mounting electric motor

[Tony Harrison 2]

I built up the nose of my trad-kit electric glider according to the instructions, but now I'm having to chop it around a lot because there wasn't enough room for the motor! I don't think the existing thin ply (2mm?) is enough so I'll double that; but how do people usually fix the cruciform, pre-drilled thingy onto which electric motors are mounted? I incline toward the smallest machine-screws/nuts I can get away with, rather than wood screws straight into the ply - it'll be fiddly getting them into place, but stronger and more secure (I think) than plain screws.

Interested to hear what others do. My Overlander 2836/08 brushless outrunner came with no instructions or recommendations and I see none on the Overlander site.

Tony

[Dave Hopkin]

4BA bolts through the fire wall into captive nuts - makes it easy to remove and replace then

Glue some ply "washers" to the back of the firewall for the captive nuts to bite into

[Tony Harrison 2]

Posted by Dave Hopkin on 20/12/2014 17:06:07:

4BA bolts through the fire wall into captive nuts - makes it easy to remove and replace then

Glue some ply "washers" to the back of the firewall for the captive nuts to bite into

Dave, thanks. I don't understand your second sentence, perhaps because you envisage a different layout from what I'm using. My motor is to be mounted inside the nose, and because it's cramped I won't be able to access the back of the cruciform mount; but borrowing your "captive nut" idea (thanks!) I could use cyano to fix nuts to the back of the mount, accepting machine screws inserted from the front through that firewall (front bulkhead?). I'll need to measure things carefully to get holes in exactly the right places - and use very thin washers beneath the heads of those m-screws. I suppose the latter cannot protrude too much or they will obstruct the folding propeller mount...?

rgds Tony

[kc]

M3 seems to fit many motor mounts.

If the nose is closed in so you cannot reach the nuts easily dont forget the old trick of using a piece of threaded rod maybe 6 inches long to thread thro the bulkhead and draw the captive nuts into place using a nut and washer from the front.. ( same as you would for a IC model where there is no tank hatch.)

[kc]

Just read your reply Tony.....

There is another trick that some people use and that is leaving access holes for the 'motor to mount' screws ( the tiny ones ) so you can fix the mount in first and then screw the motor into the mount later.

If you are building a model from scratch it is a lot easier to fix the motor to the bulkhead before construction starts.

Edited By kc on 20/12/2014 17:41:15

[Simon Chaddock]

I did use wood screws on my ST330 but I had 6mm (2x3mm) of ply to screw into.

I used countersunk screws to clear the folding prop hub.

The wood screws do not have to be undone as the motor is unscrewed from the plate mount and withdrawn through the fuselage.

It was worked ok so far.

[Tony Harrison 2]

Posted by kc on 20/12/2014 17:39:18:

Just read your reply Tony.....

There is another trick that some people use and that is leaving access holes for the 'motor to mount' screws ( the tiny ones ) so you can fix the mount in first and then screw the motor into the mount later.

If you are building a model from scratch it is a lot easier to fix the motor to the bulkhead before construction starts.

Edited By kc on 20/12/2014 17:41:15

Thanks kc - it's becoming clearer now. With your "long threaded rod" idea does this entail drawing the nut into place, putting a lock nut on the front, then hacksawing through the rod, smoothing up ...?

I like the idea of access holes for the motor/mount screws, wouldn't have thought of that - might do it. And yes, it is my first kit build, and what you say about mounting the motor in advance makes an awful lot of sense!

And it's just occurred to me that this Overlander motor has threaded mounting holes at the back too, so I could install an additional bulkhead and back-mount the motor onto that - which would be easier, and give me far better access too, for e.g. inserting washers to achieve angled thrust if that proves necessary...

I can see there's a lot of creativity in this game.

Thanks, Tony

[Tony Harrison 2]

Posted by Simon Chaddock on 20/12/2014 17:49:55:

I did use wood screws on my ST330 but I had 6mm (2x3mm) of ply to screw into.

I used countersunk screws to clear the folding prop hub.

The wood screws do not have to be undone as the motor is unscrewed from the plate mount and withdrawn through the fuselage.

It was worked ok so far.

