. Some other examples are latching on and pulling the robot straight up, or you can always go for style points by flipping upside down or “taco-ing” *. No matter which route you decide to take, the only thing that matters is that the robot is off the ground at the end of the match. There’s not even a required height!

(* Side note, many of the engineers taking part in the FTC Build Blitz are mentors on FRC Team 148. We’ve got a lot of experience when it comes to “not simple” hangers, so it was very tempting for us to go that route again. Luckily, common sense prevailed.)

Like all the other sub-systems we’ve discussed thus far, we began our work on a Climber / Hanger (Clanger?) by building with spare VEX EDR parts we had laying around our lab. We determined early on that we would build it to be durable enough to lift more than than allotted weight limit of a robot. That way, we could guarantee that it would be compatible with lifting not only our robot, but theoretically, any Robot in all of FTC this season. (Not that it’s required, but still…)

First we wanted to establish what motors we wanted to use. We initially leaned toward a motor like the AndyMark NeveRest motor. However, we realized that that would require us to add a second Expansion Hub. If you read our robot requirements post from yesterday, you’ll know that we wanted to try to make this robot with a single Expansion Hub. We decided to first try VEX EDR 393 Motors. If we could get away with this, great. If we absolutely couldn’t, we could always fall back and add a second Expansion Hub.

Remember, in our robot requirements post we said that we can use 8x 393 motors and it would still be cheaper than adding a second Expansion Hub. Since we’re already using 4x 393 Motors on our intake and scoring mechanism, that left us with 4x more 393 motors to use. Since this would be our last mechanism, we decided that we would put all 4 on our climber.

To equate this kind of power, each 393 motor is about 4 watts of mechanical power. So 4x would be a little less than a single NeveRest. So if you’re reading this and know you’re going to have 2x Expansion Hubs, just use a NeveRest. If not, or you’ve already allocated your 8x motors elsewhere, then you can definitely make a climber with 4x 393 Motors.

The first few versions of this hanger were pretty rough. Our testing benchmark was that we wanted to have the arm lift a 25 lb weight. This would make sure that not only the motors could handle the weight, but the structure could support it as well. The first few attempts admittedly left behind a lot of bent metal. However, the great part about VEX EDR is that you can quickly play with different ways to strengthen and reinforce frames.

Finally, we got something that worked.

We used 4x VEX EDR 393 motors on this 49:1 reduction to lift 25 lbs. The hook is a standoff covered by surgical tubing. If you look closely at the picture you’ll see a small polycarbonate flap. We discovered that this is actually useless, and is no longer needed.

The idea for the hanging sequence is to deploy the arm out, turn into the Lander support and then curl up (taco) to get our wheels off the ground. More on this in our next post when we get an entire robot driving around.

Intake, “Out-takes” & Early System Integration

There’s a number of different ways to intake and manipulate Minerals in Rover Ruckus, and every one of them has its pros and cons. A big cliche we’ve been echoing around here is the concept of “touch to possess” or “touch it, own it,” which is a way of saying “once my robot touches this Mineral, this Mineral is mine.” This philosophy is especially important for games with non-alliance-specific objects, since robots on opposing alliances may end up battling for the same Mineral (and we always want to be the robot that drives away with the contested Mineral).

So, how do you do this? In our experience, the answer is always “something with a lot of grip spins, touches the object, and sucks it in.” Yes, there are other (and more elegantly described) ways to intake a Mineral, including (but not limited to) pinching, suctioning, and scooping. However, these generally do not gain active control as quickly as a roller intake. When using a roller intake, you typically do not have to care about orientation or size of the object, which is a big place where teams struggle. A well designed roller intake will intake Minerals as quickly as the robot can move while many other intakes require a second motion, such as closing a pincher or adjusting the drivetrain after contact has been established.

One commonly overlooked concept of intake design is active control. This is where the object’s position in space is controlled at all times by the robot. This generally means lots of rollers or conveyor belts, since you never want to lose contact with the object after you have gained control of it. (Losing contact with the Mineral can mean wasting time trying to shake the Mineral out of your scoring mechanism or robot as a whole.)

