6 wheel drop center Question

[Ether]

Originally Posted by Kevin Leonard

I have no idea how your drivetrain could have torn itself apart.

Originally Posted by CryptoStorm

How exactly did it tear itself apart?

Do tell, please.

[LoneWo1f1998]

Again, I wasn't on the team that year so all I know is that chains were popping and the robot could barely turn even though it had been fine while testing on less grippy carpet. It apparently lurched a lot and they never quite fixed it, but were able to decrease the problem by making the wheels less grippy. As far as wheels go, we are considering 8 inch pneumatic or really anything that is 8 inch and grippy. What I really want to know is how much farther down to place the center wheel as compared to the others. This is like the fifth time I've designed a drivetrain, but we simply haven't needed the 6 wheel drop center in the past.

[Ether]

Originally Posted by LoneWo1f1998

all I know is that chains were popping and the robot could barely turn even though it had been fine while testing on less grippy carpet

Thank you. That's much more informative.

Chains popping sounds like perhaps they were not tensioned properly, or not enough teeth engaged, or chain size too small.

Not turning on more grippy carpet sounds like not enough center drop.

[LoneWo1f1998]

Thanks for helping me zero in on what went wrong that season. I'll try to look back and avoid those mistakes, but how low do you think the center wheel should be?

[Lil' Lavery]

Originally Posted by LoneWo1f1998

Thanks for helping me zero in on what went wrong that season. I'll try to look back and avoid those mistakes, but how low do you think the center wheel should be?

The most common "drop" in the center wheel is 1/8". With pneumatic wheels, you may want to increase that slightly, due to the deformation of the tires under weight. Hard to say exactly, given that it could change with your tire pressure and weight distribution. I find it highly unlikely you'd need to go beyond 1/4", however.

With regards to chain, also make sure the sprockets are aligned properly.

[FrankJ]

Andy Baker (Andymark) has a great power point on basic drive trains. There are many others presentations. Google is your friend, One of the big advantages of 6 wheel systems over 4 wheels tank drive is that the shorter effective wheel base makes it easier to turn. That is assuming that it is set so the robot is mostly supported by the center and one one set of the outboard wheels. Pneumatic wheels are going to make proper set up more critical. Any tank drive has to scrub the wheels to turn. High grip wheels are going to need a lot torque to turn from a stand still and the turn is likely to be a little jumpy. This is one reason many teams use omni wheels on the corners.