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Old Jan 08, 2007, 06:51 AM
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Newcastle NSW
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What power setups are being used for Rake models?

Hello,

As i am building some PR models (mainly 36") at the moment i am interested as to what power systems are being used with the models.

Im looking at using some of the cheaper "bell" type outrunners but i am unsure of what prop, type of motor, and batt size etc would give me resonable performace out of these models.

I would do most of th etesting myself but i have no gear to do so.

Thanks for any information

Ace
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Old Jan 08, 2007, 06:57 AM
I'm just a CAD at heart
Perth, Australia
Joined Mar 2003
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Hi Alex,

Most of the 36" were for GWS IPS from memory, so a bell will be more than powerfull. I think probably a smaller prop would be the go. If you can get me motor and model specs by Thursday I can run them through motocalc. Hope you got my email regarding indoor this Thursday 11th at 8.00pm

Pete H
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Old Jan 08, 2007, 07:03 AM
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Newcastle NSW
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Thanks mate

Check your emails as i sent you a reply ealier on today

Gotta go

Have a good one

Alex
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Old Jan 08, 2007, 08:01 AM
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The bells are a bit large for 36" monoplanes, but OK for the bipes, though finding one to swing a scale dia prop is often a challenge.

For the monoplanes, something like the baby AXI's works well, and the esskay 400XT is a good one for the bipes.

Bell motors are..well..not very good, it has to be said. A geared speed 400 will usually match performance, and the extra weight is needed to balance anyway.
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Old Jan 08, 2007, 08:14 AM
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The 36" biplanes are designed for geared sp400 setups. They work really well with the cheap bell outrunners or motors such as the EFlite 370/400/450 or the Hacker A20 size (and many others). I used the EFlite 450 in my Camel and use the A20-30S in my WACO SRE. The SRE flies really well on either 2s or 3s. The Camel was overpowered on 3s (probably be a lot of fun for some ), but was a joy to fly on 2s.

The 36" monoplanes were made for geared sp280. They would do well with the smallest outrunners you can find IF they can swing a big enough prop to clear the cowls. Hacker has a new small outrunner, I think it's the A20-50, that works well. It will swing an 8" prop on 3s and a 9" prop on 2s. Feigao/Medusa power in IPS gearboxes would be perfect for these planes. I like to use the small 3s batteries with Feigao's (3s730 Thunder Power is my favorite) but 2s is more than sufficient.

If you are looking at the 'cheap' bell outrunners look for the lowest kV rating you can find. That means it can swing a bigger prop. You want at least a 9" prop and 10" is better. When you get the motor then hook it up to an ammeter ($5 at Harbor Freight) with some props and see which gives you the performance you want. I tend to use props with pitches of 6 or 7 and then a dia that will give just under max current for the motor. For biplanes you can also go to smaller pitches (4-5) and larger dia since they won't speed up much anyway.

charlie
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Old Jan 08, 2007, 08:53 AM
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I go along with all that but with a few provisos.

Scale props on WWI machines are about 27-30% of wingspan.. Thats in general a 10" prop for 36" model. In Peter's Tiger moth its a lot less - 8". I use an 8x6 wood on that.

Even a 10x7 is fairly fine pitch compared to what the originals were..frankly a 10x10 is more the sort of region. The problem is finding a gearbox or motor to get the RPM low enough, and also the fact that at that size the torque is massive..expect these things to swing hard on throttling up.

With the can 400 motors, those sorts of props need a 4:1 gearbox on a 6v motor with a 3s LIPO pack..

The AXI 2212/34 is THE other motor that will do it on 3s LIPO. The esskay 400XT is suitable on 2s LIPO. I haved not found any other ourtrunners that are suitable on 3s LIPO at all, but a sub 1000 RPM/V 10A capable motor will work on 2s LIPO.

With the monoplanes, the power needed is less and the single wings were 'bigger' so an 8x6 or 8x8 prop works right scale wise. My 36" EIII is 'marginal' on an IPS power plant at 20W..- 30-40W is 'safer'. I will be installing a custom wound CDROM into that shortly..Komodo 257 ..

Again you need a motor that is sub 1000 RPM/volt or a 5:1 geared 280 to do the job. There is not a lot to choose from really..

