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Unread 05-01-2009, 17:35
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Joe Johnson Joe Johnson is offline
Engineer at Medrobotics
AKA: Dr. Joe
FRC #0088 (TJ2)
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Re: 4WD Turning Difficulties

Quote:
Originally Posted by GregW11 View Post
Hm... what if you had a six-wheel design (skid steer, it won't work so well for arcade style) in which the front and back wheels had motors but the center wheels didn't, and there were sensors in all the wheels. The center wheels would be the actual rotation of the wheels while the front and back would be what the motors are doing, and the controller would adjust the output of these motors based on the actual wheel rotation versus what the motors are trying to do. (if that made any sense at all) I'll try to explain in a diagram below:

| | <motors on these wheels sensor compares rpm to center wheels

| | <no motors on these wheels, sensor gets rpm for actual speed

| | <motors on these wheels, sensor compares rpm to center wheels

Controller will adjust actual output of the motors. It's not fully autonomous, since you're still controlling which direction it is supposed to be going and the speed desired.

If anyone wants me to I'll try and do a sort of block-diagram showing a general flow of possible commands.
Unpowered wheels with significant weight on them means that the powered wheels have just that much less normal force to get traction.

I believe that successful teams are going to optimize their traction. Don't be fooled by past years.

In the past you saw robots jumping as they turned corners, drive motors that cut out from the circuit breakers tripping and sometimes smoke pouring out of the motors and you knew, ah, something is less than optimal there. This year there will be none of that. Teams will think, my robot is not hopping as it turns, my motors are not tripping the breakers or even getting hot... ...everything is right with the world.

No such luck.

Many teams will not discover their lack or RELATIVE mobility until practice day. Too late.

By the way, backing up long distances is going to be impossible for all but the best teams. Think of the mobility issues that is going to cause.

This is a year I regret more than ever being on the sidelines... ...the engineering challenges are fun, not well understood and provide significant advantages...

...now if only I weren't worried about loosing the audience...

Joe J.
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