Posts: 20
Joined: 1/13/2005 From: gold coast, AUSTRALIA Status: offline
I through this rough little model together to test my theory on a tandem fixed prop heli with no cyclic or collective.
It simply tilts the motors sideways for roll and yaw --- throttle and elevator are mixed to both motors for the pitch and climb, and so far its working good enough for indoors or very light winds. Needs 2 external mixers, 2 / 3 gyros, and 2 servos.
To improve stability I need to further test : weight, height of C of G, gyros, crossmix settings, motor tilt positions etc.
If anyone is interested I have schematics, specs, videos etc.
Posts: 2284
Joined: 9/5/2002 From: Wadsworth, OH, USA Status: offline
Must have more info! Yes, video, specs, more pics. Details on the mechanical setup.
What motors? Cell count? Where did you get the counter rotating props, and what diameter/pitch are they?
How sensative is this to changes in motor tilting? I played around with a 3 rotor thingie, and I could not make small enough changes to motor tilt to have it be controllable.
Posts: 20
Joined: 1/13/2005 From: gold coast, AUSTRALIA Status: offline
For these schematics, no transmitter programming is required, however exponential may be of some benefit - to test slowly introduce it on roll, pitch and yaw, for your heli set up, one at a time and gradually increase it.
Throttle curve is very good as it dampens the hover response as it has no collective.
I used the gyro gains on Aux 1, 2, 3 to adjust the roll, pitch and yaw, from my TX.
Elevator travel adjust is only 5% up and down to vary the 2 ESC controllers, so motors will only vary 10% from each other at maximum pitch control.
Aileron travel adjust is set at 10% left and 13% right if the front prop turns clockwise. This aileron travel relates to about 12mm at the prop tip from center position to full right stick.
Rudder travel adjust is about 60% left and 52%right which relates to about 25mm travel at the prop tip, from center position to full right stick.
Yaw or rudder - the props are tilted opposite each other slightly as it hovers. ???? Someone will explain this gyroscopic progression conundrum I am sure. The rear prop is tilting to the right and front prop to the left as it hovers. At the prop tips they are about 12mm opposed to each other.
Set up the mixers as a standard vtail mix equal to each other for both mixers.
Ok I need help on clear instructions (I stuggle with this stuff) how to post my video or a link to it (ASF format and WMV format) and where to put it.
I will delete these links below if they are useless.
Posts: 20
Joined: 1/13/2005 From: gold coast, AUSTRALIA Status: offline
I am using 2 @ AXI 2212/26 with a pair of counter rotating props 10 x 4.5 props (from toddsmodels.com) Polyquest 11.1v LiPO 2600 ma 12-16c or lighter 2100ma 20c rated.
Weight flying is 750-770 grams approx.
I use the Vee-tail Omni mixers but any mixer set up to have equal mix on both chanels and the reversing function is fine.
2 Servos - any light <27grams fast servo with 4kg torque
Mechanical - the tilting pivot point of the motors, is to line up with the top of the motor. Servo output arm is 13mm long and motor pivot mount or arm is 22mm and connect them rigid with NO slop - as any helicopter it must be precise or it won't be stable to hover. (very accurate tolerances in the pivot and links is a must)
Gyros - ok here's the catch and I may be wrong but I believe the CSM SL560 mini is the go but is mainly required on roll but I think a lesser gyro will work for yaw as I flew it without a yaw gyro but its hard. Pitch may work with a cheap gyro I don’t Know. TESTING GYROS - YAW - when I swing the heli around in yaw the props at their tips are opposed tilting to each other about 50mm ROLL - when I roll the model continuous the prop tips move up or down about 12mm off center. When test hovering too high gain and it wobbles terrible the ...crash - too low a gain and it just falls to one side....crash PITCH - When the throttle is just not quite starting the motors any light pitch movement will start one or the other motor depending which way you pitch it. Holding the model at hovering throttle speed (safety glasses on now gentlemen) you will notice the distinct force against you if you try and pitch it will rev up the lower motor and the model feels steady. (I use very old heavy Arcamax gyros as they react like a partial heading hold characteristic - its not a feature on it)
I flew it more outdoors today in light wind, and it is stable enough for forward flight up to say 8 - 10 kmh or a jogging pace I guess. Faster forward than that, and it gets tricky to maintain with my current setup. Moderate forward speed achieved circles, figure eight’s, pirouettes, and good climb and descend response. It does develop a wobble if you dont smooth your stick movements - avoid 3D thats for sure !!!! Kingsley
< Message edited by vtolman -- 5/27/2006 7:31:01 AM >
Posts: 35
Joined: 5/30/2006 From: Shanghai, CHINA Status: offline
I don't know if you have given up on the Osprey but this is interesting also. Have you tried arranging the "front" motor to tilt fore and aft with the rear motor tilting left and right? Nash
Posts: 35
Joined: 5/30/2006 From: Shanghai, CHINA Status: offline
Vtolman, Sorry, I am a heli novice and I usually try to keep from rolling. I've seen the 47 fly and they don't usually roll that either. Thanks for the photo. I am working on something similiar.
Posts: 35
Joined: 5/30/2006 From: Shanghai, CHINA Status: offline
I would like to know which is more important, the gyro or the external mixers? I see from your schematic that you mix the gyro with the transmitter control. I cannot do this with internal transmitter mixes. The Arcomax gyros are not available but I will try to pick up a couple of CSM SL560's and the Veetail mixers next month. I am still working on the VTOL and I see you are using the same electronics which seem to work well. You have made tremendous progress with your experiments.
Posts: 88
Joined: 10/17/2006 From: DFW,
TX, USA Status: offline
By not overlapping the rotors (props) you have avoided one of the biggest potential disasters that can occur with the real CH47 - if the rotors get out of synch they stricke each other and the Helo will self destruct.
As far as not having counter rotating rotors and having to tilt them oppossing sides - I may try this using two cordless drill motors they are reversible to one could be trult counter rotating. Battery pack will provide ballast for stability. Will need big three bladed paddle props though. Excellent execution of an alternative to collectives!
Please keep us posted.
< Message edited by darowden -- 10/18/2006 6:42:11 PM >
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Chinook CH-47 / SeaKnight CH-46 electric heli - 
RE: Chinook CH-47 / SeaKnight CH-46 electric heli - 
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