The AXI 2208/34 is about right on 2s LIPO. A few other 300 class motors exist with KV less than 1000 as well. They will work fairly well on 2s LIPO. You need to get down to sub 650 KV for 3s LIPO, I had to wind a special for that.
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Old Jan 08, 2007, 09:43 AM
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Vint,

Yes, you are right about scale size props. Mine are no where near scale in size or pitch, they just fly good. I usually don't mind a smaller than scale dia prop as long as it flies well. 9" props will work on the 36" biplanes just fine, they aren't near scale dia.

kV, cell count, and prop dia go hand in hand. The little Hacker I have is good for an 8x5 prop on 3s and a 9x6 on 2s. The good thing about the Feigao/Medusa's and gearboxes is you can get a gearbox for just about any prop you want, even to a 9:1 ratio and huge (relatively) props.

charlie
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Old Jan 08, 2007, 01:39 PM
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St. Neots, England
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Ace

I've got a Peter Rake Currie Wot that is powered by a bell motor that is if I remember correctly just under 100Kv, using a 10x7 APC slow and 3s Lipo it pulls about 5.5 amps and flys a treat.

The motor was about 20 including the ESC. I agree with Vintage on the 2208/34, great motor, I have one in another model. But it is about 4 times the price of the bell motor

Phil
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Old Jan 08, 2007, 05:43 PM
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Very surprised you can swing a 10x7 at all on a bell motor on 3s..mine (1200KV IIRC) was up to 9A or so on an 8x6...I think to swing a 10x7 at 5.5A it must be less than 600KV. Of course you CAN rewind them..but that makes it an exercise in messing around. And you end up with less power with a large prop and a lower KV motor - the bells do best about 10000 RPM - to drop them down to 5000 or so is to lose some punch. But thats not really an issue with a WWI model. They don't need the power and look silly if they have it. The secret with Peters models is to build light, and have about 40-60W/lb. Then they have plenty in hand, and will tootle around realistically at half throttle.


The key thing is to get as low a KV as you can, or accept a smaller prop. The smaller props are definitely EASIER to fly.I tried the tiger moth on various setups - the 10x7 was definitely a 'hold in some right stick' while flying but the 8x6 was pretty neutral..and scale. I left it at that.
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Old Jan 08, 2007, 05:50 PM
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The bell motors that I have are rated for right around 10A. The commercial ones are rated for 10-16A.

The smaller ones I hold to just under 6A.

Always seraching for lower kv

charlie
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Old Jan 08, 2007, 06:12 PM
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I did some bench testing with an Eflite 400 - and came up with about 4900 RPM turning an 11X7 @ around 10.5 amps on 2 cells - including the extra drag from the pictured "rotary armature" Iv'e been toying with.

On most Camel variants - this should be almost perfect.

I'm almost looking forward to the "scalish" torque effect of this combo..
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Old Jan 08, 2007, 08:02 PM
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That's a really good data point. It seems that a kv of about 1000 will do that on 2 cell, or about 660 on three.

Theres a lot to be aid for getting a bigger motor and running it on 2s..sure its well below what it can do, but who cares?
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Old Jan 08, 2007, 08:32 PM
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Vint,

You are right about that (big motor, 2s batteries). Tritle does it all the time and it works great. Inefficiency is no big deal cause the motor still weighs less than a brushed version of same power.

I have even relented and bought some 2s batteries for that reason. 3s was just too much power/voltage. Camel and WACO are better behaved on the 2s. But, when I want to really wind it up, I slip the 3s in the WACO and do low flybys

charlie
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Old Jan 08, 2007, 10:00 PM
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Newcastle NSW
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In the end im not really looking for scale looks just "does it fly it well". Due to limited funds i dont really want to blow too much on a motor when i can buy a whole setup for the same price.

Do you want torque or speed? for these models.

Ace
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Old Jan 08, 2007, 10:24 PM
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Ace,

For the WWI types you want more torque than speed. Extra thrust does little when the model has so much drag.

Cost is one reason I recommend the inexpensive bell outrunners. Here in the US rchotdeals.com has a bell outrunner with ESC for under $40. This is cheaper than I can do a sp400 with gearbox and ESC.

In fact, Peter and now Pat Tritle are starting to design specifically for these little motors running with 2s LiPos instead of their old standby sp400 setups.

charlie
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