Let's Make Robots!

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Remarknl's picture

There are two types of tractorpulling. The fast and spectacular one, and the slow and technical one. My aim is more at the slow type. Thats because i want to learn more about traction control systems. There will be no lifting in the slow type of tractorpulling. Thats why i need the traction control systems. I want my bot to be unbeatable when there is almost no grip at all!

Just to get a few things clear ;-) 

BaseOverApex's picture
Heh heh, then you should probably disregard everything I said! My solution is probably somewhat atypical!!
Remarknl's picture
the rethink piece you said is highly usable! Simple yet theoretically effective!
TeleFox's picture

You know what would improve traction but add very little complexity or weight? A wheelie bar.
warhead4.jpg

You could spring-load it and use a mechanical limiter to keep all 4 wheels on the ground, or failing that at least keep the back 2 on the ground with good force.

Remarknl's picture
That is true but it would also take the traction off the back wheels. Have a look at this: http://www.youtube.com/watch?v=xn66IzXP5Ag my bot will probably behave the same on loose stuff
TeleFox's picture
It depends on where the load is connected, if the connection point is forward from the rear wheels it'll stop the front coming up. If the load connection is behind the rear wheels then because the wheelie bar is unpowered it will still help resist any rotation about the connection point.
Remarknl's picture
Following our regulations based on the original, the load is connected behind the axle and level or lower than the axle. Maybe i will put one on. There is a wonderful connection point i could use.
BaseOverApex's picture

I suggest encoders on teh FRONT wheel rather than the rear. I realise you have the problem of the front wheels lifting, but you really need a "slave" or "jockey" wheel in order to do traction control: you need to know if the vehicle is moving. If you put the encoders on the back, you won't know if the wheels are spinning.

One possibility is an encoder on the end of a shaft which can drop with gravity. That way you alwasy have this slave wheel onteh ground tellig you if you're moving.

My kids have this exact tractor and one trick I did to enhance teh traction was a coat of liquid latex on the wheels. It doesn't last very long because it picks up dust and stuff, but one quick wipe with warm soapy water and the "tyres" are as sticky as ever!!

Great project. I wish I had the free time!!
Remarknl's picture

Thanks for the feedback. I could find a lot on the internet about what traction control does, but not how it works.(I didn't search very long) I was planning to reinvent the wheel and this will give a head start. I am thinking about putting encoders on all the wheels now. isn't very much extra work, but it may come handy later on(information about cornering/drift) The final test will be outside on slippery surfaces, so the latex doesn't seem nessasery.

 thanks for your support! 

 

Edit: I just realized why i wanted the encoders on the back, I read an article about an electronic limited slip diff type of traction control...

BaseOverApex's picture

Ah, yes. You can do slip-diff traction control by adding rotary position sensors on the powered wheels. I don't know how effective that would be on a small model, though, if both wheels are spinning (as seems likely).

Having thought about my last post a little more, I also think you might be able to do something novel to allow you to use only  rear wheel encoders for the case where both rear wheels are spinning. Here's my thinking: for any given current through your motors, there may well be an expected maximum speed. If the wheels are turning too fast for the amount of current being supplied, then they must be spinning. For example, if you're putting 10A (ha ha) through your motors and the wheels are spinning at 60RPM, then they're probably not slipping. If they're spinning at 600RPM, then they probably are.

Edit: Actually, that's complete rubbish. Tamiya models can draw 10A when they're going like stick and also when they're under load.

Rethink: What you need to do is look for a rapid, uncommanded speed increase. Clearly, if your' making a high-torque tractor, you'll want to ramp the current slowly. If the wheels start moving disproportionately quickly, you need to back off on the juice.