Motion dampers

[ken king, King DesignParticipant @kenkingkingdesign]

Here are some sprung oleo legs for a large scale R/C model aircraft which I made for a fellow modeller. Springs were carefully chosen to support the model realistically i.e. partly compressed when on the ground, and to adequately absorb impact loads when landing heavily. Of course, after impact comes the dreaded BOUNCE. Now if the legs could be damped on the extension stroke the bounce would be reduced or eliminated,resulting in a more realistic performance, not to say a safer arrival.

Nowadays we are surrounded by natty, tiny, and fiendishly clever motion dampers which are crying out to be used in models; I'm referring to soft drawer closers, and whatever the things are which lower our toilet seat and its lid oh so gently. I presume they employ some knd of funny viscous fluid or semisolid. They are fitted into tiny spaces (simply moulded into out toilet seat pivots, you wouldn't know they were there !) and appear to take many forms, linear, rotary etc.

Has anyone any experience of these things or knowledge of where they can be obtained? If so, please do tell.

[ken king, King DesignParticipant @kenkingkingdesign]

Modern motion dampers should find uses

[jason udallParticipant @jasonudall57142]

magnet–soleniod..resistor…diode

adjustable damping…change resistor..

asimetric damping..add diode…

[Hi Speed ScrapParticipant @hispeedscrap]

Model car racing suppliers should have suitable shockers

to do your job, you may have to fiddle with them a bit to get

the correct rebound tho.

Dave

[Ian S CParticipant @iansc]

I wonder if an o- ring for the inner rod to slide through, the ring would be trapped in a groove in the bottom cover, it would take a bit of experimenting to get the right grip on the inner rod. Give the o-ring room to move sideways a little, and remember that you can't compress rubber. You might fit it in without too much changes. Ian S C

[Rob keevesParticipant @robkeeves73950]

R.C. model cars they are avalible in all different sizes (usual scales 1:10, 1:8 & 1:5) and the ones used for racing are fully ajustable in compression and rebound with internal ajustments to the piston, most model r.c. shops carry different wights in oil avalible to fill the dampers too. My 1980,s tamiya hotshot has ajustable dampers. Rob (ex model r.c. off road racer)

[Jeff DaymanParticipant @jeffdayman43397]

http://www.itwmotion.com/products.php is a link to one major maker of small motion dampers Ken. If you enquire with them they will send a sample pack of several kinds.

The hinge dampers are probably your best bet for model aircraft landing gear.

Good luck JD

[ken king, King DesignParticipant @kenkingkingdesign]

Thanks for all suggestions to date. I hadn't realised the cars were so sophiticated (don't bristle, you car nuts), and I'll follow them up, Ken.

[Ian S CParticipant @iansc]

I think I would try to do it all inhouse, Instead of the locating cones, I would make extensions with pistons on the end, and bore the leg as a cylinder, and use air as the damper. or the top of the cylinder could be sealed, and oil / air in the cylinder. The cylinder would only need to be 1/4"/ 6 mm bore, maybe less, it only just needs to reduce the bounce. Ian S C

[ken king, King DesignParticipant @kenkingkingdesign]

You know Ian, you've hit a nail on its head, and you've jarred my feeble brain into sluggish reaction as well. What you suggest is just what I would like to achieve, an integral uni-directional air/hydraulic damper. And you know what else ? I've been fiidling with these things for years, yet it has only just dawned on me thanks to your note. I refer to the damper in an S.U. carburettor as fitted to classic Jaguars and many other older cars. Honestly, my capacity for ignoring things which are, metaphorically speaking, jumping up and down and waving their arms, is staggering.

In the S.U. a thin, rigid rod projects down into a bore in the vertically sliding air piston assembly. The bore, about 8-10mm dia. is oil-filled and at the bottom of the rod is a piston incorporating a simple one-way valve. Almost free motion in one direction, oil-damped in the other. Tsimples ! Thanks Ian.

Back on the drawing board ………

[Ian S CParticipant @iansc]

You proberbly only need to put a hole in the piston to control the flow rate. The system would not increase the weight by a great amount, looks as if the legs are going on a fairly robust aircraft. Ian S C

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