1726 Electric Problem

[David Brinza]

Connectors are generally the weak link in electrical systems.

In the space business, people are trained and certified to mate and demate connectors. Before connectors are mated, the contact mating force is verified for each pin/socket, the connectors are visually inspected for bent pins/sockets, both sides of the connectors are cleaned to remove any debris (a little shard of metal can be disastrous) and the proper alignment of plug and socket is verified.

I'd check all connections (including the power distribution block) carefully before blaming the problem on other components in the electrical system.

[Tapoore]

Originally Posted by David Brinza

Connectors are generally the weak link in electrical systems.

Funny story: this year, our hurdle bot weighed only 87 lbs when we got to the competition. We decided to add some weight to get it closer to 120lbs using a couple of dumbbells. We figured that the easiest way to "secure" them would be to use zipties. We put two dumbbells in the front and one in the back near to our electronics board. During our final qualification match, we slammed into the alliance wall pretty fast and the dumbbell came loose and unplugged all of our motor connections! Ooops...

[Qbranch]

Originally Posted by Tapoore

Funny story: this year, our hurdle bot weighed only 87 lbs when we got to the competition. We decided to add some weight to get it closer to 120lbs using a couple of dumbbells. We figured that the easiest way to "secure" them would be to use zipties. We put two dumbbells in the front and one in the back near to our electronics board. During our final qualification match, we slammed into the alliance wall pretty fast and the dumbbell came loose and unplugged all of our motor connections! Ooops...

As a quick aside:

Have you tried running your robot without the extra weight? Since there isn't as much defense this year, you may gain critical extra performance from your robot's drive system.

-q

[EricH]

Troubleshooting: Find source of problem.

This means checking all the wires going into the Victor. Trace them back to wherever they originate. Test the breakers, the connections, everything. All wires includes the PWM cables, by the way, even though I'm fairly certain they aren't the problem.

If you don't find the problem before the breaker panel, figure out where everything on that panel goes. Do any of those have problems? If so, it's probably in the panel or "upstream" somewhere. If not, check the breakers.

[DonRotolo]

Troubleshooting:

When you have a circuit that loses power, there are several methods of identifying the problem. One method, while not simple, is very fast and effective:

Determine how many different things there are in the circuit. For example:
Battery, anderson connector, main breaker, wiring block, yellow thingus, circuit breaker panel, victor, motot connectr(?) and motor. That's 9.

Get several 12 volt LEDs (use a 680 Ohm dropping resistor). Put all of the LEDs in a row and make them visible to an operator or observer.

Connect an LED using clip leads at each point in the circuit where there is a change in the path - at the input to the Anderson connector, the input of the main breaker, the input of the power block, etc.

Duplicate the condition - perhaps on the practice field, I can't say these LEDs are competition-legal.

Watch which LEDs are not lit when the condition occurs, the will lead you right to the problem. Works every time, this is a common technique in automotive repair when time is of the essence. Videotape the LEDs if necessary, to catch very fast transients.

Don

[Al Skierkiewicz]

Wow, this thread went pretty far in just a few hours.
If the drive motors are all cutting out at once, this points to something in the 40 amp wiring, if you are using that. Remember that the black wiring is just as important here as the red wiring. That being said, the problem could be in either the 40 amp block or the Rockwell block. In the order of failures these problems are:
1. Improperly stripped and terminated wiring in the Rockwell Block. Strip 5/8" and do not tin the wires before insertion.
2: Improper termination of the input side of the 40 Amp Maxi Block. Better termination can be made by stripping the input wire about 1-1/4" and folding over the stripped wire before insertion in the Maxi-Block. If you use a #6 wire straight into the block, the strands tend to ride the threads of the clamp screw up the side of the hole and prevent them from becoming part of the connection. Folding over the wire, fills the hole and allows the best clamp when the screw is tightened.
3. Loose jumper strip mounting hardware.

