OH PLEASE!!!
Of course you should have a safety system in place especially with something with a spinning blade but you, me and the OP know that such a device would cause more harm then good (false readings, complicated implementation).
First off - this doesn't sound like the OP's going to use a deck mower, but rather an old-fashioned push mower (manual mower, no engine/motor) dragged behind.
Furthermore, it is better to have false readings than damaged property and/or bodily injury. A machine this size can and will cause harm if it is not properly controlled. A safety system can and should be built as part of the initial design.
You can be cavalier about it, but I consider safety in such larger-scale robots (and this is a larger scale robot) to be paramount. It's nothing like an SRL robot, surely, but you should have at the very minimum some kind of manual on-board cutout switch, as well as a remote-controlled one. Such as system is cheap and easy insurance.
Quote:
(because with relays you can't really control the speed of the motor);This is false.
I have PWM'd relays to control motor speed.
It works ok but its noisy and the speed control is alittle rough.
You might be able to get away with that on small motors, but I think at the size motors being discussed (power chair motors), you would quickly wear out (or weld the contacts - but we have a safety system in place for this, right?) the relays in short order due to arcing.
FWIW Sending video over wireless with arduino sounds challenging.
I would hope the OP isn't planning on having a first-person view camera on this thing; line-of-sight operation should be the plan, with constant monitoring while in operation, in case of any possible hazard (the proverbial child or small dog) that gets in the way - then the "all-stop" system can be activated.
This isn't paranoia - this is proper system design for a device of this nature. Take all the shortcuts you want, of course; I am only making recommendations based on "best practice" for safety. Note that in the overall cost and complexity of the system, trying to save a nickel (and time) by not implementing such a backup seems foolhardy to me, at best. YMMV.
