Power expander overheat

VEX V5 General Discussion Technical Discussion
1

when my team went to a competition our power expander overheated what could be the problem

2

Please describe what you are running through the power expander and how tough it is to get the motors attached to the PE running. Are your flywheels coming out of there? Drive motors?

We’ve had mixed luck with the PE in the past. They seem susceptible to breaking and the PTC seems sometimes to be easier to trip but it is more anecdotal on that than real hard evidence.

Make sure the power expander wires are not frayed and is still in good condition. The battery connector wire is of a stiffer material than those found on the battery and the connector has frayed on us. Look where the connector meets the power expander to ensure you do not have a short or nearly a short. That will heat up in a hurry!

If the wires are frayed, buy a new power expander. Email Vex support to see if they can help. But you may need to buy a new one. You do not want a fire or shock hazard.

One suggestion in using the PE is to put a standoff along the battery connector wire and zip tie the battery wire to the stand off. This will limit the ability for the power expander battery wire to wiggle into a frayed state at the bottom part going into the PE.

Also limiting the weaker used motors through the Power expander will help in current draw being lower than that of the Cortex. You would think the opposite would be true where the PE only has 4 motors and a well defined battery for its use. But I have not seen this be the case empirically. No heavy duty tests with scopes or current meters, just a lot of head scratching.

3

we are running 4 motors and a battery but it is super easy to get the motors unplugged from the PE

4

But what are the motors doing??? What kind of load are you putting on those poor things?

5

4 balls

6

I’ll try one more time… It is the machinery usually adding the friction and load on the system. Four foam balls is pretty minuscule. Unless you give some real information, it is difficult to get some real help.

So what are your motors driving and the more details the better. Flywheels, gear rations, and shaft layouts all matter here.

7

I can get a picture to you on Friday.

8

thanks

9

here is a pic of our luncher
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10

Wow that is a very fuzzy and rather small picture. It’s a bit hard to see what is going on.

You appear to have four motors for a single flywheel. I see a 49-12 tooth on the part to the flywheel but I can not discern what is on the chain.

Friction checks are what you want to check

  1. Check the free spinning of the top axles. Are they too tight side to side preventing free spin? Are the axles constrained by the plastic spacers that are slowing the axles down? Maybe going with a thinner space and then a few thin washers for just right wiggle room.
  2. Are the bearing blocks too tight? 3/16" drill bit comes in handy there. They can actually slow you down if too tight.
  3. Are the metal shafts hitting the metal c-channels that don;t have bearing blocks? Again drill until not hitting.
  4. the middle shaft - check that out for tightness and friction
  5. high strength 84 tooth vs regular one. Debate rages about using high strength vs regular ones.
  6. Try some lithium grease on the gear faces Does not work as well on the sprockets.
  7. The sprocket and chain introduces more friction inherently but I have seen it successfully done this year on 80Z. But theirs was not in this configuration, theirs was 1:1 all the way around from the motors so 100rpm across three sprockets to get the two drive motors to the driven shaft which then geared up to a flywheel. In your case, is the small sprocket being asked to do too much and whip around on a poor tiny sprocket?
  8. Are the internal gears on the motors all the same? You would be surprised how many times this is not the case.
  9. Chains can introduce some whiplash in there as you start up. Depending upon how rough you are on start up or shut down you could be getting a bit too much current in there causing PTC trips.
  10. drive motor shaft, check that for friction in the bearing blocks and any side ot side tightness preventing spin.
  11. Make sure the motors are all working as individual items. Sure fire source of friction there! Take out the drive shaft and verify each spins at the same speed (see number 8)
11

thanks