Re: Implementing Traction Control for an advantage in the 2009 game
 

Tom,

The FIR filter should work just as well when changing directions. Indeed, you want to back off the throttle from the one direction before increasing in the other direction. Of course, you may want to try using the new Jaguars for this. Also, something other than constant coefficients for the FIR would be interesting...

JMHO.

Mike

Re: Implementing Traction Control for an advantage in the 2009 game
 

It would be interesting to see an analysis on real output speed vs allowed acceleration on the rover wheel/CIM setup. Physics says max acceleration should always be the same, but I tend to remember CIMs being kind of sloshy in their top end. This may break a linear filtering system and limit your max acceleration.

This is all based on the non linearity of PWM duty cycle to torque in the CIM. Anyone with knowledge on this, care to share?

On a side note: I rather like the "Middle Income" situtation Paul suggested. I just don't think input filtering is enough to be super useful.

Re: Implementing Traction Control for an advantage in the 2009 game
 

Tom,

Check this out and you will see why I suggested the Jags... However, I have not been able to do any testing myself yet...

Regards,

Mike

Re: Implementing Traction Control for an advantage in the 2009 game
 

This is something I would like to see end once and for all in FIRST.

Re: Implementing Traction Control for an advantage in the 2009 game
 

All,

Warren is absolutely correct in that my analyssi did not include the dead weight of the trailer. The robot still has to accelerate the trailer, but you also get some tongue weight transfer. The actual equation break down is like this:

F = (Mrobot + Mtrailer) * accel

Ff = (Mrobot + Mtongue) * g * Mu

Setting both sides equal to each other and simplifying:

accel = (Mrobot + Mtongue)/ (Mrobot + Mtrailer) * g * Mu


Let's assume tongue weight is negligible (it is actually really small). The equation breaks down to:

accel = Mrobot * g * Mu / (Mrobot + Mtrailer)

Our estimation of a trailer weight of 40 lbs and a robot weight of 150 lbs (120 + bumpers + battery) puts us at 150 / 190 so the accel is:

accel = 0.79 * g * Mu

Warren's estimate was pretty darn good at 75%. If your robot mass is less, then your ratio gets smaller and you will have a lower available acceleration.

This analysis assumes all of your robot wheels are driving. If you do not have all of your wheels driving, then you will have to decrease your acceleration even more.

Re: Implementing Traction Control for an advantage in the 2009 game
 

In terms of effective application of power, wouldn't using all 4 motors and independently driving each wheel be better for an electronic traction control system? I say this because with a system like that you would more easily be able to isolate the slipping wheel and you would not have to take power away from a wheel that is not slipping, whereas in a one motor per two wheel design if you detect either wheel as slipping your traction control system would take away power from one wheel that is slipping, but possibly also a wheel that is not slipping.

My second thought:

Its been mentioned several times that in the automotive world cars use the anti lock braking system to perform traction control duties. Couldn't a bicycle disk break be used with a pneumatic cylinder driving it to exhibit the same result? Although the system would use a good deal of air, I would think the added driveability would definitely be worth it this year.

My final thought:

If the problem we face is that Traction=Normal Force * Coefficient of friction, and we have now way to increase our coefficient of friction why not increase the normal force? Last year 1741 used a very small vacuum to great effect in capturing balls. Why not apply the same idea to a robot? The area of the robot (28 x 38) is 1064 square inches if even 1/2 psi vacuum is applied to that area that is over 500 pounds of downward force. I know Bill has said that he doesn't like this idea, but he didn't like the idea of launchers last year, and look how many teams did that.

p.s. I know that last part isn't really traction control but its an idea I had that I wanted to throw out there. I guess the thought was who needs traction control if you aren't lacking traction.

Re: Implementing Traction Control for an advantage in the 2009 game
 

Back on a speed sensor (should this kick over to a different thread?), has anyone tried using the Ultrasonics in order to get Doppler effect? I plan on testing this this weekend, but if someone has already got some results to get us headed in the right direction, it would be great.

My thought is that if you use the Ultrasonic distance measuring sensors at an angle, they should measure different distance values for different speeds (doppler effect). What I hope my tests will show is whether or not there is enough range and resolution to get a decent speed measurement.

