3 CIM Drive Train Battery Draw

[Ether]

Originally Posted by Andrew Schreiber

Straight up wrong.

Caveat lector:

The CIM's each only draw how much power is required to accelerate the bot. 3 CIMs only become useful if your robot is playing tug-of-war (or push of war) . The CIMs are rated at 67A/hr? That doesn't mean that they will always use 67 amps. That is what will happen on full load

... The rest of the post was straight up wrong as well.

[fox46]

The past three years I've been involved with a couple teams using 6 motor drives:

2011

Cybergnomes#2013: 4x CIM + 2x RS775 on Single speed 8x8 drivetrain, 1xRS550 arm stage 1, 1xRS375 arm stage 2, pneumatic gripper.

2012

Cybergnomes#2013: 4x CIM + 2x RS775 on Single speed 8x8 drivetrain, 2x RS550 shooter, 1x AM9012 Conveyor, 1x Window motor pickup retract, 1x RS545 feeder, 1x RS375 Azimuth control.

Ramferno#3756: 4x CIM + 2x FP0673 on single speed 10x10 drivetrain, 2x RS550 shooter, 1x window motor feeder, 1x RS550 conveyor, pneumatic pickup retract.

2013

Cybergnomes#2013: 6 CIM drive single speed on 6x6 drivetrain, 2 MiniCIM on climber, 1 MiniCIM Shooter, BAG Motor Azimuth control.

Never once did we experience a main breaker trip. All machines since they were single speed drivetrains were geared to operate at the limit of traction. They had great acceleration, good *controllable* speed and phenomenal torque. As far as pushing power, they were on-par with the 2 speed 4 motor drivetrains. However, when in a prolonged shoving match they did eat much more power than the 2 speed drives. The behavior we noticed is that if the drivetrain managed to stall (was designed to break wheels free first but on a weakened battery it would occasionally happen), since no three DC motors are exactly the same (why BrianC was getting different current draws during no load) it seemed that the 40A auto-resetting breakers would trip in a cascade fashion. One would go (highest draw motor) which would increase the load on the other two whose breakers would respectively follow suit.

Personally, I think 3 motor 2 speed is a waste of money unless you can generate enough traction through mechanical interaction with the carpet to warrant it. Single speed 3 motor has the benefit of being able to compete with multiple ratio transmissions if geared properly because we are all limited by weight. Remember: force of friction (traction) = normal force (weight) x coefficient of friction (gum rubber on carpet in best case). Since we can't use studs or an apparatus to "claw" at the carpet, every robot is more or less limited in traction by its weight. Where the single speed shines is its ability to go whistling across the field, HIT a robot thus exceeding its static forces of traction with the carpet by overwhelming it with momentum and then "freight train" it across the field without ever letting up or shifting.

That being said... 3 motor 2 speed would allow you to wrestle with other robots without using as much power and with very little worry about tripping any breakers.

Instead you can worry about peeling the tread off your wheels and incurring penalties for damaging the field surface.

For this year, we are again building some very power-hungry robots and I am somewhat concerned about power draw myself but if past experience is any indicator, there shouldn't be too much to worry about. We may be implementing some current-saving techniques like shutting down the compressor or even two drive motors while reloading *the primary weapon* but all in all I would not be too worried.

One thing to mention though, keep an eye on your batteries. 6 motor drives WILL bring a frail battery to its knees during competition so be wary of that old grey battery that your team has had kicking around from 3+ seasons ago.

[JamesCH95]

Originally Posted by yash101

The CIM's each only draw how much power is required to accelerate the bot. 3 CIMs only become useful if your robot is playing tug-of-war (or push of war) . The CIMs are rated at 67A/hr? That doesn't mean that they will always use 67 amps. That is what will happen on full load, and I think you have other things to worry about by then!

Please do a LOT more homework before posting information like this. What you posted was terribly incorrect information.

6 cims can accelerate a robot faster than 4 cims, so they draw more power total.

Cims are not 'rated for 67A/hr'...motors aren't rated by charge capacity, batteries are.

Cims won't always use 67A, but at stall (maximum torque) they can draw 133A. At peak power output they will draw 68A.

[Ether]

Originally Posted by JamesCH95

Cims are not 'rated for 67A/hr'...motors aren't rated by charge capacity, batteries are.

And, when batteries are so rated, the units are not amperes per hour, they are ampere hours.

[JamesCH95]

Originally Posted by Ether

And, when batteries are so rated, the units are not amperes per hour, they are ampere hours.

Correct as always Ether! A*hr, not A/hr