Dual Motor Propellor Thrust Steering??

Dick Curtis · Jul 01, 2002, 07:55 PM

I am involved in a scale model flying boat project . The model has a large wingspan and two Astro 90's. The plane hasn't a water rudder. Any ideas on how to set up to steer during takeoff
by varying the motor thrust.? I'm using an ESC on each motor but from a single transmitter it's not clear what set up would wor,k if any.
Thanks
...Dick

Andy W · Jul 01, 2002, 08:12 PM

That would work, although I expect the turn rate would be low. It would be fairly easy to program with an appropriate transmitter. For a model of this size, however, I have to wonder why you don't add a water rudder?
..a

DaveW · Jul 01, 2002, 10:36 PM

You could probably do it with an advanced computer radio using seperate channels for each esc and mixing in rudder inputs with the throttle input to one of the motors.

Wouldn't a water rudder be easier??

My experience with flying boats (4) is that a water rudder is mandatory to move crosswind.

But mine were single engined.

If appearance is the problem, make it out of transparent Polycarbonate ( Lexan)

Good luck, sounds like a monster model!!

Dave

Kevin Murray · Jul 02, 2002, 12:05 AM

There is a section on exactly how to do this in the book "Getting The Most Out of Futaba's 8-Channel Radio Control Systems" by Don Edberg.
It uses 3 programable mixers and 3 sources of input from you.

Rudder stick input
Throdel stick input
Ch 8 rotory knob to syncronise the rpm on the 2 props (not nessicary on an e-plane ? )

Jurgen Heilig · Jul 02, 2002, 12:56 AM

You can use the same Set-up I use for my Twin-Jet.

Jürgen

Differential Thrust Set-up (requires three free mixers):

Set-up based on JR functions: Function 1 - Throttle (motor 1)
Function 2 - Aileron
Function 3 - Elevator
Function 4 - Rudder
Function 5 - Free (used for second motor)

Mix 1: Function 1 (Master - Throttle motor 1) to Function 5 (Slave - Throttle motor 2) + 100%
Mix 2: Function 4 (Master - Rudder) to Function 1 (Slave - Throttle motor 1) + 100%
Mix 3: Function 4 (Master - Rudder) to Function 5 (Slave - Throttle motor 2) - 100%

How does it work?

Mix 1 ensures that both motors react on throttle stick movements as if connected to a single ESC. Moving the rudder stick to the left will reduce the power of the left motor and increase the power of the right motor (provided it is not already running at full power).
Flying at full power and applying full rudder will reduce one motor to half throttle. Maximum effect is achieved at half throttle where full rudder will stop one motor and bring the other one to full power. While conventional rudder becomes more effective with increasing air speed, differential thrust is most effective at low speeds. Stall turns are most impressive and you can even spin an otherwise extremely stable model.

Larry Dudeck · Jul 02, 2002, 08:33 AM

I had my first differential turning experience yesterday.

My TwinStar tossed a prop during hand launch. Immediate lack of control, just a tight right hard turn. The 5 or 6 feet of launch altitude disappeared in about 1/2 second.

Hard hit, broke the aft wing hold down.

This was the first time I ever lost a Gunther prop. Usually I remove the rubber hubber, ream the prop and use an aluminum prop adapator. These were stock.

Back to the prop adaptors.

Dick Curtis · Jul 02, 2002, 03:44 PM

Thanks all for the computer radio programming ideas. The reason for no water rudder is that this is a scale WW1 twin biplane that will be flown for a museum interactive movie to be made and then hung in the museum. The original used the engines for taxi turning and we want the model as true to full size performance as possible. It is large -span of 5.4 meters.

