Five Fatal Mistakes: Why your robot is dead on the field

#1

Learn some of the most common reasons robots disconnect on the field and the steps you can take to make sure your robot doesn’t die in the middle of a critical match. Presented at Stuy Splash 2017.

Presentation: https://goo.gl/iaMEEc

Other presentations from Stuy Splash: https://stuypulse.com/resources/stuysplash2017/

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#2

Here are some more solutions to this presentation:

Slide #6 Item #1
Also make sure the lock-washer is present on the PDP power lugs, if not the lugs can slip and slide causing power outages. We learned this the hard way at our State Championship last year.

Slide #7 Item #2
POE (Power Over Ethernet is a good suggestion), but if you don’t have that, a SMALL DROP of hot glue on the side of the power barrel and the CAT5 cable goes a long way. Don’t put hot glue on the CAT5 thumb latch, just the side of the connector. Many teams and mentors have given us a hard time about hot glue, (Alan Anderson, look away) but we stick to our guns on that solution. We apply hot glue to everything, even back in the day on all the PWM cables on the robo-rio and the Victor Speed controllers.

Slide #8 Item #3
Ferrules is the answer here for us, ever since we started using number 20 AWG ferrules for these connections, things have been looking pretty solid. We also use this for all CAN-BUS connections as well. And if we get extra paranoid, we put a small drop of hot glue on the ferrule barrel as well. We get our ferrules and ferrule tool here:
http://www.ferrulesdirect.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=FD&Product_Code=SK700P&Category_Code=WIRE_FERRULES_DELUXE_KIT

I personally recommend this Ferrule tool here:
http://www.ferrulesdirect.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=FD2810HX&Store_Code=FD

DO NOT USE these kind:
http://www.ferrulesdirect.com/terminal/3210/FD2410N.htm

AndyMark carries a far cheaper version, it crimps a SQUARE on the ferrules which is still good as well.

Slide #9 Item #4
The same solution as Item #3 above, use FERRULES. They grab the wago terminals really nicely and secure and you can check and make sure you have stripped your wires long enough while you are crimping the ferrules on.

Here is a picture of with ferrules:

Slide #10 Item #5
For sure check your batteries, label each battery with a number and sequence them. We have 9 batteries in rotation, start with battery #1 and your ninth match, you should have battery #9. So you know your tenth match you got battery #1 again and should have been on the charger the longest.

Slide #11 Item #6
We ZIP TIE the battery connectors together. Also bolt down the reciever battery connector to your robot frame with a 4-40 bolt and nylock nut.

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#3

I’d recommend using the serrated lock washers over the split helical “spring” washers as the latter have been proven to be ineffective and possibly detrimental to mechanical and electrical connections.

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#4

Lock washers don’t work.

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#5

This is the most useful paper I have seen in a long time.

ChrisH
BeachBot Mentor for 20+ years
X-FTA
World Champs 05, 16

The strategy paper is also very good. We do most of the things mentioned though sometimes with our own twists.

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#6

As two others have noted, split lock washers don’t usually help maintain fastener preload under transverse slip conditions. Proper fastener torquing and good strain relief are better options here, which prevent transverse slippage in the first place.

I do like the suggestions to use ferrules on all spring-clamp type connections. This has been great for us as well and has improved reliability for many other teams.

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#7

Please please please do not hot glue your Ethernet cable in place.

There is (or has been, I don’t have access to 2018 hardware and software) an issue with the radios the last few years in which sometimes the roboRIO won’t work on one of the two ports (the non-vPoE port). As a matter of fact, it was a little known (and much violated) rule in 2017 that you were required to use the vPoE port for the roboRIO (R63).

I can’t count the number of times teams came to the field, wouldn’t connect, had it in the wrong port, and immediately connected after switching to the correct port. It is an easy mistake to make, and an easy mistake to fix.

However, if the cable is hot glued in place, that can’t happen.

In a similar vein, if you are going to label one of the two ports on the radio “RoboRIO”, please make sure it is the correct one.

I’m also not a fan of hot glue on the barrel connector for a different reason- it makes it harder to fix and diagnose the issue if there is a problem with that connection. In my experience teams that have a zip tie, hot glue, and eight layers of electrical tape on the barrel jack are more likely to find a loose connection at the VRM or the PDP.

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#8

So my one tip to add to this is that unless you are an expert at making ethernet cables (making 10+/day for many a year) then just save yourself from any issues and go buy a pre-made cable of appropriate length. Also, when the little clip dudes break off, don’t try to salvage the cable. Just throw it away and go get another one. It’s like $1.50 for the cable from Amazon or mono-price or wherever fine cables are sold. That $1.50 you saved by using an ethernet cable without a clip dude instead of buying a new one is going to bite you when you least expect it to and it will cost you a $200 (or more) match.

TLDR: Use new ethernet cables with good clip dudes.

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#9

Strain relieve wires that are plugged into devices like radio etc. When wires keep sharking they tend to get lose. Simplest way (that I know) is to secure them with zip tie or electrical tape (pls do not use duct tape or cheap electrical tape from dollar store, they get sticky and messy after some time).

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#10

Nothing a small flick of the screw driver can’t remove. Or I mean nothing by this, but for a few years my electrical team was all ladies, and they could use their finger nails to flick off the hot glue, I didn’t have finger nails so I flicked it with a small terminal screw driver. Don’t pile it on, that’s not what you want to do. Only hot glue after you have tested everything.

We are still sticking to our guns on the hot glue. These are just other solutions and suggestions. Everyone hates to see a dead bot on the field especially on your alliance. It’s sad when that happens.

I appreciated the presentation, but wanted to offer more input to the slides as “tips and tricks” our team does to not become a dead bot.

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#11

I am not a mechanical expert per say on lock washers, but more of the issue is that the OEM lock washer that came with the PDB acts as a spacer. When it’s missing, the bolts that hold your main power cables bottom out. When they bottom out, they are now not properly torqued and allowed them to slip in place. If the OEM lock washer was installed, the bolts would bottom out and the lugs could have been tight. Replacing the OEM lock washer provided with the special do-hicky type washer to insure no slippage seems like an improvement. I’ll mention that to my lead electrical students. Thanks for the tip!

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#12

Thanks!

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#13

Scotch Super 33+ (black) and 35 (colors) are the alpha and the omega of your electrical tape needs. Accept no substitute.

I’ll second the hot glue. I really don’t like using zip ties on small wires (like the radio power or PWM/CAN) when I know it will get removed often. It’s just too easy to erode the insulation over time with cutters.

Any cable that gets touched frequently, you should definitely have spares. Power leads of the right length with barrel connectors soldered on, ethernet, CAN, whatever. Have a list, have a box, keep it handy.

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#14

Yes, accept no substitutes.

To avoid damaging the wires, cables, tubes, etc. that are being fastened with the zip ties, use a small pair of cutters and cut open the “head” of the zip tie. This releases the long “tail” of the zip tie that passes through it.

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#15

As someone who spends a lot of time around 1501’s robots on the field, I can say they do a good job of staying connected to the field and not having connectivity issues.

That being said, the caveat to hot gluing your parts into place is that your connection should work without it. Don’t expect hot glue to hold a bad ethernet cable in place.

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