Thanks for the advice, very informative.
First piece of advice - protection circuitry is required between the Arduino signals and the H-bridge (even a 2k2 resistor in each signal line might be enough).
I can understand how a resistor would limit the current flowing in the circuit, but wouldn't that also waste alot of energy - energy that i'm trying to use to drive the motors?
Edit to add- No it wouldn't, because the resistors would be in the logic lines and not in the loop that drives the motors!!
Second piece - switch the MOSFETs fast, something like a MIC4422 buffer is a good idea to drive that gate capacitance. It can drive upto 9A which is plenty and it takes logic level inputs. Certainly something more like amps than milliamps is necessary or your MOSFETs will spend lots of time in the linear region and overheat/burn. You need lots of ceramic decoupling close to the gate-driver to do this successfully, at least ten times the combined gate capacitance.
Yeah I found out a bit about this later, the technician i spoke to recommended something similar ( due to current output ) so I'm trying to source on at the moment. Although the chip you suggested does look ideal - but is it available to buy?
Thirdly have suitable delays (hardware or software) so that it is impossible to have both the top and bottom MOSFETs on simultaneously. This situation is called 'shoot through' and causes all sorts of chaos. If you switch in 250ns or so the delay only needs to be a few hundred ns.
Hmm, I think I understand what you are saying. Basically, whenever I want to utilize the other two FET's, make sure I leave suitable time between turning two of them off, allow all current to leave the circuit, before turning the other 2 on? I don't think we're going to be doing running the motors using PWM so the only chance that 'shoot through' will occur is when changing directions, I presume.
There are H-bridge driver chips that do all the work for you BTW, like the HIP4081, and they let you use all n-channel MOSFETs.
You should also be aware of the Open Source Motor Controller project Robot Power OSMC Project Info
Yeah, ideally I'd like a solution I could just buy - but they cost too much. We're looking for 6, so even at a tenner each that's still £60 + delivery - double the price of making 6 of my own...
Again, thanks for the feedback.