Jul 01, 2002, 07:55 PM	#1
Dick Curtis Registered User Join Date: Mar 2002 Location: Santa Barbara, California, United States Posts: 97	Dual Motor Propellor Thrust Steering?? I am involved in a scale model flying boat project . The model has a large wingspan and two Astro 90's. The plane hasn't a water rudder. Any ideas on how to set up to steer during takeoff by varying the motor thrust.? I'm using an ESC on each motor but from a single transmitter it's not clear what set up would wor,k if any. Thanks ...Dick

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Jul 01, 2002, 08:12 PM	#2
Andy W That sickening crunch.. Join Date: Jun 1999 Location: Marietta, GA Posts: 39,796	That would work, although I expect the turn rate would be low. It would be fairly easy to program with an appropriate transmitter. For a model of this size, however, I have to wonder why you don't add a water rudder? ..a

Jul 01, 2002, 10:36 PM	#3
DaveW Registered User Join Date: Apr 2001 Location: Folsom,Ca,USA Posts: 993	You could probably do it with an advanced computer radio using seperate channels for each esc and mixing in rudder inputs with the throttle input to one of the motors. Wouldn't a water rudder be easier?? My experience with flying boats (4) is that a water rudder is mandatory to move crosswind. But mine were single engined. If appearance is the problem, make it out of transparent Polycarbonate ( Lexan) Good luck, sounds like a monster model!! Dave

Jul 02, 2002, 12:05 AM	#4
Kevin Murray Registered User Join Date: Dec 1999 Location: Greenville, NC, USA Posts: 8,760	There is a section on exactly how to do this in the book "Getting The Most Out of Futaba's 8-Channel Radio Control Systems" by Don Edberg. It uses 3 programable mixers and 3 sources of input from you. Rudder stick input Throdel stick input Ch 8 rotory knob to syncronise the rpm on the 2 props (not nessicary on an e-plane ? )

Jul 02, 2002, 12:56 AM	#5
Jurgen Heilig Registered User Join Date: Sep 2000 Location: 53859 Niederkassel, Germany Posts: 12,604	You can use the same Set-up I use for my Twin-Jet. Jürgen Differential Thrust Set-up (requires three free mixers): Set-up based on JR functions: Function 1 - Throttle (motor 1) Function 2 - Aileron Function 3 - Elevator Function 4 - Rudder Function 5 - Free (used for second motor) Mix 1: Function 1 (Master - Throttle motor 1) to Function 5 (Slave - Throttle motor 2) + 100% Mix 2: Function 4 (Master - Rudder) to Function 1 (Slave - Throttle motor 1) + 100% Mix 3: Function 4 (Master - Rudder) to Function 5 (Slave - Throttle motor 2) - 100% How does it work? Mix 1 ensures that both motors react on throttle stick movements as if connected to a single ESC. Moving the rudder stick to the left will reduce the power of the left motor and increase the power of the right motor (provided it is not already running at full power). Flying at full power and applying full rudder will reduce one motor to half throttle. Maximum effect is achieved at half throttle where full rudder will stop one motor and bring the other one to full power. While conventional rudder becomes more effective with increasing air speed, differential thrust is most effective at low speeds. Stall turns are most impressive and you can even spin an otherwise extremely stable model.

Jul 02, 2002, 08:33 AM	#6
Larry Dudeck Registered User Join Date: Sep 2000 Location: Williamsville, NY, USA Posts: 3,847	I had my first differential turning experience yesterday. My TwinStar tossed a prop during hand launch. Immediate lack of control, just a tight right hard turn. The 5 or 6 feet of launch altitude disappeared in about 1/2 second. Hard hit, broke the aft wing hold down. This was the first time I ever lost a Gunther prop. Usually I remove the rubber hubber, ream the prop and use an aluminum prop adapator. These were stock. Back to the prop adaptors.

Jul 02, 2002, 03:44 PM	#7
Dick Curtis Registered User Join Date: Mar 2002 Location: Santa Barbara, California, United States Posts: 97	Thanks all for the computer radio programming ideas. The reason for no water rudder is that this is a scale WW1 twin biplane that will be flown for a museum interactive movie to be made and then hung in the museum. The original used the engines for taxi turning and we want the model as true to full size performance as possible. It is large -span of 5.4 meters.