Cheap and easy speed controllers

Right, PICAXE i bought £50 worth of this stuff a while ago, ive not actually started messing with it yet, ill warn you now, the manual for it (which you have to print off yourself) is 400 or so pages!!

Basically its programable ics, although you dont have to remove the ic to program it, all you need to do is put a stereo jack socket, a slider switch (instead of a little jumper) and a couple of resistors on every circuit board you make. Then to program it you use a serial lead (that jas a stereo minijack on the other end) link it to your computer and the write the camands.

Im not sure if its good enough for larger robotics use, (its certanly ok for antweight type robots)

One day ill get to have a mess with it LOL.

If your going to learn about it i suggest you start off with the 8 pin picaxe ic and then move onto the 18 pin.

Start with the PicAXE 08M. The 08M has a single analog input (you use this to put you reciever signal in) and has a single PWM output (you use this to drive your fets through either a HIP chip or a Darlington Transistor bank). The 08M inly a smidgeon dearer, but is great to use. Im currently playing with the 08Ms to make a PWM speed controllers with 70amp relay reverse.

Im also using the 08M chips, only £1.50 and have an 8 bit pulsin giving a linear range of about 90 steps for my Hitec Tx, and the PWM out is OK. The debug command is useful and the serial cable is only £2.50. The software is free.
Im trying to avoid using the HIP4081 to keep cost down. You can use an cheap motor driver chip (L293) or a UNL2000 series darlodriver. Dont connect your mosfet straight to the PIC like I did!

Rob, to make it cheap you could actually connect the pic output directly to a mosfet (through a current limiting resistor) for the low side for controlling the direction and use a bootstrapped high side driver IC for the high side mosfets in PWM mode. Drawback is you can only go to about 90% PWM but you could use protected mosfets for the low side for current & temperature protection as an option without changing the circuit.

As you already know Im designing a feather speed controler as well but it wont be cheap.

Well thats spooky, http://www.technobots.co.uk>Technobots

that is really weired i mention it and then it appers hmmmmmmm....gold plated toilet :P

while searching i came across these http://www.robot-electronics.co.uk/shop/Motor_Controllers2008.htmhttp://www.robot-electronics.co.uk/s...ollers2008.htm are they any good for a FW ?and is that a good price to pay for it? has anyone else used them before?

Those are the ones technobots has started selling, so youll probably want to buy from http://www.technobots.co.ukwww.technobots.co.uk

That price doesnt include heat sink I dont think and a 2 Channel heatsinked version will set you back at least 70 pounds probably. Itll probably do about 15A with heatsinking so youll want to keep away from any bigger motors. Current limiting at 20A on the single h-bridge controller is probably too low for most decent featherweight motors.

Ewan, I would have thought that 20A @ 24V i.e 500W per motor should be adequate for most feathers. I have yet to make a heatsink for the 2-channel version but I expect it to be suitable for the 8 motor / 8 wheel drive Zeobot but as you say, keep it away from larger motors.

Ive just read one of the entries into the featherweight database (Kang) and it says it uses drill triggers to control the speed of the motors. I thought about using these as speed controllers but I wasnt sure how to connect both the speed and direction switches. Assuming that the drill controls have the trigger for speed and the slide switch for either forwards or backwards, whats the best way to connect them up so as to have both speed and direction control? Is there a way to modify them so that you dont have to slide the switch across (which would be murder to remember in the heat of a battle) or do you have to connect them both upto servos or something? I know they arent the most practical speed controllers around but it would be handy to have them fully operating.

Many regards,
Jamie :)