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Re: Electrical basics
Al, I (and perhaps others) would be interested to know if you did an in-depth root-cause analysis to determine why the crimp failed... and why soldering was the accepted solution instead of, for example, a change in the crimping process or better quality control of the crimping process. |
Re: Electrical basics
The wire pulled out during the match. It could have been anything, but we know that soldering following a crimp does produce a more in depth visual check of the terminal. We made soldering standard practice some time ago and when we started using APP terminals, we continued soldering. We use a West Mountain Radio crimper for the APP contacts. All crimps are checked with a tug test prior to soldering. We like backing up the backup.
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Re: Electrical basics
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Re: Electrical basics
I can't remember years, but I can remember standing outside the back of the Einstein Stage at Epcot looking at the bare wire. I don't even know if we were calling it Einstein at that time.
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Re: Electrical basics
Some guys wear special backpacks, some guys wear particular jerseys, some guys solder their crimps.
We've all got our superstitions and foibles. (you don't believe me? Pay attention to yourself next time you eat M&Ms) |
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So there's an open question here. |
Re: Electrical basics
We are not replacing the crimp, we are adding solder to a crimped connection.
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What I point out (and what Ether is noting) is that by soldering the crimped connection you are stress-relieving the crimped material, removing the effectiveness of the crimping. Because of this, one would get ostensibly the same result by soldering the terminal without crimping first. Assuming, of course, that what I opine is correct and factual. Edit: this has been my point all along. |
Re: Electrical basics
I disagree that the terminal would no longer be crimped after heating it for solder. I will experiment with that concept at a future time and let you know.
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Re: Electrical basics
You never want your solder to be your mechanical connection. So you want to crimp even if you soldier. You might lose some pressure from work hardening lost from solder. I am not going to speculate on that You are not going to lose the deformation though. If look at the automotive industry you will find mostly crimp connections with no solder. Cost could be a factor there. So done right, clearly you don't need solder. But that is with qualified tooling, qualified connectors & testing. Mil-HDBK-217F, a electrical reliability standard has a multiplier of 20 for failure rate calculation for non-qualified crimps to mil-spec crimps. The handbook does not have a base failure rate for crimp+solder. Not really an apples to apples thing, but shows the risks of doing the crimp poorly. The biggest down side to using solder is having the solder wick into the wire causing a stress riser & decreasing flexibility.
As for as I can see: Correctly crimped connectors do not need to be soldered. Solder done right gives you an extra bit of security for when the crimp is not done correctly. In any case you want to properly route your wires so the connection is not under tension & is not carrying the weight of the wires. |
Re: Electrical basics
A bit more on the OPs question. In diagnosing robot failures, it's almost always some sort of mechanical issue. The symptoms you'll have on the field will be jerky, unreliable operation or rebooting of the cRIO/radios.
1. Ensure that terminal screws are tight. When you arrive at the competition -- check to see that they're tight, as the process of shipping/hauling the robot might have loosened the screws. 2. Wires should have strain relief / tie downs near the point of connection to the relay/speed controller. This reduces the chance that movement on the robot causes the screw to come loose. 3. See other discussion in the thread regarding how to fasten terminals to wires. Suffice it to say that there are engineering differences about the best way to do it. For your team, it's most important to select a method that works for you, have a procedure that everyone follows, and inspect the results of every crimp/solder operation. Most robots I see have the correct wire sizes on them -- I'm not sure if it's because the inspectors are catching it before I seen it, or teams are doing a good job. |
Re: Electrical basics
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I can see where one might solder a crimped connection on a FIRST robot. It does not have to last all that long. But in a professional environment this is not an acceptable practice. One must use the correct crimp for the wire and insulation type and install with the correct tool and procedure. Curiously the military allows us to solder to braided shields but only with a sleeve that includes heat shrink and glue that stress relieves the solder joint. |
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Re: Electrical basics
Keith,
We are aware of those dangers and teach our students to carefully solder being sure to watch for solder to wick under the wire insulation. We also take other precautions that would not be practical in mass installations like ships and consumer products. However, our 2006 robot is still in service as a demo and we haven't had a failure in the electrical connections on that robot yet. It needs some mechanical repairs but we have beat it up pretty bad over the years. |
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