For the electric side of this build, I am working on the controller and battery layout first.
With most outrunner RC motor friction drive setups, an RC style speed controller is also used. With this build I am using a traditional ebike controller so I can utilize the inbuilt current limiting features plus various other features that are a standard part of an ebike controller.
The controller is KU65 and I have selected this controller because they are super cheap and also there is a great blog on how to modify these controllers.
http://www.avdweb.nl/solar-bike/electronics/ku63-motor-controller.html
However there are some major limitations when using an ebike controller with an RC motor, the main one being the maximum electrical RPM the ebike controller can output. With this in mind, I needed to match my pack voltage and motor kV to the maximum electrical RPM that the controller could stably supply. Using 200kV outrunner, I found that the output voltage of a 7S pack 18650 under load was a good fit.
Now that I had settled on a pack voltage, I now needed to make some modifications to the controller so that the low voltage cut out suited the pack chemistry. Getting the cutout voltage correct was important step on this build due to the pack being quite small and compact with no BMS fitted. Subsequently I am relying on the controller low voltage cutout to protect the battery.
A 5K pot has been installed on the throttle circuit to adjust the controller output. The pot will be mounted under the seat out of view. Drive activation is via the controller's brake input. this will be connected to the normally closed side of a microswitch which will inturn open circuit when the motor is pivoted against the tire.
Being a sensorless controller, they can have some issues starting an outrunner RC motor. When this happens, it puts a lot of strain on the controller and can blow the controller if the motor isn't given a helping flick to get it started. With this in mind, this design will pull the motor onto the tire first so it is already spinning before the microswitch activates the drive through the brake circuit.
I am still in two minds on where I am going to mount the controller and batteries on this bike. The 2 choices are in a small seat post bag or inside a custom water bottle or water bottles. I really like the water bottle path but fitting an ebike controller into a water battle doesn't leave much room for batteries. Best i could do is a 7S 2P setup which would be 130 Whrs.
Option 2 is mounting everything inside a small seatpost bag. This simplifies the build quite a bit and allows me to carry a 7S3P pack which provides about 200 Whrs. The frame has an opening under the bottom bracket to get my motor cables through together with the microswitch connection. I would however need to drill a hole in the carbon seat tube to run the wires through. I can live with that as this hole wouldn't affect the strength or structure of the bike, only the seatpost which could easily be replaced if needed.
Although the seatpost bag solution is the best practically, i am not sure if I will be happy with the aesthetics of this setup. The plan is to give this a go first and see how I go for range. If I find I am not using all the battery, i will consider going back to the water bottle solution.
Progress photos as the project stands.