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Old Jan 22, 2013, 10:24 AM
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Originally Posted by Amp Abuser View Post
9x6 should shoot the rigger out of the hole with authority just the top end wont be as peachy. I would imagine you will bust 40 mph. Given the motor kv you should see 12k + at full pull on the striaghts. Can you source a metal shop an have them cut out you an aluminum motor mount?
What size prop would you recommend for top speed? This is the motor http://www.hobbyking.com/hobbyking/s...ner_Motor.html No on the metal shop. This boat at this time is on a VERY Limited budget.
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Old Jan 22, 2013, 03:50 PM
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That is a low quality motor with a top rating of 35 amps. You can exceed that for a short time, but you will be stressing the system. I modeled the motor performance for you, and on a good 3S pack the amps, thrust, rpm and pitch speed the predicted values are:

9x5 - 44 amps - 4.1 lbs - 13,100 rpm - 62 mph
9x6 - 49 amps - 4.2 lbs - 12,800 rpm - 73 mph
9x7 - 54 amps - 4.1 lbs - 12,500 rpm - 83 mph

All are well over the motor's amp limit, but when the boat is moving forward the motor will unload a little bit and reduce the amps slightly. Thrust is virtually identical for all three props - typical for same diameters - but don't expect to obtain the pitch speeds predicted. Loss of efficiency will reduce those numbers. I'd start with the 9x6 prop you already have and spend time tuning the boat for speed before trying different props. There is usually more speed potential from getting a rigger to run light on the water than there is in a minor prop change.



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Last edited by zozer; Jan 22, 2013 at 03:58 PM.
Old Jan 22, 2013, 03:53 PM
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On 3S 7x7.5 / 8x7 with that particular motor would be worth trying. By keeping the motor tower height to a minimum -the 7in prop wins reduces the top heavyness. 3S may not be ideal for the 7in prop.

Spec.
Battery: 2~4 Cell /7.4~14.8V
RPM: 1450kv
Max current: 45A
No load current: 3.5A
Max power: 655W
Internal resistance: 0.023 ohm
Weight: 102g (including connectors)
Diameter of shaft: 5mm
Dimensions: 35x36m
Prop size: 7.4V/9x6 14.8V/8x4
Max thrust: 1380g
Old Jan 22, 2013, 04:39 PM
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Put 2 vertical stabs on the back. I did it this way so it won't change how I am doing the hatch, plus it looks cool.
Old Jan 22, 2013, 04:50 PM
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Quote:
Originally Posted by zozer View Post
That is a low quality motor with a top rating of 35 amps. You can exceed that for a short time, but you will be stressing the system. I modeled the motor performance for you, and on a good 3S pack the amps, thrust, rpm and pitch speed the predicted values are:

9x5 - 44 amps - 4.1 lbs - 13,100 rpm - 62 mph
9x6 - 49 amps - 4.2 lbs - 12,800 rpm - 73 mph
9x7 - 54 amps - 4.1 lbs - 12,500 rpm - 83 mph

All are well over the motor's amp limit, but when the boat is moving forward the motor will unload a little bit and reduce the amps slightly. Thrust is virtually identical for all three props - typical for same diameters - but don't expect to obtain the pitch speeds predicted. Loss of efficiency will reduce those numbers. I'd start with the 9x6 prop you already have and spend time tuning the boat for speed before trying different props. There is usually more speed potential from getting a rigger to run light on the water than there is in a minor prop change.



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The Max amps are 45 not 35. So it should work with the 9x5 and the 9x6, but I would be pushing motor to it's limits. I am using a "cheapy" battery http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html because this is what I already have.
Old Jan 22, 2013, 06:23 PM
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The Max amps are 45 not 35.
Right - my bad. To get speed in an airboat you need a balance between thrust and pitch speed. I would not go less than 9" in diameter, that's just 1/2" higher for the motor (not noticeable) and the gain in thrust from the larger prop ( 40%) will be worth it if speed is your goal. I understand the cost considerations for your project, the modeling above is probably slightly higher than what you'll get with low end packs - but not much. I am anxious to see how your rigger runs.



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Old Jan 22, 2013, 07:22 PM
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On the prop I am starting with a 9x6 for sure. That's all I have right now.
Old Jan 22, 2013, 07:32 PM
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THANKS!! For ALL the help you guys have given me. You have saved me from a lot of frustration. This is exactly why I started this build log in the first place.
Old Jan 23, 2013, 10:11 PM
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You're very welcome. I should have a thread on my newest airboat in a week or so - stay tuned for something completely different.



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Old Jan 24, 2013, 04:26 PM
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Here's the motor stand on. There are 2 pieces of plywood epoxyed to the inside walls of the boat, and then the motor stand glues to those. I am going to bolt it on for now, until I get it dialed in and decide exactly what prop I will be running (in case I want it shorter or taller). Then I will epoxy it to the boat.
Last edited by Dave8888; Jan 24, 2013 at 06:26 PM.
Old Feb 15, 2013, 01:18 PM
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Decided to give up on the plastic (see through) hatch covers. The plastic I have is way to thin, and I just can't find any that will work. I am now going to make hatch covers out of 1/32" ply.
Old Feb 16, 2013, 11:53 PM
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Here ya go.

https://www.rcgroups.com/forums/show....php?t=1823356



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Old Feb 18, 2013, 06:41 PM
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That's pretty cool.
Old Jun 18, 2013, 09:58 PM
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Its been a long time since I added to this log. I got a new job and moved into a better place. BUT during the move boxes fell onto my boat and busted it up pretty bad. It's going to be easier to start over then to fix it. This time I am going build a outrigger airboat with a JAE .12g. I found a thread on airboats on this site that I am going to post the build on. https://www.rcgroups.com/forums/show....php?t=1902931


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