9 motors too much?
 

So for most teams its "panic now" time and it just really hit me that my team is using 9 motors in all for our robot (4 for drive and 5 for the arm). I was wondering if any other team was using 9 or more motors. Because right now I'm having nightmares of of the 120 amp APP CB tripping :eek::ahh::yikes:. I would feel a lot better if there are other teams using 9 or more motors.

Re: 9 motors too much?
 

We are only using 7 (4 drive and 3 for arm/lift). I don't think any of our past designs used any more, some also used pneumatics to supplement that but still...

Re: 9 motors too much?
 

6 on our "little" guy. i wouldn't worry about the # of motors, so long as they were/are being used within design spec. I use that phrase loosely, because FRC is worse than GM/Ford/etc proving grounds.
Also look at which are being used for what. will they all be powered simultaneously?

Design, create, re-design, band-aids, rinse and repeat.

Re: 9 motors too much?
 

We're using 9 this year. In the past we haven't used more than 6-7 so...

- Sunny

Re: 9 motors too much?
 

We have at least 8 (4 for the drive and 4 for the elevator). We're still figuring things out but we may have up to two more, depending on our manipulator.

Re: 9 motors too much?
 

8 motors, and 6 pneumatic cylinders...

...not including the minibot, which has 2 more motors.

9 motors is not unreasonable at all.

Your 120A breaker shouldn't trip, provided all 9 of your motors are properly geared, and you aren't stalling them.

Re: 9 motors too much?
 

That is actually the exact number we are using and they are set up the same way(4 drive, 5 arm).

In my five years in FIRST the most motors that I have every used before this year was 8 and we never had a battery problem and we have never poped the 120 amp main breaker,ever.

Re: 9 motors too much?
 

8 motors and 2 or 3 pneumatic cylinders here.

Re: 9 motors too much?
 

2175 will have at least 8 (6 drive, 2 manipulator) + at least 2 pneumatic cylinders. Minibot deployment is likely going to add another cylinder or 2.

3573 is keeping simple, 5 motors total (2 drive, 2 arm, 1 minibot deployment).

Re: 9 motors too much?
 

We're currently using 7 motors: 4 CIMs, 2 RS775s, and 1 RS550/540 and 3 Pneumatic Cylinders. There is a possibility of us adding another motor or two in the coming weeks, but it's unlikely.

Considering that some teams are going to have 6 motors + in their drives this year, I think you're doing okay.

Re: 9 motors too much?
 

11 Motors and 10 Pneumatic Cylinders.

Re: 9 motors too much?
 

Andre,
Since the 120 amp breaker was introduced, I think I can count on one hand the number of tripped main breakers I have seen or were told about. Of those, I suspect most were due to defective breaker or some other catastrophic failure. The 120 amp breaker can withstand over 600 amps for several seconds before trip.

Re: 9 motors too much?
 

4 Drive, 4 Arm. 3 pneumatic cylinders. Plus Minibot deployment.

Re: 9 motors too much?
 

We have 4 drive motors, and one arm motor, and one claw cylinder. We're working on getting another motor to actuate the minibot. Since it seems to take us a week or two to mount one motor and get it operating, I don't see us having more than 6

Re: 9 motors too much?
 

it is unlikely the internal resistance of the battery is to high to deliver 120 amps unless you physically get a short. we had 10 motors on our 2009 bot and never blew the breaker we ran at 6-7 volts though.

Re: 9 motors too much?
 

It is highly unlikely you will be able to, because the internal resistance on the battery won't let you pull 120 amps, unless a freak of nature accident occurs.

Our 2009 robot had 10 motors, and we never blew the main breaker.

Re: 9 motors too much?
 

We tripped one once in 2006. :eek:

We had the four drive CIMs, and the big CIM, and the compressor and a pair of FPs running non-stop through 4 pretty darn close to back-to-back elimination matches. There was lots of pushing and shoving, plus our "ramp wiggle" to get into position involved "walking" the robot by cocking it and then running it into the drivers station over and over (which kept the CIMs fairly close to stall)

It actually took us a couple of minutes to find the problem, we didn't think it was possible to pop it under regular robot use!

OP, I've seen more than 9 motors on an FRC robot. I think you're okay.

Re: 9 motors too much?
 

10 motors here.

Re: 9 motors too much?
 

If your worried, you could put some motors on 30A or 20A breakers. Depending on how you're using the motor, they won't come close to this under normal operation.

Keep in mid <R42>:

That's at least 9 jags/spikes/relays. Make sure you leave enough space!

Re: 9 motors too much?
 

We're probably running either 9 or 10 motors this year (6 drive, 1 arm joint, 1 deploy, 1-2 claw). The 120 amp breaker isn't a big concern for us because we will only be pushing over 240 amps when stalling the drive against a wall - and at that point the 40 amps will trip first.

If our drive and arm were simultaneously completely stalled, maybe. Or if we were in a massive pushing match, then tipped, self-righted, and pushed again or something ridiculous. But really, the battery's going to drain first.

