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.

Thanks

Re: Gluing PWM connectors into Motor Controllers
 

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.

Re: Gluing PWM connectors into Motor Controllers
 

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.

Re: Gluing PWM connectors into Motor Controllers
 

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.

Re: Gluing PWM connectors into Motor Controllers
 

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. :D

Re: Gluing PWM connectors into Motor Controllers
 

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.

Re: Gluing PWM connectors into Motor Controllers
 

Jeff,
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.

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

Re: Gluing PWM connectors into Motor Controllers
 

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).

Re: Gluing PWM connectors into Motor Controllers
 

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.

Re: Gluing PWM connectors into Motor Controllers
 

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

Re: Gluing PWM connectors into Motor Controllers
 

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?

Re: Gluing PWM connectors into Motor Controllers
 

http://www.loctiteproducts.com/p/cnt...ting-Putty.htm

this stuff?

Re: Gluing PWM connectors into Motor Controllers
 

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

Re: Gluing PWM connectors into Motor Controllers
 

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.

Re: Gluing PWM connectors into Motor Controllers
 

I agree, but the rule specifically says Gluing.

Re: Gluing PWM connectors into Motor Controllers
 

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?

Re: Gluing PWM connectors into Motor Controllers
 

I'm just going to leave this here from the last thread regarding gluing PWMs: An Alternative to Glue.
Original Post: http://www.chiefdelphi.com/forums/sh...&postcount=119

Re: Gluing PWM connectors into Motor Controllers
 

Re: Gluing PWM connectors into Motor Controllers
 

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 :)

Re: Gluing PWM connectors into Motor Controllers
 

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

Re: Gluing PWM connectors into Motor Controllers
 

Really?

What students should take away from my earlier post is "if you think about it, I bet you can come up with a better idea." NASA would not hot glue a connector in place especially if it has a habit of falling out. The rule stands and should be enforced by all inspectors. If the glue is easy to remove and you can easily remove the connector should the controller fail, the glue was not applied properly and my previous reference to false security holds true. If you do nothing else, simply tywrapping the PWM cable to the power lead nearest the connector on Victors and Talons will prevent fallout. The Jaguars have a cable retention clip right on the body, use that.

Re: Gluing PWM connectors into Motor Controllers
 

I'm pretty sure we are not even close to on the same level as NASA. I mean, look around the pits, Putting anything we are capable of making into space would probably be a waste of billions of dollars. We build stuff to last 100 Hours. Satellites and rovers have to last for hundreds of thousands of hours and experience forces and vibrations that would make a car crash seem fun.

If NASA was in this situation, they would spend thousands in R&D and come up with the lightest, strongest, and most perfect solution we could never legally do. (actually they would not use a victor/spike/talon/jaguar at all, as any functioning part of them would still be too heavy)

Re: Gluing PWM connectors into Motor Controllers
 

In fairness to Al's point:

If he says it's not legal. It's just not legal. He is in a position to make that a fact.

There are many compromises FIRST teams make to fit within the frame of the rules of this competition.

He's challenging everyone to up their game with this. Fairly one could say he's even challenging the electronic motor control makers to provide facility to positive lock the connectors. So it's really not just a build issue for the teams.

However: what is not addressed is whether or not that 3D printed clip is legal for use in this context.

One could point out that prying the glue off is not really the same as the force that might otherwise eject the connector but it's sort of moot to do that. He's right that anything that obscures something could obscure an issue you might have otherwise seen right away. Giant balls of electrical tape for example might keep 2 wires together but barely connected (all too common actually).

If those clips are legal I guess we have some 3D printing to do.
So can we can an official ruling on that Al?

Also, in the interest of communicating this clearly to the potentially large number of impacted teams, can an official rule update specifically address this (I know the manuals are probably already past the point of alteration)? I suspect there's ample reason many people might not notice this development and walk right into trouble at inspection.

If preferable can we potentially make this more visible by asking an official question after kickoff even though we pretty much know the response?

Re: Gluing PWM connectors into Motor Controllers
 

Since the clips do not violate any specific rule, why would they be illegal? Especially if you print them on a 3D printer you got from First Choice.

Re: Gluing PWM connectors into Motor Controllers
 

There are lots of things I could print on a 3D printer that will break the rules.

In this case every option Al lists as lead inspector basically tries as little as possible to touch the housing of the electronic motor control.

This 3D printed item is effectively clamping the body of the unit and pressing on that connector it is not a mount to the robot or operator console. Course you could make it such but as it is shown that is not the purpose (put a tab and screw hole to hold that corner of the electronic motor control to the robot while holding the connector in...for example).

Re: Gluing PWM connectors into Motor Controllers
 

To restate my position, I am merely the Chief Robot Inspector. All rules are interpreted by the GDC and answered through the Official Q&A. That being said, in my opinion, the clips violate no current rules that I can see.
As a long time competitor, my expectation for replacing defective components is a plan that provides the simplest solution, requiring very little in the amount of thought to replace, in a minimum a length of time and takes no special tools. When I see a connector glued in place, I think to myself the solution is to cut out the controller and the PWM cable all the way back to the DSC in order to replace the controller. The solution I propose requires no thought, one tool and the snipping of three tywraps to remove the offending part. A good pit student will make the change without putting down the tool and will have the new one functioning in 30 seconds. That gives software a chance to calibrate and check operation and some time for mechanical to go over their checklist. And yes, we do practice diagnosing and making repairs.