Thanks Simon - another option. But I don't envisage my front bulkhead's being more than 4mm of ply, so might that be too weak a foundation?

rgds Tony

[kc]

Pulling the captive nuts into position using a length of threaded rod does not involve cutting the rod! You merely thread the rod thro the hole far enough to penetrate right thro the 'tank bay' , put a captive nut onto the end by half a dozen threads and pull back on the rod until the captive nut reaches the wood. Then you put a nut and a large washer onto the rod and wind the nut ( not the rod! ) down until it pulls the captive nut into the wood. When the captive nut is firmly in place, loosen the ordinary nut and the rod should be slack enough to unsrew from captive nut with just finger pressure. If it should jam then the old trick of withdrawing studs by using two nuts locknutted together can be used.

Simons picture illustrates what I meant about leaving access holes for the motor screws EXCEPT I envisaged putting the mount the other side of the wood ( ie inside the fuselage) My suggestion means a bit more wood to support the motor because it does not mean having such a large hole to clear the motor. ( I would use thinner wood with a smaller hole = just as strong. and I suppose metal could be used instead of wood ) Clearly there has to be enough shaft length for my way to work.

Whether you can mount the motor the other way depends on where the wires come out!  Obviously the wires and that part of the motor must be stationary.   If you use the adaptor on the rotating end the shaft then projects back into the fuselage which is a problem.    When i bought an Overlander motor the retailer only supplied the adaptor and mount as an expensive extra   I found that GiantShark sold the adaptors  with mount at about a pound-a quarter of the cost-  it was just a matter of deciding which one might fit.

Edited By kc on 21/12/2014 11:29:19

[Martin Harris - Moderator]

I'm probably missing something but if you're mounting the motor inside, isn't it easier to reverse the motor shaft and bolt through the front former into the motor and let the casing revolve inside i.e. don't use the "spider" at all?

Edited By Martin Harris on 21/12/2014 11:32:07

[John Privett]

Tony - I suspect you might not be familiar with the type of captive nut that others are talking about.

Sometimes called T-nuts they look like this;

Pushed in from behind, the spikes bite into the ply firewall preventing the nut from turning. The earlier suggestion of ply washers was to increase the depth of ply that the nut is biting into to prevent the pikes sticking right through the ply and out the other side!

[Stevo]

Seriously, I cannot emphasize how important it is to use best quality screws and mountings, nyloc nuts and allen bolts.

I had an old Jumper 30, and electrified it. It flew like a housebrick, but bringing it in for landing I blipped the throttle for a tad more speed/height... the motor lurched forward, but the airframe remained stationary. Never did find it!!

Edited By Stevo on 21/12/2014 11:37:24

[kc]

Tony, I think everyone has given enough info for you especially John's photo of the T nuts we all use ( available from SLEC etc ). If it still does not seem to cover your model then post a photo of the model and the motor with prop.

[Pete B]

As Martin suggests, it isn't necessary to use the X-mount, apart from as a template for the M3 machine screws bolted through to the motor backplate.

I've used 6mm ply on this 400W+ setup but a minimum of 4mm is essential in any case. It is important to make sure that the M3 machine screws are selected/cut to ensure they do not project so far into the motor as to interfere with the rotor. Note the cooling holes cut - every little helps. Use a smear of threadlock on the screws, too!

Pete

[kc]

You can make any hexagon head nut captive in wood by counterboring a hole equal to the diameter across flats -ignoring the 'point's which then cut themselves into the wood when they are drawn in by the screw.

So for M3 nuts a hole of 5.5mm will draw the nut into birch ply ( I have just carried out a workshop experiment to be sure it works on 6mm birch ply ) It's not best practice for aeromodelling but it works and it might be useful when all the shops are closed. It's really more useful in making jigs or benches in softwood and where larger nuts are used

Edited By kc on 21/12/2014 12:27:37

[Tony Harrison 2]

kc & others, hello and sorry for my delayed reply. You've generously provided loads of information that is useful and educational - lots here to consider. Right now I'm ill in bed (hope my wife doesn't notice I've slipped off to the PC) but will reply properly asap. I was planning to post some pics anyway, to clarify my situation.

Thanks, Tony