The third thing to understand when designing an intake is compliance. Something (either the object or the wheel) will have to have compliance or you end up with only two points of contact and a difficult time imparting energy to direct the object into your robot.

For soft objects like foam, we could use a hard wheel like a mecanum wheel or a traction tire. For hard objects like Minerals, we need to have compliant wheels such as VEXpro Flex Wheels.

Knowing all this, we began prototyping. First, let’s look at our list of requirements for our intake:

Intake

  • Touch to possess
  • Can pick up both Gold and Silver Minerals
  • Can hold at least 2 Minerals at a time

The most basic of all roller intakes is going to be a single wheel (or long bar of wheels) and a wall (or floor) to react against. This works, but Minerals acquired from a horizontal roller intake would still need to be funneled later in the robot-Mineral path. However, funneling is always precarious and can require a lot of tweaking and tuning to get just right. Another option would be for a wide, dedicated part of the robot to be used as a conveyor belt that dumps the Minerals out of the back of the robot. This would also work, but that’s a lot of space dedicated for something that needs to hold 2 minerals.

A simpler option is to funnel with the intake. This reduces complexity in the robot, helps us keep the weight down, and also makes designing the scoring mechanism easier since the Minerals will be neatly lined up inside the robot, ready for another wheel or something to pop them out the other end.

We did this by putting two 3”, 40A Flex Wheels on a spring loaded bar. This helps keep things center because the bars attached to the wheels always come back to center. Another thing this helps with is providing extra compliance to adapt to different object orientations. For example, if a cube (Gold) isn’t exactly square to the robot, the flexible arms can adjust to the wider shape of the object. This is pretty simple to do using some rubber bands and some hex standoffs.

We wanted to keep the acquisition zone as large as possible, so we decided to keep our intake wheels as exposed as possible. More wheel exposure = more likely to touch a Mineral = more likely to drive away with that Mineral in our possession. This means that objects that aren’t exactly centered to the intake opening can still be acquired as long as they touch part of the Flex Wheel.

This intake works pretty well! The compliance in the wheel and the intake arms absorb the sharp corners on the Gold, and the backstop forces the Gold to “square up” and form a neat line. We will have to experiment with the number of rubber bands we use and the hardstop location for the intake arms to get the perfect “pinch to flex” ratio.

If we look back at our list of requirements, this intake does everything we want:

Intake

  • Touch to possess (Check)
  • Can pick up both Gold and Silver Minerals (Check)
  • Can hold at least 2 Minerals at a time (Check)

Now that the intake is done, it’s time to focus on the Mineral Scoring mechanism. Our requirement for the Mineral Scoring mechanism was:

Mineral Scoring

  • Depot-only
  • Scores from the opposite side of intake

We weighed a couple of ideas for this. We first looked at using a number of Flex Wheels through the robot. However, we were concerned that this would end up being a lot of unnecessary weight for not a lot of gain. In addition, this type of a system would require more pinch on the object which means more load on the motors. Remember, we’re trying to get away with 4x motors and 8x VEX EDR 393 Motors. So we were worried that this type of a mechanism would require us jump to regular motors.

So we looked at using the VEX EDR Tank Tread system and the flaps that are available with the Tank Tread Upgrade Kit. The benefit of these is that they easily integrate with a VEX EDR 393 Motor and the flaps don’t have to compress the object as much to use it. This means that there’s less load on the 393 motor.

Out initial concept was to use two sets of tank treads side by side, with the Mineral sitting between them. Then we realized that this could be achieved with even less weight with a single over-the-top tank tread.

We mounted it on our drivetrain to see how this type of system would work:

One cool thing we found with this setup is that we could actually roll balls from the Crater to the Depot. This isn’t going to be very effective as someone could easily stop a ball as it’s rolling. However, this could come in handy late in a match when you don’t have enough time to leave the Crater and hang. Instead, you could roll a couple balls for some last second points and still get 25 points for parking completely inside the Crater.

Next it was time to integrate the intake and the Mineral Scoring mechanisms. This took some tweaking, but the early results look promising: IMG_1486
(Sorry, we can’t embed this particular video. WordPress can be a pain sometimes)

That’s 47 Minerals out of the Crater in a minute. Yes, there were a few times we had more than 2 Minerals in the robot, but this is a promising start for our robot. Next we need to get a control system on the robot so we can run the entire robot and see how it can be improved.

