Re: What would a safe robot look like?
 

I just wanted to expand on this a bit more. Different wires definitely flex more/less easily - this is highly dependent on the insulation used and the number of strands. Make sure you use the right wire for the right job. When you look at most robots in the competition, a majority of the wire doesn't need to flex (aside from intentional bends to follow a fixed support). For that reason, most of the wire we use is stiff. Once you've twisted it together, it becomes even stiffer. This allows you to make wire runs that don't require much support, and won't sag and flow all over the place.

As Don notes, however, in cases where flexing is required, you don't want to use stiff wire - it's more likely to break than more flexible wire. Keep your bend radius decently large (no smaller than the spool the wire came on as an absolute minimum) - from a safety standpoint, it can never be too large.

Further, include strain relief and emergency releases on any moving wire. You don't want the wire stretching very tight, and if something happens (like another robot's arm somehow hooks your wire run), you want a built in release that will come apart safely, like Anderson's PowerPole connectors.

Speaking of other robots hooking your wire... Make sure your wire is controlled at all times! Watch for pinch points on your mechanisms and keep your wires away from them. When dealing with some mechanisms, it can be easy to run wire so it's taught one or both extremes... but then it becomes very loose elsewhere in the motion. When running the mechanism, you might even notice that it forms a nice large loop. Sure, that's a large bend radius (which is good), but it's also a huge chance for other robots to hook you and pull. If your wire needs to be loose in the middle of motion in order to be taught at both ends, control it with energy chain or other methods. I think I'm going to upload some good and bad examples of this for everyone here... I'll get them linked on here when available.

Re: What would a safe robot look like?
 

Air has a higher dielectric strength than that, and 33 surely exceeds air. Absolutely, positively a typo. Check any of their other tapes.Some teams are simply not wrapped too tight...
I am inclined to agree, at least on an order of magnitude.


Electrical Tape: Can be used for marking, mechanical protection, or insulation. Other kinds of tape are better for holding things together. When used for marking, only the color or texture matters, with other mechanical properties only secondary, in that they need to be sufficient for the application (e.g., adhesive doesn't fail). Red, White and Green tape are often used in house and industrial wiring. On robots, Scotch 35 (sold most everywhere) offers several nice colors and good mechanical properties. When used for mechanical protection, color and insulation are usually the unimportant factors, abrasion resistance and adhesion being important. We already discussed insulation.

Re: What would a safe robot look like?
 

I looked at other tapes (Scotch 35), and I now believe the units were wrong. milivolts instead of volts/mil seems like a reasonable typo by an unsuspecting intern.

I'm still inclined to be wary - I would consider significant use to be only a temporary solution, but I would use it to cover a small hole in insulation instead of replacing a cable harness.


When would it be appropriate to use electrical tape for abrasion resistance?

Re: What would a safe robot look like?
 

Would a robot coated in bubblewrap fill the bill?

Re: What would a safe robot look like?
 

mark EVERYTHING. an eletronic dymo gun is good for this. as an example, my team's 20011 robot wiring label system:

all jaguars have their CAN Id's labled

all wirtes between jaguars and motors have their wires labed with the CAN ID.

All wago connectors on the PD board have the CAN ID or whereever they go labled

All sensor wires have a label to the DIO or AIO on both ends

All sensors have the above label as well


for anything other than radio wiring and stationary cameras, solid cat5 is a no-no. always go stranded (we use one for a sensor umbilical to the wrist and claw on the arm).

tension on eletrical tape is a must... otherwise it comes undone at the folds and wrinkles and snags. i usually end up with 2 layers based on the amount of overlap and I have not had issues...

never solder good mechanical connections... solder improves bad physical connections and makes good ones go bad (wires heating tot he point of thermally tripping the 120A breaker is bad).

always use a good crimper... not some chepo one like this:



ones like this are good:





the latter works the best as long as you put as much perrsure into the crimp as you can...

always remember that the wires coming out of the cims are 14 gauge... not 12. that means blue size crimps! not yellow!

always be sure to use good hardware when mounting your battery... a strap slipped on a practice bot's battery retention system yesterday during a high speed spin at an open house and flung a battery 6 feet... when in doubt, beef it up! batteries are beastly things!

