RC Mower
This build is a custom remote control lawn mower. Our yard is 0.44 acres which means a riding mower is a bit overkill but a push mower takes alot of time. I thought a remote controlled mower would fit right in. The plan began to take shape when I found a Ryobi 40 Volt push mower at Dirt Cheap for $60. Then my brother found a zero-turn riding mower that was junked. With those two pieces in place I had all of the necessary parts to begin cobbling.
This image shows the mower in its current state. It is functional but there are improvements I want to make.
This image shows the drive motors and control system.
Components list:
40 Volt Ryobi mower
Frame from a zero turn mower. This included the front caster wheels and the rear tires.
24 Volt motors from a Jazz mobility scooter. I purchased them from ebay.
2x 12 Volt sealed lead acid batteries from batterysharks.net
Sabretooth 2x32 motor controller from Dimension Engineering
Flysky FS-i6x remote control. This is typically used for RC planes.
Frame
The frame is from a zero-turn mower that went underwater in a flood. My brother took it out of the trash and used it for parts. I planned to make the RC Mower with a type of zero-turn action so I needed the front wheels to be casters. The two bars that extended back from the front wheel assembly made a good frame for mounting the Ryobi push mower.
This is the frame attached to a prototype housing for the rear wheels. The frame consists of the front wheel assembly and two pieces of metal tubing that extend to the back.
The front wheel assembly. It was helpful to have the casters already installed to a solid mounting bracket.
Motors
The motors are from a Pride Jazzy Elite Power Wheelchair. I bought the pair on ebay for $100. The part number is DRVMOTR1428 / 1429. I was able to find these motors for sale in a few places on the internet but I could not find a datasheet or CAD files.
The motor has a manual brake. I have already removed the brake handle in this image. There is also an electronic brake.
This is the wiring harness for the motor. These are temporary connections for testing. The red and blue are motor power. The smaller wires on the left are for the electronic brake. The brake is engaged by default. It is released by applying 24 Volts.
This is a control unit that I bought separately on ebay. I think it is compatible with the motors but I did not have the right joystick to test it. I ended up using only the mating connector for the motor harness. I was not able to find any information on the control signals that this unit required.
This is the mounting area of the motors. The mounting holes are designed for a specific fit in the mobility scooter. They are not designed for universal use. The shaft is a 5/8" diameter with a key. The shaft size and the key dimensions did not match with any standard wheel hub that I could find.
Wheels
I ordered some wheels that were compatible with the mobility scooter. They were about 13" diameter which is larger than the standard wheel. However, they did not provide enough ground clearance. I had the wheels from the zero-turn mower but I needed to find a way to mate them with the motor shaft. The video below shows the solution I found.
Control system
The brain of the RC mower is a Sabretooth 2x32 motor driver from Dimension Engineering. It is a versatile device that I recommend for any project like this one. Some of the most useful features of the Sabretooth were:
Settings can be set easily through a USB cable and free software from Dimension Engineering.
Multiple control signal sources - I used a joystick initially for testing. In the end I used the servo pulse mode which worked perfectly with my RC receiver.
Throttle mapping - allows you to define an exponential or linear mapping of the input signal. For example you can reduce the sensitivity around the center joystick position for more control at lower speeds.
Electric brake release - a 24Volt output that can be set to automatically release and engage a brake.
Battery protection - cuts off if battery voltage is out of range
Deadband - controls the delay between switching from forward to reverse direction or vice versa. This was crucial when I was using a joystick. This fixed a problem of the motor jerking violently when releasing the joystick to the center position.
An example screen from the DEScribe software. This screen shows the battery protection settings and the throttle mapping. There is a plethra of settings. I encourage you to read through the user manual. If there is a customization you want to make, there is probably a setting for it in this software.