As you’ve noticed in our two other posts from today we use a lot of parts from the VEX EDR and VEX IQ systems. The reason we’re doing this is because we’re trying to quickly iterate through ideas. As the final robot comes together, we will start integrating in more VEXpro parts to strengthen and reinforce weaker parts of the robot. Our goal is to try and get a robot up and running quickly so we can spend more time iterating and fine tuning the robot’s performance.

Drivetrain: For the Crater Good

For the past couple days we’ve been working on designing a drivetrain for the MCC. The one thing to keep in mind when designing a system is to always refer back to your list of robot features to make sure you’re still on the right path. You can find all our robot features in the “FTC Minimum Competitive Concept (MCC) Robot” post we made earlier today. For reference, the features for the drivetrain are:

Drivetrain

  • 4-6 wheel drive
  • Geared between 16:1 and 20:1
  • Can easily drive into and out of Crater

 

We started off by designing a simple drivetrain in CAD. This one is based on the VersaChassis Mini System:

We already know from yesterday that our new Flex Wheels can work as a drive wheel.

To help test out some of the concepts like wheel spacing and positioning we made a version of this drivetrain out of VEX EDR structure:

For the sake of speed, we moved the control system from the test platform we tested yesterday to this robot. However, we quickly found that this robot struggled with becoming high centered on game objects.

After this, we decided to try and add an additional set of wheels in the middle of the drivetrain. These wheels were idler wheels that were not driven.

Here’s a video of some testing we did with this configuration:

 

We also did some testing to see the pushing power of the Flex Wheels against other robots. So we took some of the robots sitting around the VEX office and tried to push them sideways:

 

We still weren’t happy with this drivetrain setup, as we still struggled getting into the Crater and still had trouble with becoming high-centered on Minerals. To help with this, we decided to try a larger wheel. We don’t have a 5” or 6” Flex Wheel, so this meant we would need to use a 6” VEXpro traction, omni-direction or mecanum wheel. We first tried all omni-directional wheels:

 

This worked a little better, but we found we needed a lot of speed to get into the Crater. This was due to the omni-directional wheels not having enough traction against the perimeter of the Crater. We then switched two of the omni-directional wheels out for traction wheels:

 

This worked somewhat better, but we still had issues getting high centered on the balls. We went back to the drawing board and decided to try doing something a little less conventional by creating an A-Frame chassis that created a ton of clearance between the wheels:

This design allowed us to go back to using Flex Wheels, which we believe were the best wheels we tested when it comes climbing into the crater. Here are some videos:

 

There is still some iteration testing we need to do, such as increasing the angle of the A-frame from 45 to 60 degrees, and shortening the overall robot so it can fit under the Lander to avoid defense.

Another change we want to make is putting a VersaPlanetary 180 Degree Drive on the drive motors. This will give us more space between the drive motors and reduce the amount of game objects we ‘rake’ out of the Crater when we drive in and out.

Since the 180 Degree Drive has a 2:1 reduction between the motor and the first gear stage, we can also drop a gear set from our robot, which will decrease weight even more. However, this will limit our gear reductions to 18:1 (2:1 -> 9:1) or  20:1 (2:1 -> 10:1). All the videos you’ve seen in this post use a 20:1 reduction, so we’re fine with being inside this range. If we wanted to go slower we could use a 180 Degree Drive into a 2 stage VersaPlanetary and get 24:1 (2:1 -> 4:1 -> 3:1) or 30:1 (2:1 -> 5:1 -> 3:1)

If we review our list of drivetrain features we feel like this drivetrain setup does everything we want our drivetrain to do:

Drivetrain

  • 4-6 wheel drive (Check)
  • Geared between 16:1 and 20:1 (Check)
  • Can easily drive into and out of Crater (Check)

 

 

P.S. Part of us really wanted to stick with using omni-directional wheels. There’s something oddly satisfying about jumping into the Crater at full speed. We guess we’ll have to find a way to do the same with Flex Wheels.

