The Hardest Drive System To Program:

[rahilm]

Originally Posted by mobilegamer999

swerve drive == crab drive

and yes, putting all that stuff in (in summary) sounds simple, but seems complicated in comparison to say tank drive which is read left joystick set left wheels, read right joystick set right wheels

Crab is simply a TYPE of swerve drive, but they are not the same. Swerve is just the ability to have sets of wheels that can rotate. Crab drive is a type of swerve drive where all the wheels are linked (mechanically usually), so they are always at the same angle. There are other types of swerves, including ones where each wheel is rotated independently (allows greater maneuverability and less skidding and much more complicated programming), and Winnovation's 6-wheel swerve.

[mobilegamer999]

I have helped many teams with base drive code and have encountered quite a few different drive types. The swerve drive that I worked with was 4 swerves, each with independent control, and I would say it was one of the more difficult ones to get working, fully functions, and non-wire-twisting.

Now, the code i have doesnt use PID loops, but rather 'manual' monitoring and speed adjustment of swerve modules based on current and target angles. That being said, had it not been in the heat of competition with the limited time for programming and annoyance of "its just code, whats so hard about it" (as im sure all programmers are used to), I would have taken the time to properly implement PID loops, correct stops, and more features. But what made it difficult and would make it similarly difficult in any build season is the tendency to get 'base functionality' working then add 'slightly more' over and over so you can get more testing done and get it more and more functional but have ugly and hard to manage code, instead of taking the time to properly write it with closed control loops after base functionality was working. The biggest issue was the time limitation we had on programming and had we had more time, maybe it might have been easier to work with.

[Ether]

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.

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

Originally Posted by rahilm

There are other types of swerves, including ones where each wheel is rotated independently (allows greater maneuverability and less skidding and much more complicated programming)

A swerve with four-wheel independent steering and wheel speed control allows the vehicle to be programmed to behave much like a mecanum, but without the traction limitations.

The procedure for calculating the wheel speed and steering angle for each of the 4 wheels is presented here.

For those who like to have a deeper understanding, the derivation of those equations is given here.

[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)

[bladetech932]

Dont worry david i'm in the same boat as you. Our team doesn't have the manufacturing capabilities to do a swerve drive even though i could easily program it and make it easy to use. and I HATE THE 4-6 WHEEL TANK DRIVE

[WarpSpeed10]

I think this drive base would be the hardest to program. Just watch it as they kick it. It's beautiful. :')

http://www.youtube.com/watch?v=W1czBcnX1Ww

[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.