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Old Apr 04, 2001, 09:04 PM
Registered User
Olathe, KS USA
Joined Nov 2000
35 Posts
My new Puddlemaster (twin!)

Just finished my Puddlemaster with twin 400 cobalt motors in series, spinning 6x4 props, and 16 cells. The plane looks good and seems to have good power, but the weight is a little high. The specs on the box says 44oz, but my came out to 53oz. Even with this weight, the wing loading is only 19oz/sqft and the power input is 145 watts.

Has anyone have any experience with this plane with this kind of loading? I'm sure it will fly, but would like a little assurance that I'm not going to dump it on the first flight. I may try going to a 6/7 cell 3000mha battery and run the motors in parallel.

I have a few pics on my WEB site, http://cj626761-b.olathe1.ks.home.co...s.pl?My_Planes

Thanks in advance.
Ron
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Old Apr 04, 2001, 09:15 PM
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Alexandria
Joined Apr 1999
689 Posts
Ron,

Nice looking planes! Usually the cobalt 400's can be run well at around 20 amps (each), so you could run at 20amps*16V=320 watts in.

What type of motor/cells?

Up the amps and that beauty should fly fine if the motors and cells can handle it.

Marcus
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Old Apr 04, 2001, 09:18 PM
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Texas
Joined Aug 1999
5,110 Posts
Very nice. I don't have any advice to offer. I hope your flight goes well.

Dave
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Old Apr 04, 2001, 09:31 PM
Registered User
Olathe, KS USA
Joined Nov 2000
35 Posts
Marcus,

The motors are the 14T MaxPro Cobalt 400. The specs say that they will take about 150w (20a max with 7 cells). In this set up, the batteries are 2x8 cell 1600NiMH in series. These batteries are only good for about 10a before they get hot so they are the limiting factor. I wanted the duration so this seems to be one way of getting it. I would like to get closer to 180w for this plane and still get 5 minutes of full power flight. With the current setup, I get 6+ minutes at 95% power. I expect even better in flight.

I am looking to try a single 7 cell 2400NiCad or 6 cell 3000NiMH. This will keep the weight about the same and give me the current output, but I will loose some rpms. My tests with a 9 cell RC-2000 pack gives me 25a output with the motors run in parallel (aprox 180w).

Anyone know what a 6 cell 3000mah NiMH pack weigh? I might be able to use 2 of these and get the extra power.

Thanks again,
Ron

[This message has been edited by rfrenzl (edited 04-04-2001).]
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Old Apr 05, 2001, 01:29 AM
Speed Demon
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Antioch,CA,USA
Joined Dec 1999
12,303 Posts
I have an old Puddle Master that someone else built and gave to me. With a geared SP600 12V and 16-1400AE cells, it weighs in at 67 ounces. It ROW's just fime in about 50-70 ft. I have it pulling 320 watts in which gives me a 76+ watts/lb. rating. It gets around 10 min. average flightime with a few touch and goes thrown in. Yours is around 43+ watts/lb. This is much less than mine, but may work. Taking off from water uses more power than from land or a hand launch. It may be a good idea to use the 3000 Nimh cells in parallel. You could then input better power.
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Old Apr 05, 2001, 04:33 AM
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Cocoa, Florida
Joined Mar 2001
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Do you know what RPM the MPI cobalts are turning those 6-4 props? What brand props are you running? I am planning on buying one of these motors and would like to know the RPM out-put. Thanks.
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Old Apr 05, 2001, 08:41 AM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
12,788 Posts
Hi Ron
Nice job!

Being a Puddlemaster fan - had three - suggest you try flying over land first off. Leave off the tip floats - they don't do grass landings well - and watch out for a slight nose down tendency on hand-launch.

Yours might not exhibit that pitch down, as your thrustlines are lower than the regular single motor.

That'll tell you how its going to fly. All three of mine - two Ace Puddlemasters and a HH Pondside - flew fine built and balanced as per the kit.

The one area that could give you problems with the weight is when sitting in the water. Here, the wing loading has nothing to do with it, the model will sit lower in the water and thus the motor(s) have to work harder to push the hull up onto the step to take off.