 

Design: Minimum Competitive Concept

A Minimum Competitive Concept Robot, or MCC for short, is an idea that’s been around FRC for a while. The idea is to design and build a robot that any team could build and remain reasonably competitive at an event. These aren’t world championship caliber robots, but they’re the kind of robot you’d love to have as a partner at a smaller tournament and probably even your state championship.

In FRC the two most popular MCC robots are one designed by our friends at West Coast Products (simply called MCC) and the EveryBot designed by FRC Team 118 – The Robonauts. Even though they seem very simple, clones of these robots have typically performed above average at most regionals and usually make it into eliminations.



We’ve decided that we’re going to try and do an MCC style robot for this year’s FTC game, Rover Ruckus. Our guidelines for this are:

  1. Use as many common off the shelf (COTS) items as possible
  2. Any fabrication must be achieved with basic hand and power tools (hack saw, hand drill, etc)
  3. Minimal 3D printing
  4. Give teams a solid starting point that they can use to build and improve upon
  5. Functions with simple software

Having gone through our own strategic analysis, we’ve come up with a simple MCC robot that we feel any team can build and almost any team would want to be aligned with in a qualification match (and maybe even eliminations).

Robot Features:

Drivetrain

  • 4-6 wheel drive
  • Geared between 16:1 and 20:1
  • Can easily drive into and out of Crater

Intake

  • “Touch It, Own It”
  • Can pick up both Gold and Silver Minerals
  • Can hold at least 2 Minerals at a time



Mineral Scoring

  • Depot-only
  • Scores from the opposite side of intake

End Game

  • Can attach and lift robot off ground in less than 30 seconds



Autonomous

  • Can start on Lander
  • Can lower robot from Lander
  • Ability to achieve multiple autonomous tasks
  • Capable of delivering team marker to Depot

Misc.

  • Short enough to drive under Lander
  • Ideally between 20-30 lbs
  • Can be built with one expansion hub

 

Some of this might seem crazy, so let’s walk through some of our decisions:

 

Drivetrain

Ideally we would like the drivetrain to have 4 wheels to help keep weight down. By keeping the overall weight down, we can get more aggressive with the gearing and make a faster overall robot. The heavier your robot is, the slower you have to gear it.

Intake

“Touch It, Own It” is an important concept. Many times teams struggle with intakes and waste a lot of time just trying to acquire a game object. The idea behind “Touch It, Own It” is that you want to make an intake that acquires a game object the second it touches the intake.

To help keep the robot simple, we want the intake to be able to pick up both Gold and Silver minerals. Not only does it cut down on the number of mechanisms, but it’ll also help keep the overall weight of the robot down.

Mineral Scoring

The Depot-only robot was one we talked about for awhile. The reason we decided to move forward with this concept was because we felt that if implemented correctly, it could be more effective than most of the robots that attempt to score in the Cargo Hold.

This seems like a stretch, but there’s one subtle element of scoring in the Cargo Hold that will slow down almost every robot. It may not be very obvious, but this happens to be sorting Minerals. At some point during your cycle you will have to sort objects. This means you’ll either have to make the effort to intake two of the same object, or you’re going to have to score in two different places after you pick up the Minerals.

So how can a Depot-only robot be just as, if not more, effective than a Cargo Hold robot? It’s simple, you’re just 2.5x faster. Let’s think about the two ideal list of actions that a Cargo Hold robot will have to perform:


Scenario 1

  • Find and acquire Mineral 1
  • Find and acquire Mineral 2 (the same type as Mineral 1) 
  • Drive to Lander
  • Lift Minerals
  • Score Minerals

Scenario 2

  • Find and acquire Mineral 1
  • Find and acquire Mineral 2 (not the same type as Mineral 1) 
  • Drive to Lander
  • Lift Minerals
  • Score Mineral 1
  • Lower lift (optional)
  • Drive to other side of the Lander
  • Score Mineral 2

Each of these actions require X amount of time. However, a Depot-only robot only has perform the following actions:

  • Acquire Mineral 1 
  • Acquire Mineral 2 (does not have to be the same type as Mineral 1)
  • Drive to Depot
  • Dump Minerals

Again, these actions take time, but consider that a Depot-only robot doesn’t care about sorting, doesn’t have to lift game objects and doesn’t care about the precise positioning of the objects they’re trying to score.

