Chief Delphi - Mecanum wheels friction coeff- will it work?

Chief Delphi (http://www.chiefdelphi.com/forums/index.php)

- Technical Discussion (http://www.chiefdelphi.com/forums/forumdisplay.php?f=22)

- - Mecanum wheels friction coeff- will it work? (http://www.chiefdelphi.com/forums/showthread.php?t=80490)

Re: Mecanum wheels friction coeff- will it work?

OK FINALLY got the chassis together and loaded the bot to 165 lbs.
These are standard 8" Andy Mark mechanum wheels. 16:1 transmissions, the bump is built correctly and the carpet is reasonably close to the competition type. Here's the result:

http://www.youtube.com/watch?v=jrxLAFJ2R8I

Quote:

Originally Posted by Kevin Sevcik (Post 901960)

Weight distribution may cause you problems if your CoM is too high or too far forward or rear.

I think the problem with the math is assuming 2848's robot is operating on a 45 degree incline. It's clearly never entirely on the 45 degree incline, so it never has to exert the theoretical .707 * mg force to keep it from sliding down the ramp. It always has a pair of wheels on the ground or the top of the platform, or straddling the bump. So it's never actually in a position that matches the physics land scenario of all four wheels on a 45.

Kevin, I think you may have hit on a very important point. At any given time two wheels seem to be on a level plane and not the 45 degree angle of the bump.
Thanks for that insight

Steve
Team 2848

Re: Mecanum wheels friction coeff- will it work?

Quote:

Originally Posted by Steve_Alaniz (Post 905703)

OK FINALLY got the chassis together and loaded the bot to 165 lbs.
These are standard 8" Andy Mark mechanum wheels. Here's the result:

http://www.youtube.com/watch?v=jrxLAFJ2R8I

Steve
Team 2848

I didn't see you doing a spin-in-place maneuver. Have you tried that yet?

~

Re: Mecanum wheels friction coeff- will it work?

Yes, spin in place works too. All the omni functions work correctly and as they should.

http://www.youtube.com/watch?v=jrxLAFJ2R8I

Steve

Team 2848

Re: Mecanum wheels friction coeff- will it work?

Quote:

Originally Posted by Steve_Alaniz (Post 905716)

Yes, spin in place works too. All the omni functions work correctly and as they should.

http://www.youtube.com/watch?v=jrxLAFJ2R8I

Steve

Team 2848

Hi Steve,

May I ask how you have the wheels arranged on the bot?

e.g. does TOP view look like this:

\.........../
\.........../
\.........../
.............
.............
/...........\
/...........\
/...........\

or like this:

/...........\
/...........\
/...........\
.............
.............
\.........../
\.........../
\.........../

...or some other arrangement?

Also, are you guys using a single 3-axis joystick, or 2 2-axis joysticks, or some other arrangement for your driver interface?

Thank you.

~

Re: Mecanum wheels friction coeff- will it work?

From the top.
the roller axles look like

\ /
/ \

We are using a single three axis joystick.

Steve

team 2848

Quote:

Originally Posted by Ether (Post 905720)

Re: Mecanum wheels friction coeff- will it work?

Quote:

Originally Posted by Steve_Alaniz (Post 905716)

Yes, spin in place works too. All the omni functions work correctly and as they should.

http://www.youtube.com/watch?v=jrxLAFJ2R8I

Steve

Team 2848

One other thing, the chassis is a bit unstable making the transition from the bump back to the floor and could tip over. a low center of gravity is a must so we are working to redistribute weight for a more stable bot. If you use mecanums ( or any wheel that makes for a high center of gravity ) you may want to keep this in mind.

Steve
Team 2848