we have 4 of the pnuematic wheels and each side is driven together. im not sure if driving it like a tank will work. any sugestion
This all depends on the traction of your wheels, size of your wheelbase, and CG of your robot.
The problems you’re likely to encounter are:
- Your robot doesn’t turn.
- Your robot bounces like crazy when turning.
- Your robot draws waaay too much current when turning.
Keep in mind you should test for all these things on carpet, as it has much different properties than bare concrete.
All of these are symptoms of your wheels being forced to slide sideways and not wanting to do so.
This thread has a good discussion on ways around these problems:
We also have 4x pneumatics. Our origanal design called for 2x pneumatics and 2x polyurethane, but the poly wheels were smaller than their specs claimed :rolleyes:
Anyway, skid steering is hard with our 2x drill motor 8 fps drivetrain.
But, and here is what you need, we have a gallon of poly that we will be painting on at least two of the wheels in order to drop their coefficient. We may add other, even slicker stuff if we need to, but I don’t think we will.
You should be able to find it at Lowes or Home Depot or whatever your local giant hardware megastore is.
I hope this helps!
This white paper by Chris Hibner is a great place to start. It walks you through all the calculations for a 4 wheel drive robot, including if it will turn and the minimum force required for the wheels. It also has lots of quick suggestions on how to make a 4 wheel drive robot turn.
the steering will work if you have your transmissions geared down low enough - esentially you have to be able to make the wheels spin, then they will also be able to slide sideways
If you could tell me how this works out, that would be cool. Thanks.
what is poly? polyurathane?
you need to be carefull not to put something on your wheels that will rub or melt off when the tires are spinning or dragging - if you leave deposits or substances on the carpet, your bot could be disqualified - then you will have to find something else to use for front wheels at the regional.
Maybe you should look for different wheels altogether for the two front motors?
I’ve been told its liquid polyurethane or some other kind of plastic. I’m confindent that it will hold up. If not, we will just sand em down and try something else.
We already tried other wheels: it is possible that we oculd find the perfect wheels and order them, while practicing on our current wheels. We will test. I’ll let you know how it pans out, probably by thursday evening.
we tried the poly last year and it held really well to the peices of wheel that continued to fall off(we used kit wheels)
we’ve put zip ties on two of out wheels to solve the sturning problem and it works ok. the only issue we have is that the zip ties bunch when turning.
i was comtemplating the idea of a pop down castor in the back that was down during stearing. while this will work i was hoping to find a less complicated solution.
Last year our team used the tank meathod of dirving and we found it very difficult to get used to. This year we have motors on all axles and we found out that single joystick driving works best.
I’ve never been a real fan of 1 motor per shaft, simply because I always hate getting all four to operate at the same speed. also with two motors the probablity of breakdown is (prob. motor 1 break)*(prob. motor 2 break) which is roughly the same so its (break prob.)^2 while 4 motors is (break prob)^4, much higher…
We did one motor/wheel last year and the reason is simple: we wanted power but we couldn’t make dualie gearboxes.
We put the stuff on the wheels today. I will take a pic and I guess testing is in order for tommorow.
We also did zip-ties as a temporary fix and the helped, but we had to be careful to start our turns slowly.
It was fun driving around. We zip-tied the trannies so we didn’t slip into neutral and put any more holes in walls today. heh.