Dangaras

I have built a P38 and I have an issue with managing the RPM sync of both motors. I am using a DX7/AR7000 combination. Initially I ran both ESCs off a Y-cable connected to the throttle channel.

I noticed an rpm difference where left was higher than right. With Master Airscrew 3-blade 8x7 props I notice a significant pull to the right on takeoff and during flight. The left ESC is the one where the BEC is disconnected and it starts up the motor before the right motor when the throttle is advanced from zero.

I am also running the right motor clockwise (when viewed from the front) basically counter rotation.

Now I know there is a way to slave one of the other unused channels to the throttle, I have tried /aux1 (flaps) and I am unable to get the DX7 settings correct.

Anyone able to provide pointers on this?

codimasta

My Feedback: (89)

[8D] Have you tried to swap the ESC (Right to Left, & Left to Right)..see it the problem follow the ESC.
Have you programmed the ESC ...Transmitter throttle High....turn on the Receiver...you will get a few blips..motor should not start...then move the Throttle to Low..a few blips.
This will calibrate the ESC's... recheck the speed of the motors..should be the same.
Hope this helps

Dangaras

I had the entire setup balanced back when I first flew with 2-blade props & both motors rotated counter clockwise, did the ESC programming thing before hand. However, with that said, you never know, there could have been an entry & exit to the programming mode of one of the ESCs that changed the setup, I doubt it though.

I did finally mange to get the DX7 Mix 5 setup to use Throttle->Flap1, with 100% on the high and 0% on the low & -85 on the offset. I now have the primary Esc starting the motor after 2 or 3 clicks of the throttle & the slaved ESC will start it's motor 1 click after that and runs lower RPMs on the way up. The RPMs are low on the slave until we get to around 300 RPM we then stay close until 650 RPM at which point I am well past take off anyway. I have my starboard motor counter rotating now with a Master Airscrew 3-blade pusher prop.

I rotate around 3/4 throttle. I don't drop the throttle below 1/3 at any time while flying, usually just as I am touching down will I get near 1/3 and then as I touch I chop the throttle.

I do have a problem with the counter rotating starboard motor (primary ESC/Motor) stalling at 500 RPM, and that is bad as I am just getting up to speed. This happens if I advance the throttles slowly, which forces me to advance quickly. I have to pay very close attention to the roll out and manage the front wheel until the rudders can bite. I f I were to lose the right engine on take off, I don't think I will have a happy day.

I am going to try another motor and another ESC, I kept a spare set expecting something like this to occur. I always hope for the best and plan for the worst. What I need to do is set the motor back to counter clockwise rotation to test if it still stalls.

I wrote a detailed list of thoughts for anyone trying to setup twins using ESCs at the following thread:

http://www.rcuniverse.com/forum/m_88...tm.htm#8995180

Thanks for reminding me to check the ESC programming.