Introduction: A Safety Fused Harness to Protect Your Expensive Multi-Copter Electronics.
Obviously, if a fuse were to blow in-flight, there is going to be a crash, but think of it this way… Anything that would go wrong in flight that would cause a fuse to blow would cause the aircraft to crash anyway, so why not protect those expensive electronics. I would rather replace a few broken props and un-bend a frame , even replace a motor, rather than to lose one or more ESC’s (Electronic Speed Controllers) and/or the flight controller CPU itself.
My reason for putting up this simple instructable is basically due the amount of money I lost in a big X600 class quad copter by simply plugging a throttle channel in backwards. I lost the ARDU-Pilot controller as well as a Quattro ESC. Big bucks, and if you implement one of these safety fuse harnesses, it may save you a disaster like that.
Actually, the protection is designed more for what happens on the ground, before a flight. You are always mucking around with the telemetry controls, checking the ESC connections to the BDC (Brushless) DC Motors, plugging in channel wires to the receiver… etc. A shorted connection or a polarized connector plugged in backwards can be disastrous. This fuse will blow long before any damage is done, and no doubt alert you to something you have done wrong.
In the harness, I used a blade fuse holder /w cover and a 10 amp blade fuse. These are cheap, as you can get them online for a few bucks. You will have to pick the value of your blade fuse according to the amperage draw of your copter. The example I have provided, also replaces the skimpy 2-hole power connectors found on small LIPO (Lithium Polymer) batteries, with a polarized J-Connector, that cannot be plugged in wrong.
The cheap 2-pin connectors have a slot in the middle that is supposed to protect against a reverse connection, but are easily defeated by accident. I replaced the 2-pin female from the battery with a female J-connector, and incorporated the 2-pin into the harness, so that it will always stay plugged in to the corresponding power connector of the copter, and I will use the J-Connector when switching out the battery. Also realize that this is the ultimate Kill Switch, as nothing is going to power up before this blade fuse is plugged into it’s holder.
I am using a LotusRC T-80 quad copter in the example below. You can easily modify anything I have shown here to accommodate the connectors on the copter you are protecting. Find a convenient place in your center frame to mount the blade fuse connector. It screws in with 2 #6 3mm bolts/nuts.
You want to turn it up tethered to the ground after you assemble the harness, to make sure your fuse selection meets the maximum power demands of your aircraft. Always pick a fuse that is a few amps over what your maximum should be.
And, remember that it is not Voltage that blows a fuse, it is Amperage. The Voltage factors into this scenario only in how fast the fuse will blow, and we are also NOT using any slow-blow fuse technology here. In this application, any automotive 12 Volt, regular blade fuse is adequate for any LIPO voltages you will be using, just pick the Amperage value correctly. You can pick up a selection of blade fuses real cheap online that will give you 10 each of 5,10,15,20,25 and 30 Amp , color coded fuses for about $6 to $8. No problem if you blow a few just figuring out the value you need to fly without problems.
So… That’s it really. Pictures are worth a thousand words, and a step-by-step instructable here is not required. You can easily ascertain what was done by looking at the pictures. Remember to use a wire gauge that is consistent with the power of your equipment; just match what the LIPO and ESC inputs are using.
Good soldering skills are also required here, as well as the use of shrink wrap. It is always best to tin each and every connector tab and wire before final solder assembly. Use a pen flux or at least a flux core solder. Good Luck, and be extra SAFE!