Differential?

[Jared Russell]

Originally Posted by caraddicted101

I saw a team use a differential a few years back. They steered the robot using a rack and pinion design. Since you are asking this question for a game like this it makes me want to wonder, Drifting!? It would be a hard task to accomplish seeing as the floor is carpet, but it's a thought.

Drifting sounds like a good way to completely destroy FIRST's carpets...

We've used a software differential for the last few years. Usually with encoders. Though last season we got one working using only a gyro.

Works well enough in either case. You don't even need to do the proper trig - all you want to do is reduce the slip on the inside wheel to an acceptable level.

[King Duke]

by reducing the slip you decrease the RPM's of the inner wheel?

[Darunada]

We have decided against a differential in hardware, and probably in software as well. I hope this thread can help others though!

Thanks!

[Nick02]

I have personally dealt with open diff's and locking diff's in my vehicle. My truck had the stock rearend with the open gears in it, it behaved by doing great in traffic but off-road it sucked if you got one rear wheel in dirt/gravel/air that wheel would spin and the vehicle would go backwards (I forgot to mention I have a 2wd). So I bought a powertrack locking diff and it kicks butt because it "ratchets" around corners using plates to unlock the rear wheels together however it is temperamental and you can’t WOT around a corner or else it will lock up. I can go into a corner and floor it (WOT) the locking diff will lock causing the wheels to chirp and the truck's turning is greatly decreased. When it receives alot of torque from the motor and one wheel slips it will engage and lock the two rear wheels together this makes it great offroad and when doing burnouts (no more pegged leg burnouts ;P).
I doubt that there would be a situation in this years game where you’re robot would have ½ of the drive wheels on one side of the roboto off the ground and thus, an open diff would be a good mechanical means of keeping the wheels nice and smooth through turns.
And here’s a great article on how open diff’s work
http://auto.howstuffworks.com/differential2.htm
I like the idea of programming a “diff” though.

[youngWilliam14]

if you want to build a diff, look at a lego diff, it's just a dumbed down version. i would however add in a fourth gear to make it work more like a real diff

[SgtMillhouse648]

QC Elite last year used a software/electronic differential for our coordinatated steering system. We found the two arcs that would pass through the wheels on each side, and then used a ratio between the two sides to figure out the different speeds the wheels needed to turn. Worked real well.
Malhon

[NHPilot]

((If you were to build a drivetrain that utilizes an "Open Differential", and if you were to lift one of the wheels off of the carpet, the wheel off of the carpet would receive all of the torque and it would spin. The other wheel (on the carpet) would receive no torque and would not move.))

I agree completely but suggest that both outputs from the differential transmit 'equal' torque. By that I mean that both wheels get the same amount of torque, but, because the wheel in the air only requires say .2 ft/lbs to turn it due to lack of resistance, that same .2 ft/lbs of torque at the other wheel is not enough to cause that wheel to rotate. So when the free spinning wheel gets brakes applied, the amount of torque required to turn it increases (at both wheels) until the wheel with good traction is easier to rotate than the now stopped wheel, and the vehicle moves.
Same effect but just a different explanation.