Re: 9 motors too much?
 

6 motors on drive
1 for the lift
1-2 for wrist depending on how much space we actually have
1 for end manipulator
1 to deploy mini bot

even with 11 motors total, there is no way that all will be running at the same time, for instance cruising around the field with our CG so high from the mast means that there will never be more than 7 motors running at a time under any appreciable load. also keep in mind that the window motors and the tiny bane bots do not draw much current at all.

Re: 9 motors too much?
 

we are using 5 motors
2 drive
1 arm
2 claw

and 2 on the mini bot

Re: 9 motors too much?
 

We are using 8 motors: 4 drive, 4 lift, along with somewhere around 5 or 6 pneumatic cylinders.

Re: 9 motors too much?
 

If everything works out as planned:
4 drive
2 arm (lifting)
1 minibot deploy
1 Pneumatic on claw
2 Pneumatic (extending arm)

Might swap the arm extending to a motor though

Re: 9 motors too much?
 

Whether or not one trips the 120 amp breaker has far more to do with how the motors are being used, and particularly how many of them are being simultaneously operated near stall, rather than the total number of motors.

Nine motors is more than average, but not particularly unusual for a robot which is more complicated than typical.

Our team has traditionally used more than an average number of motors, but 9 seems like it will be fairly typical this year. We are currently planning for 10 motors this year. However, more motors doesn't necessarily mean a better robot -- we managed to use only 3 motors on a very successful robot in 2008.

Our past history:

• 2005 - 8 motors
• 2006 - 11 motors
• 2007 - 7 motors
• 2008 - 3 Motors (Speed Racer) or 5 motors (Fezzik)
• 2009 - 7 motors
• 2010 - 7 motors (all controlled via Jaguars with CAN)
• 2011 - 10 motors (all controlled via Jaguars with CAN)

My concern this year is actually with controlling 10 motors on a single CAN bus. We had success with 7 motors on CAN last year, but know of other teams that had trouble getting reliable CAN operation with so many devices. We're hoping that the new firmware changes since last year will make 10 CAN devices within the realm of possibility this year.

Re: 9 motors too much?
 

Namely 4 CIMs and 4 RS 775s, which aren't low power/current draw motors. I don't foresee any problems with draw unless we're accelerating forward and sideways and lifting the elevator (and probably firing all solenoids back and forth repeatedly) - all at the same time.

Just make sure you don't do anything like this; keep all motors at or below half-stall torque most of the time and you should be fine.

Re: 9 motors too much?
 

Our team last year used 11 motors. I don't think we ever had a problem with the main breaker. Then again, some of the motors were not really used as much.

Re: 9 motors too much?
 

lol I like how this thread turned into a "what are u using motors for?" Anyway I defiantly feel better now knowing were not doing anything wrong as far as the amount of motors. We have enough jags and victors counting the ones from previous years, 2011 KOP and the ones we have coming in. And space isn't a big issue.

Haha I actually saw that and I thought it was pretty funny how everyone sort of ganged up on the team:p. But thank you for the reference. We are using 8" mecanum wheels, each directly coupled to a 2 stage GEM planetary gearbox. So I dont think we'll have any problems with the drive train specifically. as far as i know 9 motors is the most our team has ever used so it just seemed like a massive amount. But that's to CD a mental crisis has been averted. :) Guess its a good thing I'm not the electrical guy ;)

Re: 9 motors too much?
 

We are either using 8 or 12 motors, depends on which robot we use. Maybe one or two pneumatic cylinders. We have lots of sensors as well this year.

Re: 9 motors too much?
 

We're using what seems to be a low amount of motors this year.

4 Cims - 2 for drive and 2 for our arm
2 Banebots - For the grabber

We do have 2 small 2" stroke pneumatic pistons for something special however :D

Re: 9 motors too much?
 

Ian,
Is it possible you may have tripped due to mechanical stress on the breaker?

For others, the internal resistance of the battery is 11 milliohms. At 500 amps, there will be only 5.5 volts dropped across this resistance which is still enough voltage to power the PD power supplies and keep the Crio and radio up (and therefore your robot). Using smaller snap action breakers does not limit the current to the motors. A CIM will still stall at 133 amps regardless of breaker size. If you use a smaller breaker and then use smaller gauge wire, there can be significant resistance in the wire to limit the current through a motor. The down side to this option is reduced motor performance.
Caveat:breakers that are tripping will heat up. If you hear a buzzing noise from your robot, do not touch the breakers when the robot comes off the field. You will be left with an impression of the breaker size on your finger tip for several months.

Re: 9 motors too much?
 

I disagree, the battery will provide significantly more than 120 Amps. Unhappily, but it will. On what do you base your statement? As Al mentioned, the nominal internal resistance of the battery is 11 mOhm (0.011 Ohm). If I = V/R, 12/0.011 = 1090 Amps. Of course, more realistic would be about half that - for a second or two.:ahh: More than enough to ruin your day.
Hmm, I wonder how he knows that bit of information? :D

Re: 9 motors too much?
 

