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Old May 03, 2010, 08:53 AM
All under control, Grommit!
leccyflyer's Avatar
United Kingdom, Aberdeen
Joined Sep 2000
12,578 Posts
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Twin brushed sp400s on 3s1p or 2s1p?

There are quite a few Sp400 twins about. Back in the day a good set up was 2xsp400 motors, either 6 volts or 7.2v, on 7 or 8 sub-Cs or similar. This gave current draw of 22 - 28 ish amps, with Gunther or 6x3 props, if the motors were in parallel.

I've got an HVP Henschel Hs129b, bought second hand, which I've seen fly very nicely on 2xsp400s, 6x3s and a 7 cell 2000 NiCd pack. However the pack is long past it's sell-by date and has been excised from the model.

I'd pretty much resigned myself to replacing the whole power train, and bought a couple of Emax motors and Hobywing ESCs, but thought the least I could do was to give it a try with 3s1p Lipos and perhaps save all that rewiring on an already built model. As well as making use of gear that still had life in it.

No chance.

With a fresh off the charger 3000mah 3s1P 20C Tipple pack, the meter showed 25 amps before getting anywhere near half throttle and was at 45 amps at 3/4 throttle before I shut her down.

Just guesstimating, but to get down to a reasonable current draw I reckon it would need 4 inch props - which are much smaller than the cowls. The 6x3's aren't the pitchiest props anyway.

Is anyone out there still using twin brushed set-ups on 3s1p lipos? What about 2s1P?
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Old May 03, 2010, 09:59 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,053 Posts
Here's what I did on my GWS C-47 - Gone series with brushed motors

I not sure what the C-47 motors are, possibly the cheaper Mabuchi 380, but converting to series on 3s seemed to work quite well.
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Old May 03, 2010, 10:06 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
6,710 Posts
Hi Leccy

I haven't done a brushed twin setup using can motors in a while. The 3s setups I've used were for either the Speed 300 7.2V motor with 4.5" props, or the Speed 400 7.2V setup with I think twin Gunthers (I sold the airplane a few years back.) At this point, I think you've bought the farm with those motors- I wouldn't trust them having been pushed that hard. But why not just use them with a 2s setup? Generally the dramatic weight savings compared to nicads will give you a nice performance boost. However, given how cheap a decent brushless ESC has become, I don't see any reason not to go twin brushless for most airplanes.

Sam
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Old May 03, 2010, 11:21 AM
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Mark Wood's Avatar
United States, CA, Bear Valley Springs
Joined Feb 2000
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I'd certainly try a 2s lipo, Bri...especially if they are of the 6v type. 7.2v motors should be ok for 3s though.

mw
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Old May 03, 2010, 11:25 AM
All under control, Grommit!
leccyflyer's Avatar
United Kingdom, Aberdeen
Joined Sep 2000
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Quote:
Originally Posted by Megowcoupe View Post
Hi Leccy

I haven't done a brushed twin setup using can motors in a while. The 3s setups I've used were for either the Speed 300 7.2V motor with 4.5" props, or the Speed 400 7.2V setup with I think twin Gunthers (I sold the airplane a few years back.) At this point, I think you've bought the farm with those motors- I wouldn't trust them having been pushed that hard. But why not just use them with a 2s setup? Generally the dramatic weight savings compared to nicads will give you a nice performance boost. However, given how cheap a decent brushless ESC has become, I don't see any reason not to go twin brushless for most airplanes.

Sam
That's very true Sam, especially since I've already bought the motors

I don't have any 2s packs and it'll be a struggle to get this little short noser to balance, having taken out a 7 cel Sub-C pack (and moved the servos back out of the cockpit area to indulge my liking for fitting little people in the cockpit).
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Old May 03, 2010, 11:28 AM
All under control, Grommit!
leccyflyer's Avatar
United Kingdom, Aberdeen
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Quote:
Originally Posted by Mark Wood View Post
I'd certainly try a 2s lipo, Bri...especially if they are of the 6v type. 7.2v motors should be ok for 3s though.

mw
They are 7.2v Permax 400s Mark. A real blast from the past. I would have expected current draw to be quite a bit higher than on 7 cells, but was gobsmacked to see the meter climb to over 45 amps.

