| This is a project to save you a
lot of time and effort ! (edit:
well, I am not sure about the "time" factor !). This robotic lawnmower automatically and quietely mows the lawn for you. - The lawnmower stays within a RF perimeter loop that that defines the area to be mowed and follows zig-zag mowing paths. - Accurate course is given by tilt-compensated 3D magnetometers, GPS gives an estimation of the position. - 2x120W geared motors provide differential steering, and 3x900W high efficient brushless motors spin the 9 cutting blades. - The system is powered by 2x20AH lead-acid batteries, that provide about 2.5hrs of mowing. - Main processor is an ATMega644P. |
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Some pictures of the development of the first prototype (click on the pictures):
 Modelling the lawnmower: It had to be lightweight, robust, efficient and adapted to my tooling and equipement. I have done all the CAD with Solidworks. |
 A very efficient cutting system to save energy: 3 cutting discs fitted with 3 thin razor blades. Very sharp, very efficient but requires a lawn without any rocks, branchs, etc... |
 Transmission: These are strong, geared electric motors from automatic gates. |
 All the tools I had were a hacksaw and a drill ! So I had to get and learn how to weld (MMA). And these were rather thin parts (1.5mm) ! |
 Frame is completed ! |
 Adding the cutting blades. These are made out of grinding discs. Cutting motors are 3x900W brushless motors. |
 I added some R/C gear in order to test the hardware before going further and adding the electronics. |
 Successful ! Cleanly cuts in high grass, with a good grip. |
 No grass jamming ! I was very afraid of that issue, and I couldn't really validate this at the design stage. |
 Now I added electronics: mainboard, motor controllers, sensors (accelerometers, magnetometers, RF loop as a perimeter wire). It's a bit messy... |
 Autonomous ! Its stays within the perimeter loop, and follows "intelligent" mowing paths, according to sensors data and mowing algorithms. |
 Very low noise, so the system can mow at anytime without disturbing the neighborhood. This is a long exposure picture. |
 Mowing our lawn, quietly and autonomously. |
 Some updates: stronger wheels, front bumper to avoid obstacles, accelerometers are placed on a vibration absorbing system, RF sensors cables are shielded. |
 I discovered that the center of gravity of the system was highy critical when mowing in very steep slopes. So I updated the battery position. |
 The borders are clean enough, thanks to the RF perimeter wire (inductive loop). |
 The RF loop goes around obstacles, like this flower pot. |
 A part of our lawn, autonomously mowed ! |
The first version is completed, and a totally new design is under progress !
Version 2 will feature:
- 4 wheels drive system with differential steering for a better grip control in very steep zones.
- Precise aluminium machined spinning disc to avoid vibrations (today a lot of mathematics therefore computation time is required to extract data from noise).
- Better analog filters on the RF sensors to avoid false perimeter detections.
- Lithium polymer batteries: -10Kg and +2hr of mowing time....
- Aluminum frame (lighter, no corrosion).
- Plastic cover to protect the mower from rain.