Newbie - What to buy for 40" Catamaran (ABS plastic) - RC Groups
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Dec 27, 2012, 10:24 PM
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Newbie - What to buy for 40" Catamaran (ABS plastic)

Hi Everyone,

I bought a 40" catamaran, so I can upgrade it and make it do what I want it to do.
Here is the changes I made to it:

1) Took both motors off and installed only one of them back in the middle. Built my own brushed speed controller using relay and transistors. Converted the part that can be adjusted to make the boat go straight into a rudder controlled by a servo....... I burnt 2 speed controller I made. Got tired of it and moved on to the next changes.

2) Bought one 2848 water cooled brushless motor from HK along with Turnigy 120A boat ESC and ESC programmer. Made my own rudders that move in tandem......... This time the cheap motor/shaft coupler made out of plastic melted. So I made my own from aluminium.

Now... Everything is functioning correctly. But I want a better way of controlling the turns; I don't think I like using rudders. So, I decided to go back to 2 motors, but this time both brushless. Since I am controlling everything from a microcontroller, I will have better control over the turning process.

I am using 5000 mAh 20C 3S Venom battery which had bad cell and it is in process of being replaced (sleeping deep in saltwater solution as we speak). I also have 2100 mAh 20C 3S for powering the microcontroller other good stuff I have attached to the microcontroller. When I have some time, I will take pictures and put them here.

I do not want the boat to fly! With the current setup, I was able to get to 10 knots and it's enough to go up to 15 knots for me. My question is that I want to change shaft, stuffing box, possibly propeller. The motor I have might be small but I like it and I want to keep it. What recommendation can you all give me on the shaft and propeller sizes to maximize the run time while being able speed up to 15 knots?

Thank you for your time everyone,

Last edited by TheKaduu; Dec 28, 2012 at 02:15 PM.
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Dec 28, 2012, 08:37 PM
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Dec 29, 2012, 05:23 AM
RELAX. You'll live longer
785boats's Avatar
Which cat is it? Some pictures or a link would help.
Dec 29, 2012, 05:27 AM
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CornelP's Avatar
There is a link in the first post, it's the Admiral.

Probably two motors in the 3650 size range and 120A ESCs would do the job, but it will get a bit heavy. I would probably go for 2860 on 3S if you want to keep the batteries...
Dec 29, 2012, 05:55 AM
Boaters are nice people.
Originally Posted by TheKaduu
I do not want the boat to fly! With the current setup, I was able to get to 10 knots and it's enough to go up to 15 knots for me.
Hi Kadem,

I think this sentence baffles the members here, as this is the fast electrics forum...
When an 'Admiral' comes along, the question usually is: ""How do I make this cat fly?"

The best answer to that question is to buy a hull that's designed to go fast...

As you're interested in pottering around, any hobby grade propshaft and stuffing tube will do, experiment with propsize to get the speed you want, without overheating the motors.
You didn't say where you're located, so pointing you towards the nearest shop is a bit difficult.

Regards, Jan.
Dec 29, 2012, 01:23 PM
RELAX. You'll live longer
785boats's Avatar
Thanks cornel. I didn't see the link in the first post.
Jan 08, 2013, 12:33 PM
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pompebled: I did not see a slow boat section Thanks for the info.
CornelP: Thank you for the info.

I switch back to 2 motors. I bought 2 3660 brushless motors and now have 2 120A ESC. I also acquired set of the following size props (addition to 2" stock props): 1.75" (dumas), Surge Crusher props, 42mm, 38mm 35mm. What can I say, I have no patience

I might have forgotten to mention that I have a Chevy truck washerfluid pump hooked up to all motors and ESCs to keep things cool even while going slow. Since everything is controlled with microcontroller, I have temperature sensor on all motors and ESCs. And the pump can be operated manually or automatic which can turn on if any of the temperature sensor measures anything above a certain value. I am a Software Engineer, and a good one too. So, the everything but mechanical part of this project is already done.

I also have GPS, compass (which needs to be calibrated with the new setup), voltage divider to measure the cell voltages (assuming that battery is balanced - I know voltage sags under load, nonetheless, it helps).

I owe you all some pictures now... Hopefully tonight...

Now, I am considering using 2 3S batteries in parallel. I already soldered the Deans connectors and tested it. I read to confirm what I already know that batteries should (preferably) be same capacity which are already bound to come tomorrow. Do you have any tips for the parallel batteries from your experience?

Thank you for your time.

Last edited by TheKaduu; Jan 08, 2013 at 03:20 PM.
Jan 14, 2013, 11:24 PM
I feel the need for speed!
scorpion1's Avatar
I got an Admiral several years ago and threw in a set of Graupner 700's, went decent but somehow fried the motors(8.4BB's) should have gone with 9.6's and smaller props.....................anyhow I threw in a single drive Feigao 580L on 6s and here's the result. Went about 30 mph but handled like crap............put in a single 700 for a rescue boat, left it on the shore by accident when leaving, came back 5 minutes later and it was gone

NQD Admiral 40" Cat on 6s with 580L motor, 2nd run (2 min 6 sec)

Here's one that seems to have worked out pretty well.............

RC Boat , Admiral CAT heavily modified (0 min 43 sec)
Jan 14, 2013, 11:34 PM
I feel the need for speed!
scorpion1's Avatar
Here's the one i was trying to find though...................leave it to the Germans to get an ABS toy to hit 60+ mph!!

Hopf NQD PX 757 Admiral Cat (1 min 12 sec)
Jan 24, 2013, 12:18 PM
Registered User
Your's is nice too... Thanks for the videos.
Jan 24, 2013, 12:32 PM
Registered User

Different problems

As I mentioned before, I now have 2 identical* motors, 2 120A Turnigy Marine ESC and various prop sizes. I only have one set of counter-rotating props (stock). Since 2 motors pushing with 2" stock propellers, the boat was going too fast at the idle speed. So, I took the propellers off before I tested for yaw (idiot)... With the rest of the propellers, the boat was not going straight.

The weird part is that at the lowest speed the boat slightly turns to left. But at the next higher speed, boat does a hard clockwise circle... This was observed with props that rotates the same direction... Is it possible that one of the motors is not accelerating smoothly; it is slow-slow-very fast as opposed to slow-fast-very fast as it should be?

I also think this could be caused by the ESC. Have any one of you experienced this before? Can I do anything to fix this?

Thank you for your time,

Jan 24, 2013, 12:45 PM
Steps? What steps?
zozer's Avatar
This is commonly observed, it is due to the motors turning different speeds at different throttle inputs. Either the motors have slightly different Kv values - very likely - or the ESCs are not giving identical signals to the motor at the same throttle inputs. This happens with top-of-the-line motors and ESCs - I can only imagine how it is with cheap stuff. Try switching the motors to different sides, maybe the differences will cancel themselves out. That, or just run WOT most of the time and trim the boat for that.

Jan 24, 2013, 01:00 PM
Registered User
I may have forgotten to mention that both motors are 3180kv. I know this is too high of kv...
Jan 24, 2013, 01:04 PM
Registered User
Thank you for fast response zozer... What is WOT? I was planning to incorporate an accelerometer to balance the motors, but I'll put the counter-rotating propellers on and test again first.
Jan 24, 2013, 06:26 PM
Registered User
First thing I tried was the trim, but I found out that lower speed pulls left and higher speed pulls right. This is why I will try the accelerometer to balance the motors. I think I'll debug the controller next. Who knows, I might be sending the wrong speed to one of the motors. I think a bug is highly unlikely because the code is pretty much copied from the one motor code and one motor code was working just fine...

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