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Old Feb 17, 2011, 04:00 PM
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Freddie B's Avatar
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Cure GWS micro EDF's throwing rotors.

OK, I've posted in a few threads, as have others, on using the GWS 2mm prop hubs to keep the GWS rotors from launching in flight.

Problem is after a time the plastic hub which has a press fit, loosens up from heat or whatever, and comes off in flight. No amount of glue seems to keep them on after such a failure.

There are many great EDF fans in the 40mm on down size range, from many manufactures. But I as many others still like to use the GWS fans in many projects.

The GWS fans are easy to find, priced reasonable, and with a good, trusty 12mm inrunner brushless setup, a 40mm will push a decent size, 4-6 ounce, EDF Jet along using 5-7 amps. Helps keep the battery, airframe, and equipment in the lighter weight and lower cost territory.

So for all those that use the GWS fans, and want to improve reliability here is more complete explination of how I do it.

I will cover the 40mm, and 30mm fans here, but this same process will work for you 50mm fan, fans.
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Old Feb 17, 2011, 04:07 PM
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The prop hub.

First we want to aquire the recommended prop hub. GWS sells these through many vendors. There are even different part numbers, depending on the propeller that is supplied with them. I happen to use the GWS part number: GW/H001-FD5002-030B. I can usually find these selling for $2.50-$5.00 USD, and shipping varies.

All I have seen have the same 2mm prop hub included, with 2 x 1.6mm allen set screws, a 2mm flat washer, and a 2mm nut, and as a bonus, a 2 blade propeller and propeller grommet.

thes prop hubs were used on the old Dragonfly Heli, tail rotor motor.

The hubs have a 1.5mm hole for mounting on a 12mm inrunner, such as Faigo's, Hyperions, and Hextronik's. The shaft coming off the hub is 2mm, threaded.
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Old Feb 17, 2011, 04:39 PM
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If you were to just drill the rotor out for the 2mm prop adapter, the rotor would stick out the front of the shroud, possibly not even engaging enough threads to put the nut and washer on.

So we need to get down inside the rotor and relieve the plastic hub enough to clear the large part of the prop adapter.

I have seen people mess their rotor up tring to do this, and worse, making the 2mm through hole wander off when drilling, making the rotor spin out of round. This will destroy your rotor, or worse, the shaft on your precious 12mm inrunner!

There are many methods, but mine is to make a couple bushings to keep things running true and accurate.

I made mine from aluminum, on a lathe. I have supplied these similar tools to a few on a limited basis. The aluminum works well for our use, but if heavy production was to be had, brass, bronze, or steel would be used.

However if you do not have a lathe, maybe a friend does? I also think using some hardwood dowels, a drill press or wood lathe, files, sanding blocks, etc, could be substituted to make something similar. Wooden bushings would have a limited life span, but with some CA hardening could get you through a few dozen modifications.

Here is a drawing with some dimensions that you can use to make copies of what I'm using.
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Old Feb 17, 2011, 04:45 PM
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Here is a picture of what you need to do the 40mm rotor modifications.

1. Bushing to relieve the inner plastic hub.
2. Flat pointed drill (5/32" Dia./ Same as 4mm)
3. Bushing with a 2mm hole to drill all the way through the hub for prop shaft.
4. 2mm drill.
5. Your prop hub kit from GWS.
6. A 5/32 DuBro Wheel Collar to act as a drill stop.
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Old Feb 17, 2011, 04:53 PM
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A new friend of mine named Bill, wanted to be able to do the same process with the 30mm Rotors. I engineered the bushings so a 2mm prop adapter can be used to mount the 30mm rotor on a 12mm inrunner. Bill said Dave (NitroCharged) recommended modificaion of the AEO 30mm shroud for the 12mm inrunner, using the GWS Rotor and Prop hub.

Here is a picture of what you need to do the 30mm rotor modifications.

1. Bushing to relieve the inner plastic hub.
2. Flat pointed drill (3mm, #31 drill, or similar)
3. 1 Bushing with a 1.5mm hole to drill all the way through the hub for prop shaft. I use two drill sizes to get to 2mm final dimension because of the drilling properties of plastic.
4. 1 Bushing with a 2mm hole to final size the hub for the prop adapter.
4. a 1.5mm (or #53 drill), and a 2mm drill.
5. Your prop hub kit from GWS.
6. A DuBro 1/8" wheel collar to act as a drill stop.
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Old Feb 17, 2011, 05:04 PM
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While we are at it, no worries about obtaining a flat pointed drill!

Picture is the cheap man's bench grinder for sharpening drill bits. Simply grind the point off of your drill, flat, like you would a landing gear axle. Next slightly relieve each side of the drill flutes, with a slight angle on the rear side, so it has clearance to cut (like a hobby knife blade looks at the edge).

