Chief Delphi - Swerve Concept

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- - Swerve Concept (http://www.chiefdelphi.com/forums/showthread.php?t=129925)

Re: Swerve Concept

Quote:

Originally Posted by Greg Woelki (Post 1391660)

Okay, so about half a second or so.

FYI, I just tested ours using smartdashboard. It looks like 200 ms for a 90 degree turn, which matches our design calcs pretty closely.

Re: Swerve Concept

Quote:

Originally Posted by Jefferson (Post 1391720)

FYI, I just tested ours using smartdashboard. It looks like 200 ms for a 90 degree turn, which matches our design calcs pretty closely.

Mind posting motor, gearing and what the wheel is? Thanks!

Re: Swerve Concept

Quote:

Originally Posted by AdamHeard (Post 1391721)

Mind posting motor, gearing and what the wheel is? Thanks!

AM0912
100:1 VersaPlanetary
42T:66T (we think... At least that's close) sprockets

Edit: AndyMark 6" performance wheels

Re: Swerve Concept

A swerve control algorithm can always run the drive motors one direction and check to see which way to turn. Least distance. Or the algorithm can look for the shortest distance with motor reversal. Both will work. We have done the latter. This does put a stress mechanical and electrically on the module. The first has increased response times. Now say you have a CVT solution for swerve, but the response is asymmetric on the direction of the drive motors. Works really good counter clockwise, terrible clockwise shaft end. Do you accept greater than 90 degree steering solutions for CVT or is the steering response more important? That's what I've asked our team.

Re: Swerve Concept

Quote:

Originally Posted by Greg Woelki (Post 1391660)

Okay, so about half a second or so.

So... optimally, what RPM should the module turn at? What speed do teams that consistently use swerve revolve at?

Re: Swerve Concept

Quote:

Originally Posted by ekapalka (Post 1391771)

So... optimally, what RPM should the module turn at? What speed do teams that consistently use swerve revolve at?

See my response above. I measured a 90 degree turn at 200 ms. We had designed for around 1 RPM, and it looks like we are a little faster than that.

That is with the hardware-enabled ramp on the Jaguar and limiting the output to 75% in the software. Those guys can eat a battery up if you let them.

Re: Swerve Concept

Quote:

Originally Posted by Jefferson (Post 1391790)

I measured a 90 degree turn at 200 ms. We had designed for around 1 RPM, and it looks like we are a little faster than that.

A lot faster. 90deg/200ms = 75 RPM.

Re: Swerve Concept

Quote:

Originally Posted by Ether (Post 1391795)

A lot faster. 90deg/200ms = 75 RPM.

you are correct. Although, I think he meant 1 RPS.:D

Re: Swerve Concept

Quote:

Originally Posted by jimbo493 (Post 1391623)

2 Wheels allow for more traction

Quote:

Originally Posted by Greg Woelki (Post 1391625)

Well keep in mind that, while more wheels will keep the tread pattern from wearing down as quickly, doubling the number of wheels will give only a very minor improvement in traction since, while it is simplified, friction very closely equals N*mu.

Quote:

Originally Posted by Bryce Paputa (Post 1391628)

On a deformable surface like carpet, the n mu approximation isn't a valid assumption, he'd pretty much need to test it himself with his wheel setup in order to figure out how friction would be effected. With a rough top tread I would think you would get more friction

Quote:

Originally Posted by Greg Woelki (Post 1391632)

Do you know of any quantitative data that teams have collected about this with different wheels/treads? I have been unable to find any.

MOE just did this test last week. Our test rig was a simple 4 wheel cart with the wheels locked in place. We used 4 inch AM Performance Wheels (1 inch wide) with riveted on blue nitrile*. The cart was first weighed down to 127lb total and dragged with a force gauge. It slipped when the gauge read ~108lb. The test was then repeated with more weight (192lb total) and slipped at ~160lb. We took this to mean that the relationship between weight and force needed to slip was relatively linear as the % increase in force needed to pull was about the same. We then added 4 more identical wheels to the same 4 axles and locked them in place effectively creating a 2 inch wide, 4 inch diameter wheel. The cart was pulled a third time and the reading was ~180lb. This shows that (at least for a 4 inch diameter wheel with blue nitrile) wheel width will certainly give you more traction but it is not anywhere close to 1:1. More like 100% increase in width = 13% increase in traction, so it's worth is still subject to some debate.

We opted to go with the force gauge test because we felt it was safer, easier and more accurate than the ramp test (the cart tended to fall forward off the ramp before it slipped)

*not new, slight wear.

Re: Swerve Concept

Quote:

Originally Posted by Ether (Post 1391795)

A lot faster. 90deg/200ms = 75 RPM.

Ha! Yes. Good catch. 1RPM wouldn't do a lot of good in a 2 min match.

1RPS

Re: Swerve Concept

Quote:

Originally Posted by Ether (Post 1391795)

A lot faster. 90deg/200ms = 75 RPM.

Wow... that's less than half the proposed speed for this design. What is the reasoning behind that? I guess there's a threshold beyond which the speed qualifies as unnecessarily fast, but where do you draw the line?