Re: What would a safe robot look like?
 

Larry,
You have some great input on labeling and connectors. These are important to electrical safety.
However, I've chosen to disclude those from this particular thread in order to have a narrowly defined topic that facilitates thorough and comprehensive discussion of the topic.

If you'd like to create another thread covering these topics and move your post there (or ask a mod to), I'd be happy to participate.

Thanks!

Re: What would a safe robot look like?
 

A few thoughts from someone who works on 12v electronics all the time as a automotive/MD truck technician.

Speaking of wire the best is cross-linked polyethylene it is the only type of wire endorsed by SAE for underhood automotive use and has much better heat and abrasion resistance. Even the newest solder'er can't melt nor damage the insulation, Ok maybe if you use an open flame. It is called out as *xl with TXL having the thinnest insulation, SXL the thickest and GXL in-between. SGX is super heavy insulation available in 6ga or larger for "battery cables" and is what is used on the more recent Anderson Power Pole pigtails. It is identifiable by the slippery waxy feel to the insulation if it isn't marked.

The translucent PVC "stereo" wire is the worst stuff you can get. The reason it is thicker and heavier yet more flexible than standard PVC wire marketed as "primary wire" (GPT) is because the transparent insulation has a lower melting point and abrasion resistance due to its' softness.

There are boots designed to provide insulation for contacts such as the main breaker and PD, I use them all the time, and they are available from companies such as TSC.

I'm not sure what is meant by "motor protectors" any motor protection needs to be internal to the motor in the form of a thermistor. Fuses and circuit breakers fall under the category of circuit protection. They are not to protect what ever the load is but instead are to protect the wire from the load.

Re: What would a safe robot look like?
 

Again, great post.
For this thread please trim it down to the parts about insulation, wire, and heat shrink.
However, don't just delete the rest. Copy it, and save it on your computer as a text file. I'm hoping Larry will start that other thread, at which point you can repost it over there.

Would you happen to have a picture of your robot that shows the TXL wire, Delphi connectors, and insulation boots?

Re: What would a safe robot look like?
 

I'm heading to bed so I'll trim it down tomorrow.

I wish I had pics of our Robot with the mentioned items alas we attempted to get our head wiring student to do the leg work on those items and come up with a list of items to order before the season began, but he didn't do so. So we didn't have the items in time for this years Robot and worked with GPT and the resultant melted insulation. I could show you them on some of my trucks if you desire.

Re: What would a safe robot look like?
 

I am not sure what your statement is about soldering. We solder every connection. We use uninsulated crimps, then solder and add heatshrink. We do this because we lost to Beatty in the Champs finals many years ago when a crimp failed. We will not lose to Beatty for this reason ever again. They are too good!
The last crimper in your post is also meant for uninsulated terminals. It is the very one we use for those terminals.

Re: What would a safe robot look like?
 

Al,
please save this for another thread.

On second thought, as a mod, don't you have power to move and delete posts?
Does someone else need to create that new thread first?

Re: What would a safe robot look like?
 

Marshall, Not sure what you are asking of me?

Re: What would a safe robot look like?
 

I'm asking that the posts on connectors and labeling be moved to a seperate thread. This thread is about insulation, motor protectors, and battery protectors.

Re: What would a safe robot look like?
 

Is there any more that should be said about insulation?

If not, lets move on to motor protection.

Is it reasonable to say "any motor that gets hot enough to smoke presents a safety hazard"?
Or is there a more stringent requirement, that we must stay within 135% of normal load to prevent abusing our motors?

What sort of electrical device should be used to prevent damage in an overload situation? Are we going to find a NEMA class 20 overload relay for low-voltage DC?