pic: Team 148 Robowranglers: Swerve Module and Motors

[Morgan Gillespie]

Originally Posted by Cory

If you want to go 20 fps you need 6 motors.

If you need 6 motors, you have to do coaxial crab.

If you want to save weight/complexity, you use 3 wheels.

If you use 3 wheels, you have to use all 6 motors in one gearbox.

I think both are each very much their own designs.

You may wish to check up on the factuality of some of these statements.

[lukevanoort]

Originally Posted by Morgan Gillespie

You may wish to check up on the factuality of some of these statements.

True, I wouldn't necessarily make all of those statements as written, particularly in that order, but I think the point still stands. If your goal is to go as fast as robotically possible, you want 6 motors to help acceleration. If your goal is maneuverability while putting all that power to the ground, you want a swerve. Three wheel (67-esque) is a simpler and lighter way to make a swerve. With six-motors and any odd number of modules (except one module), you probably want a coaxial method powering all of them from one gearbox, otherwise you'll have an unequal power distribution between your modules. The module itself was stated to be inspired by 217's systems from about six years ago. I wouldn't be surprised if there was some Robonaut influence in the design (how they steer all the modules together, for example), but it isn't a really obvious one like using a West Coast Drive or something like that.

[Karthik]

Originally Posted by Cory

Not to take anything away from the Robonauts, who clearly have a great design, but it seems like the decision to do what 148 did was simply out of necessity.

If you want to go 20 fps you need 6 motors.

If you need 6 motors, you have to do coaxial crab.

If you want to save weight/complexity, you use 3 wheels.

If you use 3 wheels, you have to use all 6 motors in one gearbox.

I think both are each very much their own designs.

Originally Posted by Morgan Gillespie

You may wish to check up on the factuality of some of these statements.

Morgan,

Although your point is well taken, you may want to be less vague with your statement. If you believe that some or all of Cory's statements aren't valid, specifically address them with your rationale.

I'm not trying to single you out, but lately there's been far too many posts where people make claimss without any real justifications.

As for the meat of Cory's post, I'll attempt to point out the flaws that I think Morgan was trying to get at.

- Although not impossible to go 20 fps without 6 motors, it is incredibly difficult to so with a typical FIRST robot. Unless your robot is significantly lighter than usual, or uses a very low traction wheel, issues such as breaker tripping and battery power become quite serious when only using four motors.
- If trying to do a swerve with 6 motors powering your modules, coaxial is by far the easiest way to do it. As you increase the motors in your system, having to rotate them with the swerve module becomes cumbersome. (In 2004 we used two two-motor swerve modules to drive our robot. Designing our modules such that they remained compact was a significant challenge.)

[Cory]

Originally Posted by EricH

Really...This from a team known for putting 2 CIMs and 1 FP in the same gearbox for a 6WD drop-center.

If you want to do crab and need six motors*

254 has never had a 6 motor drive before. Not sure who you're referring to?

Originally Posted by Morgan Gillespie

You may wish to check up on the factuality of some of these statements.

I'll stick to my guns on all of them, with the exception of the edit I made above. Those statements were not meant to be absolute truths--merely points related to 148's design choices.

I was brief in my description, but it shows you what I believe their design path to be, and why. If you think about it, I think it's not unreasonable to come to the same conclusion

[chaoticprout]

Originally Posted by Cory

If you want to do crab and need six motors*

254 has never had a 6 motor drive before. Not sure who you're referring to?

[EricH]

Originally Posted by Cory

254 has never had a 6 motor drive before. Not sure who you're referring to?

Might have been 968, in 2006. I also know that 696 had 6 motors in 2005, as have other teams.

The point is, you don't have to have a crab with 6 motors. Though I see you've edited for clarity, and I do agree with the 6-motor swerve needing a coaxial (otherwise, you've got two motors loose...), unless you have a three-wheel crab, and if you have that, one wheel will have more power if you don't have a coaxial.

[Cory]

Originally Posted by EricH

Might have been 968, in 2006. I also know that 696 had 6 motors in 2005, as have other teams.

The point is, you don't have to have a crab with 6 motors. Though I see you've edited for clarity, and I do agree with the 6-motor swerve needing a coaxial (otherwise, you've got two motors loose...), unless you have a three-wheel crab, and if you have that, one wheel will have more power if you don't have a coaxial.

968 never had 6 motors either in 2006. We used one CIM and one FP per drive transmission.

Even if you had a 3 wheel crab, it would make no sense to have two wheels with two CIM's each, and one wheel with two FP motors. Hence the need for a coax drive.