Will that mean that a Depot-only robot will always be better? Of course not. Again, we’re not trying to build a world championship caliber robot. We’re trying to build a robot that any team could build and be competitive with.

Since we want to cut down on our cycle times, we need to do everything we can to optimize the robot’s cycles. One of our key design choices is putting the ‘outtake’ on the opposite end of the intake. This will eliminate the additional action of our robot having to turn around and outtaking elements, while also improving overall cycle times.

Not to mention that a Depot-only robot also requires much less sophisticated software, which makes it more accessible to teams.

End Game

Since Minerals in the Depot are only worth 2 points, we wanted to optimize our scoring potential by making the robot hang from the Lander at the end of the match.

Autonomous

The same reason we want the robot to hang is why we want the robot to start on the Lander and lower itself down. We’re trying to maximize our scoring potential. We also believe that we can complete both of these actions by using the same system. Using the same system for multiple tasks is a great way to optimize your robot and keep its weight low.

Since claiming the Depot is a must for a Depot-only robot, we want the robot to be able to do its part in autonomous.

Lastly, this robot could have the potential (assuming time is still available) to receive points for parking and the sample bonus. This would give the robot an 80 point autonomous mode.

Misc.

Since the Depot can be defended, we wanted to give the robot the ability to “beat” a defender. There are two concepts here – the first is make the robot very agile and minimize the areas of the field it cannot access. The second is to make the robot faster than most (or all) robots. When combining these two concepts, it becomes much more difficult for a potential defender.

With this in mind, we wanted to make the robot drive under the Lander. This way, if an opponent tries to block our path to the Depot, we can simply drive under the Lander instead. Weight is also an important factor to this as well. The lighter the robot is, the faster we can gear it and the easier it’ll be to drive around defense.

Finally, we also wanted to build the robot with a single Expansion Hub. This seems like an odd requirement, but there’s a couple design and resource benefits here:

  1. Reduced cost. 2x REV Expansion Hubs are $350, or $175 each. The REV Servo Power Module is $40 and can run 2x VEX EDR 393 Motors each. So we could use up to 8x VEX EDR 393 Motors and still be cheaper than buying 2x Expansion Hubs.
  2. Limiting ourselves to 4x motors and achieving the rest of our movements with servos allow us to keep weight down. Less weight means less power required to move the robot, and also allows us to gear the robot faster and keep our cycle times down.

This is our idea of an MCC for FTC. Stay tuned for later as we discuss different gameplay strategies for the MCC robot!

Design Concept: Flexing On the Competition


One idea we had during our brainstorming was to see if we could use our new Flex Wheels as a drive wheel. This seems ludicrous at first, but there are some unique advantages. One of the big ones being that Flex Wheels give the drivetrain a suspension without having to complicate it with linkages. In the past, FRC teams have used pneumatic tires to achieve a similar effect.

However for FTC, pneumatic tires have a number of disadvantages:

  1. They’re heavy
  2. You can’t easily find tires smaller than 6”
  3. The tread pattern can be too aggressive and could potentially damage field tiles.

Our hope is that we can use the VEXpro Flex Wheels to give us all the advantages of pneumatic tires, without the disadvantages listed above.

The first thing we wanted to check was how well the traction wheels perform on a fully weighted robot. (If you took our advice from our Strategic Analysis Post and re-read the Rover Ruckus game manual multiple times, you should already know what this weight is!) The weight of your drivetrain always matters when testing, but it’s especially important with the flex wheels because the heavier your robot is, the more the wheels will deflect.

In our initial test, we ran a drivetrain with two 4”, 60A Flex Wheels (217-6452) and two 4”, 40A Flex Wheels (217-6451). While both would work, the 40A wheels deflect quite a bit under 42 lbs. The 60A wheels had enough rigidity that we feel we could use these as a drive wheel. If the robot was lighter (probably in the 20lbs range) the 40A wheels could definitely be usable.  


