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-   -   Brushless ESC for an Air-Boat (http://www.rcuniverse.com/forum/rc-airboats-246/11338980-brushless-esc-air-boat.html)

Nodd 12-20-2012 07:03 PM

Brushless ESC for an Air-Boat
 
First off I'm an airplane guy, I know little to nothing about boats. Nevertheless I'm planning to scratch build an air-boat using the electronics from a crashed plane.

Ordinarily I'd just use the airplane's ESC but I'm thinking this boat may double as a recovery tug for my seaplanes. So I'd like the ability to backup (reverse the motor). For obvious reasons airplane ESC don't have a reverse feature. So I figured I'd look at boat ESC but they all seem to be water cooled. As I may run my air-boat on snow or grass that's not going to work. So then I started looking at car ESC. They seem like a good choice as they're designed to operate in an enclosed space & have big heat sinks or fans to cool them. But then I noticed they have features like braking & other car specific stuff that maybe not work for an air-boat. I'm also not sure how they handle low voltage cutoff, I don't want to get stranded out on the water once the LiPo gets low.

Anyway I figure you guys have all this sorted out already so any advice would be appreciated. Here's some basic stats...

Airboat Size: medium, somewhere between 1½ to 3 feet long
Donor Plane:
50" park sized Piper Cub
Motor: no-name Chinese 35mm 800kv brushless (I may replace with a higher kv motor)
ESC: 30a
Battery: 3S 2200 LiPo
Radio: 7 channel Spektrum DX7s (airplane radio)
Project Budget: less than $50

My other issue is I'm using an airplane radio. Any suggestions how to setup the throttle with reverse baring in mind the left stick (usually used for throttle) has no centering?

Got RPM 12-20-2012 08:01 PM

RE: Brushless ESC for an Air-Boat
 
I'm not sure how the car ESC will work with the aircraft radio, the signals from the transmitter are considerably different. We often have to use a converter between an aircraft ESC and the receiver to make it work normally with a pistol transmitter. Perhaps others have tried one. You should have at least a 60 amp controller, the motor on a boat does not 'coast' as in a plane, it is constantly working. Frankly, using our club recovery boat with no reverse has never been a problem. You may not need it.

As to the boat size, I'd aim for at least 30" with large air rudders close behind the prop - a pusher setup may work better (uses standard tractor props). This size adds stability and flotation for batteries, et al and is easier to see when trying to maneuver at a distance. My latest airboat (below) uses an 780KV motor on 4S with a 13x6.5 prop - quite quick but way too much power and not enough rudder for a recovery boat. Larger props are more efficient with the airboat giving more thrust, but for fine maneuvering with an air rudder a smaller prop with higher pitch will allow better steering. On 3S your motor will spin around 8000 rpm with an 11x6, but running 4S and a 9x7 will up the rpm to ~10,500 with more wind going by the rudders for improved steering. A recovery boat doesn't need to be fast, just maneuverable with enough power to make the tow.


http://i46.tinypic.com/nwdl5k.jpg


Nodd 12-20-2012 09:45 PM

RE: Brushless ESC for an Air-Boat
 
I'd assumed air & surface radios used the same throttle signal but yeah if not then I need to re-think this. Can anyone confirm that's the case?

My other option is to use a mechanical dual-pole dual-throw (DPDT) switch that reverses two of the motor leads, have an extra servo that flips the switch. That may actually end up being a good solution as it's better suited for air radio (flip a switch to put her in reverse) setup. It'd also let me use an air ESC which I already have plenty of. Good point about the amperage rating. I have a 50a air ESC that'd probably work fine.

I'm now thinking I'm going to make this a dual purpose boat. I think I want to set her up as a regular air-boat for tooling around the pond but also make one of those floating PVP pipe/swimming pool noodle U shaped catcher rigs that could be attached to the boat when its needed for rescue work. So basically I'm leaning more towards a traditional air-boat setup.

Love the float-plane rig you have there, saw that in another thread here. That thing looks bad-ass.

rangerfredbob 12-21-2012 08:04 PM

RE: Brushless ESC for an Air-Boat
 
the difference in signal is the neutral point on a car radio is in the middle of the "throw", where air ESC's are set up to start at the low throttle setting., some won't work unless the throttle trim is maxxed out down either...

Nodd 12-21-2012 08:18 PM

RE: Brushless ESC for an Air-Boat
 
Thanks for the clarification. I talked to a few other car guys & they confirmed what you just said.

My workaround will be to place the throttle on the right stick (elevator channel). As that stick has centering, the neutral point should mirror a pistol-grip radio & be in the middle. I'll push forward to go, pull back to brake/reverse. Left & right will be steering. So everything will be on the right stick, should work fine. I'm gonna order a cheap car ESC & see how it goes. Thanks.

Got RPM 12-22-2012 09:21 AM

RE: Brushless ESC for an Air-Boat
 
One other thing to keep in mind is that ESCs do not like water. Most - even marine versions - will eventually blow if they are run when wet. Many of us boat guys spray our receivers and ESCs with CorrosionX once or twice a year to help with the waterproofing. It isn't perfect but will provide some protection. If the ESC does get wet, blow out as much of the water as possible and let it dry for a week before running it again. If you try to run it right away while it may still be damp inside you will risk a burndown.


http://i45.tinypic.com/1174v3d.jpg
http://i50.tinypic.com/op45z9.jpg
http://i46.tinypic.com/1z6sgu1.jpg


.

Nodd 12-22-2012 10:30 AM

RE: Brushless ESC for an Air-Boat
 
Yikes! Point taken. I was thinking of using a tupperware container to house my electronics, hopefully that'll keep things dry. If not then yeah, don't run it wet, got it. Thanks.


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