Blowing spike fuses

Technical Electrical
1

Ok here is the setup:
All motors are RS-550 motors

256:1 Banebot on a conveyor system -> VexSpike -> PDBoard (20AMP fuse)
64:1 Banebot on a loader wheel -> VexSpike (@ 2.5 in compression on ball) -> PDBoard (20AMP fuse)
4:1 Banebot on launcher wheel -> Jag -> PDBoard (20AMP fuse)

Wires have been double checked. We have blown three fuses in the spike connected to the 64:1 loader wheel (it lasts for several test runs and then blows and yet never develops enough consistency to pinpoint any one thing).

We have toyed with wiring, code, and fuses (both the standard 20AMP yellow fuses and the reset fuses in the PDboard) and just can’t seem to locate our issue. Ideas would be appreciated regarding what we might be missing.

2

The answer is simple: your motors are drawing more than the 20amp fuse in the Spike can handle.

Try moving these motors over to Victor or Jaguar speed controllers on 30amp circuit breakers.

3

That’s what we thought at first as well…however…it is only the fuse on the 64:1 that is blowing the other (256:1 Banebot with RS-550) is solid and steady with no blown fuses at all, that’s why we’re confuzzled…

4

There are various reasons that this particular system could require more than 20A; there may be more resistance in the system, the power necessary to drive is greater despite the comparatively lower reduction (with respect to the 256:1), etc.

Have you tried art’s suggestion and swapped out the controller & fuse for those of a 30A circuit?

5

In the meantime use the big black 20amp fuses that fit in the pd board (they automatically reset)… Those little yellow ones can start adding up. It sounds like a motor controller is the best solution.

6

Keep in mind the ONLY time this can be done in competition is for the spike controlling the compressor!

7

You are missing nothing. It is simply that the motor is drawing far more than 20 amps. Remember that every motor draw stall current when you first apply power to the motor. When you couple the motor to a mechanism that adds a load to the motor, the stall current (or near to that amount) will flow for long enough to blow the fuse. The 20 amp fuse in the Spike is designed to protect the contacts of the relays inside the Spike. Your only choice is to reduce the load on the motor or swap the Spike for a speed controller.

8

Thanks for all the advice guys. I’m a NEMO/Coach (I knew nothing about engineering and motors when I started this 5 years ago and now I learn new things everyday about really cool stuff. Much of it I have learned from you guys here on Delphi and trial and error (and pretty magic smoke coming out of motors :yikes: )

Will look at what we can do about switching to a different controller.

Have a great day!

9

Even though you’re using the same motor, the fact that you’re using different gear boxes and using them in different applications is comparing apples to oranges to bananas.

The stall current of the RS550 is 85 amps. Thus you can use less then 1/4 of the stall torque before blowing the fuse. Your gearboxes also play a role. With the 256:1 gearbox, you can get 4 times as much torque before blowing the fuse as the 64:1.

Fuses don’t blow immediately when the fuse current is exceeded. It takes a little time for the metal inside the fuse to heat up and blow. The higher the current, the faster this happens. Most likely, your intake is drawing a little more then 20 amps, and after a few activations, it’s finally enough to blow your fuse.

Besides changing to a speed controller, other options would be to change the gearbox to a larger reduction, or decrease the compression on the ball (this should require less torque and thus draw less current).

10

Which rule says you cannot use the self resetting circuit breaker in the spike? Or says you have to use a fuse rather than the 20 amp CB? I cannot find mention of that in the 2012 rule book.

The vex web site says specifically the spike is designed for the self resetting CB.

11

R58.

The control system is designed to allow wireless control of the Robots. The Driver Station software, FirstTouch I/O module, cRIO, speed controllers, relay modules, wireless bridge, and batteries shall not be tampered with, modified, or adjusted in any way (tampering includes drilling, cutting, machining, gluing, rewiring, disassembling, etc.), with the following exceptions:

Emphasis mine.

12

Since this rule only specifically says that the spike regulating the compressor may have a replaced fuse, my interpretation of the rule is that you can only replace the fuse on the compressor’s spike; I feel that the manual would have been worded differently if you were allowed to replace fuses on all spikes.

But of course, it’s not my interpretation that matters, it’s the GDC’s. Someone should ask this in Q&A and get a clear answer.

13

But of course, it’s not my interpretation that matters, it’s the GDC’s. Someone should ask this in Q&A and get a clear answer.

I expect I will do that since without anything official, it will be the inspector’s definition I would have to follow. :slight_smile:

In any case you need to know why the fuse is blowing and be sure you are not masking something that needs to be fixed.

14

What needs to be fixed has been said already. They are stalling the motor, which stalls at over 20amps. So they need which to a speed controller.

15

But the important thing here is that it’s perfectly legal for you to run those Banebot RS-550 motors on that Spike and blow your fuses. Just don’t try to run a FisherPrice branded RS-550 motor (with a lower stall current) on a Spike, or you won’t pass inspection. So sayeth the GDC.