Re: Team 2471 swerve drives
 

Gdeaver alluded to the importance of swerve/omni Driver Interface (DI), and that segues into a question I've been wondering about lately.

Does anyone know of a team who has implemented a DI mode I will call¹ a HaloAR (AR=Auto Rotate), as described in this thread posts 5, 6, and 9?


¹until someone informs me that such DI has already been named

Re: Team 2471 swerve drives
 

Interesting question, although I can't give you a definitive answer because I haven't seen every omni-directional drive. I can say, that I have never seen one that was programmed like this.

The proposed DI is somewhat similar to the system we will try to implement after we get a regular field-centric drive working. It is also quite similar to a DI that we have planed, and may end up using in future seasons.

I will just explain the one that we are implementing this off season right now. As I mentioned earlier, the primary challenge this off-season competition, is herding multiple 6" foam dodge balls with a three sided corral. The fact that you can only use a three sided corral means that if the robot were to drive straight forward at speed and the stop, the balls that are inside would roll out.

The solution to this problem was difficult to determine, but it is relatively simple to explain. There will be standard field-centric dive code running (one joystick gives field heading, the other gives rotation), but there will be another piece of code that will be added to the rotational part. The code will use an accelerometer to tell which direction we are accelerating, then is will run a control loop to make the front of the robot face in the direction of acceleration to automatically for any motion that the drive makes in field space. Probably, there will be a button that must be held down to enable this driving code, because for some operations in this game, the driver will want to control orientation.
Feedback on if you think it will work or not, and why would be appreciated.

Re: Team 2471 swerve drives
 

What is the benefit of rotating based on acceleration, instead of joystick angle?

Re: Team 2471 swerve drives
 

Good question, essentially because the balls always want to roll in the direction they were previously heading, and so we want to adjust that heading with the back of the robot. Also, many times, the robot's acceleration is not in the direction of joystick position.

Here's an example. Driver presses left on the joystick causing the the robot to accelerate left in field space. The robot automatically rotates to be facing left, just as it would if the code followed joystick position. Then, as the driver approaches where he wants to be, he slowly lets up on the joystick. with code that is tied to the joystick, the robot would continue to be facing left until it came to a stop. this would allow any balls that are being corralled to escape. If the code is tied to acceleration, then as the driver lets up on the joystick, the robot will be accelerating to the right and so the robot will turn around to and catch the balls.

As far as I can tell, this sort of thing applies to all situations, so the driver ideally won't have to worry about orienting the robot to move the balls around.

Re: Team 2471 swerve drives
 

I'm not trying to grief here, but 28 pounds for the drivetrain sounds horrendous! I do not know how much our mecanum drivetrain weighed, but I know that it is well under 28 pounds!

Re: Team 2471 swerve drives
 

I'm not sure where you got the 28 lb figure, but that is irrelevant. This is one of the lightest swerve drive train that i know of. The point is not to be lighter than a mecanum drive. The point it to out preform a mecanum and try to stay as close as posible on weight. But, in some ways you are right, one of the disadvantages of swerve drive is the weight.

Look at it this way, there's over 15 lbs of motors. Maby someone will point out that there is a swerve that weighs much less, and prove me wrong.

Re: Team 2471 swerve drives
 

The first post shows it on the weighing scale.
Also, mecanum gave all the performance we needed. Your robot gets as good as your drivers get. Crappy drivers and a million dollar robot would be worth pennies. Great driver and ten dollar robot would make the robot worth millions, (if you think of it in money). In this case, the money is the points!

Also, doesn't swerve have a high latency? As of what I know, holonomic drive can have very little latency

Re: Team 2471 swerve drives
 

A good swerve doesn't have high latency, though it will have a bit.

Re: Team 2471 swerve drives
 

No, it's even more. Add the motor controllers and wire to that weight. Yes, there is a big buy in for swerve. For this reason I would tell the largest majority of First teams to look at the cad models and learn but, do not do swerve. It is not for you. Perfect a 6 wheel drive and devote the rest of the teams resources to scoring mechanisms. There are a few teams that have the resources and ability to pursue swerve or other complex drives. The poster appears to have the capability and commitment to do swerve. The rewards can be big. Putting aside the competition aspect of swerve and think how much knowledge and skill a swerve project can give students.
Yes, swerve does affect the weight budget of the robot. That leads to another favorite subject of mine. How do you build light weight strong structures to make up for the weight that was put into the swerve? Composites. I try my best to get as many students as possible to assist in at least 1 composite project.

Re: Team 2471 swerve drives
 

If your swerve really weighs 28lbs (which I doubt includes everything, but nonetheless), then it's extremely light. 28lbs is a pretty decent weight for a WCD, at least in my book. If your drivetrain's over 40lbs (not including electronics), only then might weight be a potential issue.

Oh, yeah, one more thing to add. It's been said many times before, but not in this thread (at least as far as I can see). You've probably already figured this out, but swerve is a ton of work, not just in terms of design or programming, but also in terms of raw manufacturing time and effort. Be careful before you decide (especially before the season) that because swerve is so awesome and you've done it in the offseason that you should do it in-season. Just in terms of manufacturing and assembly time, you could essentially free up enough time to do a full manipulator iteration in season by choosing a WCD or an off the shelf drivetrain over swerve.

All in all, cool swerve, and it looks like you've had fun building it! Congratulations, you've succeeded where many have failed.

Re: Team 2471 swerve drives
 

If done correctly, mecanum will also get the same things done. Our robot was able to push the other robots around at competition. With locking mecanum, we will be able to stun the other teams when we enable it and sideload ourselves, making it impossible for us to be moved! I will inquire about how much our drivetrain weighs tomorrow, when we have robotics.

Re: Team 2471 swerve drives
 

Not quite. There is no real replacement for traction and a second speed.

Re: Team 2471 swerve drives
 

Locking mecanum makes your mecanums into regular solid wheels, giving you a greater traction.

If you want traction, here's what to do next:
A claw drive system that uses claws to pull the robot along. Things can easily get impractical :(
:deadhorse: :deadhorse: :deadhorse: :deadhorse:

Re: Team 2471 swerve drives
 

Locking mecanums doesn't change the interaction between your wheels and the ground(traction). Swerve can run much higher traction wheels. Furthermore, it still doesn't change the fact that a swerve can run two speeds.

Re: Team 2471 swerve drives
 

Yes it does. He's talking about locking the rollers. See posts 5 & 50 of this thread.


You can make mec wheels out of high-traction material if you've got the budget to do it.