I think Kev (who has pretty much given up flying) has a couple of 2s packs, so I might give him a bell and see what the numbers look like, just to satisfy my curiosity.
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Old May 03, 2010, 11:39 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
6,710 Posts
Hi Leccy

Hmm, I think I'm getting the problem. Aren't the motors on that airplane in front of the snoot? In that case, you might as well go with a heavy motor. What about the Permax Turbo 450? That should help with the cg and give you something on the order of 400 watts under the hood using a 3s setup and swinging a 6.5 x 4 prop.

Cheers,

Sam
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Old May 03, 2010, 11:43 AM
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Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
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Quote:
Originally Posted by leccyflyer View Post
I would have expected current draw to be quite a bit higher than on 7 cells, but was gobsmacked to see the meter climb to over 45 amps.
Yup, RPM increases with voltage and power required to spin the prop at the higher speed increases with the cube of the RPM. Therefore current will increase with the square of the voltage increase. With an original current draw of 22 amps, going from 7v to 11v would put you at >50 amps full throttle.

I don't know if it is feasable, but you can bring your current draw down close to the original by slowing down the props with a 1.5:1 gearbox.

Larry
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Old May 03, 2010, 11:54 AM
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Canada
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Lose the Gunther's as a first step to reduce Amp suck. Despite appearances, Gunthers are Hi performance props, they load an s400 to it's maximum.
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Old May 03, 2010, 12:08 PM
All under control, Grommit!
leccyflyer's Avatar
United Kingdom, Aberdeen
Joined Sep 2000
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Good points all.

The props aren't Gunthers Bare, they are Grapuner 6x3 nylon props. Going down to much smaller props isn't really an option, they'd be lost in the cowls.

Sam -I have several Permax T450s and have seen the sister model to this one - the HVP Beaufighter - fly on a pair of those on 8 cells. However as a long term fan of the 450T in my experience they really are current hungry beasts and would possibly be even higher in current draw than the 7.2V Sp400s.

Larry - when you put it like that it's not surprising. I hunted round my multitude of boxes and have got some geared Sp 400s, but, of course not a pair with the same ratio.

On balance it'll be better to strip out the brushed motor set-up and replace it with the pair of E-Power 2215/20 1200KV 25A Brushless Outrunner Motors that I got to do the job.
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Old May 03, 2010, 12:17 PM
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United States, CA, Bear Valley Springs
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Quote:
Originally Posted by leccyflyer View Post
On balance it'll be better to strip out the brushed motor set-up and replace it with the pair of E-Power 2215/20 1200KV 25A Brushless Outrunner Motors that I got to do the job.
True dat!

mw
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Old May 03, 2010, 12:40 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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Can you try your motor is series to the battery ?, (I assume you have them in parallel for the high current). It worked on my C-47.

Edit - Plus you only need one ESC, (suitably rated).
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Old May 03, 2010, 12:59 PM
All under control, Grommit!
leccyflyer's Avatar
United Kingdom, Aberdeen
Joined Sep 2000
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Ray - that's right, they are in parallel. The harness is mostly inside the already built wings. I could desolder the wires where they access the wing and try a series set-up, but it'd mean a new ESC to take the high voltage of extra cells. None of my brushed controllers that are available will take more than 12 Nicds (3s lipo).

The battery situation is also very tight. To stand any chance of balancing, with a shorter nose than Charlie Drake, the Henschel needs the batteries as far forward as possible. The battery box just holds a 3000mah 3s1p pack, my 4500 3s1p pack won't fit. So it's not really an option to fit more cells and go series.
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Old May 03, 2010, 03:00 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
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The way I was thinking you wouldn't need to change the battery.

If you were drawing 45amps+ in parallel on 3s, then you should be drawing probably 25amps+ in series on the same 3s.
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Old May 03, 2010, 03:07 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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This was the only change to my C-47's wiring -
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