Power issues...Electrical? Mechanical?
 

This year we have been plagued with what at first sounds like an electrical problem, then trouble shooting points us more towards a possible mechanical problem.

Here is what we have:
- Drive train is the kit base and transmission, 4wd run by 4 brand new CIM motors. (Gearing is a 21 tooth sprocket at the transmission, 28 tooth sprocket at each wheel) This is nearly identical to the setup we had last year and could easily run 2 matches without a battery change.
- Shooter motor is the large CIM motor spinning an axle with two wheelchair wheels. (It does not run continuously during a match, only when the kids pull the trigger.)
- A Fisher Price motor runs a set of rollers for the ball collector. (Normally off unless the operator turns it on.)
A van door motor run our turret. (Also normally off unless the driver is aiming.)
- We are using the 2005 fuse panel instead of the gold blocks because we want 40 amp breakers on all 5 CIM motors.
- Each motor has it’s own speed controller

The symptoms:
The first time we really drove was at the CT practice competition before ship day. During matches, the robot drive starts out fine but about ½ way through it begins to get sluggish despite having a brand new battery. Eventually we can’t turn or drive and it just stalls on the field. On the OI you can see our voltage drop from 13v to 5v or less. People running the playing field see the same thing. Bring it back to the pits and the battery has recovered back up to 12+ volts.

In the pits we can reproduce this by putting the robot up on blocks (no load on the wheels). Run just the drive motors (4 CIMS) full forward, then full reverse, the battery voltage drops dramatically and the robot controller restarts. You can run the robot full forward on the ground and hold it back with just your foot (not possible with last year’s setup). The bot will gently push, stall, reset the controller, push again, stall, reset, etc…
The problem seems to be pretty equal on both left and right side drive.

On the 2005 circuit breaker board there is a green LED that turns to red after almost every match. We have not been able to watch it closely enough to see exactly when it turns to red. However, if you run the dashboard program it says that none of the breakers have tripped.

Troubleshooting:
First thing we did was check the wiring and replace the robot controller. No change.
Just before ship we replaced this year’s transmission and motors with last years. Things seemed to improve for a short time. We could not get it to stall anymore with the push test and had much more reasonable pushing power. However, at the NJ regional the problem has come back.

Team 11 spent a long time with us in the pits in NJ (Thanks Guys!!!). We ran each CIM directly off the battery, bypassing all the electronics. We noticed that when you run just one CIM it spins at a certain RPM. Power up the second CIM in the transmission and it actually slows down the RPMs. This is true of both the left and right side, as well as the spare transmissions/CIM motors that we have.

We are aware that we have many motors and running all of them at once will drain the battery very fast. However, disabling everything else and using just the 4 CIM’s to drive should not be causing this big of an issue. Last match of the regional the drivers did not use any motors except to drive and we were still dead on the field after 1:30.

Any thoughts?

Re: Power issues...Electrical? Mechanical?
 

is it possible your battery charger is defective, and you are not getting a full charge on your bats?

an ammeter on your motor leads (clamp style) will tell you what you need to know instantly: How much current is each motor taking?

Re: Power issues...Electrical? Mechanical?
 

We have several battery chargers and batteries. They are all fully charged before we use them.

We checked the current while the base was up on blocks. Got around a 6 amp draw from one side (two motors per side) and it peaked at around 14 amps when we quickly shifted from forward to reverse.

Re: Power issues...Electrical? Mechanical?
 

The fact that it's occuring to all the CIMs basically rules out bad motors.

In addition to the battery check to make sure all your connector crimps on the wires are good. Also check the alignment of your drive train parts. Sprockets, gears, chains, shafts, side plates, ect. out of alignment could be causing more drag on the motors.

Do you know if the motors are getting very hot before your robot dies in it's tracks?

Re: Power issues...Electrical? Mechanical?
 

Is the breaker panel connected to the programming port? You won't get status from it unless it is.

Are your motors turning opposite each other and interfering?

Re: Power issues...Electrical? Mechanical?
 

Are motors are spinning in the correct directions, I thought that immediately too.

The motors are not getting hot before they die. Our power cable from the battery was very hot to the touch supposedly after it died during a match.