See Photos. I use a diamond cutoff whell, set of 5 from Harbor Freight, around $2.00 USD.
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Old Feb 17, 2011, 05:21 PM
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Making the cuts.

So to help with your learning curve, let's go through the process here in photos.

Tip: Do not use powered equipment to drill the rotors, or relieve the hubs. I do this all by hand. REASON? Plastic likes to grab in the drill bits, causing the parts to twist violently in your hands! This will cut you, rip the vanes off the rotor, or ??????? I use a vise, pin vise, an old drill chuck, or put the drills into a drill motor just to hold them and gain leverage. Do not tun the power on!

Tip #2: Practice holding the rotor while working on it, without touching the vanes. They are fragile! Avoid vane destruction at all costs! Even if you need rubber gloves to grip the tiny parts! Trust me, I know, and rotors get expensive.

Tip #3: Work the drill slow, light, and steady pressure. The drill will want to dig in quick and deep. It may help to do a back and clockwise, counter-clockwise, rocking motion as you drill to clear the chips from the hole.

Drilling slowly by hand assures a more accurate finished product. Remember how fast these little babies spin up under 3-4 cell loads! We want them to run very true!

1. Place the hub relief bushing into the back of the rotor. The shoulder will butt up to the face of the outer hub surface.

2. Using your flat pointed drill AND DuBro Wheel Collar as a stop, cut the inner hub to depth. I am using a drill chuck, but spinning everything by hand. Doesn't matter if the bushing rotates, the drill stop will finally come to rest on the end of the bushing, and the bushing is resting on the shoulder to hub face.

Small adjustments, go slow, until the drill stop is set just right. The prop hub should have a little bit sticking out the back side of the hub, just enough so the rotor hub does not rub the shroud, or the motor mounting screws. Once set you can repeat the depth of your cuts on more rotors over and over again.

On my 40mm rotors, the depth of my cuts is just shy of 3/16", for the shroud and screws I'm using.
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Old Feb 17, 2011, 05:35 PM
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Next I insert the drill guide bushing, in the case of the 40mm, this is the 2mm size one.

Get out your 2mm drill bit, and put in a pin vise or similar. Simply take your time and drill the original hub diameter out to a final size of 2mm.

The big secret is that using this guide keeps the hole running true all the way through. Heavy hands, using a dremel, or similar it's easy to get the drill going through crooked! My rotors spin like they were made that way!

In fact, often my final 2mm hole is a little tight, so after the fact, I 'ream it out' a little by spinning up the 2mm drill in the pre-drilled hole, using the Dremel, until I get a nice sliding fit.
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Old Feb 17, 2011, 05:36 PM
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Didn't take long at all, now we have a rotor that looks like this! (40mm rotor modified, shown).
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Old Feb 17, 2011, 05:42 PM
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I premount the prop hub on my 12mm inrunner, then mount that into the shroud.

Then I put the rotor on the adapter, and tighten the nut and washer.

Last recommendation. The tiny wrench that comes with the prop adapter always seems to strip when trying to tighten the little set screws. See photo below. The Wiha drivers were my answer! The size you need is the .9mm one.
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Old Feb 17, 2011, 05:49 PM
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Ready for business!

No more throwing rotors in flight, or hogging out fans to replace one. Isn't life sweet!

Ready for action!

Good luck, have fun!

Fred
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Old Feb 17, 2011, 07:17 PM
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Fantastic tutorial Fred! It's pretty obvious you've been there and done that. Your technique is very refined. Great job!
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Old Feb 17, 2011, 08:44 PM
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Freddie B's Avatar
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Quote:
Originally Posted by pdawg View Post
Fantastic tutorial Fred! It's pretty obvious you've been there and done that. Your technique is very refined. Great job!
Thanks. All those years back when I was a prototype machinist, mold-maker, and tool designer in Aerospace comes in handy. . Makes life easy if you want multiple copies and all of them exactly the same, plus have them work right!

Hope you get back to Cali soon so Brent, Dave, and Mega Tesla can talk you out of spare/repair parts! Just what you are going to want to do! Hope Med school is being kind to you, Doc!

Fred
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Old Feb 17, 2011, 09:13 PM
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Fred,

Great instructions! I was wondering if I was the only one having problems with stripping the set screws on the hubs.

Now I can't wait to get the tooling.

Bill
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Old Feb 17, 2011, 10:28 PM
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Bill,

Let me know how you fair with the tooling. EDIT: Bill the rotor work and finished fan unit in this tutorial was done with the tools I sent to you. Had to test them and the results are as shown!

I've had some other people talk about stripping the wrench/set screws, or not getting them tight enough to hold the adapter on. The Wiha wrench set looks to have a stainless/hardened tip added right at the business end. Most of all, they fit like a glove. Got to love the German made tools. You get what you pay for.

Fred
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