Razor Scream Machine

Please tell me if I would be able to put a motor on these
and if so, how would I do and what I need to buy please give informative answers

Bike: http://ecx.images-amazon.com/images/I/51 ...

Trike: http://www.rc-trucks.org/razor-scream-ma ...
(Please note that I have better wheels on the machine crying now (rubber wheel))

Friction drive is the easiest, but there are many ways.
Check this out. http://cyclehappy.com/bicycle_engine_kit ...