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new to me TD throttle of sorts. Cox_ba12





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Happy new to me TD throttle of sorts.

Post  Yabby Tue Nov 16, 2021 9:44 pm

Thanks to Balogh and others I am looking at creating my own TD 049 throttle. Or to be honest its a choke, neither a throttle or a carby, but I think it will do what I want cheeply, easily and work! cheers

Im not a big fan of throttling by adjusting the exhaust, although I do always use a muffler. My lad wants to have a go at RC. Not really my thing but I will knock up some cheapo RC wheel platforms and planes for him to muck with. Buying a cheap TX and RX and Im not new to inflight telemetry and command and control, so its not a big stress, just I prefer control line, as the RC stuff is a bit like what I do for my job, but the things being flown are bigger, more dangerous and cost hugely more, but the ideas are the same. But on thr weekend I love my little cox engines and control line.

Anyway need a TD 049 carby/choke and USPS isnt sending to Oz anymore so Im making one. This thread will logg the great or sad story. HaHaHa

new to me TD throttle of sorts. Yabby_12

So there is the start. A piece of aluminum drilled and shamfered to hold the top of the venturi and the start of a choke plate. more to come. but I reckon its gonna work. I hope.

Off to the oncologist now. Do more when I get back.

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Post  balogh Wed Nov 17, 2021 12:48 am

Yabby, seems to be a clean and simple throttle idea.

If I may add my view,  depending on how well the rotating flap will seal the rim of the venturi top, you may need a small air bleeding hole on the flap because a too rich idle mixture will cause flame out in the combustion chamber of COX engines in my experience. And depending on what muffler you have for heat retention,  select a hot plug for the glow head adaptor. I see you also use Kamtechnik heads, hot turbo plugs are luckily sold in most hobby shops that survived (at least in my area) I am all ears and eyes to watch your project unfold. Good luck. And trust the oncologist visit is just a routine and nothing serious.
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Post  Yabby Wed Nov 17, 2021 1:16 pm

Thanks Balogh, any ideas and thoughts etc are good ideas and welcome Thumbs Up Thumbs Up I had thought about the idle and an air bleed hole, i can test that with different flaps, my first want was to be able to obtain full revs to shutoff. Then to be able to idle. my thoughts on idle given I also want shutoff are a bit tricky and maybe needs more thinking a to how configure the flap, a bleed hole and probably a flap for the bleed hole, and then setup the radio to perform this in a natural manner. Or I could do it mechanically such that once the throttle closes beyond a certain point it closes both, or uses the channels to drive two servos. This is very prototype at the moment. Photos below.

new to me TD throttle of sorts. Carby_10

Looks to fit fine with everything.
new to me TD throttle of sorts. Carby110


If you look closely you can see the 3 little pieces of spring wire on the venturi holder. one of them spaces it against the NVB and then the rubber band wraps around tight and they bend in and hold it all in place very firmly. Yiu could use a cable tie or round hose clamp, lots of ways, but thats my quick and dirty prototype way of doing things. Lol.



Another view of the assembly. I hope to be able to run and test it very soon, but work and weather are conspiring against me. Lol.

new to me TD throttle of sorts. Carby210



I also found a super easy way to do a surestart with a grey backplate using a plastic elevator hinge glued to the intake pipe and the a servo to lift it up and down. again I need the chance to try it but looks ok. and quick, cheap and easy to make. Just gotta see if they work OK. Lol.

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Post  balogh Wed Nov 17, 2021 2:05 pm

Lots of good ideas there, Yabbi.

If I may add some thoughts to your project:

Given some freedom of the flap to bow up and down due to the assumed radial play of its shaft in the flap bore, no matter if it seals less than perfect, the depression in fully closed position will suck it to the venturi rim strongly and will more or less cut the air flow i.e. stop the engine. So you may need an airbleed if you go for a stable idle.
For reference, here are 2 RC carbs, the COX on the right has an adjustable airbleed cross section, the Tarno on the left has a fixed one. This latter has a bleed hole diameter of about 2mm. This may orient you as to the trial and error optimization of the required hole size for airbleed on the flap. I would drill it in the middle so that the engine should not starve air while the flap is moving near to the closed position..just my 10 cents..


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Post  Yabby Wed Nov 17, 2021 2:22 pm

Thanks Balogh, that puts me in the general area to start from with a bleed hole. might save me making lots of flaps to get there. :-)

Please fell free, and anyone else to add thoughts and ideas.

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