|Feb 21, 2009, 05:47 AM|
Installing 26mm outrunner into GWS EDF-55 fan
Here's how I installed a 26mm diameter outrunner (Turnigy 2627-3800Kv) into a GWS EDF55 fan unit.
There are many cheap high-Kv outrunners (most designed for helicopters) which would be suitable for the EDF55 fan, if only its motor tube was a little wider. Unfortunately the inside diameter is only 24.5mm, but most outrunner motors are just too large at 26~28mm diameter. Therefore the motor has to be mounted at the rear of the fan, with a longer shaft and an additional mounting extension to support the motor and shaft. A commercial solution is available, but it costs twice as much as some motors! My goal was to find a way to do it at minmal cost, and without turning up any parts on the lathe.
- 3mm x 50mm drive shaft (I used a guide rail scavenged from an old CDROM drive).
- 2x 12mm long stand-offs, with 3mm threaded male/female ends (mine came out of an old PC).
- 15mm length of 3mm or 1/8" id (inside diameter) aluminum or brass tubing, eg. K&S 5/32" #11103.
- 2x short 3mm screws.
- GWADP003C, EDF55/64 impeller hub with D cut, for 3mm shaft. These are provided with the latest GWS NPS kits (eg. ME262, F15).
1. Remove the old shaft from the motor. First remove the circlip, take off the bell, and undo the grubscrew. The shaft will probably be a tight fit, so you will have to press it out in a vise or drill-press. Do not put any pressure on the outside of the bell. Instead, slide a length of tubing over the shaft to support the center of the bell. Then press the shaft out, using a 3mm flat-head screw (in the vise) or inverted drill bit (in the drill-press) to push on the rear of the shaft.
2. Cut the new shaft to length if necessary. You may also want to file a flat onto the shaft. Press the new shaft into the bell. Tighten the grubscrew onto the shaft.
3. Screw the stand-offs into the motor base (Be careful. You may need to file or cut off the ends of the screw threads, so that they don't hit the motor windings!).
4. Drill a hole in the side of the motor tube in the fan unit. Enlarge the hole using a modeling knife, so that the motor wires will easily fit through. NOTE: make sure to orient the hole so that the motor's mounting holes line up with the mounting holes in the fan.
5. Install the motor base into the fan. Enlarge the fan's motor mounting holes towards the outside, to line up with the stand-offs. Secure the motor base to the fan (via the stand-offs) with the 3mm screws.
6. Fit the motor bell back into the motor base. Slide the 3mm (1/8") id tubing over the shaft to prevent the front ball bearing from coming out.
7. Install the impeller hub onto the shaft (butted up to the tubing) and tighten its grubscrews. Mount the impeller onto the hub and secure with the front screw (don't tighten it too much, or it will strip the thread in the hub!).
As always, you should trim and balance the impeller to ensure smooth running. The motor shaft does not have a front support, so it is even more vital that the impeller be well balanced.
Hold a piece of 400 grit sandpaper between the blade tips and shroud, at the point where the gap is narrowest. Turn the motor over by hand to sand the blade tips down. When the blades stop scuffing you are done!
The EDF55 impeller is very light and usually doesn't require much (if any) balancing. However the hubs often have a bit of runout, which must be compensated for by adding weight to the impeller.
Run the motor up slowly, while checking for vibration and/or blade strike. If either problem occurs then you will have to remove the impeller. After removal, Mark the hub and impeller with a felt pen, so that you know which way around to reassemble them. First try reinstalling the impeller rotated 180º. Choose the rotation which gives the least vibration.
If it's still not good enough then you will have to add weight (eg. electrical tape) to the inside of the impeller. If a blade strike occurred then you may be able to see which blade tip(s) are worn, and add tape to the opposite side. Otherwise just add tape in a random location. Reinstall the impeller and try again. If it gets a little better then add more tape. If it gets worse then move the tape to a different location, or remove excess tape.
My EDF-55 with Turnigy 2627-3800Kv motor gave the following results on 3S lipo (fan installed in GWS A10 nacelle):-
10.6V, 22.4A, 238W, 36764rpm, 422g static thrust, 107mph efflux velocity, 74% motor efficiency.
Not bad for $12
|Aug 07, 2009, 08:01 AM|
USA, PA, Pittsburgh
Joined Jul 2001
Very nice, simple. Another thing to do, fill the fan hub with epoxy, all the way to the top, balance it then report the numbers and fan sound.
|Aug 07, 2009, 08:46 AM|
It would be nice if the GWS fan had just a slightly larger motor housing so you wouldn't have to jump through all these hoops to get an outrunner to fit. Nice work around Bruce.
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