Gluing PWM connectors into Motor Controllers

I was talking to another one of our mentors the other day and he told me something interesting.

I have always (past 4 years of FIRST electrical) that it is a good idea to put a drop of hot melt glue on your PWM connections on the motor controllers to keep them from falling out. This is especially true for older Victor style controllers whose connections can become loose.

However, he told me that ‘gluing’ the PWM connectors is illegal as it counts as ‘modifying’ the controller.

Does anyone know for sure? I wanted to make sure before we decided to follow this strategy and maybe make a mistake.


I’ve seen discussion of this before. Most people agree that it is technically illegal, but depending on the inspector may or may not get looked at.

We did it last year at 3 competitions, never had an issue.

I would agree that it is technically illegal. However if one follows that rule that strictly, it would probably also disallow labels, Velcro and anything else that uses adhesive to bond to the motor controller.
In my opinion, it is an example of taking a rule too literally.

We do this on a regular basis with both 884 Victors and Spike relays. Not once has an inspector had an issue with it.

Honestly, I can’t even imagine why it would be an issue or even be considered modifying a speed controller any more than using thread locking compound on a motor mounting screw is modifying the motor.

Ah, the semi-annual PWM-gluing thread.

Its not really an uncertain matter of opinion whether or not gluing is considered tampering with a motor controller. R65 specifically states that gluing is prohibited on a motor controller. Its a dumb rule, but its a clearly stated dumb rule. :smiley:

The nice thing about using hot glue, whether you believe its legal or not, is that it can be easily removed if an inspector has a problem with it.

Thank you! Whether I agree with the rule or not, it is a rule, and I was unaware of it. There is no one to blame for that but me. Time to change our practices.

That said, it is a hard and fast rule. So, if it is still in place this coming season, we WILL follow it.

Remember the standard disclaimer that the rule could possibly change next year. And this is one case where that really should happen (at least put in a blue box beneath the rule creating an exception for this).

For what it’s worth, here’s the rule (2013 Manual) that’s being cited as preventing hot glue from being used to secure PWM connectors to speed controllers.

If you read the rule in it’s black and white context, speed controllers are not allowed to be modified other than the above exceptions. (Fans, Connect Wires to/from, Labeling, etc.)

Depending on how you interpret the rule, arguments can be made on both sides for why hot-gluing the PWM cable is legal or not legal.

On one hand, you can argue that the speed controller is not being modified, as it still performs and functions the same as a commercial off the shelf unit, with the only real change being that the PWM cable will not come unplugged at random. (And you are allowed to connect PWM cables to the controller per R56.F)

On the other hand, it could be argued that if the hot glue were to remain on the speed controller after the PWM cable is removed (it happens) then the speed controller has now been modified. The hot glue could also be interpreted as making the ‘standard connection’ a ‘non-standard connection’, depending on the inspector.

I guess if someone really wanted to stretch things a bit, one could argue that if the PWM cable comes unplugged during operation, then the speed controller is not functioning as intended, and is therefore in need of repair. Since the speed controller is designed to retain a PWM cable under normal operating conditions, a dab of hot glue on the connector would allow the speed controller to be restored to it’s intended function. (Although, it could be argued as being different in function than a COTS unit, depends on the inspector.)

In any case, in my 8-ish seasons of doing FRC, I can’t remember a single instance of an inspector giving us a hard time about hot gluing the PWM’s into the speed controllers - heck, some have even suggested it. If you decide to go through and apply hot glue to the connections in the coming season, make sure that you re-read the rules, and see if they’ve changed at all. If they don’t, be aware that you may have to remove the hot glue down the road, and if you’re told to do so, to just go with it.

Unfortunately, the “gluing” restriction falls under the category of tampering, so any argument about modifications is not relevant.

We have used a substance a lot like modeling clay* to hold the PWM cables on a Victor in place (back when we used Victors). We never had a problem with inspections, and it isn’t gluing, nor is it permanent, so it does not appear to be tampering (no more than using a label to mark the Victor, for example).

*I think it is the stuff used to hold fine china and vases down to a shelf so it doesn’t fall over. Museum putty?

this stuff?

Yes. I remember it was blue, didn’t leave any residue, and wasn’t Silly Putty.

I’d disagree that this is in any way tampering with motor controllers. You haven’t changed the motor controller one bit with hot glue. If you, say, cut the plastic casing to make them more accessible, then you’ve tampered with it, but doing anything additive isn’t changing it, especially since you can take the hot snot off and the motor controller is identical. It’s the same as taping. As an inspector at QCR and CMP, I never told anyone to remove it. It’s common sense and good practice IMO, and until Al or the Lead Inspector at competitions says it’s wrong, I don’t think any inspector should DQ for it.

I agree, but the rule specifically says Gluing.

1st reaction: Oh great another thread on motor controller glue

2nd reaction: Didn’t I post a comic about this last time? (yes)

3rd reaction:
Why we use bolts on the robot: To securely fasten parts to other parts in a secure fashion, while at the same time being easily removable without any damage.

Why we use hot glue on the motor controller: To securely fasten PWM cables to the controller in a secure fashion, while at the same time being easily removable without any damage.

Rules aside, What is the difference?

I’m just going to leave this here from the last thread regarding gluing PWMs: An Alternative to Glue.
Original Post:

Al says it’s wrong.

From the link:
“Gluing also makes it almost impossible to reuse the parts next year.”

If you can’t remove hot glue from that someone was quite overzealous.

“Often the glue does not adhere to the parts in the way you want so you have a false sense of security thinking the parts are secure when they are not.”

In point of fact it can’t be both ways: it can’t both not stick and be too stuck.
In various applications it might be both but not for any one single example.
It’s a bit contradictory.

That said it’s ironic that the clip linked above appears to be 3D printed.
Given the similarity between a hot glue gun and early RepRap 3D printer extruders.
So it’s hot glue (sort of): held on by tension instead of adhesion :slight_smile:

The answer here is to 3D print clips with hot glue, will report back after testing this.