AirBoat build

[Chop]

The long motor leads are making it tough for the ESC to keep phase with the rotor position.

Can you explain what you mean by this?

I see the potential to remove 12" or more of wire length in your application. Do it.

I don't think I can shorten the motor extension wires, but I can change them to 10 ga. wire. I can take about 4" of wire off either side of the ESC. I don't want to do this to a real good ESC, do you think that I can get away with shortening the wires on another 200a Mystery ESC?

Get a better ESC, ditch the motor wire extensions from the ESC, move the latter as close as possible to the motor, shorten all wires a lot, and use a vented hatch in the winter. In the summer on water the motor will draw even more amps than on snow, so you'll have to come up with a cooling workaround of some kind.

I have a Hydra 240 that I can take out of another boat. I'm not sure that I want to shorten the wires just yet - but since it is already "used" I suppose it won't matter. I guess I want to see it the modifications to a Mystery make a difference first.

THANKS FOR THE HELP!!!

[Fluid]

Can you explain what you mean by this?

It means that long motor wires are a no-no. Very simply: the ESC reads the back EMF from the motor to know how to adjust the timing. Long leads dampen this feedback and the ESC can't properly time the motor. Hence the motor and ESC overheat and can be damaged. Twisting the leads together does nothing but reduce radio interference. You clearly have too much wire and can shorten the motor leads at least 6". Move the ESC to the very rear of the radio box and run the ESC wires out through the deck. Band the wires coming out of the motor sharply forward (carefully).

I can take about 4" of wire off either side of the ESC. I don't want to do this to a real good ESC, do you think that I can get away with shortening the wires on another 200a Mystery ESC?

The long motor wires are likely part of the reason your Mystery blew. Why don't you want to shorten the wires - ALL controllers should run a minimum of wiring, most guys have way too much and this is one reason for the blowing up of ESCs which "should work". (You can always send the Hydra back to Castle later to have them lengthen the wires for a small fee.) Get out the dykes and solder and get after it!




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[Chop]

Thanks for the explanation on the timing thing.

It is not that I "don't want" to shorten the wires to the motor, I just don’t know if I can do too much. I took some pictures; the distance from the radio box bulkhead to the stern is 7” (17.78 cm.). I bent the motor wires as suggested and pulled the slack out of the wires. I might be able to take 2” (2.54 cm) out of the extension wires. This, with the 4” (5.08 cm.) taken off the ESC, I can remove a total of 6” (7.62 cm) from the mess.

Worst case scenario, I can tear out the existing bulkhead and move it back another 2”. The only “problem” with this is the extra work and refinishing to the hull. Not a real big deal, just time consuming. This would take the original 15” of wire and shorten it to 7” (17.78 cm.).

There have been no comments on switching from 12 ga to 10 ga wire, is it not a significant change?

Projects like this are real learning experiences!!! Let’s hope we learn from our mistakes.

[Fluid]

Without taking a saw to the hull, I still see at least 4-5" of useless wire that can be cut off the motor side of the ESC.



As for using 10 gauge instead of 12 - no material difference. The length is the problem. As long as your wires are - and with the problems you are having - anything practical to reduce the wire length is worth it to improve performance and reliability.



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[Chop]

Without taking a saw to the hull, I still see at least 4-5" of useless wire that can be cut off the motor side of the ESC.

The length is the problem.

Thanks.

I will take a knife to the wires tonight! Do I even bother messing with the 200a Mystery?

[ReddyWatts]

wire length

As for using 10 gauge instead of 12 - no material difference. The length is the problem. As long as your wires are - and with the problems you are having - anything practical to reduce the wire length is worth it to improve performance and reliability..

If a wire is 12 inches long, it is not the length but the resistance and voltage drop that causes the problem. Doubling the wire size has the same effect as shortening it to 6 inches.

[Chop]

If a wire is 12 inches long, it is not the length but the resistance and voltage drop that causes the problem. Doubling the wire size has the same effect as shortening it to 6 inches.

That's what I thought. I'll do that too.

Thanks Reddy

[ReddyWatts]

Also keep your wires seperated so you dont get induced voltages. (noise).

[Fluid]

If a wire is 12 inches long, it is not the length but the resistance and voltage drop that causes the problem. Doubling the wire size has the same effect as shortening it to 6 inches.

It isn't the resistance or voltage drop that causes the problem for the ESC, but the impedence of the long wires. Waste of time going to 10 gauge. And twisting the motor wires is a comon practice to reduce radio interfrerence, recommended by Schulze and others....but not on 12" motor wires.



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[ReddyWatts]

impedance is resistance. Only capacitance and inductance is added in for an ac circuit. You still get a voltage drop for the a certain length of wire.

[ReddyWatts]

Twisting of pairs is for keeping out external interference.

[Chop]

The length of the new extension wires is 10.5” (26.67cm), I might be able to remove another inch. The wires on the ESC have been shortened to about 1” (2.54cm).




I found some wire that was a lot heavier; I think it is 4mm diameter. The labeling on it reads: “Muldental - Elektronik GmbH 6 4mm 1548 x 0,07”




Just a bit of trivia here, the picture of the wire was taken using a Nikon D60 camera and a Nikon telephoto (70/300) lens with a doubler (makes the lens a 140/600) from a distance of about 15’ (4.57m).

Twisting of pairs is for keeping out external interference.

I only braided them because it looked cleaner. Since they are going to the motor do I have to worry about interference?

[Fluid]

impedance is resistance.....

Ready, you know better than that! Impedence is a combination of resistance and reactance. These are AC motors and both components must be considered. The reactance delays the back-EMF signal to the ESC causing the ESC to lose the motor's rotor position and goof up the timing. In other words, when there is inductance in the circuit the voltage and current are out of phase.

Don't take my word for it. Steve Rogers @ CC will tell you that the wire length to the motor should be a short as practical; if you need longer wires, make them the battery wires (and add capacitors).

(We don't care about any loss of voltage here - that effects power, not how the ESC reads the rotor position.)


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[Fluid]

The length of the new extension wires is 10.5” (26.67cm), I might be able to remove another inch. The wires on the ESC have been shortened to about 1” (2.54cm).

This is much better! At least try it this way and see how it performs. The longest motor wire length - from ESC board to motor can - on any of my boats is about 7". That's longer than I like but it works fine.

I would love to see some video of the EDF boat running on water.






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[Scott T]

Is it possible to move the fan unit a couple of inches forward to reduce your wire length a bit more? Looks like you have a bit of room on the mount.

You could add a tube to the rear of the unit so it still ends just in front of the rudder if that is a requirement.

Cool project, I like people thinking differently.