questions for those who have built twins

steve wood · Sep 26, 2011

1) throttle linkage in the radio box,or in front of engines? one servo with linkage or 2 servos,1 for each motor.if you use cross bar type linkage,what do you use? is there any place that sells aluminum arms for this type of setup? i don't like plastic.

2) mixture control pros and cons.inside motor,outside motor or both? i've been told both doesn't work,but haven't got a reason why won't it work,and how can it work on only one motor?

setting up a new boat and never ran a twin before.just looking for options

Tim Kish · Sep 26, 2011

I have only owned three twins now but I prefer the linkage in the radio box with one servo , there is already enough going on in the engine compartment and the radio boxes are large enought to fit a twenty in so just kinda makes sense to me.

On my first twin I tried dual remote needles then one and could not get it to work , just a pain in the ass and for some reason did not work.

I now set the boat up by ear and then check and record readings later with Boris meter , I can usually get both needles identical by ear .

Hope that helps a little , Tim

Chris Wood · Sep 26, 2011

you could always call your kid and ask him his thoughts?

Tim Kish · Sep 26, 2011

Chris Wood said:
you could always call your kid and ask him his thoughts?

Now that's funny lol.

Tim k

Buckshot · Sep 26, 2011

Steve,

I have always set up the throttle linkages using one servo operating a “crossbar” system in the radio box with .125” SS push rods running to the carbs. The trick is to stiffen up the area where the “crossbar” system mounts to the boat in the radio box. If you mount it straight to the floor of the tub it will flex under any kind of load as the floor of the tub flexes. Mine is mounted to an additional bulked in the radio box. I made my own aluminum arms for the throttle linkages as I too do not like the nylon arms.

I have tried running the needles in every configuration: both fixed, One remote and one fixed, Both on one servo with a “crossbar” like the carbs but now I’m using my 4 channel radio to operate each needle separately with each one having it’s own servo and channel. Truthfully I usually set the needles in the pits and don’t touch the remote during a run BUT I have the option to adjust each motor independently while it’s running IF I wanted.

Good Luck.

Marty Davis · Sep 26, 2011

Steve:

I saw John Ackerman use a SINGLE mixture control on just the hard working engine and it worked VERY WELL. I personally tried 2 mixture controls and could never get them syncronized.

ALLAN YUEN · Sep 26, 2011

My Cobra twin and Jagaur twin use one servo to crossbar to two trottle linkages for engines another one servo to crossbar to two linkages for better : 2 CMDI or best: Don F mixture needle values because if you go to travell to different place or depend on weather ( cold , hot or rain) and easy adjust good balance needles so become peace!! . I keep away BVM remotes because sometime leak air from o rings and stuck also servo can burn out. I am very glad with them No problem!! B)

Mike Hughes · Sep 26, 2011

On both my twins (45 & 84) the throtle comes out of the radio box with one pushrod. Then it is split into two. The carb arms are setup in the middle of the boat. Works fine. As to the needles, I have them both tied together. One pushrod changing them both together. I do not use them to tune each engine. That is done by ear and reading plugs. Like Allen said, works great for getting in the ballpark when travelling to races. Which is really what I have to do if I want to run in real twin class.

Mike

Mark Bullard · Sep 26, 2011

I have always used front landing gear for airplanes over the years. Here is a picture of one our new Twins that we are building for Charleston.

ALLAN YUEN · Sep 26, 2011

Mark Bullard said:
I have always used front landing gear for airplanes over the years. Here is a picture of one our new Twins that we are building for Charleston.

View attachment 30522

Nice enough room anyway I didn't see you at hobart so will meet you next year

Piston1 · Sep 26, 2011

I use 2 Futaba S9650 Mini Servos (Digital) to control BVM needles. I stick the servos to the sides of the hull using double sided foam tape. I can adjust 5 numbers on the Boris meter, both needles tracking together. I use a 4ch reciever with a 4pk radio. My throttle system is similar to Bullard's. I think he copy me.

Bob Morton · Sep 27, 2011

Mark Bullard said:
I have always used front landing gear for airplanes over the years. Here is a picture of one our new Twins that we are building for Charleston.
View attachment 30522

Nice looking work on the needles and the throttles and two receivers. Also one oiler for two shafts. Who makes those Clevis connectors on the throttle arms?

Buckshot · Sep 27, 2011

Mark Bullard said:
I have always used front landing gear for airplanes over the years. Here is a picture of one our new Twins that we are building for Charleston.

View attachment 30522

Nice Mark! Interesting head buttons.

Here is what I built to go in my current twin for the throttles. It is mounted up against a short bulked to stiffen the whole assembly.

Mark Bullard · Sep 27, 2011

Piston1 said:
I use 2 Futaba S9650 Mini Servos (Digital) to control BVM needles. I stick the servos to the sides of the hull using double sided foam tape. I can adjust 5 numbers on the Boris meter, both needles tracking together. I use a 4ch reciever with a 4pk radio. My throttle system is similar to Bullard's. I think he copy me.

That a good one Jose. Copy me LOL

Bob Morton said:
Mark Bullard said:

I have always used front landing gear for airplanes over the years. Here is a picture of one our new Twins that we are building for Charleston.
View attachment 30522

Click to expand...

Nice looking work on the needles and the throttles and two receivers. Also one oiler for two shafts. Who makes those Clevis connectors on the throttle arms?

Those are standard Dubro 2/56 clevis. I make all of my pushrods out of 3/32 stainless rod threaded to 4-40 on the ends. I then tap out the 2-56 clevis to 4-40. On the big boats I use a 1/8 stainless rod threaded to 4-40 with Dubro 4-40 clevis for rudder only.

BUCKSHOT said:
Mark Bullard said:

I have always used front landing gear for airplanes over the years. Here is a picture of one our new Twins that we are building for Charleston.

View attachment 30522

Click to expand...

Nice Mark! Interesting head buttons.

Here is what I built to go in my current twin for the throttles. It is mounted up against a short bulked to stiffen the whole assembly.

Looks good Buckshot. The main thing is to make sure there is no binding and free movement. I also like to set my radio up with everything set at zero or in the middle. This allows me to jump from transmitter to transmitter without a lot of setup. I guess this is old school from the old days of not having all the bells and knobs in the radio.

Will Gallagher · Sep 27, 2011

Don't overlook the Throttle Servo. Twice the load and vibration, and I would bet that you throttle a twin more during a heat then a single..... Use a high quality / high torque servo...

Don Ferrette · Sep 27, 2011

Will Gallagher said:
Don't overlook the Throttle Servo. Twice the load and vibration, and I would bet that you throttle a twin more during a heat then a single..... Use a high quality / high torque servo...

Agreed. I prefer a Futaba 9405 high torque servo on the in radio box pedestal mounted bellcrank set up. B)

Mike Larson · Sep 27, 2011

Don, thats almost surgical.... nice work.... Steve... call your kid anyway..... take care, man.. Mike

Scott Schneider · Sep 28, 2011

Could not resist ... Not all twins are alki/nitro or 2 engines ... zoom zoom :lol:

Rigged · Sep 28, 2011

that aint a multi-engine hydro...thats just a multi-cylinder single

Don...where do you get those pushrod seals?

Tom Foley · Sep 29, 2011

Mark Bullard said:
I have always used front landing gear for airplanes over the years. Here is a picture of one our new Twins that we are building for Charleston.

View attachment 30522

Very nice ,all you guys do nice work . See you in a few days .

questions for those who have built twins

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