Turning with 4 kit wheels

[2185Bilal]

So our team is using 4 kit wheels on our robot competing at GTR West
But the problem we are experiencing is that the robot starts to jump every time we start to turn.

Specs:
- 4 cim motors, 2 on each side connecting to the Toughbox gearboxes
- 4 kit wheels
- And all four wheels are geared

What can we do to smooth out the turning of the robot

thanks, btw we want something that is a easy fix

[Akash Rastogi]

....Are you in long configuration?

[Ether]

Originally Posted by 2185Bilal

So our team is using 4 kit wheels on our robot competing at GTR West
But the problem we are experiencing is that the robot starts to jump every time we start to turn.

Specs:
- 4 cim motors, 2 on each side connecting to the Toughbox gearboxes
- 4 kit wheels
- And all four wheels are geared

What can we do to smooth out the turning of the robot

thanks, btw we want something that is a easy fix

Replace the front (or rear) wheels with omni wheels.

By the way, do you have 4 Toughboxes (one for each wheel) so that all 4 wheels are independently driven, or do you have one Toughbox on each side driving a front and rear wheel via chain?

[EricH]

Reduce traction for one set of wheels. Now that I've given the solution, here are some possible ways to implement it:

--Add a middle wheel to each side, dropped slightly from the rest.
--Swap 2 of the 4 wheels for omni wheels (not easy if you don't have said omnis, but that's something to think about for later seasons)
--Swap one end's wheels for lower-traction wheels (or possibly higher-traction wheels... but that's not something I'd try)
--Grab a roll of duct tape and wrap it around the tread on one end of the robot. Replace every couple matches or so.
--Grab a couple containers of zip ties and put zip ties around the treads.

And, at the end of the event, grab a roll of field carpet if you can (talk to the FTA and arrange a transport vehicle); this will allow you to test your drivetrain under competition field conditions in future years.

[Kyle A]

If you can't get omni wheels, the 2009 Lunacy wheels work really nice to help turn. We did this back in 2011 and it helped performance a bunch.

[Racer26]

Frustrating that a 7th year team is still having this problem.

But yes, the problem is too much traction on too long of a wheelbase.

Either shorten the wheelbase (move the wheels closer together), which might cause tipping problems or reduce traction on one set of wheels (front or back) by swapping for lower traction wheels (2009 rover wheels, or omni wheels are likely best choices) or by adding tape or zipties to the wheels you have.

[2185Bilal]

Though we are a 7th year team, because of the Ontario Strike Problems, many of our metors were not able to come back and help us out and since the team roster is all rookie....its tuff

[2185Bilal]

Originally Posted by Ether

Replace the front (or rear) wheels with omni wheels.

By the way, do you have 4 Toughboxes (one for each wheel) so that all 4 wheels are independently driven, or do you have one Toughbox on each side driving a front and rear wheel via chain?

Yeah we have two CIM on one Toughbox on each side, and yes we are driving via chain

[mman1506]

We added 2 lunacy wheels to the front of our KOP robot. After that are drivers said it was one of the best driving robots we have.

[nickcvet89]

This is a very common issue when most of us start building robots. The reason why 4wd is hard to work with (assuming your robot is in this configuration) is if all wheels are placed on the corners of the robot you have a problem with turning. The wheels are traveling at different speeds and distances. This is why cars have differentials, so that one side is slowed while in a turn. Check this website for more info. Our team was able to make 4wd work by placing the 2 wheels on each side almost side by side with less than 6 inch gap in between them. The short distance overcomes the issues I mentioned before. But we have not done this in years and opted to go with 6wd instead.

[Racer26]

Skid steering is actually quite different from differentials in cars.

The problem has more to do with a high lateral coefficient of friction between the carpet and your wheels (meaning how hard is it to push the wheels across the carpet perpendicular to the wheels plane of rotation). A high lateral coefficient of friction, plus a wheelbase that is longer than its track width makes for a robot that doesn't turn.

Building a long orientation bot with 6wd, dropping the center set of wheels by 1/8" has the effect of creating two stable 4wd configurations with a short wheelbase.

[cmrnpizzo14]

This white paper covers what you want to know pretty thoroughly.