Sub miniature right angle gearbox wanted.

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21 June 2013 at 18:36 #5236
Colin Bishop
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@colinbishop34627
Anyone have any suggestions?
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21 June 2013 at 18:36 #41699
Colin Bishop
Moderator
@colinbishop34627
I am having another look at my unbuilt Revell Queen Mary 2 liner plastic kit which I would like to convert to R/C.

The actual ship has four pods mounted beneath the stern, two of which are steerable, the other two are fixed. Obviously I can 'cheat' and fit conventional shaft drives along the axis of two of the pods and use the other two as rudders but it would be nice if it were possible to simulate the actual pod drives, not necessarily totally to scale, but close to it.

To do this I would need a submersible right angle gearbox for each pod. The dimensions of the scale pods are approximately 20mm vertically and 25mm horizontally which is quite small. If I could find/make a mechanism within those dimensions I could make a dummy housing to surround it.

I did find some cheap Chinese toy motor boats with wind up motors and plastic right angle drives of the right size which could be cut off but it was obvious that the poor quality 'engineering' would mean that they would wear out in no time at all.

If anyone has any ideas on how I could do this I would be grateful. I have searched the web but not found anything obviously suitable.

Colin
21 June 2013 at 19:14 #41700
Paul T
Participant
@pault84577
Colin

You could try robotic micro motors such as Faulhaber.

Or buy some dentists drills and strip the gear heads out.

Paul

Edited By Paul T on 21/06/2013 19:27:35
21 June 2013 at 19:34 #41701
Colin Bishop
Moderator
@colinbishop34627
Paul,

Buying four drills could be a bit pricey I suspect.

The problem win micromotors (including pager motors) is that they would be running in a submerged environment and water would inevitably eventiually get in.

Colin
21 June 2013 at 19:51 #41702
Paul T
Participant
@pault84577
Colin

Its true that dentists drills might be expensive but fleabay might have used items. Have you considered the ends of electric toothbrushes as donors for right angled waterproof housings

Looking at the Faulhaber kit it looks as though the gearbox can be separated from the motor and so only the gearbox would be submerged but this isn't an ideal soloution.

I do know that there are some fully sealed micro gearboxes available from China if you have the time to search.

Captain Bob might know of a suitable gearbox.

Paul

I do have some micro motors if you could build them into a waterproof pod and then direct drive the props.

Edited By Paul T on 21/06/2013 20:04:06

Edited By Paul T on 21/06/2013 20:10:58
21 June 2013 at 20:02 #41703
Keith Long
Participant
@keithlong89920
Colin

You might find suitable right angle drives or gear sets in old (or new) slot racing cars and the spares for them. From memory quite a number used plastic (nylon?) crown wheels and brass pinions. Usually about a 3:1 reduction. It would mean some "engineering" on your part but should be do-able.

Keith
22 June 2013 at 09:25 #41707
ashley needham
Participant
@ashleyneedham69188
Colin. Might there be sufficient scope here to use a flexible drive? You could make your own with thin stainless Bowden inner cable (cycle) or I dont know what the smallest commercial drive cables are. A lot of model outboards use them, and I dont suppose you are talking a lot of power. The drive motors could of course be mounted vertically over the wires, and you would be using a solid coupling, which are very short. As long as you can get a small enough bend in the drive…may have to modify the drive unit pods a bit, and you could always have them fixed then use differential thrust to steer??? Very small props are likely simply to be able to be glued on the end of the cable.

I think ultimately you could find bevel gears small enough, but then some nifty machine work will be needed to hold everything in place without slop and disengagement.

Ashley

Gosh.. sudden thought.. I wonder if one could use thick nylon "wire"…shark line or something..strimmer plastic wire, instead of metal wire for the drive?? this would take a very small bend, and be very happy with water lubrication.. it might then be possible to use the pods as they are, almost, and just build up the inside with filler an/or set plastic bits of tube in them for bearings..

Edited By ashley needham on 22/06/2013 09:42:03
22 June 2013 at 10:10 #41712
Colin Bishop
Moderator
@colinbishop34627
Strimmer cord is worth trying, I'll look into that – just the sort of thinking I'd hoped from you Ashley but slightly disappointed that it didn't include using hardboard somewhere….

Colin
22 June 2013 at 11:48 #41715
Malcolm Frary
Participant
@malcolmfrary95515
Just looked at some gears from a dead servo. While they are not bevels, there might be enough meat there to bevel the teeth and leave them viable as meshing gears. One had 10 teeth and an OD of about 5mm, the other 16 teeth and an OD of about 9mm, at least the interesting bits did.
22 June 2013 at 16:25 #41725
Malcolm Frary
Participant
@malcolmfrary95515
Had another random thought while messing with an aquarium power head – the "motor" consists of a magnet on a spindle, and is caused to rotate by the current flowing in coils arranged around it. The big difference between that and a "normal" brushless motor is that the spinning magnet is in a closed camber in water, the coils are nearby, but effectively in a separate box. At the voltages that we are interested in, having the coils immersed should not be a problem if it can be ensured that ALL of the bare metal carrying any voltage has a coating of waterproof enamel. Probably a small version of what the real thing uses anyway.
22 June 2013 at 17:24 #41731
Colin Bishop
Moderator
@colinbishop34627
Thanks for all the ideas. The solution has to take into account that I am a model maker and not a model engineer, bevelling gears would be beyond me!