The last thing we needed to check was to see if the Flex Wheels pass the 42 lbs wall test to make sure there wasn’t a risk of damaging the field.


The flex wheels passed without a problem.

So far, Flex Wheels look like a promising drive wheel option for Rover Ruckus!

Educational Resource: Rover Ruckus Game Analysis

 

We’re really excited for the 2018-2019 FIRST Tech Challenge game, Rover Ruckus! Before we get started with Build Blitz, we’re going to strategically analyze the game to help determine what robot actions we should focus on.

One of the important factors in doing strategic analysis is working within your team’s resources to maximize your strategic impact. It’s important to be honest and realistic about your team’s resources and what you will be able to achieve before competitions begin. For example, if your team doesn’t have a strong programming foundation, it’s unlikely that you’ll be able to achieve an autonomous routine that requires complex field navigation. However, this doesn’t mean you’re doomed! Doing this kind of strategic analysis allows you to break down the game and focus your team’s efforts and resources on things that are going to allow you to maximize your impact, and (hopefully) win more matches. You don’t always have to do everything!

As we’ve said before, the goal of Build Blitz is not to make a fully custom world championship caliber robot. Instead, we’re trying to work within the means of an average team. This means constructing a robot with common off the shelf (COTS) components, basic hand tools and some light (but optional) 3D printing.

The strategic design process is broken down into 3 main areas:

1) Read the game manual
You can’t begin to break down a game if you haven’t read the rules.

1b) Re-read the game manual
Seriously, you should make sure you know the rules inside and out before even considering building something. Take it from us, there’s nothing more disappointing (read:heartbreaking) than spending a ton of time on a “game-breaking” mechanism, that turns out to be illegal.

2) Understanding the ranking system
We’re going to assume that your goal at a competition is to seed high and win the event. While there are several paths you can take to winning an event, seeding high is always going to increase your chances of doing so. Understanding tiebreakers can also help you understand the priority of scoring options in a game.

3) Understanding scoring and what actions are required to score.
In almost every game, you need to score points to win matches. Understanding the weight of different scoring tasks is imperative to strategic analysis. For example, if Task A is worth 2 points and can be repeated 8 times in a match, but Task B is worth 5 points and can only be repeated twice, which task should you focus on?

Additionally, understanding the actions required to complete a scoring task is vital. Making a list that includes actions required for that task will help clarify what actions your robot will need to be capable of.

We’ll assume all of you have read the Rover Ruckus manual (twice) by now, and will skip to step 2, understanding the ranking system.

In Part 1 of the Rover Ruckus game manual, section 5.8 calls out the ranking criteria:

Since the primary ranking criteria is winning matches, there’s a high likelihood that multiple teams will end up with the same win/loss/tie record. This means that tie breaker criteria are going to be extremely important.

The secondary sorting criteria is TieBreaker Points. This means that while you want to win a match to get 2 Ranking Points (RP’s), you want to keep the final score close to maximize your TieBreaker Points. (i.e. It’s much more beneficial for you to win a “nail-biter” than a blowout) Since this criteria is based on the sum of an alliances points, it’s unlikely that the 3rd and subsequent sorting criteria are going to be used often.

Now that we understand the ranking criteria, let’s move on to understanding scoring tasks and the robot actions associated with it. Keep in mind that this is not meant to be an all encompassing list. It’s important that your team goes through this exercise on their own to make sure you consider all possibilities.

The highest possible (penalty-free) score if you scored every Mineral would be 1,070 points.

The formula for this “perfect” match is a 2 robot landing bonus (60 pts) + 2 autonomous claiming bonuses (30 pts) + 2 autonomous sampling bonuses (50 pts) + 2 parked robots in autonomous (20 pts)  + 94 scored gold in Depot (470 pts) + 68 scored silver in Depot (340 pts) + 2 latched robots in the end game (100 pts).

Now, scoring all 162 Minerals would require an average cycle time of less than 3 seconds. So it’s unlikely we will ever see this. Instead, let’s look at the cycle time required to score half of the Minerals on the field (81). This would require an average robot cycle time of less than 6 seconds and would net an alliance 670 points.