Should we be using one speed controller per motor, or should we have one speed controller per pair of motors? That way they are running the same speed and one isn't dragging down the other.

Re: Power issues...Electrical? Mechanical?
 

If the CIM's check out OK, and it sounds like they are.

Then, one item I would check is the internals of your transmission. Was it assembled correctly and was it lubricated. We noticed a couple of teams in the past that were so anxious to get their robot started in early January that they hurriedly assembled the trannys and missed a few important details.

Re: Power issues...Electrical? Mechanical?
 

Legally you can only put one CIM per Victor.

Re: Power issues...Electrical? Mechanical?
 

I suspect the set screw wasn't ground down and is causing extra mechanical load in the tranny due to interference or something along that line of reasoning.

Re: Power issues...Electrical? Mechanical?
 

Remember to check your battery under load - a battery will test as though it is fully charged until a load is applied. Check all connections and try using a different charging unit.
It doesn't sound like a motor problem, look at the transmission and your chain routing as too much drag can cause problems too - due to the motors having to work really hard to rotate the wheels.
You mentioned that your gear ratio was nearly identical as last year - relook at last years machine and make sure you didn't miss anything (a gear in the tranny for instance), because it sounds like you may be geared wrong or there is additional friction in your system.
Put last years machine up on blocks and measure how much force it takes to rotate the wheels, then do the same test with this years drive train. I'll bet you will see a big difference.

Re: Power issues...Electrical? Mechanical?
 

Lets see... battery wires hot, means the current is flowing through there too much so the fault is after it. CIMs cold, means the fault is prior to the CIMs. I also assume that you're robot didn't give you a massive shock as if it had a short to the frame. (540's machine did this in our last elim match) The red light is blinking, but the breakers aren't tripping. The RC is good and the Victors still work (can't be a short there, you'd likely damage the Victor if it was on input, or you'd pop the breaker if it was in output. This leads me to think you have a internal fault in your IFI breaker panel. (further evidenced by trannys that worked in a robot with identical power distro failing here) As to the temporary improvment, maybe the replacemnt moved something around that fixed it for a short time. (At VCU our pwm02 was ignoring input and constantly giving reverse values, a little messing with the cable, and it worked. Then after a match it messed up again, only fixed by changing the fuction over to pwm03. The moral? Don't assume the IFI part works perfectly, IFI makes quality components, but has manufacturing faults just like everyone else, especially when their parts are used in a rough, competitive environment, being handled by high school students who are running on very little sleep) As to the loss in RPM, I haven't a clue.

Re: Power issues...Electrical? Mechanical?
 

thats a sure sign that something is wrong with your battery cable, which would explain everything.

There is no way the 6 gauge wire in the battery cable should be getting hot. The breakers would kick off long before you could draw enough current through the cable to heat it up.

I think you will find that either the cable is not securely attached to the connector, or the crimp terminal at one end is loose. Its also possible the cable has been damaged and there are only a few strands connected at some point. If so you should see visable damage to the cable.

We always soldered the terminals on the end of the battery cable, you need the right equipment to solder them on, but it makes the connection bulletproof.

Re: Power issues...Electrical? Mechanical?
 

It sounds like your batteries are surface charging. What I mean is, they look like they are full, but the charge wears off immediately. Have you left your batteries in a hot place for an extended period of time? If so, I'd say you need brand new batteries. If not, I'd have to say it's in the wiring somewhere.

Re: Power issues...Electrical? Mechanical?
 

I would say the batteries are ok based on the hot power wire. We have many new batteries that we try to keep fully charged.

Re: Power issues...Electrical? Mechanical?
 

A lead-acid battery reacting like that is normal. As you are loading it down, the voltage drops, but when the load is removed, it will recover significantly. The exact volatges are critical, a tenth of a volt can help diagnosis. For example, 12.6 is charged and 12.4 is half charged...

I'd suspect your trannies - high friction. But, if that hot wire can be verified, that's something that I'd look at closely, because it shouldn't get any more than pleasantly warm, if anything.

Measure the current draw (since you can verify it on the bench) from the battery, if it is about 50 amps average the battery should last at least 5-7 minutes.

Don