I just wanted to share the manual drive system that I created for my gasoline powered zero-turn lawn mower. My mower is the typical Ardupilot converted large zero-turn mower. It is a Hustler Raptor SD 54 inch mower, but this manual drive system could be implemented on any of the Ardupilot zero-turn mowers that have the mechanical drive handles. My goal was to use the mower in the automatic Ardupilot mode and then after the big areas are done, then drive the mower with the original drive handles to finish the more critical mowing. The system I have put together using commercial parts allows me, with a flip of a switch to change control of the servos over from Ardupilot control to the onboard mechanical drive system. I configured the multiplexer switch to recognize the flight controller as the (Master) and the manual drive system as the (secondary or slave system). In this configuration it always defaults to the flight controller as being in control, unless manual control is intentionally selected.
The main components of the mechanical drive system are the Hall Effect Rotation sensors on the drive handles, the 4 channel voltage to PWM servo card, and the 4 channel RC Servo Multiplexer switch. The Pololu 4-Channel RC Servo Multiplexer can be used to allow easy switching of servo control between two independent sources using a separate PWM channel as the input selector. In this case I multiplex between the Flight Controller PWM output and the manual servo controller, which allows switching between autonomous and manual control of a set of servos.
A key to this system is the robust little hall effect rotational sensors. Here is a picture of one of these small sensors assembled.
Rotary Hall Angle 0-90 Rotation Sensor 0-5V Rotary Hall Angle Non-contact 0-90 Degree Angular Torque Rotation Sensor 0-5V | eBay The hall effect rotation sensor is clamped with pinch clamp, allowing rotation for setup and positive clamping after installation. I found the thin phenolic adjusting plate supplied with the sensor to be inadequate in being sturdy enough and lacking adjustment range.
The throttle handle is also equipped with a hall effect sensor so the engine speed can be controlled by an onboard operator (normally the RC transmitter controls the engine throttle through the flight controller. The electrical systems are configured so that an onboard operator can also control the starting of the engine, mower blade PTO engagement, and have the safety interlocks back operating as they came from the factory (including the seat interlock).
The mower has a pretty amazing feel to it. With the gas dampeners still installed on the handles, it feels like a normal manual drive system.
Zero-Turn manual drive system parts list
Rotary Hall Angle 0-90 Rotation Sensor 0-5V Rotary Hall Angle Non-contact 0-90 Degree Angular Torque Rotation Sensor 0-5V | eBay
6mm Flange Coupling, Shaft Coupler QCQIANG 5PCS 6mm Flange Coupling, Motor Shaft Coupler, Flanged Shaft Mount, for DIY Handmade Model: Amazon.com: Industrial & Scientific
Servo controller card, pan tilt joystick control Amazon.com: servo controller DIY device pan tilt joystick control : Video Games
4-Channel RC Servo Multiplexer Amazon.com: 4-Channel RC Servo Multiplexer : Toys & Games
RC Servo Signal Reverser Amazon.com: 3Packs RC Servo Signal Reverser Rotation Inverter 3.6V - 24V 5A Steering Gear Reverser for JR Futaba Aircraft Airplane Steering Gear and Any Servos : Toys & Games
Servo Travel Tuner Amazon.com: Servo Travel Tuner : Toys & Games
Toggle Switch ON/ON DPDT 6 Pin 2 Pos TWTADE 3 Pcs Toggle Rocker Switches ON/ON 6 Pin 2 Position Latching DPDT Heavy Duty 16A 250VAC Spade Terminal Metal Bat Switch with Waterproof Boat Cap and 6.3mm Terminal Wires TEN-1321MZX-B202: Amazon.com: Industrial & Scientific
Julet 3 Pin Cable/Waterproof F Connector Julet-Connector 2,3,4,5,6Pin Cable Waterproof Connector For Ebike Display | eBay
Julet 3 Pin Cable/Waterproof M Connector Julet Small Connector 2/3/4/5/6 Pin Cable Waterproof Connector For Ebike Display | eBay
DC 12V To 7.5V Power Step Down Supply DC 12V To 5V 3.3V 3.7V 4.2V 6V 7.5V 9V Power Step Down Supply Converter For Car# | eBay
Throttle Cable Compatible with Hustler Amazon.com : GardenP+ 601096 Throttle Cable Compatible with Hustler Raptor SD and SDX Years 2019 and Prior, Lawn Mower Drive Control Cable, Replaces OEM 601096 : Patio, Lawn & Garden
5mm Female RH Metric Threaded Rod End Female Right /Left Hand Thread Rod End Joint Bearing Metric M4 - M30 All Sizes | eBay
M5 A2 Stainless Steel Fully Threaded Rod M2 to M20 A2 Stainless Steel Fully Threaded Rod Bar Studding, Length 150mm-500mm | eBay
Here is a link to a KiCad schematic of the overall system that I drew up. It was actually my first KiCad schematic and it took a little learning, but it was well worth the effort. Since then, I have done other schematics and I am glad I took the time to learn the application (at least at an elementary level). The schematic of the drive system is a PDF and is drawn to a fairly large scale. It will require downloading and zooming in to see the details. I printed out my work copy on a large format printer. KiCad Mower manual drive system schematic_121424_NB.pdf - Google Drive
Here are links to all the documentation I could find on the 4 channel servo controller and the 4-Channel RC Servo Multiplexer.
DHMCU Servo controller Documentation DHMCU Servo controllerl Documentation.pdf - Google Drive
Pololu RC Switch User’s Guide Pololu RC Switch User’s Guide2.pdf - Google Drive
I’ll also be happy to share details of my machined mechanical parts after I get them sketched up, although they may differ from mower to mower because each mower is a bit different.
I also learned a lot about setting this system up, which I will also be happy to share.