Motors overheating on Linear Puncher

VEX V5 General Discussion General Forum
#1

Hi,
We’re using a linear slipgear launcher with two motors and about 3-4 #64 rubber bands. After a while of shooting, it will overheat, obviously due to the PTC tripping. However it has 4 amps of current through 2-5, then 6-9 and 1 and 10, with both motors being on 1 and 10. What could be a fix to this and the cause specifically?

#2

What size is the slipgear?

#3

36 tooth with 9 shaved off.

#4

Are the motors geared for strength or speed?

#5

strength

#6

Are the motors and the slipgear all on one driveshaft or is there a gear ratio?

#7

All on one driveshaft, however we have seen multiple robots with the same layout work without overheating problems.

#8

Do you run the motors continuously and how many times will the gear slip before the motor overheats?

#9

We do and it usually gets around all 32 pre-loads about 3-4 times before overheating, but how long does a PTC take to completely cool-down?

#10

I don’t know how long it takes to cool, but I run my motors with a slight break between each slip (5 milliseconds) which we have found helps the motors not overheat as quickly.

#11

If you can go through that many shots without burning out, why does it matter?

Waiting 10 seconds should be enough for a ptc to reset.

#12

Alright we will try that out. How much slower does that make you getting the pre-loads in.

#13

It matters for back to back matches, plus being able to run skills as well in those fast-paced tournaments, like the State Tournaments are typically.

#14

It does not change the speed that much since when the gear slips, the driveshaft spins enough before stopping so that it is at the point where the gear almost meshes. In the long run it is more useful than harmful.

#15

Alright we will see if that helps, thank you.

#16

Even in matches, a lot of the time is spent getting balls or driving rather than running your puncher. Back to back matches may be of concern, but running through 4 sets of 32 balls is more than enough to do that. In skills, I highly doubt that it is necessary to run more than at most 3 sets. That rate of burnout is fine.

#17

What you could try doing is put your linear puncher motors on any other ports than 1 and 10. From the hardware specifications ports 1 and 10 should have faster response time and no downsides but from experience ports 1 and 10 are weaker. This is just from what I’ve noticed and I don’t have any evidence to prove it.

#18

A round windup/slip gear starts out with low torque (wasting time), and ends with high-torque == high current state. If you do any waiting in the wound-up state, your motors are stalled at the highest torque requirements.

Your motors overheat because of the high current required by the way you use your design:

  • You can change your use to reduce current by driving around in the tripped state, and only wind up and fire immediately when you are ready to fire. If you reduce your cycle time by waiting, be sure to do it in the tripped state, not in the wound-up state.

  • You could change your design to use a spiral trip-hammer cam, which has flatter torque requirement, and can have low current at the full-wound wait state. One of the “3 days” reveal threads shows a spiral trip-hammer cam.

#19

When we were troubleshooting our catapults a few months ago, ports 1 and 10 were spinning visibly slower than the other ports. Not really sure what it means, but it didn’t impact the functionality of the catapult.

#20