When we talk about cycle times, we’re talking about the average time it takes to acquire a game object(s) and score it. This is important to keep in mind when deciding things like what scoring tasks you should attempt, how fast your robot needs to be at doing said task, etc.

Next it’s time to look at the actions listed in the table above and figure out how important they are to our robot.

  1. Driving (9/10)

    With the exception of Landing, every task requires driving. Yes, you could play this game without moving, but that is not something that a team with average resources could easily achieve.

    Though it may seem redundant, the ability to drive is the #1 robot function in almost any robot game. Even if you only field a reliable drivetrain, you can still play defense or push objects into the Depot to contribute to your alliance’s score. Likewise, even if you had the best scoring mechanisms, your robot won’t be very good without a reliable drivetrain.

  2. Driving Into the Crater (6/10)

    This was almost as important as driving, but there are still ways you can play this game without ever driving into the Crater. Being able to drive into the Crater opens up a lot of scoring options for your team. You can park in the Crater during autonomous for 10 points and park completely in the Crater during the end game for 25 points. That’s 35 points you can score for your alliance just by being able to drive in the Crater!

    Driving into the Crater also gives you another option to retrieve game objects. There are lots of different ways to do this, including reaching into the Crater. However, some of these can be non-trivial mechanisms. So you have to ask yourself, what are you gaining by not driving into the Crater that’s going to make up for the 35 points you’re leaving there?

  3. Picking Up Minerals Off The Floor (4/10)

    This is a requirement if you’re going to score Minerals in the Cargo Hold. Scoring Minerals seems like a given, so the importance of this task seems low. However it’s possible for you to contribute to a match without scoring Minerals at all.

    Let’s assume that each robot equally contributed to the 610 point match we talked about above – so 305 points each. 130 of those points were scored without even touching a Mineral. So it’s possible for a single robot with a perfect autonomous mode (80 points) and the ability to latch at the end of the match to make a significant contribution to their alliance. If you want to think about it another way, that 130 points is worth 13 Minerals in the Cargo Hold.

  4. Picking Up Minerals From Crater (3/10)

    Since the vast majority of Minerals start in the crater, this is pretty much a given if you are planning on scoring Minerals. There are two options where you don’t have to do this:

    A) You’re planning on only picking up Minerals off the floor. There are 9 Minerals on the floor to start a match. If you score all of those into the Cargo Hold that would be 45 points. In addition, teams will inevitably drop Minerals as they are trying to score them into the Cargo Holds, or push them out of the Crater as they drive in and out of it.

    Another possibility here is that if your opponent doesn’t claim their Depot, you can steal objects from their Depot. If you do this, you’re actually creating some pretty significant point swings by taking 2 points from them and adding 2-5 points for yourself. That makes each object you steal from your opponent’s Depot really worth between 4-7 points!

    B) You decide not to score Minerals at all.

  5. Drop Off Mineral (3/10)

    This is similar to picking up a Mineral off the floor. If you’re planning on scoring Minerals, you’re going to need some way for dropping or dumping them into the Depot or the Cargo Hold. There is a very interesting tradeoff that Rover Ruckus presents.

    When you’re scoring in the Depot you don’t care about what’s in your possession. However, when you’re scoring in the Cargo Hold you need to sort at some point during the cycle. This means you’re either going to look for 2 of the same object on the floor/in the Crater or you’re going to need a way to drop off one type of Mineral and then the other. Most likely this is going to add additional time to your cycles.

    Keep in mind that scoring in the Depot can be a big risk if it is not claimed during autonomous mode. If this is the case, your opponent can steal Minerals from your Depot which, as we explained, above can be a big hit to your alliance.

  6. Lift Mineral Up To Cargo Hold (2/10)

    This is a requirement if you’re planning on scoring in the Cargo Hold. The reason this is lower on the list is because you can still score a Mineral by just dropping it in the Depot. Lifting a Mineral up to the Cargo Hold is only required if your analysis determines that those additional points are worth your time.

  7. Attach To Lander Bracket & Lift Off Ground In <30 Seconds (1/10)

    This is the highest of the actions that were listed once because it’s worth so many points. Think about it like this. If you give up climbing and are going up against a robot that has the ability to climb, you need to be able to score score at least 50 points in that 30 second to make up the difference. This is the equivalent of 10 Minerals in the Cargo Hold, which breaks down to 5 cycles with an average cycle time of 6 seconds. We imagine this is going to be incredibly difficult for a robot to pull off.

