The Hardest Drive System To Program:

[davidthefat]

Originally Posted by Chris is me

Programming a drive so that you CAN control all of its functions is easy.

Programming a swerve drive so that it's intuitive and easy to control those functions is not.

From your experience, how long does it take for the swerving wheels to actually orient itself to the right angle? What kind of motors are required to be able to rotate the wheels and not stress out the motors?

[buildmaster5000]

Originally Posted by davidthefat

From your experience, how long does it take for the swerving wheels to actually orient itself to the right angle? What kind of motors are required to be able to rotate the wheels and not stress out the motors?

Depending on the gear ratio and the distance required, about .5 second is a reasonable estimate. We used swerve and didnt use PID loops without a visible performance loss. Using window motors and the wildswerve pods, we probably averaged .25 seconds between posisitons using window motors. We also limited the wheel to only have a 180 degree range of rotation.

[Chris is me]

Originally Posted by davidthefat

From your experience, how long does it take for the swerving wheels to actually orient itself to the right angle? What kind of motors are required to be able to rotate the wheels and not stress out the motors?

I haven't built a swerve out of "FRC parts", but this depends on your coefficient of friction and number of wheels. What motors and gearing you can use depends on how fast you want the pivots to be able to rotate and what tread material you use.

That said, with proper gearing I've heard of teams using anything from Window motors to the FP.

[Duncan Macdonald]

Originally Posted by davidthefat

I just realized why more teams don't do swerve: it is hard to do the actually mechanical fabrication than it is to code it. I am not sure if my team is capable of producing such a drive system. Most of the mechanical guys are seniors and are graduating. My mentor will not let me learn any mechanical skills because he deems me as a too valuable of a programmer to be welding and stuff.

The most "advanced" drive we can fabricate will probably be a mecanum drive, possibly an omni drive.

But, if there are any teams that are willing to invite me to help program something more advanced, I will be glad to do it. I really have our doubts for next year. Chances are, we will go with our 6 wheel again (which I loath)

you could fund raise really hard and help your mechanical team out if you really want to build one.http://www.team221.com/order.php?cat=3

I wouldn't recommend doing something solely because it is hard. Most teams do a cost/time vs return analysis and decide that focusing on an effective manipulator and simple drive will result in a better final product. We did this and decided that in this game* a mecanum has some advantages when hanging tubes and we wanted to add it to our bag of tricks.

*Chose not to in '07 because we anticipated heavy defense

[PAR_WIG1350]

Originally Posted by Siri

I'd say Unicorn drive is up there. There's so many modes available: tank (uncommon if snake works), full crab (all wheels pointed same direction), snake (front & back point opposite directions), center spin, arbitrary center spin, each potentially with x and y-orientation.

Originally Posted by Ether

You left out the most interesting one: full 3-degree-of-freedom control, like a mecanum or omni.

The full 3 degree of freedom mode makes all other modes, except for tank which is inferior anyways and should be left out, redundant. That is not to say that redundancy is bad, Being able to lock into a single mode can compensate for oversensitive controls.

[Ether]

Originally Posted by PAR_WIG1350

The full 3 degree of freedom mode makes all other modes, except for tank which is inferior anyways and should be left out, redundant. That is not to say that redundancy is bad, Being able to lock into a single mode can compensate for oversensitive controls.

Interestingly, all the other modes are subsets of the 3-degree-of-freedom mode. So once you have the 3-degree-off-freedom programmed, you can get the other modes just* by converting the driver interface commands to the equivalent 3 degree commands. For example, the conversion for Ackermann steering is shown here.



* "just" software. I hate that phrase. Don't you?

[Tom Line]

Originally Posted by PAR_WIG1350

The full 3 degree of freedom mode makes all other modes, except for tank which is inferior anyways and should be left out, redundant. That is not to say that redundancy is bad, Being able to lock into a single mode can compensate for oversensitive controls.

Tank drive is inferior? That's a pretty interesting statement to make considering the number of Einstein teams who have run tank vs. any other system.

On what do you base tank's perceived inferiority?

[davidthefat]

Now, for the people that said swerve drive is hard to drive with, can you explain why? I see no reason why it would be hard to drive at all. IMHO it would be harder to maneuver a 6 wheel drive than a swerve

[The Lucas]

Probably this one
I can't figure out which combination of outputs make it move, let alone reach its top speed of 154 fps or Warp 9 (I am not really sure).

Seriously, I think a Field-Centric 3 degrees of freedom drive is the toughest I've seen in FIRST.

[Chris is me]

Originally Posted by davidthefat

Now, for the people that said swerve drive is hard to drive with, can you explain why? I see no reason why it would be hard to drive at all. IMHO it would be harder to maneuver a 6 wheel drive than a swerve

All I can say is build one and try it.

I agreed - until I picked up the Revolution demobot at IRI and tried to make it drive around without ramming into anyone. Wow it is hard.

[Josh Fox]

I think that all depends on how you program it and how much practice a driver has.

After 4 years of driving Team RUSH's robots, I'd like to consider myself to be a fairly competent chassis driver. That being said, I only had experience practicing and operating with 6wd. I only had one real chance to drive a swerve-based chassis. It was programmed with one stick controlling rotation and the other translation, and it was a completely different beast than standard 6wd. That being said, with more practice it's possible I would've been able to do just as much with swerve as a 6wd robot, but I wasn't since I hadn't practiced with it.

[davidthefat]

How I interpreted the controls was that the joystick was to move around the field and the shoulder buttons were for zero point turning. The gyros (double redundancy) would orient it self relative to the driver, so when ever the driver presses down, it will come toward the driver.

That sounds a lot easier than how you described it.

[Josh Fox]

That definitely sounds like an interesting control method, and I've never heard it done that way.

That being said, I feel like having a set speed that the robot rotated at might not be the most efficient way of doing things.

I'm not sure though and I could be wrong, I'm not very experienced with the programming/control of swerve drives.

[Garret]

Is swerve supposed to be more difficult than Mecanum to drive?

I don't see how it could be that difficult from the drivers perspective. We have a mecanum robot, and our driver did fine even though he had to deal with reversed controls for our first matches and was controlling all the robots functions. After that was fixed we didn't have any difficulty driving. I am trying to figure out what you mean by difficult. is there something that swerve has that makes it more difficult than mecanum.

Also our driver had no real prior practice with mecanum.

[Alan Anderson]

Originally Posted by Siri

The other possibility that comes to mind is Nonadrive. It's incredible, but I have no idea how complicated the programming is. (148, are you here?)

I don't know how 148 actually did it, but the way I'd program it is almost ridiculously simple. For all practical purposes, the joystick axes drive motors directly, with a single pushbutton controlling a drop wheel.