Addition:
Found this paper describing the physics and moth and testing results from someone elses experimentation.
http://cigr-ejournal.tamu.edu/submis...2001%20007.pdf

Re: Implementing Traction Control for an advantage in the 2009 game
 

As Adam Savage, Jamie Hyneman, and countless others have said,"Close enough." Mathematically you will never be able to create a differentiators using analog or digital components. It does not actually stop you from implementing systems like PID controllers. You just have to realize that the differentiators only acts like a differentiators at certain frequencies. I wonder how Labview implements analog filters because it does have the capability to use the Laplace transform but its an analog construct.
Going much farther would require the expertise of someone with his PHD. At the undergraduate level you really only learn how to implement linear control systems.

Re: Implementing Traction Control for an advantage in the 2009 game
 

Not quite:
Max acceleration = CoF * g (ft/s^2)
dynamic: .05 * 32.174 = 1.6087
static: .06 * 32.174 = 1.93044
thus the 0-10ft/s times are:
dynamic: 10/1.6087 = 6.2162
static: 10/1.9304 = 5.1802
difference: 1.0359

That's just a bit over a second, a fairly significant difference. Not to mention the fact that preventing slip will improve handling.

Re: Implementing Traction Control for an advantage in the 2009 game
 

Also at the end of 5 seconds one will be about 4 feet ahead of the other. Of course this is 24 vs 20 feetwhich means you have traveled about half way across the field.

Re: Implementing Traction Control for an advantage in the 2009 game
 

what might help would be to reverse one of the cims to make them both spin clockwise ( or counterclockwise i forget which way) any way electric motors favor one direction the other direction give less accl.

just a thought

also can someone correct me if im wrong ,because its been a while for me , isn't it just the torque that makes the wheels slip; and if so couldn't you simple create a drivetrain like a 4wd with a cim on each wheel and put a high gear ratio on it.

Re: Implementing Traction Control for an advantage in the 2009 game
 

Therefore, max weight overpowered robots have most acceleration.
I get max acceleration of about 1.5 fpss, and top speed of 10fps,
which is top wheel speed of about [overstrike]32rpm [/Overstrike] 380rpm

Here are two opposite approaches to gear design to aid traction control:
- use little to no reduction on motors so that the peak motor torque is near the friction x torque on wheel. Highcurrent on slow speed motors.
Note Low rotational momentum of gear train, and high current deltas.
Jaguar speed controllers are reported to be better at low speed control.
I don't like this approach....

- use huge reduction (5000/32?) on motors so that the fuller range of motor speeds can be applied and more torque to drive wheel at exactly right speed.
No reason for wheels to ever go > 380rpm.
Note higher rotational momentum of gear train, but lower current deltas.

Re: Implementing Traction Control for an advantage in the 2009 game
 

CIM motors have no significant directional bias.

Re: Implementing Traction Control for an advantage in the 2009 game
 

I finally have something to say and registered, it seems my OCD for computers ' and its peripherals' performance have a use!
Anyways, about mice: I was very ecstatic after I saw the first ever precise and quantified mouse benchmark published on esreality.com http://www.esreality.com/?a=longpost&id=1265679

In short, All mouses ARE NOT created equal, even if they are optical, laser, wireless, wired, high DPI. Many generic mouses(in my opinion) have a very low what esreality terms "malfunction speed", a maximum threshold speed when the mouse begins to report very inaccurate changes in position causing the cursor to seemingly go crazy or unresponsive. Luckily there are some very good mice made years ago that are still even one of the best today.
this benchmark was done in 2006
http://www.esreality.com/?a=longpost&id=1265679&page=21
This page shows all the mice and their perfect control and malfunction speeds on a graph.The best are the mx500 and mx300 capable of performing at 4 m/s if the usb polling rate is overclocked to 1000hz from 125hz; i'm not sure if the robot controller can do that.. I also have an mx518 that may be able to perform at those speeds according to this post http://forums.logitech.com/logitech/...17117#M17 117
Maybe the mx500, mx300, mx518, a4tech x7



hmm what do you mean by getting dirty? how?

Re: Implementing Traction Control for an advantage in the 2009 game
 

Yes, absolutely.I don't think [neumatic cylinders can react fast enough. Even a slow automotive system operates at 15 Hz, far above what a pneumatic system might achieve. Not only are you limited by the valves, air needs to flow and is compressible; pressuretakes time to reach a certain level - this is different from hydraulic systems.read Bill's Blog from January 6th.
Think dust bunnies: bits of hair, thread, and other crud; the object touching the floor but not rolling will act something like a broom, and stuff on the floor will clog up the optical sensor. Maybe not enough in one round, but it should be considered.