In-line geared motors? - RC Groups
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Jan 19, 2013, 07:52 AM
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In-line geared motors?

Hi guys, does anyone know of a readily available in-line geared 7 or 8 mm motor suitable for single cell operation? I have a 10 mm brushless that would fit, but if possible I'd like to use a Vapor brick and brushed motor to keep the weight/complexity down and I really don't need that much thrust.
Without a lot of expense, once you get into brushless it needs ESC and separate servos, etc. As far as I'm aware, the Spektrum compatible brushless receiver is for 2S use, further adding to the weight. A thrust/weight ratio of more than 2:1 sounds a shade excessive for this type of model.
I'm drawing up an 18" (or thereabouts) version of my Eastbourne Monoplane which has a 3 cylinder Anzani stuck on the nose. Conventional 7 mm geared units won't fit within the available space and I don't know of a direct drive motor that will do the job without drawing too many amps for the brick ESC.
Any advice about a geared unit, or suitable direct drive set up would be most welcome. I'm hoping total weight of the model will be around 40 grams, so if I have to I suppose a 5 gram outrunner on 1S would do but that involves the same complications as the 10 gram outrunner - just lighter.

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Jan 19, 2013, 08:29 AM
Registered User
Could you just take a geared setup and extend the shaft? The bulk of the motor/gearing would be farther back into the bulk of the plane. Doesn't seem like the shaft would need to be so long to cause any problems.

Otherwise to answer your question, you have this little guy weighs under 2 grams but might not have enough power.

Then there are these motors. They are available in a wide range of gear ratios and weigh about 10 grams.
Last edited by Quartza; Jan 19, 2013 at 08:36 AM.
Jan 19, 2013, 08:53 AM
Quad Erat Demonstrandum
scousethief's Avatar
I am attempting to build something similar using the motor and gearbox from a WLToys V929 and a control board from a V911.
Jan 19, 2013, 01:29 PM
Only nerd in the village
Quartza, none of those motors are suitable. The reduction ratio is too high.

A geared 7mm the axle facing towards the rear and a longer shaft should to the trick. I've never seen one commercially available so it will be a DIY project.
Jan 19, 2013, 03:20 PM
Registered User
Yeah epilot, way to high. Maybe that web page was a bad example. Those type gearmotors are available in a 5:1 ratio. Should of just linked to the manufacture, Pololu.

Though the front of the gearbox is only slightly smaller than the spur gear on most setups
Last edited by Quartza; Jan 19, 2013 at 03:26 PM.
Jan 19, 2013, 08:17 PM
I have two Astroflight Firefly motors. They are coreless brushed motors with 4:1 planetary gearing. They will fly very light models up to around 28" span.
Jan 20, 2013, 07:50 AM
Registered User
I'm trying to avoid DIY on this because if the plan gets published it will appeal more using a commercial unit. The crankcase it has to fit into is only .72" diameter x .36" deep so perhaps you can visualise the problem getting a conventional geared unit in there. It has to sit quite a long way back to be fully enclosed and extended shafts are too likely to cause problems.

I liked the look of the Firefly, if not the price. However, it appears to need the dedicated ESC, which is aimed at 2 or 3S operation. Obviously the cut-off isn't going to suit a single cell.
Again it's the voltage it's intended for that is the problem with the other geared unit. I just think it will be too heavy for what it does on 1S.
With a quoted thrust of around 30 grams on a single cell I'm seriously having to consider a 2 gram outrunner, Orange 415 receiver and a couple of 1.5 gram servos. Not as neat or as compact as I'd have liked but about the only obvious solution showing up at the moment.

The problem is looking to be access. On the Eastbourne the simplest, and neatest, way to get at the gear seems to be to mount everything as far forward as possible and make the forward decking a removeable hollowed balsa block - or the lower fuselage a hatch. The consequence of this being that I can't afford a heavy motor that extends too far back into the fuselage. I might consider direct drive brushed, but will have to investigate props, thrust, etc.

Jan 20, 2013, 08:25 AM
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I R Irv's Avatar
Originally Posted by PETERRAKE
With a quoted thrust of around 30 grams on a single cell I'm seriously having to consider a 2 gram outrunner,Pete
This must be a HobbyKing quote. I think I was getting just over 20grams on a fresh battery and it quickly fell from there. You also need to keep the front and rear bushings well oiled to keep it from getting hot. This would have been a great motor if they would have just used bearings instead of bushings. Don't get me wrong it's still a nice little motor especially at 2gr but could have been so much better.
Jan 20, 2013, 10:54 AM
Only nerd in the village
IMHO the 2 gram motor would be a poor choice as it only spins a very small prop.
Jan 20, 2013, 02:09 PM
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MUTCAKE's Avatar
Some of the airhogs/cheap type free flight toys have a long shaft in them that may work. But these would probably have to be modified since most have an M20 motor attached to their capacitors. They seem to do better at slightly higher voltages 4.5+v . But that could be fixed with the right prop. Kid Galaxy Backyard flyers have this type gearbox.
Jan 20, 2013, 05:26 PM
Or current resident
glewis's Avatar
Could you modify the crankcase to allow the 8.5mm motor to hang out the bottom?
Make the crankcase the motor mount and enclose the spur gear behind the crankcase front. Paint the exposed motor to camouflage it.
I know, now exactly what you want, but uses readily available parts.

Jan 20, 2013, 06:25 PM
Power Wheels Guru
UNGN's Avatar
The flyzone Playmate gearbox uses a 7mm motor with a rear facing gearbox.

Without the gear up front it might be easier to hide in the thin nose.

This Gearbox will make enough thrust for a 30g plane for a full 8 minutes with a 160 battery. A DD brushless motor won't come close to this.

Jan 22, 2013, 05:14 AM
Registered User
Thanks for all your suggestions guys, they are appreciated. Unfortunately, nothing really seems to quite fit the bill. It isn't the spur gear that's the issue, or the length of the unit but the depth of the thing. As Glenn suggests, it's going to hang out the bottom of the model no matter which way round the gears face. Without a bush in the model crankcase I think an extended shaft would be too likely to bend easily - apart from moving the weight aft.
Anyway, it looks as if I'll have to go with what I've got - Vapor brick and 7 mm geared motor - and learn to live with what shows below the nose. Not what I'd hoped for, but the simplest and most readily available set-up. The disadvatage is that it means the brick has to go further back in the fuselage, severely restricting access. Oh well, such is life.

Jan 22, 2013, 06:51 AM
Or current resident
glewis's Avatar
Maybe once you have the motor mounted you could paint it to make it kind of blend in with the aircraft. I have extended the prop shaft on the PZ gearbox about 10mm without any noticeable vibration but that is about as far as I would go without an additional bushing.
What if you enlarge the model to say 24" span, would the motor fit inside then?
My 24" span Stuka flies fine on the 8.5mm motor and a single cell at 70 grams.
Jan 22, 2013, 08:55 AM
Weltherrschaft will be mine
Do it like scousethief suggestet, use a v929 gearbox with the black/white wired motor, works quite well. Ratio is about 6:1 props that I have testet for this config are 5/4,5/5,6/5, 6/4,6/3 they generate btwenn 30 and 45 gramms of static thrust. best thrust without excessive motor heating I get from an selfbuilt 3,3:1 gearbox and a hacker 4,5/4,5 prop, around 47 gramms static thrust and 12+ min of flying time one a non-tech 150mah lipo.

Another easy way is to buy the gearbox of the NE yak 54, either with the NE prop or you use your own. If you use one of the mentioned gearboxes in combo with other props it would be nice to hear about your experiences

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