Implementing Traction Control for an advantage in the 2009 game

[keehun]

Originally Posted by DadDean

I think this game is going to fun to build, play, and watch

Do you mean: "I think this game is going to be fun to build, frustrating to play, and funniest to watch"

;-)

[DavidGitz]

Originally Posted by Abwehr

3b. Even in a 4WD robot with 4 independently-powered wheels with encoders, you can detect (some kinds of) slip without the need for additional sensors. You know where on your robot the wheels are mounted. You can measure the speeds of all four wheels. If you examine the speeds of three wheels at a time, you can compute what the speed of the fourth you HAVE to be in order for there to be no slippage. You can do this for all 4 combinations of three wheels and deduce which wheel(s) are lying to you. If all four (or even three, and sometimes two) wheels are slipping, you're still out of luck, but if one wheel loses traction before the others, you will know.

So far this is pretty much exactly what we are doing, but we have a couple other methods too, like an E-Brake that senses the direction of the angle that you are drifting at and when enabled (a joystick button) turns our wheels perpendicular to the drift angle. You wouldn't have much control during the braking but it might help some. We will post our results when available.

[windell747]

Although this might be overly complex, something out of the box would be to create some sort of velocimeter that bounces sound off the ground and measures the change in reflected frequency due to the sound doppler shift. Ocean current profilers work in this fashion. Of course an encoder can accomplish the same thing, in a simler fashion, but just wanted to throw the idea out there.

I like the idea brought up earlier about monitoring the motor's current to detect a drop in load due to the transition from static to kinetic friction.

[XXShadowXX]

Some one might have posted this, but if you use the accelerometer to measure the acceleration of the robot, and solve for what your acceleration should be if the limit of the wheels speed is approaching the speed of the robot, to achieve maximum traction you can multiply the forward force by 120%! Of course you need some serious math for this, but nearly three quarters of it will be math, so if you can solve the math you should be able to program it.

[purduephotog]

Originally Posted by windell747

Although this might be overly complex, something out of the box would be to create some sort of velocimeter that bounces sound off the ground and measures the change in reflected frequency due to the sound doppler shift. Ocean current profilers work in this fashion. Of course an encoder can accomplish the same thing, in a similar fashion, but just wanted to throw the idea out there.

I like the idea brought up earlier about monitoring the motor's current to detect a drop in load due to the transition from static to kinetic friction.

http://cigr-ejournal.tamu.edu/submis...2001%20007.pdf

Ocean current profilers are called sounders, I think? Check out how the weather satellites do it if you're really interested.

[EricVanWyk]

windell747 & purduephotog -

Very cool! That is essentially a radar gun using sound instead of RF. That got me thinking - why not use a radar gun?

Do you know of any vendors that sell an accoustic radar gun?

[Dave Flowerday]

Originally Posted by EricVanWyk

That got me thinking - why not use a radar gun?

I thought of that earlier, but I assume the GDC would take issue with me sticking a 10GHz transmitter on my robot. Then again, the rules as worded don't really address it - they only discuss wireless communication. But, I think the intent is clear - no RF transmitters or receivers on the robot other than the wireless bridge.

[IKE]

I know that for braking and acceleration testing at Chrysler we had an optical 5th wheel device that I believe used laser system similar to an optical mouse just with better range. I think these are pretty expensive, and the ones I found online are heavy (0.5Kg for sensor and 1Kg for single converter).

If anyone finds an optical mouse that reads the surface well without touching it, I would love to know the model!

[Clinton Bolinger]

If your Coefficient of Friction of the mouse is less than the Rover Wheels would that be expectable because it does not increase your traction and you are using it for input rather then output?

-Oris-

[IKE]

Originally Posted by Paul Copioli

To answer the earlier question, what we do on carpet is use an idler wheel on a spring connected to an encoder. this will not really take away from normal force (very, very small spring load) but we are concerned this year that we have to use the actual wheel instead of a small wheel and that the low friction will make that one slip too.

I think that we are going to ask in the Official Q&A if a small caster with no motive force, and no way of providing traction can be used to get surface speed and direction, but I am fairly certain they will give a resounding "NO".

[Tom Bottiglieri]

Has anyone thought about using an FIR filter on joystick inputs? It would work for acceleration from a stop in either direction (F/R), but I am stuck on how change directions or stop without considerable lag.

Thoughts?

[Clinton Bolinger]

Just make the wheel of the caster a Rover Wheel.

-Oris-

[Madison]

Originally Posted by IKE

I think that we are going to ask in the Official Q&A if a small caster with no motive force, and no way of providing traction can be used to get surface speed and direction, but I am fairly certain they will give a resounding "NO".

One of the first responses on the Q&A system indicates that this is legal.

http://forums.usfirst.org/showthread.php?t=10917

[Warren Boudreau]

First, I want to thank everyone for such a wonderful open flow of information on this topic. This is such a tremendous paradigm shift from previous years that teams could fall into a "Cold War" mentality and not share this information with others.

Now, Paul Coplioi's post on the second page made one assumption that I thought I would try to correct.

I don't think that the mass cancels out in the equation for maximum acceleration (amax=g*CoF). If you walk through it carefully, you will see that while the friction force is Cof*robot weight, the mass that you are acceleating includes the trailer weight. In that case, the maximum acceleration of the system will be limited to roughly 75% of g*CoF.

This should only affect teams who are measuring acceleration. Teams using encoders and follower wheels (thank you FIRST GDC for the rapid response to that question) should not see a problem.

[Justin Stiltner]

With the recent allowing of idler wheels this will probably not be needed but my thought was to have a pivoting motor mount with a load cell under one of the mounts, thus you could sense the torque applied to the motor shaft. you should be able to calculate, and after it is done test to find your maximum torque that can be applied before slippage occurs, then write your software to drive the motor to this condition. In this case, if you diden't use speed input (would be a good idea to do so) your joystick would become not a speed input, but a torque input, or just like the accelerator pedal in your car!

But the sensor wheel will most likely give you 95% of the benefit that you are looking for anyway, but I like to throw my ideas out there and see if anyone bites.