I believe that micromotors have been used for this conversion by encapsulating where the wires come out in resin and putting grease around the output shaft and that may indeed be the way to go, especially if I can fix it so they can be replaced if necessary. I think the motors will work with a bit of water inside but it's the corrosion which could gum up the works.

I have had a trawl around for slot car gears but not seen anything suitable so far and of course this would mean the bearings would need to be made although it might not be too difficult.

In the meantime i have been playing around with Ashley's idea – see photo below. Strimmer cord proved to be too stiff but I have some round section elasticated drive belt material which does permit rotation with 'bearings' comprising the round hole in s square section of plastruct rod. However, there is quite a bit of friction and the elasticity of the material causes it to twist before rotation takes place so I suspect it might not be very long lived. Whether control wire would work better I don't know, I will have to root about in my bits box to see what i have got.

Colin
22 June 2013 at 17:38 #41732
Bob Abell 2
Participant
@bobabell2
Hi Colin

Would a motor on top with a simple belt drive down to the prop shaft…..Be any good?

Bob
22 June 2013 at 17:52 #41733
Colin Bishop
Moderator
@colinbishop34627
You would need to get the belt withing a very small tube Bob so I don't think it is really feasible at this scale – plus there isn't much space to mount motors above the waterline but still under the deck.

An all brass or nylon & brass bevel set up would probably be the most robust arrangement with a horizontally mounted pulley at the top to accept a belt drive from a vertically mounted motor next to it. I have not found any really small bevel gear sets though. You can see from the 50p piece in the photo in my last post what sort of size we are looking at.

This is only a Plastic Magic side project so there is a limit to the amount of time and cost I want to put into it.

Colin

Edited By Colin Bishop, Website Editor on 22/06/2013 17:53:37
22 June 2013 at 18:54 #41737
ashley needham
Participant
@ashleyneedham69188
Colin. If you were to find some stainless cycle inner cable and then a bit of Plastrut plastic tube..

nah… all these ideas are too frictiony for the small motors envisaged.

As you say, motors run perfectly well underwater (for whatever reason) and so making some new pods with a small electric motor inside (simple mould..cast pods in resin?) would be the way to go. IF one was to make them easily removable from the ship (threaded rod/nyloc) then when the inevitable happens and the corrode up, you simply replace them.

Small motors might be able to be glued inside slightly fatter plastic tube…positively ALLOWING the water in, but by the same token, allowing it be blown ouit and so dried off after sailing. The plastic outer allows the fitting of pivots and or what have you, and would not look too much out of place.

Also as you say, it would be easy to cheat, but much more satisfaction would be gained by having four little pods. My Sunderland would undoubtably go much faster with aspeed 480 motor and shaft…but I like having it driven by the little air props, it is that bit extra.

Ashley
22 June 2013 at 18:59 #41738
ashley needham
Participant
@ashleyneedham69188
Further more, as it IS such a feature of the ship, If I could NOT make some little pods,… I would build something else!! For me, this would be the attraction of the model in the first place.

There must be an article you could read for inspiration??

Ashley
22 June 2013 at 19:05 #41739
Colin Bishop
Moderator
@colinbishop34627
Ashley,

Yes, there is an article here:

**LINK**

Amazing stuff.

Colin
22 June 2013 at 19:11 #41740
Colin Bishop
Moderator
@colinbishop34627
Paul,

Where did you get the motor shown in your post and what is the operating voltage and diamenter.

Looks like it could be a solution.

Colin
22 June 2013 at 20:54 #41745
ashley needham
Participant
@ashleyneedham69188
Impressive video, the way to go and probably the easiest. Ashley
23 June 2013 at 17:51 #41771
ashley needham
Participant
@ashleyneedham69188
Just had a thought..you should go with Pauls dentist drill setup, and then when anyone asks about the power train you can say "its brushless"…..

Ashley
23 June 2013 at 18:30 #41773
Colin Bishop
Moderator
@colinbishop34627
Ouch!
25 June 2013 at 08:05 #41818
Paul T
Participant
@pault84577
Hi Colin

Sorry for the late reply, I missed your posting.

I bought a lot of these motors from Toys r Us when the local store was getting rid of them, they are spares for micro racing cars and operate at 1.5 to 3v with diameters of 6 and 8mm. They came with a selection of different size gear cogs.

If they are any help I will post some to you.

Paul
25 June 2013 at 09:04 #41822
Colin Bishop
Moderator
@colinbishop34627
Paul,

That's very kind of you. I am sending you a PM.

Thanks,

Colin
25 June 2013 at 10:42 #41826
Colin Bishop
Moderator
@colinbishop34627
Just need a small 6v reversible water pump for the bow thruster now. Does anyone have any suggestions? The Graupner & Robbe ones look a bit expensive.

Colin
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