    Alternatively, you could park completely in the Crater and score 5 Minerals in the Cargo Hold. Assuming it takes you 5 seconds to park in the Crater, you are left with 25 seconds to run 3 cycles, which means your average cycle time has to be  about 8.3 seconds. This is a little easier, but still requires some elite level speed and execution from your robot.

    While we say this needs to be done in less than 30 seconds, ideally you want to be faster. Every second you can shave off this task, buys you another second to continue scoring Minerals, playing defense, etc.

    When evaluating the value of a given action, this type of tradeoff analysis can often help you to get a feeling for what is ‘most important’ or not. This can also extend into tradeoffs in the middle of a match. For example, there are 10 seconds left in a match. Do you stop and go for a climb you might not finish and therefore get 0 points for, or do you try and score another Mineral or two?

  8. Lower From Lander (1/10)

    8 and 9 seem like they go hand in hand, but lowering from the Lander has more importance because if you can start on the Lander, but can’t lower your robot from it, you effectively didn’t show up to your match. The landing bonus is a high scoring task you can do in autonomous and doesn’t require any complicated sensing and navigation to achieve this. We think this can end up being one of those tasks that “looks hard, but is (fairly) easy”.

  9. Start on Lander (1/10)

    This is really 8b since you need to start on the Lander to get the landing bonus.

  10. Remove Mineral From Sample Field (1/10)

    Removing only gold from the Sample Field is worth 25 points if done in autonomous. Since it’s the second highest point value in autonomous it ends up down here. This is interesting because it can dually reward you. For example, say your method of removing gold is to just pick it up off the floor. If you use dead reckoning (always picking up the Mineral in one of the three specific locations) to try and achieve this task and you pick up a Silver Mineral instead of a Gold Mineral, you will forfeit the 25 point bonus, but will start with 1 object in your possession. This means right out of driver control, you can go pick up another object and score it. However, if you use dead reckoning and do manage to pick up a piece of Gold, you then get the 25 points AND you start with one object in your possession.

    Starting with an object in your possession is important because it’ll cut down your first cycle time, which will help lower your average throughout the match, thus allowing you to maximize your Mineral scoring potential.

  11. Remove Only Gold From Sample Field (1/10)

    This is related to “Remove Mineral From Sample Field”. While your immediate reaction when you see “Remove Gold From Sample Field” is to start pouring resources into an advanced autonomous routine that can detect Gold. However, as mentioned above, if you use dead reckoning you and miss, you’re still starting the driver controlled period with a Mineral in your possession, which is still helpful.

    With that in mind, this action was weighted below “Remove Mineral From Sample Field”. This is another example of a tradeoff your team will have to evaluate as they analyze Rover Ruckus.

  12. Deploy Team Marker (1/10)

    This task is interesting, as you can only get points for it in autonomous. This means that if your alliance isn’t planning on scoring in the Depot it might not be worth doing this at all. However, if you think there’s even the slightest chance that you’ll need to score in the Depot, you should probably do this since it goes toward claiming your Depot and preventing your opponent from stealing objects. As we mentioned previously, stealing objects from your opponent’s Depot and scoring them for yourself has a greater impact on the score than scoring objects from the floor or Crater for yourself.

That’s a pretty simple priority list for Rover Ruckus. This should hopefully be a pretty good starting point that your team can reference when they go through this process on their own. We can’t stress enough how important it is that teams complete this process themselves. Each team will have a different set of resources and priorities, so it’s impossible for there to be a one-size-fits-all ranked priority list that applied to teams. When doing this on your own, be realistic about your team’s resources and capabilities. It’s good to challenge yourself, but make sure you’re not going overboard and taking on more than your team can handle.

If you want some additional tools to help you out when figuring out your robot strategy, we’ve created a calculator that breakdowns scoring and cycle times in Rover Ruckus. It can be downloaded here: https://link.vex.com/RR-Cycle-Calculator