Thursday, October 31, 2013

Remote Control Lawn Mower

Its hard to find people that actually WANT to mow their lawn.  I am no different. I don't enjoy it. It takes me away from fiddling with electronics!  My solution to the problem was to build a remote control lawn mower.  It took a few months from start to finish, but its been a robust tool for our family.  A video first, then the rest of this blog post documents all the major components and peels back the layers of the onion on how it works.

I started with a standard 6HP push mower.  I removed the front drive wheels and replaced them with mini-bike tires that had a built in gear tooth sprocket.  I replaced the back wheels with large caster wheels so they could spin freely in 360 degrees.  I used motors and gear boxes from National Power Chair -- the folks that sell components for motorized wheel chairs and combat robots.  The motors are large DC 12-24V motors.  

I use a Futaba remote control transmitter and receiver to send signals from me to the lawn mower. 
You can see me holding it in the video.  To drive the motors, I use a Vantec speed controller.  It takes the RC signals and converts them to PWM DC forward and reverse controls to each motor.  The two motors drive the two front wheels independently, so the driving experience is kind of like driving a tank with skid steering. 
The power system is a little complicated.  In order to have enough energy to drive the lawn mower long enough to mow the lawn, you need multiple large 12V lead acid batteries, but there is no room for them, and the weight would kill the mower's speed, so I decided to copy what they do in automobiles.  I bought the cheapest alternator I could from the local auto parts store.  One for a 1979 Ford Pinto!  I added a pulley wheel to the mower's gas engine output shaft, and used a rubber belt to drive the alternator shaft.  This allowed me to use a single, smaller battery in the system. 
I used a 12V lead acid battery designed for motorcycles, the size was a good fit right in the front where the weight helps with the traction.
It took me a few months to perfect the system, but once it was working good, and I had some practice driving, I was able to mow the lawn consistently in about 45 minutes.  I used the mower for a few years, but eventually starting paying the neighbor kids to do it for me.
Here is a video from a few years ago showing how it works.  Its pretty quick and spins around quickly on the cement where there is no grass slowing it down!