I've seen a Puddlemaster made so heavy that it wouldn't take off despite an Astro 05 and eight cells. To be fair to the design, the builder had 'improved' the heck out of the model to the point where it turned into an unwieldy boat.

Once you get her trimmed out over land, you might want to do your first water flights on a single pack to make life easier for the motors.

I've stuck a bunch of Pondside / Puddlemaster shots on my webpage - have a section devoted to an "Owners Club" (Dues, $0.00, payable 31 Feb next ) Would love to add your twin to them. This has to be one of the most popular kits around.
www.weekendpilot.homestead.com

(Also the homepage for our June 27/28 electric funfly - two days, all funfly, NO comps!)
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Old Apr 05, 2001, 09:21 AM
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Fall River MA
Joined Feb 2000
25 Posts
Nice planes...

I think you will need more than 145W to get off the water.

I use an Astro 05 direct on 7 cells in my puddlemaster (250W). It gets off the water in about 10 meters, at ~ 40 oz. weight.
With a ferrite motor at 170W input, it made a nice tugboat...

Putting the motors in parallel sounds like the way to go.

Good luck!
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Old Apr 05, 2001, 10:29 AM
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Lynnwood, WA USA
Joined Jan 2000
547 Posts
I believe a 6x3000 NiMH pack from MEC (powertube) will weigh ~13.6 oz.

Check here: http://www.ezonemag.com/disc/Forum1/HTML/005168.html

MMGM

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Old Apr 05, 2001, 10:50 AM
Registered User
Olathe, KS USA
Joined Nov 2000
35 Posts
Quote:
Originally posted by injunnut:
Do you know what RPM the MPI cobalts are turning those 6-4 props? What brand props are you running? I am planning on buying one of these motors and would like to know the RPM out-put. Thanks.
The Cobalt 400 motors from ProMax come in different windings. The 14T units I have will turn a MA 6x4 at 13K on 8 cells and 10a draw. I've tried some 5x3 3 bladed props and get a little more rpm with the same current and cell count. The APC 5.7x3 cox type prop will also turn about the same as the 5x3. Given the right battery, I would suggest a 6x5 Aeronaught (sp?) prop on 7-8 cells. This will give you about 150w and close to the 20a limit for this motor. The spec sheet for this motor show this version spinning a 7x3 prop at 14K and 17a on 7 cells.

So far, the motor dosen't seem to care what prop you use, but I would use a good high current battery and 7-8 cells. Use a WattMeter to get the current you want. I would suggest 15a in a static test to keep the motor heat down.

As for testing the plane on land first, I had planned to do just that. It is a little hard to compare the twin to a single motor configeration as the prop areas are different. A 9" prop has 63sqin and 2 x 6" props have 56sqin. The water test shows that it will ride rather shallow in the water. I need to test the complete plane as my test was with a 48oz weight.

My next test will be to put the motors in parallel and use my 1700mah 6 cell pack to see what the rpms and current draw will be. If this looks good, I will try a 3000NiMH, 6 cell pack to check its current delivery. The weight will be close to the 50oz mark which should be fine with the 400sqin wing. If all else fails, I will try a gear reduction unit and see if a 2:1 and 7 or 8" prop will work better. My goal is to get 15a per motor and a prop speed of 50mph, and a weight closer to 45oz than 50oz.

Dereck, if you want to add the pics of my PM to you site, feel welcome. Just make sure to spell the name right , its Ron Frenzl

Thanks for the advice,
Ron
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Old Apr 05, 2001, 06:44 PM
Registered User
Olathe, KS USA
Joined Nov 2000
35 Posts
I spent all day at work thinking about this plane and how to power it. When I got home, I re-weighed everything and came out 49oz. I don't know what happened to make me think it was 53oz (must of had my hand on the scales). Anyway, I put together an 8 cell RC2000 battery pack and set the motors up in parallel. When I put the Wattmeter on this setup, the input went from 150w to 310w, and from 10a to each motor to 35a to the pair.

