In-line geared motors? - Page 2 - RC Groups
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Jan 22, 2013, 02:53 PM
Quad Erat Demonstrandum
scousethief's Avatar
This is what you end up with , relatively cheap ( well cost me nothing after the quads main board died) not the most gorgeous of things ill admit but it works.
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Jan 23, 2013, 04:05 PM
Registered User
Either I'm not making myself clear or some of you aren't aware of the type of model I'm talking about. My fault for not posting pictures.
I aready have both 7 and 8 mm geared motors, so don't need to locate something very similar to what I have to hand.
The Eastbourne Monoplane is a 1913 pioneering type aircraft with a fairly slim nose and an Anzani engine bolted to the front. As such it should fly slowly and sedately.
I have ample width to get the motor into the nose, but not enough depth to totally hide it unless it goes a long way back - taking up space I could use for the radio gear and involving an extended shaft.
The original request for an in-line geared unit that will work on 1 cell was so it could be contained within the dummy crankcase. The typical, off-set gearbox, such as most are talking about, just won't fit entirely within the nose.
I have my heart set on 18" span, so don't want to make the model any larger if I can avoid it.
If I were to enlarge it to 24" the 7 mm unit would fit but I doubt it would be powerful enough. An 8 mm unit takes us right back to where we started and a 5 or 10 gram outrunner means we're back up to around 80+ grams weight and running on 2S. Something of a vicious circle.

Jan 23, 2013, 04:22 PM
Quad Erat Demonstrandum
scousethief's Avatar
Ahhh now i understand , sorry for the misunderstanding.
Jan 23, 2013, 05:01 PM
Registered User
Not a problem, I appreciate you were trying to help. As I said, it's probably my fault for not making it more clear.

Jan 23, 2013, 05:08 PM
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PietenpolAC's Avatar

Gasparin used to make a very nice N20 based motor with a long shaft. I've got one back in Budapest ( I'm currently in the States) so I can't get the model number. I think it is just the motor you need. I plan on using it for an upcoming model that has the same needs as yours.

Jan 23, 2013, 06:12 PM
Or current resident
glewis's Avatar
I just did a few quick measurements.
You stated a crankcase diameter of 3/4". That's 19mm for a radius of 9.5mm.
Measuring the PZ 8.5mm gearbox I get close to 12mm from the center of the prop shaft to the bottom of the motor mount plastic. That leaves only 2.5mm interference.
Figuring a rolled 1/16 (1.5mm) balsa crankcase with an ID of 3/4" that leaves only 1mm exposed. You could just fudge the crankcase by 6mm and fit the whole thing inside with plenty of room to spare.
I would expect the 7mm gearbox is a bit smaller but I don't have one to measure.
I doubt anyone will take calipers to it and comment that the dummy engine is oversize by a few mm!

Maybe my measurements are all foamed up by the pint I just drank, but it looks good in my head....

Jan 23, 2013, 08:47 PM
Registered User
Except, of course, it's the widest part of the mount that would be exposed - the mounting plates.
Actual OUTSIDE diameter is 0.73" -18.25 mm. Take the wall thickness off that and it starts to get a bit cramped. Add in that I don't actually have a PZ 8.5 mm unit, and even if I did it's unlikely my old Vapor brick would handle it and you start to see my problem. That's why I'm keen to use the 7 mm unit. That, according to my drawing of it is14.45 mm from centre of shaft to outer edge of motor ring - almost 1/4" of motor/gearbox hanging out in the breeze.

I'm pretty sure I'll have to fudge the nose a little, but just wanted to make sure I couldn't get a neater solution first.

If the motor is under .7" diameter, isn't too heavy and will run on 1S effectively, shaft length isn't an issue with this model.

