pic: off season chassis

[JVN]

Originally Posted by jsasaki

This is great I put this up to see what kind of comments i would get .. to clarify things up... we can swap all 3 wheels and I think we were also looking at going for all 6 wheels to be plaction style wheels. we are going to run it on friday soooo we'll see

Jun,
Try it in the configuration shown! If nothing else I'm extremely curious how it performs. I don't know if it will perform well (in fact I suspect it won't)... but you'd be my hero if you tried it out and took some video...

I bet if nothing else you could teach some students a cool lesson on drivetrain turning (the video would also be giving me a tool I could use to teach the same things).

-John

[Chris is me]

I think this is really cool. Imagine a robot that could shift its CG at will by moving an arm or a weight. You could pivot among whichever axis you chose, if for whatever reason you didn't want to rotate about your center.

[IKE]

I am with JVN, give it a spin (pun intended) and shoot some video. I would suspect it would have a very crazy behavior if you had a slightly rear biased CG. Take the 2008 game, where you are trying to do laps. If the weight is rear biased, going into the turn I would suspect the robot to initially push (understeer), but then as the weight shifts to the front, and those wheels grab, it would have crazy snap oversteer. With a lot of practice, you could probably make an "FRC Tokyo Drift" video...

[,4lex S.]

Interesting, I think this wheel configuration would be handy in a way. If you ended up pinned, you could shift CG and slip out of it in a lot of cases. My old team designed mechanisms to make the robot 'slippery' in '09 and it worked fantastically. If you can shift CG and need to escape pinning this could be viable.

[Brandon Holley]

Unless theres some sort of optical illusion going on here, it seems that the omni wheels are smaller than the traction ones. The sprockets on all the wheels appear to be the same size as well, meaning the ground speed of the omni and traction wheels will be different. I still think its worth a shot at trying and showing everyone here your results, just wanted to point that out.

-Brando

[PAR_WIG1350]

Originally Posted by Brandon Holley

Unless theres some sort of optical illusion going on here, it seems that the omni wheels are smaller than the traction ones. The sprockets on all the wheels appear to be the same size as well, meaning the ground speed of the omni and traction wheels will be different. I still think its worth a shot at trying and showing everyone here your results, just wanted to point that out.

-Brando

I measured the wheels and the omni wheel seems to bee about 6/7x the size of the outer wheels. Good observation.

[jsasaki]

here's the video a day early.

[Chris is me]

Well that's unexpected. It looks like it's driving exactly like any other drivetrain. Is the omniwheel touching the ground at all? Is it dropped lower than the other wheels, or are all the wheels collinear?

[jsasaki]

Originally Posted by Chris is me

Well that's unexpected. It looks like it's driving exactly like any other drivetrain. Is the omniwheel touching the ground at all? Is it dropped lower than the other wheels, or are all the wheels collinear?

its the dropped 1/8 center. it rocks just a little bit eventually I would like to put on supershifters and run it with that.

[IndySam]

Originally Posted by Chris is me

Well that's unexpected. It looks like it's driving exactly like any other drivetrain. Is the omniwheel touching the ground at all? Is it dropped lower than the other wheels, or are all the wheels collinear?

But it's on a hard surface. Most any drive will work well on that. Carpet will tell the real tale!

[theprgramerdude]

It looks like the front wheel isn't being used at all, like it's acting just as a 4WD with omni's on the front for sliding.

[Chris is me]

Originally Posted by IndySam

But it's on a hard surface. Most any drive will work well on that. Carpet will tell the real tale!

What seemed most odd was that the drive rotated roughly on a dime despite conventional wisdom saying it would have a very odd center of rotation.

[Chris Fultz]

From the video, it looks like most of the weight is on the back, and the robot is acting like a 4 WD, with the omni's being the "front" wheels. The other "front" wheels do not appear to be in contact with the surface.

When it spins, it is turning around a center somewhere between the back and middle wheels - hard to tell by just doing stop frames on the video.

As others said - try it on carpet. The carpet will give a little and absorb the wheels, whick may allow all 6 to have some surface contact.

[PAR_WIG1350]

It did seem to oversteer a bit and hit the pole in the beginning, but that could be due to lag or driver error.

[artdutra04]

Originally Posted by PAR_WIG1350

I measured the wheels and the omni wheel seems to bee about 6/7x the size of the outer wheels. Good observation.

The original photo showed the same size sprockets for the chain runs between the omni wheels and the traction wheels. If this was unchanged, and the wheel diameters of the omni wheels is significantly different (I'm guessing the outer wheels are 8" AM wheels and the omni wheels are 6"), this could be adding another variable into this equation.

If this is the case, the surface velocity of the traction wheels will be faster than the omni wheel, so the omni wheel will experience longitudinal scrubbing (collinear with the omni wheel roller shafts) which may yield weird results when driving or cloud the the expected results of what would happen with equal size OR equal surface velocity wheels.