The problem that I see is that with the weight transfer, up and forward, the rear of the wheelchair would want to raise and possibly tip over. Adding a battery, and an electrical mechanism would add some weight to the rear to make it more stable while making it easier to operate the lifting mechanism, but then would make it harder to move around the rest of the time, but so would the extra weight added by reinforcing the frame.
My thought is that if you could use their body weight to assist them, instead of trying to lift all their weight. Perhaps instead of moving the foot pads to the side when exiting the chair, you could use some cables and pulleys to transmit that force to under their armpits, assisting them instead of lifting them. I would think it possible to maybe give them a third of their body weight in lifting assistance, for a foot or so, since the foot pads are only about 4 inches off the ground, but then when they went to step off the pads, they would want to pop up, some type of locking mechanism could prevent that. Once I find my camera, i'll draw something and post it.
The easiest way to lift them would be with a simple lever, bent at around 90 deg(cantilever?) and rotating on a center pivot point. A threadscrew attached to the lower point, the chair seat attached to the upper. When the threadscrew was turned it would raise the seat and move it forward at the same time, you could either use arm strength to turn the threadscrew(you could even use a ballscrew to reduce friction making it easier, but that would increase cost quite a bit) or a battery powered electric motor. Either way I think you would want some type of outrigger on the front to stop the chair from wanting to tip forward, or to roll backwards.
I am off to find my camera to post some pictures.