If power is being lost to other robot systems or if your Anderson connector is getting hot, the likely cause is scratched surfaces on the Anderson connector. Often teams use the alligator clips on the charger to connect to the open Anderson connector on the batteries. This raises scratches that reduce the amount of current carrying metal to a fraction of the design surface. The resulting high resistance connection causes heat and a voltage drop across the connector. Spend the money to buy an extra Anderson connector kit. Remove the alligator clips and replace them with the Anderson connectors. You will have to strip the wires from the charger at least two inches and fold them twice to be able to solder into the connector if you con't have the proper crimper.
Breakers do go, bad but rarely. Hot breakers trip more easily than those at room temperature. These are temperature contolled devices after all. (that includes the main breaker.) Hot wiring conducts it's heat to the breaker it is connected to.
If the problem exists on the floor and not on blocks you should suspect loose wiring that is pulled or pushed by the robot frame when on the blocks. Or on rare occasions, wiring is contacting the frame and is shorting out that branch circuit. Suspect any wiring that passes through frame tubing. An errant drill may have put a hole in the tube and damaged the wiring running through it.
As to unbalanced current in a two motor transmission, suspect that the speed contollers are not calibrated. Although rare, a motor does go open and therefore no current flows. If the current draw does approach the same current at a higher speed or load, check the calibration. It is simple to move your joysticks while watching the LEDs on the Victors. Watch to see that both light the LED fully at the same point on the joystick.

[MrForbes]

Thanks for the suggestions, Al. I didn't really get a chance to get into trying to figure out what was going on during competition Saturday afternoon, but we do have some things to look over when we get to LA. We have Andersen connectors on our chargers, we have not used the clips at all.

[copperhead47]

I dont know if somebodys already posted this scenario, b/c i didnt bother to read all posts. your issue could in fact be that you are loading your drive motors too high- we at team 1647 from new jersey have had the same problem and we had the same assumptions (one of the questions i would like to ask is what kind of drive system are you using?) we used the omni drive setup where we have 2 sets of wheels on perpindicular axis to each other- one CIM to a transmission (4 trannys) and the gearing and the diameter of the wheels were factors in overloading on the amperage needed. we solved the problem by creating a whole new drive system that we are goin to swap out at the philadelphia regional. what i would suggest instead of such a darastic change that we did would be to change the gearing inside the tranny or change out to a different brand tranny if thats possible- or maybe find a more powerful matter of CIM. (that can still handle the 40 amp breakers- which may not be possible) other than that... i cant tell you anything else. basically we solved our problem by keeping the same number of motors but dropping trannys by 2 and shifting drive to one axis instead of 2 and shifting to a more tacky wheel for defense... aight thats all i ahve to say... oops i wrote alot sry!

[Al Skierkiewicz]

Jim,
There is one other possibility but you are not going to like it. On rare occassions, the screws that hold the 40 amp Maxi block together come loose. They can only be accessed from the bottom side of the block. If they loosen up, the contact between the input and output terminals of the breakers do not make good contact. If you remove the cover and then pull all of the 40 amp breakers, try moving each of the contacts. If they move, the screws underneath have come loose. I am betting you are going to find a loose wire on the input to the block or on the Rockwell block. Let us know what you find.

[Matt H.]

Thank you all for the advice, I don't believe that the problem is a loose connection as we checked and double checked all of the connections frantically on Saturday and were unable to find anything loose. We also redid the majority of connections examining the wiring for signs of damage.
We did not however fold over the wiring in the maxi fuse block, of check to see if the screws were loose.

[Ken Streeter]

Originally Posted by Qbranch

As a quick aside:
Have you tried running your robot without the extra weight? Since there isn't as much defense this year, you may gain critical extra performance from your robot's drive system.

We ran our hurdling configuration all day on Thursday and Friday without the extra weight. (In hopes that our other configuration could be added on Saturday if we received permission to do so from the GDC.) We found that our robot was a little tippy in a situation we hadn't anticipated -- when carrying a trackball and then bumping up sideways against a trackball which was wedged against the side wall, the two trackballs would smoosh together, storing up energy which would then rebound and flip our robot over onto its side. Amazingly, this happened not just once, but twice in qualifying rounds while driving around the field with a trackball while the arm (and the trackball) where in the "stowed" position!)

[dpc131]

I'm not going to be a big help here, but during semifinals last year, we had a similiar problem. The left motor of our drive system cut out during the first 15 secs. of the tele-operated period. We frantically tried to figure out what was wrong. We tethered and everything worked fine. During our second match the exact same thing happened with the same duration. The IFI guys ensured us it was not a field fault. We hadn't made any program changes for both regionals we went to and still have never been able to duplicate the fault outside the field.

Anyway, I would also take a look at the backup battery charge and connection, we have had issues with large current draws dropping the RC voltage just for a fraction of a second and resetting itself if the backup battery is low or not connected well. Sometimes the terminals in the molex connector can get loose. Just a thought

[MrForbes]

We found the problem pretty quickly this morning,the screw that holds the 6 gage feed wire into the Maxi fuse block was loose, so we put in a new wire (stripped a bit longer) and tightened all the connections on it and the Rockwell block, and it worked fine all day.

Thanks for all the help!