Last update 4/05/07
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It all starts with removing the original shaft and fitting a longer shaft. I used 7" as I'd rather lop some off than make a longer one later. Simply cross drill with a #48 bit 4mm down the shaft like the original. 01 tool steel can be drilled with a good drill set. If you went with a harder steel you may need carbide. Don't forget to test fit your bearings! you want a reasonably easy slip fit. I needed to chuck it in the drill press and give it a few seconds with 320 grit to scratch it up and polished back out with 600 grit.
Seen here with original shaft off to the right side and the longer shaft installed. This head was chosen mainly on price. It was delightful to find that it is equipped with 2mm linkage rods. IMO the 1mm links just suck.
If you have a leftover head laying around give it a try!
Next we need a crutch I prefer to make my own with a few mods. Store bought from HeliHobby or Mike Roffee will do fine. I like to chop 3/8" off the front landing gear mount and add 1/2" to the rear for better use on grassy fields. There is also the extra motor position for the BT Hyper Drive.
Nothing is glued we just have a successful fit test. I have no idea how this will get changed so being able to knock it flat can't hurt. I also didn't cut out the servo holes as I know pretty well they won't be put there.
The rest of the evening was just tear it all down and soak thin CA into the wood on both pieces of the motor mount and around all the bearing/tail mount holes. This is simply to keep the nuts/screw heads from sinking into the wood and causing problems later. Yeah I know this is temporary but it's easy.
Mounting up the head and main shaft. It's all pretty straightforward and simple. Pictured here are Corona bearing housings, home made bearing stoppers (x400 trex450, BP Explorer stops will all work). Since I'm gonna start with a Corona tail the Tail Drive bevel gear was drilled out to 5mm to fit, as was the main spur gear (not shown). The overly long AR bracket is just a temporary to keep the swash in place as measurements are taken.
Mockup Mk1, the motor mount, doubler and front strut mount are glued together but nothing is glued to the frame. The struts and skids are installed to make it easier to deal with. The bearing retainers are home made simply because I didn't have 2 spares on hand, and didn't want to wait on an order. X400 Trex 450 etc would work fine.
Part 2 of phase1
Having gotten a good start with the frame and fitting up parts, it became obvious there was going to be some problems. Foremost was lack of places to put holes to mount the pitch servo plate. Simple solution was to cut a new frame with 1/4" added to the top. Next problem was getting the swash not to drag on the AR fork which was achieved by moving the main bearing mount holes back .065". Please ignore the paint job in an attempt to use left over Krylon H20 from foamy planks it's what resulted. Definitely too temporary to redo.
Just click on the image to open the 1:1 .pdf of the comparison. The easiest way to go is buy an LMH-120 crutch kit (wooden as the AL crutch is craptastic) so you'll have the motor mounts etc. trace and transfer punch the original crutch. Align the template's blue areas with the original. Center punch the modified holes. Best to mark them so you don't drill the wrong holes. There is nothing to lose but a 3$ piece of 3/32" ply
I don't think this gives away any of LMH's Voodoo, and should let you better envision the changes.
I chose BMS-371 servos as they were on hand and gear sets are cheap! One of the priorities on this heli is quick and easy servo changes. Hopefully the small size won't be a big problem but fitting larger servos would be a problem in phase 1.
Front view showing the need for longer standoffs. The standoffs were calculated based on normal thickness arms with the balls pointing outwards. That'll be easy to fix, or not needed as there seems to be no adverse effect.
Funny stuff can be noticed in pictures. There is a screw that didn't get tightened, and the antenna tube from the BPE that went unnoticed through the picture taking.
Front top view for a better idea of the way things are laid out.
The arms aren't adjusted exactly yet and the retaining screws are still wanting. This picture shows the best compromise on plumbing the linkages. The aileron servo couldn't be moved farther back because of the AR fork. The elevator servo was pushed back a like amount, resulting in little pitch/cyclic interaction.
CF reinforced keel and another view of stuff
Topish view showing pitch servo plate. Which should also make a fine location for the RX and separate it from the rest of the stuff.
Top view with rotor in one position.
Top view with rotor slightly rotated.
It has now been flown for a few check hovers (kinda). It's wearing a set of align 325 fiber (paint mixers) as there was no reason to risk a real set of blades on such a gusty day (17-25mph) There is some bad blade flutter on spin up right at liftoff. Once the flutter stops it gets up pretty good. Common sense dictated that further testing be postponed until a better day. I just had to see some air under it. vids can be seen <click Here> they ain't much. There is indication of potential with the gyro gain set right and perhaps a set of 365mm blades.