Motors not running full speed?

[JamesCH95]

Originally Posted by team3511

Hello!
Originally we had thought that our code or the cRio was at fault, but it seems that swapping Java with Labview and the 2012 with the older 2011 cRio doesn't solve the issue of our motors running full speed.

The Jag's put out 12V, but the motors seem to be running significantly slower than last year.

What has been checked and is fine:
Code
cRio
Battery
Sidecar
Jaguars

Could it be a safety setting of some type in the new driver station software? Or maybe we're insane and the motors are fine?

Any thoughts are welcome, thanks!

What motors? What gear ratios and end effectors are they connected to? How are you gauging "significantly slower"?

Not sure if Jags need it (probably not) but you may want to check its calibration and also ensure the cRIO and DSC are indeed putting out a full-speed signal. Read "12V" on a multimeter is not sufficient to determine if it is indeed sending full-speed power. Unless you see it as a solid 12V on an oscilloscope remain skeptical.

This might help: http://www.ti.com/lit/an/spma033a/spma033a.pdf

[the man]

Wont the signal light on the jag be solid red or green? Or is that only with the victors?

[Ether]

Originally Posted by JamesCH95

Read "12V" on a multimeter is not sufficient to determine if it is indeed sending full-speed power. Unless you see it as a solid 12V on an oscilloscope remain skeptical.

How about if the multimeter reads the same value at the Jag's power inputs and outputs?

[JamesCH95]

Originally Posted by Ether

How about if the multimeter reads the same value at the Jag's power inputs and outputs?

That would be encouraging.

I will amend my original statement and say that I would remain skeptical using a multimeter unless I absolutely understood how it interpreted DC voltage readings.

I recall (in my ignorance) looking at a pulsed DC voltage signal with two different voltmeters and getting two different readings. Eventually I bought a multimeter with "true RMS" capability that provided a usable value.

[Ether]

Originally Posted by JamesCH95

I would remain skeptical using a multimeter unless I absolutely understood how it interpreted DC voltage readings.

...a pulsed DC voltage signal with two different voltmeters and getting two different readings.

Fair enough.

Has anyone ever done any tests on a variety of voltmeters commonly used by FRC teams to determine how they respond to pulsed DC voltages? I searched but couldn't find anything.

[team3511]

Originally Posted by JamesCH95

What motors? What gear ratios and end effectors are they connected to? How are you gauging "significantly slower"?

The speed difference is noticeable. Last year we could spin the tires in place if we really wanted, now it's hardly moving fast enough to keep up with someone walking.

We're using the CIM motors and toughboxes from andymark. Not sure of the gear ratios.

Will do more testing on the Jags' outputs tomorrow.

[JamesCH95]

Originally Posted by team3511

The speed difference is noticeable. Last year we could spin the tires in place if we really wanted, now it's hardly moving fast enough to keep up with someone walking.

We're using the CIM motors and toughboxes from andymark. Not sure of the gear ratios.

Will do more testing on the Jags' outputs tomorrow.

I'd check your gear ratios and expected drive speed against your previous robot. It is easy to miss something like that.

[jblay]

Have you tried swapping to victors and seeing if the problem magically disappears? Every time we have a problem with a mechanism that uses jags we do this and it is magically fixed.

[billbo911]

Originally Posted by team3511

The speed difference is noticeable. Last year we could spin the tires in place if we really wanted, now it's hardly moving fast enough to keep up with someone walking.

We're using the CIM motors and toughboxes from andymark. Not sure of the gear ratios.

Will do more testing on the Jags' outputs tomorrow.

Assuming everything other than the ToughBox is from the KOP:


Let's start with some basic math. Last year's KOP transmission used a 4.66:1 ratio. It drove 8" wheels through a 2.17:1 chain sprocket reduction. So the overall reduction was 10.1:1 to 8" wheels. So for every revolution the motor makes, the wheel turns 2.49".

An AndyMark ToughBox has 12.75:1 reduction. Add to that the 2.17:1 chain sprocket reduction and the overall drive train reduction would be 27.66:1 driving 6" wheels. So for every motor revolution you get .68 inches of travel.

Yep, way slower. But, you might be able to climb a wall with that drive train!

[AlexH]

How do you know the motors are running slower than last year? Are you basing this of how they sound? Were you running Victors last year? Victors and Jags run at different frequency's. I think, (but can't exactly remember if this is true) that Jags run at a higher frequency than Victors which would make the motor run quieter.

[slijin]

Originally Posted by AlexH

How do you know the motors are running slower than last year? Are you basing this of how they sound? Were you running Victors last year? Victors and Jags run at different frequency's. I think, (but can't exactly remember if this is true) that Jags run at a higher frequency than Victors which would make the motor run quieter.

This only has an effect while ramping up to full speed and during speed control (depending on the application) - it wouldn't decelerate a drive train. What will is a different gear ratio.

[Dominator1619]

I second a re-look at the code. I know in 2010 we switched to labview and were using jags for our drive motors and the robot was noticeably slower than last years robot. In labview the code was set on Vic's and when in the code they were switched, instant return of power. So even though you've checked the code, a second look couldn't hurt

[PhilBot]

Originally Posted by billbo911

Yep, way slower. But, you might be able to climb a wall with that drive train!

Just reading the posts made me suspect gear ratios. But people don't seem to be biting

Don't you hate it when people don't believe the "numbers"

Phil.

[billbo911]

Originally Posted by PhilBot

Just reading the posts made me suspect gear ratios. But people don't seem to be biting

Don't you hate it when people don't believe the "numbers"

Phil.

Hate it? No, but it makes me laugh when the answer is right there and they ignore it.