Re: 3 CIM Drive Train Battery Draw
 

We ran in our 3 CIM gearboxes over the weekend. Measured with a DC clamp on ammeter the total currrent draw for all 3 motors on an unloaded transmission was 9.2 amps. The funny thing is when checked individually 1 motor was pulling 4.4 amps, the next was at 3.3 amps and the 3rd was at 1.5amps.

When the next transmission was run in we found similar readings as well. The same motor positions in both transmissions had the same basic readings inasmuch that they went from a high current draw to a lower current draw based on their mounting position. The readings only varied by a few tenths of an amp.

After checking gear lash there were no significant differences when run again. These are the AndyMark 3 CIM upgrades for the AM14U chassis..

Re: 3 CIM Drive Train Battery Draw
 

Straight up wrong. We're rocking 3 CIMs in our DT and have 0 intent on pushing anyone. They provide more torque which allows faster acceleration given proper gearing. And let me just say, this beast drives far different than anything I've played with.

Re: 3 CIM Drive Train Battery Draw
 

Caveat lector:

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

Re: 3 CIM Drive Train Battery Draw
 

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.

Re: 3 CIM Drive Train Battery Draw
 

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.

Re: 3 CIM Drive Train Battery Draw
 

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

Re: 3 CIM Drive Train Battery Draw
 

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

Re: 3 CIM Drive Train Battery Draw
 

A circuit breaker doesn't limit your current. It will give you all the current you want until you hang yourself and it trips out.

Re: 3 CIM Drive Train Battery Draw
 

Well if were being nit-picky about my wording. The circuit breaker doesn't give me any current, it allows all the current to pass through it.

Re: 3 CIM Drive Train Battery Draw
 

I disagree with you saying it was nit-picking. Saying it is limiting your current implies it will somehow reduce current draw if it goes above 120A. Whereas, what really happens is if you go above the limit for too long, the breaker will trip and cut out everything on your robot. The second one, which actually happens, is obviously worse.

Re: 3 CIM Drive Train Battery Draw
 

We ran 6 CIMs on our drive train last year and are running 4 CIMs + 4 MiniCIMs on our drive train this year.

Yes it will can eat batteries, we plan to buy 6 new batteries every year, it's just simpler that way and we know we have good batteries. We donate some of the older ones to rookie teams, they still work pretty well but we know they have been run very hard.

For our first two events we were traction limited but our top end speed couldn't keep up with the likes of 118 and 1477. We changed our gearing for Razorback and IRI and knew that if we went for too long in any pushing match we would blow the main breaker or brown out. We still got in pushing matches but we actually had our driver trained to react to the underglow on our robot. It was run directly off the PD board so when voltage would dip low enough to completely kill the lights we knew we only had about 1.5 secs before we would likely brown out the radio. It took some drive practice to get the hang of it but we only blow the main breaker once (that was when we ran into the pyramid and it might have been due to shock and not current) and we browned out in our first match at IRI and never again.

It's entirely doable to run 6+ motors on your drivetrain and can be very advantageous but understand that there our trade offs.

Re: 3 CIM Drive Train Battery Draw
 

You're right it doesnt control the current but it does reduces it to 0 if you go above 120A for too long. In my mind that is a limit.

Re: 3 CIM Drive Train Battery Draw
 

Make EXTRA sure your Battery is fully charged. (at 12 Volts). Today we were at 11.89 and the CIMs started to lag after 30 seconds. They really do take a lot of battery power.

Re: 3 CIM Drive Train Battery Draw
 

Fully charged is well above 12volts, we rarely will start a match with a battery below 12.8 volts.

Re: 3 CIM Drive Train Battery Draw
 

I'm noticing significantly less charge over time than I'm used to, but we are running 5 cims (4 drivetrain, 1 intake). Mostly our high-load fast paced practice with lots of intake run has seen this drop. We're running it a lot more in practice than I expect to under live fire, but I will continue gladly enforce my "1 match, 1 battery" guideline for my team. Can't risk running low and killing effectiveness.

That being said, I still don't expect noticeable voltage drop with less than 3 minutes of intense play like previous years for most teams. I think I've only run one robot in competition doing 2 matches per battery, and that was the unmentionable year, where we had, IIRC, only 3 motors.