Jan 23, 2013, 09:21 PM
Or current resident
glewis's Avatar
See, told you my brain was foamed,,, I didn't even consider the mounting plates. You could cut them down some, but not much.
I knew you meant outside diameter, I was tying to squeeze it into a diameter larger only by the thickness of the crankcase wood. Maybe a thin plastic crankcase will gain you some room?
I really think you can hide it in a slightly larger dummy engine and leave the nose as the original.
If your soldering skills are up for the challenge you could piggy back the esc FET and double the current capacity.
Last edited by glewis; Jan 23, 2013 at 09:38 PM.
Jan 23, 2013, 10:02 PM
Registered User
PietenpolAC's Avatar

The motor I have is a Gasparin GB32. Not sure what gear ratio is as there were several versions. I was mistaken. It uses a POT00 motor. Diameter wise I think it would fit. Depending on how you mount it, it may have the right length shaft that the motor flange could be mounted on the firewall with just the shaft extending through the firewall. They ran on one cell and Gasparin has a Bückner Jungmeister on his website that weighs 35 grams that it powers. You might be on the borderline with thrust, but the Eastbourne is a slow flyer.

But after rereading your post, if you may want to market this, you really need to design it for the equipment that people are currently using and what is easily available. If you look at Gasparin's and MicroInvent's websites, there are a number of solutions that should work. Their equipment is quality, but pricey.

A 1S brushless setup really seems to ge the way to go. Spektrum has two brushless bricks, one with two linear servos on the board and the other without. Both have a built-in ESC that can handle about five amps. But you'd need a 2S battery. At 18", if you build light, it should be doable with 2S, since the Eastbourne doesn't need a lot of power. A1S setup would be even better, but not quite so "off-the-shelf" a solution as the Spektrum.

I'm just now building and converting models to brushless and the biggest bugaboo for me is amp draw and battery weight. Plus throw in all the various sized connectors, it gets confusing real fast for a newbie used to brushed, actuator systems.

Jan 24, 2013, 03:16 PM
Originally Posted by dayhead
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.
that sounds like a good option.
What is a source on these?

nm... I found em... discontinued, special controller... and they were pricey, too...
Oh well...
Jan 26, 2013, 06:05 AM
Registered User
I think I have it more or less sorted out now. Currently the plan shows an AEO 7 mm geared unit, but if the weight looks good, I may yet be tempted to go with the 2 gram brushless which will allow more flexibility with battery position.
Here's what I have drawn up and if it looks as if I might be able to get it down to 30 grams (highly unlikely knowing me) the brushless option might work out quite well, despite that the gear will be a little heavier. The small prop isn't really too much of an issue because there's only clearance for a 4" prop anyway. IIRC the 2 gram brushless uses a 3" prop which won't be too far off. I'm figuring that a thrust of half the model weight should be ample for the way it's supposed to fly.
Anyway, have a look, see what you think and make any comments you think may help. Feel free to avail yourself of the plan if you like.

Jan 26, 2013, 06:49 PM
Or current resident
glewis's Avatar
Looks good to me! There is a little dangly bit showing, but it's not that noticeable really. You could carve a balsa bump to cover it if it really bothers you. I would just leave it as is and chalk it up as a motor cooling strategy...
Jan 26, 2013, 10:18 PM
Registered User
Why the assumption that a wee brushless needs 2s?
The Hobby King 2 grammer at 7700 kv is a 1S wind.
Although a bit of wire / fiddling and most any outrunner can be diy rewound to suit precise needs
Albeit a 2gm outrunner seems a bit miniscule for anything beyond oddity value imo.
4/5 gram motor is too heavy?
In the very least an outrunner would be quite silent.. not a small bonus
1s brushless esc's are both tiny and inexpensive, being basically a single chip gizmo and these connect signal wires to any Rx, in the usual esc fashion, brushless or brushed.
immediate example:
Jan 27, 2013, 06:43 AM
Registered User
Yes, I know the 2 gram brushless is wound for 1S and no, a 5 gram motor isn't too heavy. As regards re-winding motors, I have less than no interest in that sort of thing. My main reason for trying to avoid going brushless was simply that it would require separate receiver, ESC and servos, rather than the compact neatness of the Vapor brick. As you can see, space is at something of a premium. The PZ brushless brick would help but I don't have a transmitter that will do the mixing to make the rudder servo operate on the 'aileron' stick - primary steering function on the right stick.

All things taken into account, I'm happy enough with the way it looks. Yes, an in-line geared or direct drive motor would have been neater, but I can live with it as is. Just need to sort out some parts sheets, print a plan and get building.

Jan 27, 2013, 11:00 AM
Registered User
scrubs's Avatar
Very nice Pete I like this size much better than the 13 incher you had drawn up earlier.


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