A robot lawnmower

Cut your grass while drinking a beer in a chair!

Version française

Cutting the grass can be boring...

You can buy a commercial robot... But you must spend about 3000 $ and install special cables..





This one works alone, your green must be surrounded with a, at least 10 cm high border. Then the robot will go everywhere, cutting the grass.

Video: robot lawnmower: a short movie



(Ctrl & + to increase text and picture size on IE)

How does it work?

A 8 mm plywood chassis is equipped with the cutting motor attached to an stainless steel 300 x 25 x 1.5 mm metal plate

There are 4 x 12 V gearbox motors (30 to 50 rpm), each one equipped with a children toy wheel. An internal 12V 4Ah Dryffit rechargeable battery power it. A front bumper (in wood and gray plastic) can move and actuate 2 switches: when robots meets an obstacle, it can avoid it.

Hard to program microprocessor? complex computer? No! just few relays: simple and no bugs!

Caution: this is not a toy: Do not use in children or pets area. Even with protections and if the cutting motor isn't very powerful, due to blade inertia, putting his fingers or his nude feet in the cutting area while the robot is operating can make severe injuries. Always power off AND wait for the cutting blade to stop completely before handle it. Always keylock off the robot after operation to prevent children to play with.

When the robot is power on, the cutting motor starts, the 4 wheels drive in the front way in straight line. If any obstacle: wall, border, foot (even not recommanded), chair... the bumper move, push the left or the right corresponding switches: relays are powered and the robot make 1 meter in the back way and then change it's direction (about 30 degrees) to avoid obstacle.

A mechanical timer (red button) stop it automatically (1h max)

(to prevent being jam, each 1mn 30s, robots make a 1m backward and change direction)

In fact, the robot is stupid and can cut more than one time the same place but if you let it operate, in 1 or 2 hours it can cut about 500 m2 (square meters). 

The robot is quiet and make about the same noise as a vacuum cleaner...


Bottom view:


How to build it:

All components has been soldered on a "ready to use" multi hole epoxy PCB, soldered wires connect component together under the board

simplified schematic:

electronic board:

Open ( with NiCd batteries):



4mm diameter wheel axis motor wasn't very strong and sometimes was broken.

To prevent it, each wheel axis is installed in a bearing and the motor is "free" with just a trick to prevent it to turn..

Simplified Bill Of Material (07/07/2012):

Qty Designation Manufacturer Reference Unit Price Web
1 Cutting motor Radiospares 321-3186 29.70E http://radiospares-fr.rs-online.com/web/p/moteurs-v-cc/3213186/?searchTerm=RE800&relevancy-data=636F3D3226696E3D4931384E4B6E6F776E41734D504E266C753D6672266D6D3D6D61746368616C6C7061727469616C26706D3D5E5C772B2426706F3D313326736E3D592673743D4D414E5F504152545F4E554D424552267573743D52453830302677633D424F544826
    Gotronic RE800 34.50E http://www.gotronic.fr/art-moteur-mfa-re800-11707.htm
    Hobby RE800 27.60£ http://hobby.uk.com/catalogsearch/result/?q=RE800&x=0&y=0
    Technobots   10.23£ http://www.technobotsonline.com/mfa-motor-re-800-30544.html
4 Wheel motor Radiospares   31.10E http://radiospares-fr.rs-online.com/web/p/products/0440082/
        35.71$ http://uk.rs-online.com/web/p/dc-geared-motors/0440082/
    Ebay   14.8E http://cgi.ebay.fr/ws/eBayISAPI.dll?ViewItem&item=251095558131&fromMakeTrack=true&ssPageName=VIP:watchlink:top:fr#ht_2163wt_854
1 Battery EBAY 12V 8Ah 19E http://cgi.ebay.fr/BATTERIE-YUASA-SW280-Gel-12V-8-5Ah-Passez-de-7Ah-a-8-5-Ah-meme-gabarit--/271007198679?pt=FR_YO_Jeux_RadioComRobots_VehiculesRadiocommandes&hash=item3f1949add7#ht_2667wt_1175
2 Relay Ebay     http://cgi.ebay.fr/971-12-10-Relais-pour-circuit-imprime-2RT-bobine-de-12V-10pcs-relay-/190641047390?pt=FR_YO_MaisonJardin_Bricolage_ElectroniqueComposants&hash=item2c6317875e#ht_1228wt_896
    dealextreme     http://www.dealextreme.com/p/dip-type-hk19f-dc12v-shg-8-pin-power-relay-yellow-5-piece-134203?item=34
1 Blade       stainless steel sheet 300x20x1.5 mm approx.
1 chassis Plywood 8mm      
4 Ball bearing


    1.2$ http://cgi.ebay.fr/RCS-Model-698-2RS-High-Precision-Bearing-8x19x6mm-10pcs-CS634-/390380023901?pt=Radio_Control_Parts_Accessories&hash=item5ae476705d
2 switch       http://cgi.ebay.fr/micro-switch-DEFOND-DMC-1115-T-15-3-A-250V-T125-5E4-/320876588116?pt=FR_YO_MaisonJardin_Bricolage_InstallationElectrique&hash=item4ab5bc2c54#ht_500wt_867


After years mowing, the glued plywood chassis is out of order.

So, we build a new more simple, more robust chassis. Few evolution for motors and electronics (main electronic is realized with an Arduino microprocessor but relays based electronic can work well too).

We also improve battery charge circuit with a little switching power supply, with tension and current regulation an battery voltage display while charging.

Chassis is realized with 8mm "marine" plywood, glued and screwed. It's made with an horizontal base, 2 sides, front and rear panels connected with 30x30mm pieces of wood.

2 white PVC corners protect from blade. Wheels and motors are installed in the same (floating bearing) as previous model.

Back: mechanical timer, On/Off switch, a temporary handset, charging circuit with battery tension display, the 12V 7Ah battery (lying down to save height), blade motor with switching regulator, and the Arduino Nano microprocessor and relays.

Front: the bumper has been simplified: only one switch, and four wires and Plexiglas bumper:


The "roof" is made with Plexiglas attached with 4 stainless wires with hooks through a big hole and in a little one: fast and simple.

Lawnmower is well protected against wet and rain:


The bottom is about the same as previous model: white PVC corners protect form blade, wheels and motors are still "floating" with ball bearings.

2 Plastic parts protect motors from grass.


Caution: to properly work, the 4 bumper wires length attachments must be properly adjust.



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