Asymetrical Drive

[frank26080115]

I want to build a mini sumo robot that can stand a chance in competitions, and I think the trick is to have a wide wheel.

Has anybody built a robot with a differential drive but with one wheel in front of the other? Is it a good idea if i needed to save space?

[Rebelgium]

I don't get what you mean, can you draw it.

[Robotboy86]

i *THINK* he means that instead of your standard motor per wheel setup, you could instead go with something like 2 huge motors, powering the wheels through a differential?  Like your car, the two drive wheels are powered by ONE power source, but split via a diff.  If so, he wants to split it between front right, rear right, and front left, rear left.


If that is what you are saying, I can understand what your thinking..  to save space you would only need 2 motors.  Perhaps set in the middle of the 4 tires.


Is that what you meant?

[frank26080115]

here is an example of what i mean
notice how the axles are not in line
http://www.flickr.com/photos/68357501@N00/466357333/

[Rebelgium]

oh like that.
Yeah, that's not a big problem.

The downsides are that there'll be slightly more wear on your tyres when turning (which will not be much because the weight of your robot will be very small).
This will cause the robot to turn not as fast as it would if the wheels were lined up.
Which is not so good for a sumo bot...

but I don't think the effect will be very bad. Just get your wheels lined up as much as possible.

[Tsukubadaisei]

I dont recomend this design. The bigger the wheel, the weaker the torque. It will be easier to push your robot backwards. About the motors, dont use stearing and diff gears for two reasons: difficult to build and only one motor for power. There are a number of reasons for cars to use diff. gears and the biggest is the fact that you cant precisely control the rotation speed of an engine. If you had 2 engines one connect to each wheel it would be very difficult to drive the car. Some electric cars I have seen use 2 motors. Some with double steering use 8. If you use diff steering in your robot you will need a very big motor in order to defeat the opponents. Also you would lose a lot of mobility. Using a normal robot I could easyly move to your side and and push you while you would be wasting time steering. I recommend 2 steeper motors connected to small wheels. The higher the torque the better.

[Rebelgium]

I dont recomend this design. The bigger the wheel, the weaker the torque.

He never said he'd use a big wheel. right?
He said he believes it's better to use a wide wheel.

About the motors, dont use stearing and diff gears for two reasons: difficult to build and only one motor for power. There are a number of reasons for cars to use diff. gears and the biggest is the fact that you cant precisely control the rotation speed of an engine. If you had 2 engines one connect to each wheel it would be very difficult to drive the car. Some electric cars I have seen use 2 motors. Some with double steering use 8. If you use diff steering in your robot you will need a very big motor in order to defeat the opponents. Also you would lose a lot of mobility. Using a normal robot I could easyly move to your side and and push you while you would be wasting time steering. I recommend 2 steeper motors connected to small wheels. The higher the torque the better.

Differential drive is the name of the technique where your left wheels are attached to one motor, and your right wheels are attached to another motor. Differential drive is used by almost all robots...
He didn't mean he'll use differential gears like in a car.

[Tsukubadaisei]

I dont know about the differential drive/gear definition difference but whatever, I hardly ever use 2 wheels.

But about the wide wheel It can mean a big wheel. Wide means big area and the one of the areas(and the most noticeable) of a wheel is pi*r*r so I believe it is pretty natural to assume he is going to use long radius wheel. The best word whould be thick wheel. Anyway, I dont see the point of using a think wheel. Friction is not a function of the contact area(Friction=u*N and N is the contact force between the floor and the wheel. For a sumo robot it will mostly be the weigth of the robot). It is going to be an waste of space and resources.

[frank26080115]

but doesn't the static friction coefficient increase with contacting surface area?

anyways, it's not a problem now, i'm using tracks

[Tsukubadaisei]

No. Area has nothing to do with friction in macroscale.

If you look at a micro/nanoscale picture of a surface, you can see that friction is all about area shape. But in macroscale the things work differently.

About threads, I have never seen a sumo robot that uses threads. Not because they are bad but because they are easy to take appart. Try to find some and try to take them apart. For most of them(as far as I know) you will easily unconnect them. I see a lot of not-sumo-robots that use tracks but depending on the movement the tracks suddenly unconnect. The only good ones I have seen so far are the lego ones.

[ed1380]

I dont recomend this design. The bigger the wheel, the weaker the torque. It will be easier to push your robot backwards. About the motors, dont use stearing and diff gears for two reasons: difficult to build and only one motor for power. There are a number of reasons for cars to use diff. gears and the biggest is the fact that you cant precisely control the rotation speed of an engine. If you had 2 engines one connect to each wheel it would be very difficult to drive the car. Some electric cars I have seen use 2 motors. Some with double steering use 8. If you use diff steering in your robot you will need a very big motor in order to defeat the opponents. Also you would lose a lot of mobility. Using a normal robot I could easyly move to your side and and push you while you would be wasting time steering. I recommend 2 steeper motors connected to small wheels. The higher the torque the better.

check this out. and speaking of power. this thing has enough of it 

[Tsukubadaisei]

HeyHey, this is completely different from what I said(or at least what I wanted to say). I was talking about connecting 1 engine to 1 wheel. We would have 2 engines or 4 engines, a lot of power, but unable to drive because each engine would have diferent rpm. The mechanism in your picture, both engines are conected to the same axis so their rpm must be the same. MillenWorks dual steering system rocks by the way.

[Ro-Bot-X]

Frank, I sugest getting a Lego Robotics Invention System and a few extra parts (2 more motors, 2 more light sensors, gears, one extra differential) and the book Building Robots with Lego Mindstorms. There are lots of samples of different drive systems, pros and cons, and you can custom build a chassis and a gear system to learn how things work. Put the Lego robot against your tank style robot and see how the last one can be improved. You will learn a lot from this.