HOWTO Wiki Prevent Main Motor Wire Short

From Heli-Wiki

This guide is to show you what can happen when your motor shorts out and how to prevent it.

The main motor in most of these smaller heli's (not just the blades), have small motors with sharp metal edges that the main wire leads pass over to get to the ESC that is usually found in a 3 or 4 in 1. This can have devastating effects, such as blowing out your main motor ESC (which usually involves replacing the 3 or 4 in 1), making your heli loose control and power causing it to crash, causing interference to the servo's which makes it twitchy causing it to crash, significantly reducing flight time, causing the motor to heat up alot, and in the most extreme cases causing the battery to catch fire in flight (not very likely at all, but hey, it could happen ;).

Here is a pic of what happened to my motor when the edges shorted out the wire. How I figured it out is that the helicopter was acting really twitchy and the servos were moving without input, and the flight times were down to less than half of what they should be, but I was still using the whole battery pack (the charger put back in how many mAh the battery was rated at). At first I thought it was just a bad motor, but when I took the motor out I found this... I am very lucky that my 3 in 1 is still working properly!

Burnt Main Motor

This mod is to prevent that from happening. This is the way I did the mod, and the solution I came up with. There are many many things that could keep the motor from cutting through the insulation, so just be creative and see what you can come up with.

What you'll need

• Soldering Iron
• Heat shrink (I used 5/32" diameter), and something to melt it with (I used a lighter, but you can also use a heat gun)
• Main motor wire that is fully intact without any shorts or nicks
• Scissors (to cut the heat shrink down to size)
• Philips screw driver (if you want to take the motor off for better access to the motor for soldering)
• A zip tie (to hold the wire above the motor)

Steps

The first thing you are going to need to do is disconnect your motor from the ESC. Make sure to note the polarity so you can hook it back up the same way (if you don't that's ok too, you'll just need to make sure that in the end your blades are going clockwise when looked at from above). Next, if you want more room, you can remove the motor from the heli. I chose not to do this because it was an extra step, and I feel comfortable with soldering in more confined places (if you do this just be careful not to melt any of the plastic or anything with the iron, watch the hot tip all the time).

After that you are going to want to heat up your iron. Grab the electrical wire, and put a slight amount of tension on it so that when you touch the solder joint with the iron the wire will slip out of the joint. Careful to not give too much pressure or you could have solder flipping in your eyes or something. When you touch the joint with the solder, it should be very brief, only about 1 sec. If you do it longer than that you'll probably the insulation on the ceramic capacitor. Also make sure to note which side of the motor each of the leads went to. And yes, I usually use the desolder pump to do most of my soldering.

De-Soldering

After you have the power cable loose you are going to want to cut two short lengths of the heat shrink about 3/8". The reason why we want to do this is so that the main power cable remains flexible, but has extra protection where it needs it. The first place we want to heat shrink is the lower area of the cable where the wire touches the heat sink. You can see in this pic about where it should be. The other pic is a final pic of where it will end up when we get to installing the cable. This second picture is so you can see what this bit of heat shrink is for.

Heat Sink Heat Shrink Positioning

Next you are just going to put another piece of heat shrink on that is the same size, but this time for the upper part of the wire where it touches the edge of the motor. On this one you'll want to be careful that you do not get it too far up or down. Too far up and there wont be enough spread to solder the connections back down. Too far down, and it wont protect the wire. See pictures for placement.

Heat Shrink Positioning on the Main Motor Edge

Now it's time to solder the connector back on to the motor. The way I do this is get everything ready to solder, get your solder tip tinned (some fresh solder on the tip, but not too much), touch one of the main motor contacts until the solder flows then quickly remove the iron. Immediately put the end of the wire down to the solder, and touch it again just long enough for it to flow. Wait for it to cool (about 5 to 10 sec) and give it a good tug. If it sticks and the joint looks shiny, you've got a good one. If you can't get it shiny, but it sticks, then it should work. Repeat for the other side. See the above pic for how shiny solder looks.

Lastly place a zip tie around the part of the wire with the thick part of it down so that the zip tie elevates the wire off of the motor. I cut the end pretty short so it would sit flat. Don't cut it too short though or otherwise it could come undone. This tie also helps hold the heat shrink where it needs to be. See the above picture for placement.

mrasmm

PS feel free to PM me either on RCU or RCgroups if you have any questions or comments