Introduction: Remote Control Lawnmower

This project was born after talking with a few friends one night. Build a remote control lawnmower using as much of the shelves parts as I had and buying the least.

This lawnmower has forward - reverse - left - right commands, cutting height adjustment and throttle control. All this from my Hobbyking heli RC.

Using 2x 12Volts DC motors to drive invidually the back wheels.

1 electric jack for the cutting height

1 servo the actuate the throttle

The working principle is fairly simple as at the time my knowledge of programming was fairly low. I used servos to activate micro switches which then are read by a PIC. The PIC then outputs to couplers which drive the relays.

The two motors are driven through the relays by a brushed ESC for speed control.

Step 1: Mechanical Side

The support where the motors are mounted on has been built with some 50mm by 50mm angled aluminium. I used tension spring to keep the drive chains tensionned on the wheels.

Primary drive with toothed belt with a ratio of 8 to 24 teeth pulleys and final drive from 6 to 66 teeth sprockets which give me a speed of 1.21 turns per second which is pretty close to the speed you would push your lawnmower around the garden. I didn't have time to built a proper bearing housing for the drive shafts for each wheels so I used plummer blocks and it ended up working quite well I must say.

The electric jack has a strenght of 50kg push or pull. I had to add a spring to help it raise the height of cutting as it is quite heavy.
One end is bolted on the frame of the mower and the other is bolted on the connecting bar from the back to front wheels.

For the front wheels, I replaced the normal wheels by caster wheels to imrpove the turning.

You also have possibility to remove the chains on the back wheels and push your lawnmover by hand.

Step 2: Electric Side

The main board is fairly simple. 1 PIC16F628a taking care of outputing to the relays. I added for fun a temperature driven fan starting at 25° and reaching maximum speed at 55°.

The PIC outputs are connected to 2 double MC34152P. They basically just react to a change on their input pin (0V or 5V) and will drive their output pin high or low(0V or 12V) accordingly with a maximum current of 1Amp, which is great for relays as the PIC can't handle that kind of load on its pins. These IC's are designed to drive MOSFETS but work very well with relays.

A brushed ESC is an Electronic Speed Controller for motors with brushes. It is connected to the receiver and will output 0 to 100% of the speed I can get depending on my stick position on the remote control to the motors through the relays.

I used 4 pair of 12Vdc relays:

2 relays for the left wheel to go forward and 2 for it to go backward. And the same config for the right wheel.

When turning left, the right wheel will turn forward and the left wheel backwards which give the mower the ability to turn around on its axis. A bit like a tank.

In the black box there is 2 servos and 4 microswitches. 1 servo will give me wether I go forward or backward activating the microswitch needed.
Same thing for left and right.

In the second box, as I added it afterwards I had to built it in a separate box, we find all the relevant parts for the cutting height adjustment.

12Vdc from the battery is then transformed into 24Vdc through a DC-DC converter. It is then outputed to the electric jack through 2 relays (0V;24V) or (24V;0V) to invert the direction of the jack.
These two relays are driven by microswitches and 1 servo.
Each of these 2 relays drive as well a third relay which outputs the 12V into the DC-DC converter. The DC-DC converter is only used when we want to raise or lower the cutting height, it does spare the battery doing it this way.

Step 3: Boards Drawings + Assembly Program for PIC

Here you will find the different drawing of the boards and as well the program uploaded in the PIC.

Every board has wires going from and to another, they are labeled to match the title of the board file name.

Don't hesitate commenting or asking questions if you want or need more informations about anything concerning this project.

The .asm file is really basic, I could if I had time, rewrite it a bit better but hay, it works great so it is what we need.

As well, on the main board drawing, I didnt include the 5pins connector for the programming. I will happily help anyone out if needed.

Comments

author
JoLoveN (author)2016-03-14

How much did it cost to make?

author
nerd7473 (author)2013-10-09

This is a very cool project makes me want to buy some servo motors.

author
eszy (author)2013-05-13

Where's the video of it in action??? That's the finally. No?

author
pfoglietta (author)eszy2013-05-15

Yes i know, I need to make one soon. Still going good tho!

author
AirbornG (author)2012-11-28

First of all THANKS for posting this instructuble!

The electronics are very well documented and this will certainly be the basis for my own mower :)

Still I have some questions:

- Can you give us the full specs of the motors? Mainly the power and where did you get them. Also do you find they are powerful enough (do you use the mower for mulching only or also with the collecting bag)?

- Regarding the motor control: as far as I know the ESC works by PWM that will control motor speed. The way you setup the motor control the pic, through the relays, will set the direction (forward, backward, pivot left and pivot right) and the ESC will control motor speed. My question is: do you know and did you consider a solution where you would use the left-right proportional input to generate different PWM to each motor, enabling smooth turns? For instance going forward at a certain speed if you acted the joystick slightly to the left it would slightly increase the speed of the right motor and reduce that of the left motor.

author
pfoglietta (author)AirbornG2012-12-19

Hi there,

Sorry for the looooong delay in resplaying to your comment.

Thank you, it always feels cool that someone likes whagt you make.

To answer your questions, the motors are 12Vdc 100W 2750rpm 11.9A
I bought these from motiondynamics here in australia. They are very cheap as well.

All depend if your lawn is hilly or flat. Mine is flat and they are powerful enough. You can even do short wheelies on the concrete when you go backwards and forward straight after.

I do use the bag at the back to collect the grass. The design make it fit, I made sure it would.

Yes that is right, the ESC works by PWM. It should be possible to control each motor's speed using PWM's on the PIC. Some PIC's do have multi PWM outputs. It would probably invlove an analog input telling us what speed does each motor goes to. (LIke 2.5V = max speed of each motor ; 0V = left motor max speed BWD , right motor max speed FWD ; 5V = the opposite) You could get up to 1024 different speed settings using the ADC of a PIC16F886 which is already heaps I think. It would take a lot of programming tho, I guess.

I think I would use the potentiometer of the "left right" servo to give me the analog value to simplify the design a bit. That is what came up in my mind straight away, might be some better ideas for sure.

Link for the motors: http://www.motiondynamics.com.au/dc-motor/dcmotor/my6812-motor.html