It is definitely possible. Were playing defense, but not particularly hard defense. IIRC, it was pretty toasty when we found it.

It is near the end of this video. Our robot is the red bumpered ramp shooter. In the final 10 seconds of the match 562 runs back down the field, and we don't move.

Re: 9 motors too much?
 

Ian,
The breaker was warm when you got to it after the match? had it been warm on previous matches?
I should have mentioned there is another failure mode that I have not seen for a long time. Way back in 2006, the KOP contained an SLU terminal for use with the battery wiring and the 120 amp circuit breaker. These terminals were notorious for loosening with vibration. Teams were required by the robot rules to use these terminals. As the robot current draw went up and the terminal became loose on the #6 wire, heat would develop in the connection. Since the 120 amp circuit breaker is a temperature controlled device, this heat changed the trip characteristic of the breaker. The heat from the connection migrated into the breaker. If you check my electrical presentation (WPI site and linked in several threads.) you will see an actual #6 wire damaged (read that melted) due to a loose and improperly terminated battery wire.

Re: 9 motors too much?
 

3: 2 for drive and 1 for arm.

Re: 9 motors too much?
 

I learned early on to observe others and learn from their mistakes.

Re: 9 motors too much?
 

While I don't doubt that it is possible for an FRC bot to trip the 120A breaker, in 8 years of FRC (multiple events per season) I have never once seen my team, or any team at an event we were at trip the main breaker. I'm sure you'll be fine so long as you're geared sensibly. Even if you ARENT geared sensibly, you're much more likely to just kill batteries in no time flat than you are to trip the main breaker. As Don Rotolo and Al Skierkiewicz have been saying, the breaker will happily conduct 600A+ for a few seconds, and the battery will only provide that much current for a few seconds before become fully depleted. I've seen many robots, my own included, that had major issues keeping batteries charged because of incorrect gearing.

Re: 9 motors too much?
 

4 Drive, 4 Manipulators, 1 Compressor (4 pneumatic cyllinders, 3 of which are 3/4" bore and less than 4"; the 4th is single-use for the minibot deployment)

We could easily use 2 less motors, yet they're added in order to balance the load under heavy usage during elims and after competition season. This typically only adds 2-4 amps of usage overall. We may swap the motors on our wrist joint for a dual-cyllinder pneumatic setup depending on driver desires in control.

By using some calculators out there, I've figured that if we're not pushing any other robots and no manipulators experience catastrophic failure, we will use 80 amps IF and only if we run absolutely everything at once. The current moves up by 25-ish amps if we're moving and turning. Of course, the chances that our elevator will run while we move at 13 fps is next to nill in the practicality of our strategy, so this is a worse-case scenario at best.

For fun (and to inspire someone to want to do batteries this year) I can estimate that a single match where we successfully put up 5 tubes on the top row and deploy a minibot will require 24 minutes of recharge time on a 6 amp charger. I think that this is a bigger indicator of whether or not a robot has too much current draw -- low batteries in elims lead to all sorts of incoherent behavior on the field. Again, it's an estimate, but it's useful to know how many chargers and spare batteries we need (and is good fodder for inspiration/training).

Re: 9 motors too much?
 

Yes. It was actually after the robot had been removed from the field and we were done celebrating that someone went over and said "whoah! The breaker's popped!" We were pretty "caught up in the moment" so no one could really recall who had done what, or whether it had been hot previously.

Now that you mention it that loose terminal issue sounds vaguely familiar... but things tend to blur together after a while. :)

Re: 9 motors too much?
 

We're using 10-11 motors.

Drive - 4 motors
Lift - 2 (upgradeable to 3) motors
Arm - 2 motors
Manipulator - 2 motors

Re: 9 motors too much?
 

I feel like we might be under-doing it now... 3 motors. (2 drive, 1 arm) 2 pistons (1 claw, one deploy) I suppose we did keep it super simple. :D

Re: 9 motors too much?
 

You should be fine... normally the big drains...(the drive motors) won't be operating during the lift/arm motion... and even if they do the 120 A breaker can handle much more for short periods...

We are using 8 motors and 8 pneumatic cylinders ...
so far... (not counting the minibot.)

Re: 9 motors too much?
 

It gets worse as you get older or maybe it is just the sixteen years of competition. Yeah that's it!

Re: 9 motors too much?
 

hello yes we are using 8 motors 4 for chasis and 4 for the arm so far we have had no probles with the amps so i would believe you would be okay

Re: 9 motors too much?
 

If anyone is going to trip the 120A breaker this year, it will be us.

We have 9 motors + Air compressor, the important thing here, is that 8 of these motors are for the drive chassis where stall conditions is a possibility, but highly unlikely due to the friction co-efficient of the wheels.

Re: 9 motors too much?
 

Current expectation is 6 motors and an assortment of cylinders for ours.

Re: 9 motors too much?
 

This I cannot WAIT to see! :yikes:

We will have 8 motors (4 CIMs, 3 775s, 1 FP) + the compressor in 2011.