AirBoat build

[Chop]

Is it possible to move the fan unit a couple of inches forward to reduce your wire length a bit more?

I should have thought of that when I was considering making the radio box bigger.

Cool project, I like people thinking differently.

Actually, it was j.m.'s idea, I just went along with it - it made a lot of sense (if you don't mind breaking from tradition).

[ReddyWatts]

Fluid, you should know there is no inductance or capacitance in wires that are this short, only resistance. Make the wire size bigger and lengthen them. It will not effect the circuit. This cannot change the phase angle.

The only phase angle change will be produced from the motor itself, since it is an inductor.

[ReddyWatts]

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

IMO, I would seperate the wires.

[Chop]

IMO, I would seperate the wires.

meh, I can do that: practical is better than pretty.

[wparsons]

Chop, if you're still having trouble with the power system, check out an EDF forum. Just keep in mind that your fan will never fully unload, so your amp draw will be higher than in a plane.

Before you do too much else, is the fan balanced? Is there any resistance in it (touching the casing anywhere)?

Is the timing on the ESC right for the motor?

[ReddyWatts]

Here is a quote from Bob Boucher on the topic of which wire to lengthen:
“I will repeat the message previously given. I hope you heed some sound
advice based on theory and practice.

1. Wire resistance may rob you of a bit of power but will not destroy
your speed control or motor.
2. Wire inductance will not damage your motor nor will you be able to
detect any effect even with 100 feet of wire.
3. Wire inductance will kill the mosfets in your control and may even
blow the caps.
[NOTE: Bob is comparing inductance in the motor to ESC wire to
inductance in the ESC to battery wire]
I’ve been a design engineer and manufacturer of motors and controls for
over 30 years. You must keep battery wires as short as practical. Short
means 1 foot or less, brushed or brushless makes no difference.”
Bob is better known as “AstroBob”, owner of AstroFlight and holder of a
patent on electric flight. When AstroBob talks, I tend to listen.
I could include a lot of other text on this subject, but I think you
get the idea. If it’s possible, always lengthen the wires from the motor
to the ESC. The best possible solution of course is to keep all wires as
short as possible, but we know that’s not always easy when you’re doing
that special scale project.
Thanks to the guys at AstroFlight, Castle Creations, Schulze, and Doug
Ingraham for the help.

[Chop]

Before you do too much else, is the fan balanced? Is there any resistance in it (touching the casing anywhere)?

The 7 bladed fan is balanced (UGH!). The fan spins freely.

Is the timing on the ESC right for the motor?

I wondered about that too. With the potential for the variations in wire length this might not be (too) possible to account for. In this build, I have not messed with the ESC settings for timing.

3. Wire inductance will kill the mosfets in your control and may even
blow the caps.
[NOTE: Bob is comparing inductance in the motor to ESC wire to
inductance in the ESC to battery wire]

Wires on which side of the ESC?

[ReddyWatts]

He says, If you get your wires to long (12") on either side, it can burn the esc. Lengthening is less critical on the motor-esc side. Shorter is always better.

I say use larger wire on the motor/esc side to lower wire impedance (resistance) for high current or longer wire than normal apps.

Add capacitors, use larger wire between the battery/ESC for high current or longer wire than normal apps.

[ReddyWatts]

We use capacitors on the battery/esc side to support the input DC voltage. I wonder why they have not added three capacitors on the motor/esc side to bring the current back in phase with the voltage due the inductance of a motor. it would hold a higher voltage on the motor windings for more usable power. Less vars going back into the esc for better reliability.

[Chop]

Add capacitors, use larger wire between the battery/ESC for high current or longer wire than normal apps.

So...
Larger wire = Larger gauge? Do I shorten the battery side wires on the E.S.C.? This makes it sound like I shouldn't.
Use larger (gauge) wire in longer than normal applications?

[ReddyWatts]

Shorter is always better. I would remove any that is not needed to reach your components.

Normal to me is less than 8 inches of wire. I would replace with a larger guage wire for longer apps. I have doubled up on the DC wires before, just keep them the same length, but cant do this on the motor/esc side. On the battery side (bat/esc) you can also add caps.

The expert recommended lengthening wires on the motor/esc side first.

[wparsons]

We use capacitors on the battery/esc side to support the input DC voltage. I wonder why they have not added three capacitors on the motor/esc side to bring the current back in phase with the voltage due the inductance of a motor. it would hold a higher voltage on the motor windings for more usable power. Less vars going back into the esc for better reliability.

The point of capacitors on the input side is to smooth out power delivery from the battery, the caps can handle little spikes better (and faster) than the battery can.

If you put it on the motor side, wouldn't it interfere with motor response and the feedback the ESC needs for timing? I would think the spikes are what lets the ESC "read" where the motor is.

[ReddyWatts]

On a motor the amps start lagging the volts due to its inductance. Caps in parallel with the load would pull it back in phase for a higher voltage (power) to the motor.

You may have the answer, it might effect the feedback pulse. It also might take different values of caps for different apps and it is not a true sine wave.

[Chop]

Sorry about the picture quality - I didn't have my good video camera and didn't have anyone to run the one I had.

http://www.youtube.com/watch?v=sxBJYPrqkiQ

I ran the boat for about 2 minutes more than the video shows. Nothing was more than warm to the touch.

A little different thought process when turning, you can't coast.

[Chop]

After hitting the rocks I examined the boat closely for damage. I had taken the precaution of painting a rub rail on the hull. I had seen lots of paint chipping because the boat, when on land, hit curbs, house foundations, trees etc., along with rocks and piers when on the water. I suppose I could learn how to drive better, but until then this will do.

For the rub rail I used Plasti Dip and thinned it with xylol. It paints on very easily, but it is hard to get the coat smooth. I masked the trim with Frog Tape, which does not allow for much “wicking” under the tape and pulls off cleanly. The problem here is that the Plasti Dip sticks together (it is very "rubbery") and when you pull off the tape it peels off like dead skin after a sunburn. I had to score the Plastic Dip with a Xacto knife to get a relatively clean line. The area where the boat hit the rocks is just right of center in the picture. I think it held up well.

******

After the run in the video (about 3 minutes longer than the video itself) the electrical components were only slightly warm to the touch (THANKS every one for the advise – especially Reddy & Fluid!).

The electrical changes that I made consisted of:
1) removing about 6” of length of wire between the ESC and the motor.
2) Increasing the wire diameter between the motor and ESC: the old wires were 12 gauge, the new wires are 4mm diameter (more than twice the diameter).
3) I used silver solder instead of the usual tin/lead combination.