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Re: Mayfly - by Peter Valentine

Posted: 13 Sep 2020, 09:06
by Pchristy
Glad you enjoyed it, Tobe!

I can't recall if I've posted this here before, but it shows my first efforts with a helicopter. It also includes some very fuzzy shots of the original OS 10 powered "Mayfly", so I can justify posting it here! ;)

Enjoy!



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Pete

Re: Mayfly - by Peter Valentine

Posted: 13 Sep 2020, 11:17
by Wayne_H
Great videos Pete, thanks for sharing. I suspect your performance at those early comps should be put down to the missing tie - if the hot shots wore a tie, then .......

Progress in Aus at the same time, certainly in the Sydney area, appears to mirror the progress in your videos. The first genuinely successful (i.e. under control at all times) R/C heli flight I saw was at the Sydney Royal Easter Show in 1973. I don't remember the pilot - he was as I recall, from overseas and sponsored by OS - and the heli was a Schluter(?) Cobra.

One thing I noticed very early on at those Sydney heli events was that if "the gun" wore a red cap & jacket, then you could bet your house that at the next event, all the "wanna be's" would be sporting a red cap & jacket :o I referred to it as fake it til you make it syndrome?!? :lol: but then I was a slightly cynical 17 year old back then :oops:

Very entertaining stuff - please keep posting & good luck with the Mayfly repairs ;)

Re: Mayfly - by Peter Valentine

Posted: 13 Sep 2020, 12:05
by Shaun
Great video Pete but why did all the pilots of the day take their heli's for a walk. Wasn't the range on heli radios great back then.😆😆

Re: Mayfly - by Peter Valentine

Posted: 04 Oct 2020, 11:22
by Pchristy
Its taken a little while, but the MayFly is nearing completion again!

My aim has been to re-use as many original parts as possible, and it is this that has slowed down the repair process!

The model was always slightly tail-heavy, not helped by that chunky (and fragile!) experimental tail-rotor gearbox. Looking through the piles of stuff I collected after PV passed away, I found a modified Lark tail rotor gearbox frame. This was basically the same as a stock Lark, but without the stub for the tail-rotor control bell-crank. I also found some steel bevel gears that would fit.

So far ,so good!

The next issue was that the original experimental gearbox used 3/16" shafts, whereas the Lark uses 1/8". This meant that either the original hub and pitch linkage wouldn't fit, or the shafts wouldn't fit!

I approached my old flying buddy, Geoff Bell, who has a very comprehensive mechanical workshop, and is usually up for a challenge! He made me some new 3/16" shafts, but turned down to 1/8" where they pass through the bearings. This has enabled me to assemble a new TR gearbox using many of the original bits:
ImageNewTR_2 by Peter Christy, on Flickr
ImageNewTR_4 by Peter Christy, on Flickr
ImageNewTR_5 by Peter Christy, on Flickr

I've now fitted it to the boom:
ImageNewTR_6 by Peter Christy, on Flickr

Now I have to sort out all the drive and linkage paths:
ImageNewTR_7 by Peter Christy, on Flickr

The tail rotor is now on the opposite side of the boom from the original, but still rotates in the correct direction due to the different gears. This means that all the guides for the drive shaft will need altering. The same applies to the control push-rod! Also, I think the direction of the servo will need reversing, which in turn will mean re-mounting the (very basic!) gyro fitted.

None of these are show-stoppers, just time consuming and fiddly! I also need to devise some way of mounting a tail skid to protect the tail-rotor. However I have a cunning plan for this!

Watch this space.....

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Pete

Re: Mayfly - by Peter Valentine

Posted: 15 Oct 2020, 16:54
by Pchristy
Its been a while since I updated, as I've had to do quite a bit of "fettling" to get everything as I wanted.

Although all the parts of the new TR gearbox worked fine on their own, the pitch linkage got very stiff when I connected the slider to the blade grips! After a lot of head scratching, I came to the conclusion that the modern ball joints were much stiffer that the originals - one of which had broken, and had to be replaced. This, coupled with the very rigid aluminium slider meant that the linkage could not accommodate the varying spacing between the ball links as the grips rotated.

I tried a number of solutions, none of which worked to my satisfaction, before making a new slider part out of thin fibre-glass:
ImageNewTR_10 by Peter Christy, on Flickr

This worked fine! I have now finished re-routing the drive and pushrod wires, and have test hopped it in the back garden again:
ImageNewTR_8 by Peter Christy, on Flickr

All I need now is a calm day to take it out and try it properly!

Finally, I found another picture of Peter Valentine with the OS10 powered Mayfly-2:
ImagePV.Mayfly by Peter Christy, on Flickr

:)

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Pete

Re: Mayfly - by Peter Valentine

Posted: 17 Oct 2020, 16:22
by Pchristy
Another test flight, and another disaster narrowly averted! This time it was the tail-rotor drive coupling!

