stunthanger.com
Electric Stunt => Gettin all AMP'ed up! => Topic started by: Kim Doherty on August 22, 2013, 02:38:57 PM
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I thought someone might be interested in seeing the motor mounting method used in my Fly-By-Wire model that I took to the W/C's last year.
The motor is mounted to a full depth former made of a sandwich of 1/32" ply and 1/4" balsa. The first two photos show the front and rear of the machined aluminum mount. The mount is 2 1/8" in diameter 3/8" deep with a .050" square lip. The face of the mount is .030 thick with a stiffening ring of .085". The machined mount weighs 8 grams. The holes around the edge are drilled to increase mechanical bonding and keep it light. Motor is a Plettenberg 20-16.
The next photo shows the former cut from the sandwich with the hole drilled via a hole saw.
Now the former and the mount are epoxied together.
Motor mounted (rear mount)
Motor mounted rear view. Note magnets in holes and carbon pins to secure cowl.
Kim.
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You put a lot of thought into that mount.
Joe
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Neat job Kim! One thing that has always puzzled me about motors with fans up front is how they get cooled. Is it that the air is sucked in through the rear and blown out through the centrifugal fan up front?
Keith R
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Neat job Kim! One thing that has always puzzled me about motors with fans up front is how they get cooled. Is it that the air is sucked in through the rear and blown out through the centrifugal fan up front?
Keith R
Hi Keith! Great to hear from such a renowned composer S?P
There is so much force throwing the air out it does not matter which end it is at. You are going to put a spinner on anyway so the diameter is no issue.
Kim.
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Thanks Kim, Beethoven is indeed alive and well! #^ I need to try my Pletty again with a decent, solid mount, so thanks for sharing that good installation.
Keith R
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Just a couple of notes should anyone attempt to make one of these.
It is imperative that the fit of the mount and the former be exact. Cut the hole first then measure and fabricate the aluminum mount.
It is also important that the front face of the mount project fully through the front ply lamination by a few thou.
The mount must be glued with real 24 hour cure industrial epoxy.
All aluminum bonding surfaces must be abraded with 120 grit sandpaper and cleaned with alcohol prior to bonding.
Machine the front face and lip first. Flip around and mount with the lip up against the jaw face. Grasp lightly! Be careful thicknessing the face.
The layout of the holes is not critical and can be done with a protractor and drilled on the drill press.
Kim.
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Thanks for the inspiration Kim!
Well, my motor is front mounted so the mount became slightly differend. I want to have some airstream through firewall.
Firewall is 0,5mm carbon-5mm vertical balsa-0,5mm carbon.
Lauri
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Looks a little over-tech for us Po' Folks... n~
W.
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Why? It's very light and very rigid. L
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Hello Lauri,
I very much like the separate collet-locking nut and then a single purpose prop-nut.
This will greatly improve reliability, so that propellor crush does not loosen the collet with time and use.
Regards,
Dean P.
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Dean,
If I understood right your explanation, that sounds like a great idea. Thanks! I may make one as per your explanation later.
The one I have now should be ok with carbon props, with wooden ones I must make sure of the tightness every now and then I guess.
Lauri
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Hello again,
Apparently, I misunderstood the significance of the fine set of threads half way between the tapered section and the propnut threads.
Still, it is a good idea!
Dean
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Nono, the first M8x0,75 thread is for prop nut, and the second, M6, is for spinner cone. So you propably misunderstood it. However, your misunderstanding made me think about a locknut under the propeller to secure the cone. It may be possible. But how necessary, I have no idea.
I have no experience of electric things, so I went to a modelshop to see how the parts look like, and then made my own with better materials and smaller tolerances. :) L
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Hi again Lauri,
So we find a happy accident.
The tapered collet prop drive washer is a well used design, but a number of flyers have had problems with them in electric Stunt and R/C.
The biggest reason is that the shafts on electric motors tend have smaller diameters than glow engines.
Also, some flyers did not appreciate:
1) the need for extreme cleanliness on the mating face of the shaft and collet, and
2) the need to compensate for loosening as the propeller hub crushes.
Together we have possibly solved #2. A spanner wrench to hold the spinner backplate would allow very secure tightening of the nut behind the prop.
I trust these pieces will, one day, be available for sale?
Dean
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I thought someone might be interested in seeing the motor mounting method used in my Fly-By-Wire model that I took to the W/C's last year.
Kim: why not just make a thin "washer" to present a hard surface for the motor to mate to, then bolt through that to the firewall? That way the epoxy is only providing a "bed" to interface between metal and wood, and doesn't have to supply the strength to actually hold the motor in.
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Kim: why not just make a thin "washer" to present a hard surface for the motor to mate to, then bolt through that to the firewall? That way the epoxy is only providing a "bed" to interface between metal and wood, and doesn't have to supply the strength to actually hold the motor in.
Tim,
This eliminates 4 steel bolts, 8 steel washers and 4 steel nuts and a fiberglass "X" mount. The machined mount weighs only 8 grams. The epoxy only locates the mount and hardens up the balsa former. The lip on the back side resists all forward motion. The depth allows me to use very thin sections to achieve a great deal of strength. There is very little epoxy used.
The other rationale would be that I have spent a lot of time flying indoor rubber and am quite conscious of weight.
A third rationale might be that I have the tools to make it and so I must justify their ownership. mw~ LL~
Kim.
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A third rationale might be that I have the tools to make it and so I must justify their ownership. mw~ LL~
There's a few machined bits that pop out of my shop under that rational.
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Hi again Lauri,
So we find a happy accident.
The tapered collet prop drive washer is a well used design, but a number of flyers have had problems with them in electric Stunt and R/C.
The biggest reason is that the shafts on electric motors tend have smaller diameters than glow engines.
Also, some flyers did not appreciate:
1) the need for extreme cleanliness on the mating face of the shaft and collet, and
2) the need to compensate for loosening as the propeller hub crushes.
Together we have possibly solved #2. A spanner wrench to hold the spinner backplate would allow very secure tightening of the nut behind the prop.
I trust these pieces will, one day, be available for sale?
Dean
Has anyone thought about making a double angle, ER style collet for these things? Or even just going with a medium press fit and a locking screw? K&B used that system for quite a few years on engines up to 40 pylon with good success. Electric has much less vibration to deal with.