Repost: Making a Mighty Midget-Style Actuator

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Wayne_H
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Re: Repost: Making a Mighty Midget-Style Actuator

Post by Wayne_H »

My progress in making a Mighty Midget type GG actuator (a "twitcherator"??) has been slower than I would have liked, but such is life! I've now got all the bits to make the repo mighty midget or Twitcher Rand (as Shaun christened it), thanks to David's detailed explanation/instructions.

While waiting for the last of the bits to arrive I did some experimenting with a GWS motor & gearbox saved from a worn out GWS Lite Stick (remember them?). I've now got it running happily on one of Phil's pulse propo emulators (as meant for Ace magnetic actuators).
don't look too closely - it is a "proof of concept" construction (i.e. it was a rush job!?!)
don't look too closely - it is a "proof of concept" construction (i.e. it was a rush job!?!)
all the wood bits were salvaged from my "useful(?) scrap" box. Rod for the spring is a bamboo skewer
all the wood bits were salvaged from my "useful(?) scrap" box. Rod for the spring is a bamboo skewer
Next, I've got to make a Rand emulator to then try it with the converted GWS unit. Interestingly, even though the GWS unit was meant to run on 6 or 7 NiMh cells, on a 2s pack it over rotates, but when powered on 3.3 - 3.7v through a regulator, it runs very nicely with plenty of torque. This seems to parallel David's experiences with his Mighty Midget clones.
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
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Wayne_H
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Re: Repost: Making a Mighty Midget-Style Actuator

Post by Wayne_H »

Twitcher wrote: 25 Mar 2018, 16:48 Out flying the o/d Mangled Wot Mik. 2 and the Veron Robot today at Middle Wallop: .......... The MW2 has the homemade actuator .........

David
Just wanted to say that I was very impressed by the flight characteristics of the MW Mk2 in Phil's video from Ponty - top job David ;)
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
Spike S
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Re: Repost: Making a Mighty Midget-Style Actuator

Post by Spike S »

How appropriately descriptive, a "Twitcherator". Another Nostalgista's label to add to "Tobe Rand" etc.
This Forum continues to coin apposite words and phrases. :D
Spike S
(Tune for maximum smoke)
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Wayne_H
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Re: Repost: Making a Mighty Midget-Style Actuator

Post by Wayne_H »

Calling all Mighty Midget Gurus!

Well I've now made another of Phil's GG emulators, this one with an integral 3.5v regulated supply. The converted GWS mighty midget clone initially ran very happily on it - you little rippa I thought!! :D
emulator with integrated 3.5v regulator
emulator with integrated 3.5v regulator
I decided to be safe & give it a 'burn in' on the bench. At 12 minutes, the spring broke. I replaced it with a lighter spring of the same length, but it stretched & distorted. OK, try another replacement the same as the first. This one broke at 10 minutes. Clearly I was doing something wrong, but what? :( Remember, I've never seen a MM type actuator "in the flesh", so had nothing to compare the GWS unit to - other than a few seconds of footage of the Mangled Wot waiting to take off @ Ponty, I don't know what good/correct MM actuator operation looks like! :?

Time for some investigation & methodical experimenting with springs. Several more springs were sacrificed on the Mighty Midget altar to the GG god before I sussed several of my mistakes:
spring sacrifices.jpg
  • Initially I had the spring anchor point close to the outer radius of the gear. By moving it in closer to the axis, I reduced the travel & hence the amount the spring had to stretch. The resultant reduced force to stretch the spring also reduced the current drawn by the unit.
main gear.jpg
  • Typical current draw is 300-350mah but when moving the stick around this can momentarily go up to over 800mah. Is this normal?
  • By placing a short length of silicon fuel tubing over the output shaft, it protects the spring, stops that source of metal-to-metal noise and stops the spring from binding on the shaft
modified GWS actuator.jpg
  • I had inadvertently over tightened the spring anchor bolt on the big gear, so the spring was flexing at the same point every rotation rather than rotating as needed about the anchor point = fatigue failure.
  • The GWS unit seems very sensitive to spring tension. I suspect it also has more rotational travel than is normal(?) I made this short video in the hope that those more knowledgeable/experienced could review and provide feedback.


Please let me know your thoughts.

Meanwhile, one thing I know for sure, I won't be using it on any stealth models! :shock:
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
jmendoza
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Re: Repost: Making a Mighty Midget-Style Actuator

Post by jmendoza »

Mny guys used a rubber band to center the mightly midget , try a strip of 1/4" rubber and see how that works.
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Shaun
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Re: Repost: Making a Mighty Midget-Style Actuator

Post by Shaun »

Hi Wayne,
The actuator looks like it is over rotating. MM actuators usually go 270 deg end to end and have mechanical stops. I use springs from ball point pens and use brass tube sleeves on bolts for the springs to run on as a bearing surface. Rubber bands also work well. You don't need a lot of tension . It isn't necessary for the spring/band to centre the actuator.

Cheers,

Shaun.
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Wayne_H
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Re: Repost: Making a Mighty Midget-Style Actuator

Post by Wayne_H »

Shaun wrote: 18 Jul 2018, 21:41 Hi Wayne,
The actuator looks like it is over rotating. MM actuators usually go 270 deg end to end and have mechanical stops. I use springs from ball point pens and use brass tube sleeves on bolts for the springs to run on as a bearing surface..........

Cheers,

Shaun.
Thanks Shaun, in my reading I obviously missed the bit about using stops :oops: When I checked again closely, to get maximum travel (control deflection) within the birdcage, a single double-sided stop under the shaft located on the shaft centre-line should do the trick nicely - would give about 290-300 deg max travel. Then I can reduce the centering springs since they won't have to stretch nearly so far. :D

I'll install the stop when I get back in a week, and report back.
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
Twitcher
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Re: Repost: Making a Mighty Midget-Style Actuator

Post by Twitcher »

Hi Wayne
Just got round to reading your recent posts - you've obviously been working through a similar series of "suck it and see" experimental exercises as I did, narrowing down what works.
A couple of observations:
1. your actuator is going like the demented clappers. Why not try reducing the input voltage to slow it down and restrict the rotation to 270 degrees? And I haven't used, or found the need for mechanical stops, although I know the guys used to back in the 60's. Just tweaking the voltage did it for me.
2. if the rotational speed is right the return spring/rubber band need only be VERY light, i.e., virtually no tension at all when the shaft is in the middle position, and just helping the shaft back to centre from the extremes. It definitely does not need to be twanging it back under high tension.
Finding the right spring can be difficult but if you PM me your address in Oz I'll send you one. There are sources here in the UK and I'm sure there must be down there as well. If you have internet suppliers to the model robotics guys, they often have them. Alternatively, remember those loom bands that were all the rage a year or two ago? They do the job well but need frequent replacement. A couple of flying sessions at most.
3. You've got the attachment point on the shaft positioned spot-on. That's where it needs to be (see above). A light metal spring will work perfectly well with a final loop just hooked over a wire hook bound and soldered to the shaft. I'll try to do some photos of the embarrassingly crude arrangement I've used and post them here.
You're nearly there!
David
Stewart
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Joined: 17 Feb 2018, 04:57

Re: Repost: Making a Mighty Midget-Style Actuator

Post by Stewart »

Theres an actuator build pdf amongst the files on Phils site "ACE mini GG actuator " that shows a unit using push/pull setup - looks simple enough to make, and this coupled with Martins pot adjustable decoder would be easy to setup.
Stewart
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mini actuator-d.jpg
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