H9 Twin Otter Saga

A saga?  It could have been. Not as bad as some of Brian J's sagas let me add.     Let's go to the beginning.  Scale Day is fast approaching so this year I thought, "How about my two Twin Otters?".  The Canadian version has flown a few times last year but the H9 Twin Otter that I built back in 2012 has not seen the light of day for over a year, maybe more.  OMG. That long?

A few months ago I stripped out the JR DSM2 radio system which with limited channels of 6 it would no longer do what I wanted.  Therefore whilst the weather outside was keeping me indoors I installed a Frsky 16 channel hub powered by two LiFe batteries and signals from an X8R receiver and a M+ receiver via SBUS.  Plus a Vario sensor for Altitude and VS.  Every servo or item as it's own channel therefore able to modify or sub-trim remotely via the Horus TX.
So after drawing up some plans for wiring I needed to make up two harnesses for left and right side of the aircraft.   one end would have standard jr plugs and most cables at the other end would terminate at multi-pin socket.  This meant that the wing wiring would terminate with a multi-plug making it simpler to connect up.  After some trial runs to determine the harnesses length, I then spent quite a few hours making these items up.  Pin crimping and soldering too.

With the harnesses and sockets installed time to plug it all in.  With a break in the weather a few days later, assembled the plane to test check.  Control surfaces, flaps, lighting, motor power.  Not good!  One motor will not power up.  Went through various checks. Motor failed?  Nope. The Hobbywing Platinum 60 Pro was not lighting up. (I have to say that is very rare for Hobbywing ESC's to fail)  Being a twin both ESCs ideally need to be from the same batch.  So I purchased from Motion RC a twin pack of 65 amp Mantis ESCs.  A few days later when they arrived via Fedex were quickly installed and all is well again.  Now waiting on an ideal day to test fly.  And waited and waited.

Eventually last Monday 17th April I loaded the Otter up for Cashmoor.  Let's just taxi up and down the runway first.  On the third run up the Otter suddenly turned hard left. Uh?  Starboard motor not running.  I had nothing at hand to test so the Otter went back into the car.

Next day I took a look at the starboard motor.  The ESC is pulsating slightly other than that nothing.  My programmer does not see it either.  Swapped in a spare ESC and the motor runs.  Damn!  Guess what?  Motion RC is out of stock of a replacement ESC.  I beginning to think Scale Day might be a No Go.

Checking my previous specs for current draw on the 3 blade 11x7 APC props I reckon I could get away with two 45 amp Mantis which Motion RC does have in stock but going fast.  Click click and they are mine.

Today Friday the ESCs turned up. Hooray!  While I am at it I think I will modify where the ESCs sit.  Rather than alongside the battery pack (Hangar 9's idea) I have placed them under the battery floor where they will get more airflow from prop wash, etc.  Friday afternoon after the rain shower I dived out quick , assembled the Otter and powered up.  Max wattage at WOT 600 watts, around 39 amps.  Total engine power = 1200 watts. Although it fairness once in flight the Twin Otter can stooge around at half throttle very easily.  Waiting on hopefully an ideal day BEFORE Scale Day to to test fly it.

Now let me see. I had a B25 bomber somewhere.

Glad to hear that the "event" with the motor didn't happen in flight Phil. I wondered whether it was just me, but odd happenings seem to follow me around, I'm  comforted by the fact that I don't seem to be alone. The business with twin electrics appears to have more problems than it should, do you really have to have two ESCs made on the same day by the same person to get a "matched" pair? I must admit that as a time served dyed in the wool mechanical engineer, I am distinctly uncomfortable  when in the presence of anything electronic. I don't trust anything that has no moving parts. Now to revert from "Dinosaur mode" to the present time, somewhere I read that there's a thing called a programming card for setting up ESCs. I wondered if it would be possible to use the card to be able to get the ESCs to play together?

I have loads of programming cards, although annoyingly there can be multiple versions for different versions of ESC due to how the ESC chip is programmed.  Another issue is the tolerance of the components, resistors, capacitors and the standard of the chip.  Is it an A grade or B?  You get what you pay for in most cases.

Most ESCs automatically detect the cell count of the battery and also the "Timing"  although in the latter case it may be  necessary to Time it manually depending on motor and number of "Poles".  So other than setting the throttle range it will work.  You may want to program "Brake" for the prop but you can do that using the throttle stick.  Usually menu 1.

Eflite Power 25 suggest 15 degrees timing and that is easily done with my programmer rather using the TX throttle stick and counting "beeps".  I tended to get lost after the first few beeps and have to start again.

Matched pair?  It is more that the ESCs were made from same batch of components lending the better chance they match.  Previously the Twin Otter RPMs were slightly out of synch by about 100 RPM from Idle but matched up above 1/5 throttle so you would never notice any ill effects. Well I didn't. 

Thanks for the comprehensive reply Phil, you mentioned the number of Poles, that might be the problem, always trouble when there's Poles involved, Neville Chamberlain knew all about that.