Large Model Association Forum

This will be a fairly short thread. I just thought it might be interesting to show the conversion of a 100cc CAP580 to electric. My son Sam got this plane for Christmas, off Josh who posts on here as well. I think that the plane was first owned by Rob Gardner - as it says "Pilot - Rob Gardner" on both sides .

We have a 20hp electric motor and a 300amp speed controller that can run on 15 cell LiPo batteries. This means it runs at 60volts. With a motor continuous rating of 250amps this gives 250 * 60 = 15kw (20hp).

We have just fitted the motor and new mounting, so I will put photos on tomorrow when I get my camera sorted out.


One thing that would be usefulis to hear peoples views on prop sizing. The reason I ask is that the electric motor might run faster than its petrol equivalent. At full whack this motor can turn at 9000rpm. As it is needing to replicate the performance of a 110cc motor it should give a pull of around 25kg.

Sam has been doing lots of reading online and has found a reference to not exceeding mach 0.91. What maximum prop tip speed would you suggest?

Cheers, Andy

Hi Andy
I'm looking forward to this
I'm useless with electronics, but I'd love to see the performance difference between the setup I had and electric

Cheers
Josh

Well here is progress so far....

On the bench.....


The 300amp speed controller.....


The first job was not easy, soldering 8mm bullet connectors on 8AWG wire. The wire is so thick that it requires a blow torch to get the heat heat in quickly enough, which of course burns the silicone outer. These were done using piece of potato with a hole in it, slid over the wire to protect the outer.....


Next job, to mount the esc in place. All of the 'inards' of the plane have been stripped out. There are no tanks, batteries or switches left in place - batteries and switches will be fitted later. The esc is put as close as possible to the fire wall, so as to minimise the length of the wires from the esc to the motorI have built a platform on which the esc sits. With velcrow on the under side of the esc and then straps round the top of the unit it is nicely held in place....


Note that much of the mounting is cut out to ensure lots of airflow to the underside. Here is the unit in place....

And here is the view from the front end..................


Now, having stripped off all the old motor mount parts I have this.....


With the cowl back on I measured that there is a need for a spacer of 68mm behind the electric motor I will be using such that it matches the original prop position. I have now built what has become a standard type of spacer for us when we convert i.c. to electric. Strong marine ply and B&Q aluminium angle epoxied and bolted in the corners....




And here is me holding the motor in place by hand , to try the fit....

Hi Andy
It's looking good
When I had it I had about 3.5 degrees right thrust and about 2.5degrees down thrust
Keep going
Josh

Cheers Josh,
I asked Sam what he wanted and he said straight. He seems to prefer the straighter set-up and finds it an easier start point for trimming to suit all orientations. He sometimes has a little down-thrust in so your suggetsion might be needed.
Andy

I have competed 'repair' of the cowl - by that I mean the filling in of all the holes that have been cut out to fit petrol engines.
Ready to glass...


Done....

In the above photo you can see a problem with using a large electric motor. The motor is a large diameter and too big for the cowl. I have kept the motor on the centre line of the plane and lifted the cowl slightly so that it is now off-set.

I have also finished the motor mounting now. Here it is all bolted up..


And then with those pesky hard to solder wires all soldered up as well...

Houston we have a problem. Plane is pretty mush finished now so we fired it all up for a test. The esc does not work .
We are now waiting for a replacement.

In the mean time we have been looking to choose the prop so we can get one ready. Here is our motor on test http://www.youtube.com/watch?v=fe9kyi5_JtM
With a 24x10 prop it gives 24kg thrust. That should be plenty

Hooray - our replacement esc arrived today, so we can get this finished now.

Andy,
I fried my fatboy 0n 12s at a little under 120 amps ,feedback from others reflects the problems with this esc??
what happened to your spacewalker project??
cheers Euan.

Euan Galloway wrote:Andy,
I fried my fatboy 0n 12s at a little under 120 amps ,feedback from others reflects the problems with this esc??
what happened to your spacewalker project??
cheers Euan.

Euan, Thanks for the feedback. I have not had any problems with any of the Turnigy esc's. I cant say the same for others though!
On my LMA Genesis the esc chucks out 6KW on 12 cell so is running at 120amps. Sam knife edges this plane continuously in a big circuit and we have had no isues with it. However, the key to not frying them is likely to be good cooling and we work hard to keep them cool. On the Genesis the esc hangs out front directly in the air flow. On this CAP580 (above) I have sealed all the holes in the cowl (except for the front) so that the air flow that comes in through the holes in the front (behind the prop) and can then only go into the fus through the large holes made in the front bulkhead, right in front of the esc. I will also be making exit air holes in the fus near the rear so that good flow is maintained. When I did this on another plane I have I found it worked really well and even on the ground I could could feel a good flow of air coming out of the exit holes.
Cheers, Andy