New wheels / floor and encoders for position.

[willson.thomas]

How about simply using two omni wheels with encoders mounted at a 90 degree angle from each other. These would not generate resistance when changing direction and could easily be the x and y for movement.

[Daniel_LaFleur]

Originally Posted by willson.thomas

How about simply using two omni wheels with encoders mounted at a 90 degree angle from each other. These would not generate resistance when changing direction and could easily be the x and y for movement.

Omniwheels do, indeed, add traction (albiet minimal) and thus would be illegal

[BlackBird11891]

you could just use a kit wheel and make it pivot that way your not breaking any rules because its not being powered it would not slip so the encoder would know where it was

[ebarker]

years ago the railroads used quantity four 3,600 hp locomotives to pull a large unit train.

today they use at most three. the way they did that is by automated traction control.

a doppler radar is under the locomotive measuring the actual speed. the traction computers optimize the power delivered to the wheels so that there is optimal slippage driving wheel, about 3%

they got rid of a whole locomotive, plus they get greatly improved fuel economy and operating performance.

anyone game for trying this ? we certainly have the computer to do the job !!

put a dedicated speed controller, drive motor combo on each wheel, figure out where you are actually going, versus where you want to go and off you go.

[paulcd2000]

Originally Posted by BlackBird11891

you could just use a kit wheel and make it pivot that way your not breaking any rules because its not being powered it would not slip so the encoder would know where it was

You're proposing to make a castor out of the rover wheels? that sounds legit but difficult.

[BlackBird11891]

Originally Posted by paulcd2000

You're proposing to make a castor out of the rover wheels? that sounds legit but difficult.

not really it be really easy with a piece like this



attache the caster plate to the top and throw some encoders on it along with a giro

dimension are not exact i gust threw it together in cad

[Dick Linn]

Originally Posted by squirrel

How about using and old ball type computer mouse? it's a sensor...so it's not intended to provide traction. I wonder if they're still available COTS?

I just tried placing my optical mouse on top of a round marble ball and scooting it around. Seems to work, and provides no traction. COTS - Came Out of The Scrap. I'll bet something like that would be legal.

[DonRotolo]

Originally Posted by BlackBird11891

not really it be really easy with a piece like this

Look at a rear caster and you'll see the axle is located significantly away from the vertical axis of rotation, meaning the wheel 'trails' the vertical axle. Look up the automotive term "Caster" to see where the name came from...

Originally Posted by mluckham

Anti-lock brakes in cars use accelerometers plus wheel encoders to detect wheel slip.

No, only wheel speed is needed for ABS - the derivative of the wheel speed is monitored and any decelerations in excess of a 'known' amount (slope) means the wheel is locking up. Accelerometers are not used for traction control either, where the undriven wheel speeds are compared to the driven wheel speeds to address the effects of excess acceleration. ESP control uses accelerometers.

Originally Posted by Dick Linn

I just tried placing my optical mouse on top of a round marble ball and scooting it around. Seems to work, and provides no traction. COTS - Came Out of The Scrap. I'll bet something like that would be legal.

I think that an optical mouse, 1/16 - 1/32" off the surface, might work well. Doppler radar or some similar method would be pretty cool - can that be done with light or ultrasonics? Or just get a radar gun (Ramsey Electronics sells a kit for $60) and point it at an angle to the floor.

[solopilot]

Use an inertial mouse. Or refocus an optical mouse to measure movements...

[EricVanWyk]

The hard part of using the mouse is interfacing to it. The new controller doesn't have any USB inputs on the Robot side, so you would either have to add a microcontroller or learn the PS/2 standard.

Alternatively, you can poke directly into the chip inside the mouse. There is no guarantee that this is a standard protocol - each vendor can use their own. This is the route we chose.

[Jeff Pahl]

The kit also came with a nice accelerometer. If the wheel speed does not match the expected value from the accelerometer, then .....

I think the encoders are going to be very useful this year.

And my gut feeling is that anything touching the floor other than the approved wheels is going to not pass inspection.

[Dave Flowerday]

Originally Posted by EricVanWyk

Alternatively, you can poke directly into the chip inside the mouse. There is no guarantee that this is a standard protocol - each vendor can use their own. This is the route we chose.

Back in 2004 when we worked with Technokats to rework an optical mouse to detect robot movement, we interfaced directly into the chip in the optical mouse and bit-banged the protocol. It was pretty easy with the IFI RC. At that time, there was only 1 manufacturer of the optical interface chips (probably due to patents etc). Not sure if that has changed since then.

[chmp09]

You could use a combination of encoders and an accelerometer to create a traction control system. Traction control works by transferring power to the wheel(s) that is not slipping (ex. if you're driving a car and one of your powered wheels is on ice and the other is on pavement). This wont work when all your drive wheels are on the same surface.

Preventing your driver from spinning out the wheels is the best that you can do (this will provide rolling friction rather than sliding friction). Anti-lock braking wouldn't be a bad idea either.

As far as telling where you are at, a system using an accelerometer and gyro should do the job.

[Tom Line]

Using the accelerometer and gyro for traction control are a bit more difficult that people have been saying without a pretty decent bit of math.

The accelerometer gives linear acceleration.

The gyro can give angular acceleration.

You will need to combine the two mathmatically and integrate to get the expected wheel speed.

Most quadrature encoders that are reasonably expensive are 256 counts a turn (or thereabouts).

When you start to compare the wheel speeds to the expected speeds, the error introduced by the integration of the acceleration and the inaccuracies due to the counts / turn calculation of wheel speed create a very non-trivial problem to keep your wheels from slipping all the time.

Most people I know who have traction control turn it off in the snow. Many times you NEED to floor it, and the traction control simply won't let you. Plus, you can't accelerate at all.

This isn't ice - it's simply low friction. Desensitized joysticks and careful drivers will likely be a better idea than traction control for 'most' teams.

[windell747]

Has anyone considered using an omni-wheel to act as an encoder wheel? I agree with the last post that other than an encoder, an accelerometer can be used to correlate the bots acceleration to what the wheel's angualar acceleration is. The wheel's angular acceleration can be figured out using the kits's encoders. If there is a deviation then you would know that the wheel is slipping and will need to slow down the drive wheels to regain traction. It is important to note however...for this method to work it is assumed that the bot's acceleration is due only to the wheels. If another bot is pushing your's or you hit something while trying to maintain traction, it will be harder to sort out (using the accelerometer and wheel encoder method) wether or not your bot has lost traction due to wheel slippage.