Installed motor test run!

With a good friend, we did a few test runs of the installed motor & power system.  

Here is a very short run just to show you it spins.

Firstly, it is quite scary sitting that close to a spinning motor putting out 4.5kW.  Wearing a helmet helps, but it's just a LOT of power super close to your body.  Neither of us ran beyond 100A and we both kept our feet on the ground out of the plane of the propeller ... just in case.

At about 60-70A, there is a slight structural resonance in the nose tube assembly.  It's not present on either side of that RPM, so we just tried to avoid that.  Balancing the propeller would help.  Tightening things up more should help too.  Most of the play appears to be in the nose down tube connections, at either end, so I probably will start with getting the proper length bolts everywhere and snugging things up.  Replacing the nose tube with an aero strut would probably make a difference.

The throttle in the end of the control stick did not work for some reason.  It moves a servo just fine, but did not move the ESC.  I suspect the ESC calibration needs to be done using the same throttle driver.  For this test, I used a different servo driver that was the one used to set up the ESC in the first place.

The batteries and the ESC and the wires all were quite cool to the touch, even after a 60s run.  Rough math suggests about 10min run time at 4.5kW.

I did try balancing on the wheel to see if the thrust would roll Goat forward.  The ground is pretty soggy and the tire was partly flat, so there was no forward motion.  Howe er, it was a definite feeling of being pulled nose-down.  This is not surprising given the high thrust-line and low pitch rotation axis (here: the wheel axle), but it was nice to feel thrust as an external force, if that makes sense.

There is a fair amount of air movement along the structure, most visible in some vibration of the inboard edge of the flaps.  There was a little drumming of the lower wing skin covering.  The rudder tended to center up with the airflow, but the elevator had enough bungee that it mostly sat stationary.  Nothing was scary.

Also, a weight check with a bathroom scale came in at 158lb including motor & batteries.  The motor itself is 5.6lb, so I am clearly below the Part 103 glider 155lb weight limit without the power system.  Adding propulsion essentially ups the legal weight limit to 255lb, so I'm also clearly below that.  Super.

 

What improvements are on the short list?

• Fix the throttle knob --- having throttle in the stick would be much nicer
  
• Improve the throttle wiring --- need a second look at the throttle wiring & battery location
• Tachometer --- having RPM would be really nice
• Move the wattmeter display? --- it was awkward looking down to the right for power readings
• Larger propeller --- the 30x10 just looks teensy.  May have to couple this with re-winding the motor for a lower KV, which is a much larger project
  

I'm also getting some hangar rash in the covering from strut or jury strut bolts poking into the covering.  Some of these looked avoidable.

Gap seal for the control surfaces is a necessary next step.  I really don't want to fly without gap seal.

Strut fairings is on the semi-short list.  It will fly fine without them, but I know the drag is unhelpful.

A trim color along the leading edge would be sweet too :-) 

Here's the battery tray installed.  It works.

Here is how the motor tube mounts.  It's sturdy in itself, but the nose tube seems like what is vibrating.

More work toward a motor-Goat

A test assembly outdoors was necessary to get the thrust angle to match with what I picked for the starting visual.  I suspect that some thrust-line changes will be needed based on cruise attitude and the pitch coupling (noting the Romanian Goat said it took a lot of up elevator in this mount location), but for now I simply set it parallel with the bottom of the wing and match-drilled.

Mounting the battery is the next major task.  With 25ft of 8AWG wire tripled over for an ~8ft extension, I was able to reach from the motor, down the nose tube, back along the nose side rail, to beside the seat.  Like most others, I'll mount the battery beside the seat.  Instead of mounting to the struts, I decided to extend the seat tubes to make a little shelf of sorts. It did take removing the seat and destroying a couple torque seal marks to get it all, but that was a fun afternoon.

Seat off!  You can also see the final structural mounting for the motor and see the wiring runs.

New little shelf.  In retrospect, I should have put it on the left side so my right hand can stay on the stick, but maybe next version.

And here's the first mock-up of the battery tray.  The ESC is going here also.

Let's talk a bit about the battery tray.  I watched several videos about the e-help and related DIY systems (this one was particularly useful) to decide a rough plan was to make a u-shaped tray with Velcro loops to secure the batteries.  The other major decision was to place the ESC directly on the battery tray.  The battery to ESC leads apparently need to be short due to inductance issues, and let the three phase AC lines be the long runs (EMI and start-up routine are potential issues).  

I ended up making a small aluminum bracket to hold the ESC.  This was the first time I bent up a complicated sheet metal bracket, and it went pretty well.

 

Here's how the ESC is held in its bracket.  It will be riveted (or bolted) to the bottom of the battery tray.  There is lots of metal surface area to help with heat transfer.

The battery tray itself was fabricated in a similar manner, bent from sheet metal.  The cylindrical bosses are handles.

And here are the batteries and a watt-meter (this model) mounted in the tray.  I still need to put slots for the Velcro straps to hold the batteries in place.  There will also be a couple switches in the panel for ESC arming and the throttle power.

The last major component to solve is/was the throttle actuator.  For this ESC, I need a PWM signal going from 1.0 to 2.0ms and bringing its own power (the ESC is opto-isolated).  The awkward part to me was that no small servo driver had a convenient remote-mount potentiometer.  I ended up buying a $7 servo driver, de-soldering the rotary potentiometer, and remote-mounting it in a custom 3D printed mount that will fit in the end of the control stick.  I stuffed the servo driver inside the same 3D printed mount, so I only need to run it power and get back the PWM signal.

Here's the final servo driver and remote potentiometer arrangement.

The bracket fits inside the control stick tube (ignore the holes --- same size tube from the scrap bin!).

That's all for now.  I'm still working on tidying up the wiring for the panel and then will need another beautiful spring day for a test re-assembly and run in the back yard.  Stand by for more...