there is a couple of threads regarding decoding the ppm stream from a RC transmitter or reciever. Some RC systems have a DSC(direct servo control) that is mearly the ppm stream sent via a cable to the reciever from the transmitter. but this function is not available on all RC systems.
I came over this simple circuit at the arduino forum: http://myweb.tiscali.co.uk/norcimradioc ... Radio6.htm
this circuit could be a really cheap solution if you have a reciever or transmitter with ppm output, and you dont really need that advanced features on controlling.
i tought id buy the components and try it out on my el-cheapo hobbyking transmitter/reciever(HK-t6a) both the transmitter and reciever is said to have a ppm output. i havent confirmed it yet, but i'll get a scope and check the pins, and see how long the framespace on the system is.
a nice thing about the hk-t6a(except for its cheap price) is that it has mixing capabilites(you need the usb cable also) so you could easy make a 3-thruster rov, with using delta-ving mixing on two of the channels to control the forward/back and turn function.
with a 6 channel reciever you could then drive 3 esc for movement, 2 servoes for pan and tilt. and a brushed-esc for full brightness controll on LED's
simple PPM to servo pwm decoder
Re: simple PPM to servo pwm decoder
here is a more advanced solution that also can be used: https://bitbucket.org/fpvkiwi/channel-wizard/wiki/Home