An alternative means of driving the body from the brushless motor could be friction. I have no idea where to find the video but I remember seeing an American FBS (one of the light weight classes, but not as high as feather) that spun its shell up using two brushless motors with small rubber wheels on them that made contact with the underside of the top (it was a hockey puck style FBS rather than cone-shaped, Typhoons etc). The spin-up time was minimal and it performed like the clappers. With this method it's a bit more lightweight and perhaps easier to fit in a small robot than using a belt and pulleys. Plus you've got the added bonus of it acting like a clutch to allow a little slippage if you hit an immovable object.