The tech read over 16K rpm with the 6x4 MA props. The best thing is that I only gained 1.25oz in weight. Now I have a 400sqin wing, with 310w of input power and a wing loading of 18oz/sqft.

Bottom line is that this bird will fly and should even ROG when on grass. We have a float-fly next weekend so I'll have a chance to use water.

Thanks for all of the suggestions and information. It really helped a lot.

Ron
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Old Apr 06, 2001, 12:10 AM
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Austin, Texas USA
Joined Mar 2001
848 Posts
It looks like you got the numbers to where they ought to be...

The nimh cells do not quite put out as much voltage as nicads, so I would use one more cell. I think the performance gain would be well worth the extra weight of one cell.
So, instead of a 6 cell nicad, use a 7 cell NIMH pack, etc.
A pack of 3000 NIMH cells should be really nice.
Of course, you would gain better effeciency using gearboxes, also.

[This message has been edited by sf_247 (edited 04-06-2001).]
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Old Apr 16, 2001, 10:19 PM
Registered User
Olathe, KS USA
Joined Nov 2000
35 Posts
I got a chance to fly this bird over the weekend. I was not able to get it to lift off of the grass because of a 10-15mph headwind. So I got someone to hand launch it. It took off like a homesick Angel. I had to give it full down trim to get iy to fly level. I guess mounting the motors on the wing offset the down thrust provided by a pylon mounted motor. The two cobalt 400's worked great. I was able to cruise at 1/2 throttle and had no problems with the wind. The landing was un-eventful. All-in-all, the plane looks to be a winner. I can't wait until this comming weekend when we have our floatfly. I hope the weather is good.

Thanks again for all of the advice.

Ron
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Old Apr 17, 2001, 12:15 AM
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Cocoa, Florida
Joined Mar 2001
101 Posts
Ron,
Please let us know how it flys off water at your float fly. What kind of flight times are you getting?
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Old Apr 23, 2001, 11:44 AM
Registered User
Olathe, KS USA
Joined Nov 2000
35 Posts
Here is the low-down from the Float-Fly this past weekend. The day started a little "iffy" with winds at 15+mph and overcast. About 10:00am, the winds went dead calm and we had two hours of great weather, after which the previous forcast came true. The winds went to 20+mph and there was some rain.

As for the two good hours, my Puddlemaster flew great. The first hand launch (with 15mph winds) was good and the landing went well as I was able to bring it into a small protected area with small waves. Once the wind died, the ROF went very smooth. The plane was on step in about 12ft and I could run it on top of the water as long as I wanted. It rose very smoothly and the landing was just as nice. But due to the poor weather forcast, we had few cameras there and I did not get any pictures of the takeoff or landing. I did try a float test in the medium waves and the plane did OK, but the props were hitting the wake more than I'd like. I'm guessing that by giving it full power, it would get on step very quickly and get airborne in just a few feet. It easlily has enough thrust to climb out with only a little air speed.

As far as flight times, I backed the power off to about 1/2 after takeoff and coasted. I did a few loops and low passes and then landed after 4 minutes. With the taxi and initial power test, the battery was down to 800mah from the 2000mah capacity. Based on this, I'm guessing that the flight times will be in the 5-6 minute range with enough to get the plane back to shore. Since I did not have much air time on this plane, I kept the flights down to 4 minutes. As I get more experience with it, I'll run out the battery and see what the max flight times will be.

All-in-all, this configuration turned into a great combination. I think that I will see about getting a 9-cell 3000NiMH pack and get flight times up to 8 minutes. The plane also really needs airlerons. I might add them next month and see what the effects are.

Next project: a Dare C-119 boxcar. I have the fuselage is sheeted and I'm on the first boom. I'll probably go with the sp400 6v as suggested and a 8-9 cell 3000mah NiMH pack.

I do have a few pictures of the float-fly on my web site. Check the first post for the URL.

Ron

[This message has been edited by rfrenzl (edited 04-23-2001).]

[This message has been edited by rfrenzl (edited 04-23-2001).]
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