pic: Did Somebody Say Defense Game?

[BBray_T1296]

Originally Posted by wilsonmw04

link is broken, please try again. I'm worried about the snap fuses. I've seen what a resetting snap fuse does to a robots drive train. It isn't pretty.

Really? I can see it just fine.
Anyways, that pic is a screenshot from this pdf, page 34 you will find our switch.

So long as you do stay within the 40amps per motor, you should not need to worry too much about the main

[wilsonmw04]

Originally Posted by BBray_T1296

Really? I can see it just fine.
Anyways, that pic is a screenshot from this pdf, page 34 you will find our switch.

So long as you do stay within the 40amps per motor, you should not need to worry too much about the main

yep, still broken for me. the 40 amp resetting fuses are what scare me. I have never seen a main blow, but the quick resetting 40's popping = a bad day with robots.

[cbale2000]

Originally Posted by wilsonmw04

yep, still broken for me. the 40 amp resetting fuses are what scare me. I have never seen a main blow, but the quick resetting 40's popping = a bad day with robots.

Not saying it can't happen, but in my 8 years on my team I've never seen us trip a 40 amp breaker.

Correct me if I'm wrong here, but doesn't adding the 3rd motor to the gearbox take some of the load off of the other two, thus making a breaker reset less likely?

Originally Posted by cbale2000

Not saying it can't happen, but in my 8 years on my team I've never seen us trip a 40 amp breaker.

Correct me if I'm wrong here, but doesn't adding the 3rd motor to the gearbox take some of the load off of the other two, thus making a breaker reset less likely?

In normal driving, it does take a bit of load off the other motors, but in a pushing match where all motors are giving maximum output you have a larger chance of tripping the breaker with a 6 motor drive than a 4 motor drive. The solution is to just not get into heavy and sustained pushing matches.

[Chris is me]

Originally Posted by Andrew Lawrence

In normal driving, it does take a bit of load off the other motors, but in a pushing match where all motors are giving maximum output you have a larger chance of tripping the breaker with a 6 motor drive than a 4 motor drive. The solution is to just not get into heavy and sustained pushing matches.

This is not a universal, blanket statement. It's less correct than the statement you were referring to actually, which is pretty much always true. With a 6 motor drive, all other things equal, each individual motor will draw less current than each individual motor in a 4 motor system. This makes it harder to trip the 40 amp resetting breakers, which tend to trip first in a 4 motor drive. The tradeoff is that, at certain gear ratios, you are more likely to trip the 120A breaker. The most vulnerable edge case is an extended pushing match when geared above ~10 feet per second. A low gear for a 6 motor 2 speed drive can certainly be geared low enough to prevent this from basically ever happening in a 2 minute long match.

This tradeoff is something teams should carefully analyze and play with when deciding to use a 6 motor drive. Study the breaker spec sheets, both 40A and 120A. Experiment with different motors or robot cooling systems. Run a shifter and push in low gear. There are a lot of ways to try and mitigate this potential pitfall.

(By the way, consider running a low gear that is traction limited with each motor drawing, say, 30 amps instead of 40, if you are extra paranoid)

[Deke]

Originally Posted by Chris is me

(By the way, consider running a low gear that is traction limited with each motor drawing, say, 30 amps instead of 40, if you are extra paranoid)

Or at ~25-30 amps if your team 703. Loving this drive train.

They could push for the entire season and not break a sweat with the motors, breakers, or batteries.

[Lil' Lavery]

Having competed against their 2007 robot....

[Deke]

Originally Posted by cbale2000

Correct me if I'm wrong here, but doesn't adding the 3rd motor to the gearbox take some of the load off of the other two, thus making a breaker reset less likely?

Correct, current = torque. So by adding a 3rd motor to each gearbox you reduce the load on the 40amp breakers while the load on the main breaker will remain the same for the same torque, regardless of motor count.

[dellagd]

To answer your question, yes I did.

[wilsonmw04]

Originally Posted by Infinity2718

Correct, current = torque. So by adding a 3rd motor to each gearbox you reduce the load on the 40amp breakers while the load on the main breaker will remain the same for the same torque, regardless of motor count.

so adding three motors doesn't increase torque? interesting.

[MooreteP]

Mad Crazy Drivetrain.

IMHO, this may be the year that Mecanums make it to Einstein.

A defensive Robot that can strafe in the Goalie zone or between two robots passing is more akin to defensive play in Hockey, Soccer, and Basketball.

Pushing or preventing is another issue, but that may not be the key to defense in Aerial Assist.

[JamesCH95]

Originally Posted by wilsonmw04

so adding three motors doesn't increase torque? interesting.

Adding an extra motor per side does increase the theoretical maximum available torque. However, traction limitations and battery limitations do not allow that torque to be fully utilized.

[Deke]

Originally Posted by JamesCH95

Adding an extra motor per side does increase the theoretical maximum available torque. However, traction limitations and battery limitations do not allow that torque to be fully utilized.

Correct, you would have to be able to feed the motor the extra current to increase the torque. So basically you increase the system stall torque by increasing motors, but can you feed it the extra current?

If two drivetrains exactly the same in traction, weight, gear ratios were in a push off/breaker cook race and the only difference is the motor count (lets say a 4 cim versus a 6 cim), the 4 cim drivetrain will pop its breakers faster. The 6 cims will have less current going through the individual 40a breakers (total flow divided by 6 instead of 4), and slightly less through the main breaker (because they should be running at a slightly higher efficiency).

My assumption why people pop breakers with 6 cims faster than 4 cims is because they think they can push while geared high, when really both systems are limited by their breakers. So you would need the correct gearing in either case to be a good pushing robot.

[JamesCH95]

I think that a brown-out and re-set of the cRIO is a very likely drivetrain induced failure. Not just the breakers blowing. I don't know which one, 6cim or 4cim, would be more likely to trigger a brown-out, though I think a brown-out or low-voltage reset is much more likely than blowing a main breaker.

Full disclosure: I have not a lot of experience blowing 40A breakers, or main breakers for that matter. I've always geared transmissions on robots a little conservatively, prioritizing robustness over ultimate performance. One robot team 95 made had issues with that, a full 4-wheel swerve in 2003, that could drain a battery down to the point of brown-out half-way through a match.

[magnets]

Originally Posted by wilsonmw04

so adding three motors doesn't increase torque? interesting.

There's a limited amount of pushing force that you can have before the wheels start slipping. So if you have two CIMs geared really slow, or 15 CIMs geared really slow, once the wheels slip, you won't see any difference. However, with more CIMs, your traction limited speed will be faster, which is useful for playing defense. If you've got a crazy high traction robot that moves really slowly, it'll be hard to catch up to somebody.