Hi.
Our robot has 6 wheels on it, but we dont know how to motor the wheels.
Should we motor the middle and the back wheels, both attached to the same motor, and the front wheel is connected to the middle wheel.
The other option is to motor only the middle wheel, while the back wheel and the front wheel are free.
For both things we have good and bad thoughts, and we have no idea which one we should choose.
If you motor the middle and the back you’ll actually produce a different torque when rocked one way over the other.
If you do the back and middle, then use chains and create a chain drive. Alternatively, you can use a belt drive. Take a look at this ChiefDelphi white page: http://www.chiefdelphi.com/media/papers/2216.
Chain drives usually work well.
I would say most teams probably do a chain drive of some sort.
Generally speaking, you probably want all of your wheels powered in some way - it really helps if you’re being pushed, or are off balanced when climbing a ramp, or a dozen other situations that can lift one or more wheels off the ground.
Here’s our setup for 6-wheel drive in the past (we’ve used it 3/5 years since the team started. The other two we used a 4 wheel design for Lunacy and Mecanum drive for Breakaway):
This way, every chain wraps halfway around each sprocket, which helps prevent jumping your chain off the sprocket.
We’ve never direct-driven a wheel (where the output shaft from the motor is used as the axle for the wheel) - we feel that the failure modes for that are a little too risky, compared to running a short chain between the motor and the wheel.
Our standard 6 wheel base has all 6 wheels powered. As long as you drop the center wheel, you shouldn’t have a problem with turning and it will react nearly the same whether it’s rocked forwards or backwards as long as the weight is distributed evenly. We also direct drive our middle wheels off of the gearbox shaft and then use belts to drive the back/front wheels. That way if all the belts break, we’ll still be moving because the middle wheel should always be on the ground.
Alternatively, you can change the center of rotation on a tank drive by driving say the back 4 wheels and putting omnis on the front. This would be good if you had a rear mounted tower and wanted to rotate around the base of the tower, for instance.
Since this was the only post that actually answered what the OP was asking, I’ll tack on a few pictures to help.
For the OP:
This is a direct drive, meaning the center wheel is mounted on the output shaft of the gearbox. The center wheels have double sprockets which then chain to the outside wheels. http://www.chiefdelphi.com/media/photos/32160
This is a 6wd made using the kit gearbox without direct driving the wheel off of the gearbox’s output shaft. http://www.chiefdelphi.com/media/photos/34531
The output shaft of the gearbox has a double sprocket on it. Like this http://www.andymark.com/product-p/am-0421.htm
So, one of the sprockets chains to the back wheel and one chains to the center wheel. The center wheel has a sprocket on both sides. The center wheel is then chained to the front wheel which has another sprocket on it.
Here’s another example: http://www.andymark.com/product-p/am-0959.htm If this had another sprocket on the center wheel and a sprocket on the front wheels, those could be chained together to create a proper 6 wheel drive.
Another example http://www.chiefdelphi.com/media/photos/29579
Hope that answers your question without any confusion.
330 tends to mount their gearboxes aft of center, then do a chain run to the center and another to the back wheel. Then another chain is run from the center to the front. This is best seen in http://www.chiefdelphi.com/media/img/cbe/cbe689388b850647a922111b05e54dc2_l.jpg, which is of our 2007 practice robot. (Also used in 2005 and I think 2008.)
We’ve also put it above the center wheel and run one chain to the center and back wheels and another to the center and front wheels on our 2006 robot: http://www.chiefdelphi.com/media/img/761/76187bce773a93a032c2c2e800d247fd_l.jpg
Found some pictures of our method, on a couple of different robots.
Last year:
http://www.chiefdelphi.com/media/photos/36210
http://www.chiefdelphi.com/media/photos/36211
2008:
http://www.chiefdelphi.com/media/photos/30269
http://www.chiefdelphi.com/media/photos/30266
whoops, I guess I didn’t explained my self good enough.
the options we are considering are either use chains that connect the back wheel to the motor, another chain that connects the middle and the motor, and a third one that connects the middle wheel to the front wheel.
the other option is to connect only the middle wheels to the motor, while the rest are free.
It’s almost always a good idea to power all your wheels. Leaving unpowered wheels reduces your tractive force, since not all of the robot’s weight is supported by powered wheels. It can cause problems with climbing, if your powered wheels get lifted off the ground. The same thing can happen during a pushing match. If an opponent even momentarily lifts you off your powered wheels, they will be able to carry you around the field on your free wheels with practically no effort.
This thread has some good ideas for how to do an all-wheel-drive setup like this in a six wheel drive.
Yes, use the first option. The second option has no benefits.
My team used a six wheel drive this season, and we motored the wheels that way. Worked perfectly.
reported.