The Lark used a very crude, but reliable, coupling for the tail-rotor drive. The drive itself was just a piece of piano-wire. The secondary pulley on the mechanics had a square recess in it, about 1/2" sq. Into this loosely fitted a 1/2" sq rectangular piece of aluminium, drilled to take the piano-wire, with a grub screw to bite onto the piano-wire. This provided a very simple kind of universal joint, allowing a little bit of play, whilst ensuring a positive drive to the tail.

For this Mayfly, Peter Valentine tried something more sophisticated! He cut a circle of leather (!) to produce a coupling similar to the rubber donuts used on some cars in the 60s. Anyone who has changed the gearbox in a Hillman Imp will know what I mean!

Unfortunately the leather wasn't man enough for the job - or maybe it had just deteriorated with age. I had been suspicious of it from the start, so it came as no surprise when it let go with a bang!

Luckily (again!), I wasn't very high and managed to land safely!

The quick and easy fix would have been to simply fit a Lark pulley (which I had). Unfortunately, I didn't have the matching aluminium block!

After a bit of head scratching I tried a rubber tap washer, but it was too thick. Eventually, I settled on a small servo output arm:
ImageCoupling by Peter Christy, on Flickr

This fitted absolutely perfectly! Even the holes in the arms were in the right place! The plastic is a little on the rigid side, so I've left the mounting screws slightly loose (hope the Loctite holds!) and I've test flown it successfully in the back garden!

Proper "kitchen sink" engineering! :D

I have hit another problem though! The ESCs keep overheating! The model draws just over 20 amps in the hover, and I fitted a 40A speed controller. After 2 mins of operation, it throttles itself back, and the model sinks to the ground!

I tried a "higher tech" 30A speed controller, but that one cuts without warning! (I tested it tethered to the ground!.)

I think the motor I have has a too high kV rating (3000). Ideally I need around 2500 kV and 400 watts, but so far I've failed to locate anything suitable. I do have a very old, but higher rated speed controller in my junk box, but I can't remember just WHY it was in the junk box! Oh, well, if I don't try it, I'll never know!

Onward and upwards!

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Pete

Re: Mayfly - by Peter Valentine

Posted: 21 Oct 2020, 02:26
by Wayne_H
Pete, great to see progress & I love the engineering - definitely pre-ARF era :lol:

Do you think fatigue of the servo arm may be a problem? Did you consider a 1.5mm PCB (or an engineering plastic such as Delrin) 'duplicate' of the servo arm or is the servo arm's mounting socket an essential part of the required solution?

Many years ago, I achieved a similar result on my RCM Polecat by soldering a suitably sized wheel collar to a piece of PCB cut to the required shape. I still have the Polecat, which will be restored 'one day' :roll:

Re: Mayfly - by Peter Valentine

Posted: 21 Oct 2020, 08:40
by PaulJ
Wayne_H wrote: ↑21 Oct 2020, 02:26 Do you think fatigue of the servo arm may be a problem?
I agree...... Following an expensive disaster, I am deeply suspicious of servo arms that are under a lot of load. In the investigation following my crash I found a bubble in the servo arm moulding and that is where it had failed and caused the crash. Since then I have always used a disc in high load situations. I appreciate that a disc may be too rigid for Pete's application but I fear that that servo arm solution looks like an accident waiting to happen...... :?

Paul

Re: Mayfly - by Peter Valentine

Posted: 21 Oct 2020, 09:26
by Pchristy
Thanks for the comments, folks!

Yes, I hear what you are saying about the servo arm "fix", and will be keeping an eye on it. I would have preferred to use a disk, but didn't have one of an appropriate size lying around (the arm I've used is off a quite small servo).

The screws locating it are not done up tight, so the arms don't need to flex much, if at all. They simply rock between the washers. Two of the screws are held with nyloc nuts, so no worries about those coming loose. The other two screw into the pulley, and are loctited. These two are my biggest concern.

Actually, it all runs very smoothly, with little or no vibration. It has to be better than the original leather disk!

I'm only regarding this as a "stop-gap" solution until I can either locate some thin rubber sheet or find a suitably sized disk. I did use very thin PC board for the replacement slider plate on the tail-rotor. However, I wasn't sure this was thick enough to withstand the potential constant rocking as a universal joint.

Ideally, I'd like to use a very old servo disk. Some of those were very "bendy" and would be ideal for the job. Modern ones are a bit too hard and inflexible for this application! I still have a couple of boxes of old bits to locate and search through.

In the meantime, Shaun is kindly sending me a motor which sounds as if it may be a better match for the Mayfly than the presently installed EDF motor. Alternatively, I have bought a higher rated ESC, but I would like to reduce the current consumption a bit, ideally.

Cheers,

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Pete

Re: Mayfly - by Peter Valentine

Posted: 21 Oct 2020, 13:30
by Spike S
Great to see the Mayfly reborn.
The leather disc flex coupling (simple/reliable) was frequently used for model boats back then and probably still is. Engineering finesse has moved on somewhat but the Aerospatial/Westlands Puma Mk1 used a similar flexible coupling to drive its tail rotor. Similar shaft end configuration to your leather jobbie but a pack of thin stainless steel rings to transfer the power across a small but variable angle. :geek: