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Author Topic: How to Set Up a Throttled Four Engine Model with a Three Lined Bellcrank?  (Read 2808 times)

Offline Michael Boucher

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Hi, I have seen how to set up a twin engine model for throttle. I was wondering how to set up a four engine model? Thanks, Michael Boucher  H^^
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Offline chuck snyder

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Could you describe or draw the linkage with which you are familiar? The linkage I used in an F-5-F could easily be expanded to two more engines. (not that I would want to given the availability of electronic systems)
Chuck

Offline Tim Wescott

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I think that the "simplicity" of a mechanical system in this case will be a lot more complicated to achieve than using servos, particularly if you've got dihedral.  In fact, if I were tasked to do this I'd be tempted to drive a pot with the throttle arm of the bellcrank, and put servoes in each nacell.

At any rate -- it's going to be different for each plane.  I'd probably use little ball links on 90-degree bellcranks to actuate the throttles from rods moving span-wise in the wings.  I'd probably have a master 90-degree bellcrank in the center section (assuming dihedral) to translate motion from the bellcrank to the throttles.  I may decide halfway through that ball links have too much friction and need to be replaced by z-bends.

You're going to have huge mechanical fit and friction issues.  If it were me I'd probably dummy up the whole control system on a slab of plywood, leadouts to motors, with all the appropriate dihedral breaks and all the engines in their final positions.  I would do this as the very first step in actual construction.  I would make it work perfectly, knowing that whatever goes into the plane won't be any better than what I could achieve in such ideal circumstances.  I wouldn't start on the plane  construction until I'd satisfied myself that the control system worked well enough, had low enough friction, didn't have leadouts rubbing on any throttle-control bits, and had room to fit in the actual wing.  Then I'd build the wing first, referring back to the control system as I went.  There is a good chance that I'd transfer the actual bits of the control system from plywood to plane.  I'd make everything adjustable.  I think I'd also see if there were any scale or scale-like access panels that I could put in over all the critical points so that I could maintain the thing, so I didn't have to cut into my nice scale plane halfway into the first competition season.

Then, before I started work, I'd think again about the convenience of just bunging in a receiver, battery, four servoes, and some servo-wire tunnels...
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Fred Cronenwett

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Having flown with 3-line and the electronic controls which have been replaced with 2.4 Ghz I would highly recommend the 2.4 Ghz systems. As a rule CL pilots tend to want to use the older systems because we are afraid of change. the mechanical system for a Quad will get complicated fast and you don't want any friction points in the system that would make the response of the 3-line system jam up. The 3-line system needs to be free of any friction that reduces the response from the 3-line bellcrank.

in the 1990's while flying with a single channel electronic control system I put one servo on a twin engine model and put all of the bellcranks and pushrods to control the throttle. The linkage between the two engines got very busy and it worked.

Then I put a servo in each nacelle and ran a wire to the nacelle. Then I simply had a servo and short pushrod going to the engine. I found this to work much better and easier to hook up and adjust

This is how I sync up 2 or more engines on a model so that they all shut down at the same time and idle when the throttle stick is pulled back to the idle position.

1) Tune each engine at full power with the high speed needle valve and make sure you can idle down and shut the engine down. Do each engine individually, one at a time

2) run all of the engines together and then throttle back until you get to the idle position and then shut down the engines, take note of which engine will shut down first, second, third and fourth.

3) On the engine that shut down first lengthen the pushrod going to the servo to speed it up, turn the clevis maybe 2 or 3 turns. do not adjust the needle valve, we are going to speed up or slow down the engine by adjusting the pushrod length

4) restart all of the engines and repeat step #2, the engine that shut down should be more closely matched with the other engines. Take note on the order the engines shut down on this round. repeat step #2 and #3 until they all shut down at the same time when the engines are shut down. This may take 4 or 5 rounds to get it right. You only have to do this once, not every time you go flying.

Hope this helps,
Fred

These are some videos from my channel that might help








Fred Cronenwett
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Offline Michael Boucher

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Hi Chuck, Thanks for answering, Brodak makes a twin throttle linkage set up. That is the one I was referring to. Hi Tim, I would have to agree with you now. Thanks for pointing out how smoothly the mech. system would have to operate. Hi Fred, Thanks for making and posting the great videos to bring me up to speed. It would be interesting to see how folks are using the 2.4 Ghz system now. What they use for handles and the modifications made to them. I really appreciate all the responses, thanks again all. Michael Boucher  H^^
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Offline Tim Wescott

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It would be interesting to see how folks are using the 2.4 Ghz system now. What they use for handles and the modifications made to them. I really appreciate all the responses, thanks again all. Michael Boucher  H^^

Three ways that I know of:

1: Hang a transmitter from your belt.  I believe this is what Fred does (Fred, do you have a video?)
2: Get an RC car set, and build it into your handle (or a handle onto it).  This puts everything into your dominant hand, but limits you to two or three channels.
3: Get an RC car set, and hold it in your off hand.  When I fly Carrier I fly with my right and throttle with my left -- it works great.  In fact, for Carrier I use the fact that the RC car throttle has a "neutral" that's at about 1/3 of the range: I set the engine up so that neutral is as low an idle as the engine will do reliably, and a push with my finger cuts the thing off.  Alternately, the Hobby King radios can be modified with a bit of work to spring to "off" -- I posted pictures once, a long time ago.

I suspect that if you're electronically astute you could make a "buddy box" to mount on your handle that would wire to a transmitter on your belt -- this would make sense if you're hopeless with your left hand, or if you aren't good at operating a transmitter by feel, but personally I'll either use my RC Car method or Fred's.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Fred Cronenwett

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Yeah I just hang the transmitter on my hip, I have a video planned on how to use the separate transmitter and hang it on the hip. I use a normal stunt handle and lines.

On the subject to the RC car transmitter in the left hand that has also been done before, works great and your left hand moves the trigger. If all you want to do is throttle that is probably the cheapest and easier way to go, the RC car units are not that expensive.

Fred
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Offline chuck snyder

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Michael,
If you are building a four-engine scale model surely you want more mechanical options than the throttle. Without flaps and retracts your realism score in competition will be reduced by at least 3 points. Electronics make this much more viable.

I have a deHavilland Hornet twin where I hang the transmitter on my belt. For all the others I hang the transmitter on a neck strap. My left hand works everything except the elevator.

Chuck

Offline Paul Smith

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I agree with Chuck.

With the current punitive penalties for the lack of retracts and flaps, it is a futile mission to build a multi-engine model, unless you are building a ancient design which had four engines, a fixed gear and no flaps.  Not impossible, but near-impossible.

Four engines, retracts, and flaps that work in the true scale manner is a tough nut to crack.

Paul Smith

Offline Fred Cronenwett

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Flaps are very easy in that you put a battery, receiver and one or two servos and you are done. I like to use one servo per flap, adjust the clevis to get them even and use end point to control how much flap you put down

This video shows how I hook up flaps and control how much flaps are deployed. My new radio (Tactic 850) even can control how fast the flaps are lowered

Plug in a throttle servo and use End Point to control the idle speed, I have a belt clip and hang the transmitter from my hip

Fred


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Offline Michael Boucher

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Very nice flap set up Fred, the ability to control the speed that slow makes it look very realistic. Thank you, Michael
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