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Arduino R/C Lawnmower (painted)

Arduino R/C Lawnmower (painted)
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What this is:

This instructable will show you how to make your Arduino into an R/C interface that you can use for just about anything requiring remote control. I will also show you how I built an R/C lawnmower using my Arduino, a cheap R/C transmitter and receiver pair, and a couple of electric-wheelchair motors from Ebay.  I have used this interface to control anything from basic LED's to Bipolar stepper motors, mini-robots, lifeless R/C cars from the thrift store, and even a 100lb lawnmower (all with appropriate motor controllers). It is very flexible and easy to change and very simple to set up.

See a slightly different version of the Lawnbot400 in my new book "Arduino Robotics" , as well as a DIY Segway and several other bots.

Check it out in MAKE magazine in the April 2010 issue (#22) or here:


UPDATE 3-24-10

New wheel-barrow bucket mounted on top with hinges so it can dump its contents.


UPDATE 3-10-10: NEW CODE

And new video of the Lawnbot400 moving a bunch of dirt from my truck to the flower beds across the yard, also I updated the code again.


.

I added some new code to the project that is safer, including a manual kill-switch and a Failsafe switch.

To implement the Failsafe, I used another Atmega168 (or an Arduino), to control a normally-open 60amp power relay. The relay disconnects the power to the motor-controller unless receiving a "good" signal from the 2nd microcontroller. This signal is updated 2 times every second and is either ON or OFF. If the bot gets out of range, it loses power to the motors. If I flip the kill-switch on the Transmitter, it loses power to the motors. This is also a handy way to disable it remotely if anything were to go near it that wasn't supposed to. The updated code for both microcontrollers is on the CODE page.
 
In addition to the failsafe, I changed the way the code reads the PPM signals to make it more reliable. Also, I realized that I was only able to run the bot at 80% speed with the old code, so now it is quite a bit faster and has more power (it can carry me across the yard @ 155lb).

Check out this new video of me riding the Lawnbot400, my wife driving it over a bunch of branches, then me making do some wheelies. Don't worry, the mower was turned off this time since the grass didn't need cutting, we were just having fun.



Disclaimer:
DANGER!!! This is a VERY dangerous piece of equipment if not handled appropriately. Since all the electronics have been home-built and the Arduino code is new, you MUST be very careful while operating anything heavy with this code. I have had 1 or 2 times during testing - and before adding a secondary failsafe - that the main Arduino jammed up and I temporarily lost control of the mower for a few seconds!!!! Though I have added several filters to discard unwanted signals and I rarely have any issues, an un-manned lawnmower IS STILL A POTENTIAL DEATH TRAP and I assume no responsibility for anything that happens as a result of your use of this code or this tutorial. This is meant as a guide for people who not only have the ability to build such a contraption, but the responsibiltity to operate it safely as well. Any suggestions or ideas on how to make this a safer project is always gladly accepted. Having said that, it's also awesome.

Background:

Most R/C equipment comes packaged for a single specific use, which makes it easy to use but is very limited in what you can do with it. So using the Arduino as an interpreter between the R/C system and the motor driver, I can use any motor controller that I want (depending on the size of the motor and power required), reprogramming the Arduino to supply the required signals. 

What I ended up with:

After successfully hacking a few R/C cars from the thrift store, I got bored driving them around the driveway and I was having a hard time convincing my wife that there was any usefulness in the revived toy car. So I decided it was time to make my biggest chore at home, a whole lot easier and actually put my Arduino to work, and thats how I ended up building an R/C lawnmower.

While designing the lawnmower, I thought it would be cool to learn about the electronics that made it move, so I designed and built my own motor speed controller (or H-bridge) to power the lawnmower. I looked around at every H-bridge design I could find before deciding to go with a Mosfet h-bridge that uses both N-channel and P-channel Mosfets.

I built several different motor driver boards for this project, the first two were on Radio-Shack perf-board and the next 4 were designed using EagleCad and etched to a piece of copper-clad PCB, using the toner-transfer method. The most recent board is the one I use to mow the lawn as it has the ability to stay cool even while operating for long periods of time (30-40 mins straight) at 10-20amps and 24vdc. FWIW, I had to burn up a lot of Mosfets to find this out. If you want to see any of my other motor controllers, go to www.rediculouslygoodlooking.com and check out the Mosfet shield.

Here is what I bought already assembled:
FM R/C transmitter and receiver pair from ebay = $40
Arduino = $30
I already had a used push-mower = $60

Here is what I bought and assembled into the Lawnbot400 (as I call it):
(2) electric-wheelchair motors from ebay = $40 ea
(2) 12v marine deep cycle batteries - Walmart - $60 ea new (used batteries might work)
36" pieces of 2" angle-iron (2) and 1" square-tubing (2) from Home Depot = $8 ea
36" pieces of 1" angle-iron (2) and 1" flat steel bar (2) from Home Depot = $5 ea
(a lot) of nuts, bolts, washers, lock washers 3/8" or 1/2" with drill bit = $20
(2) caster wheels from Harbor Freight Tools = $14 ea
(2) drive wheels from Harbor Freight Tools = $8 ea
(36") 5/8" threaded rod with several 5/8" nuts and washers from Home Depot = $8
(2) sprockets from Allelectronics = $5 ea
#25 roller chain and a few universal links from Allelectronics = $10 for 3'
sprockets from Electronics Goldmine = $1.50 ea
(24) mosfets from Digikey = $1 ea
(there were quite a few small parts for building the H-bridge, they are listed later on)

 
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Step 1Setting up

Setting up
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1. Get R/C transmitter and receiver (I have tested FM and AM systems and they both work)
2. Upload code to Arduino (it is on the last page)
3. Make sure you are getting a good signal


You will need an R/C radio transmitter(Tx) and receiver(Rx) pair, which is the most expensive part of the project, but can be used for every future project you might have involving R/C.  I went with a 6-channel FM system, but  I have tested a 27mHz AM transmitter/receiver and it works just as well. The beauty of the Arduino is that if you want to adjust the deadband or the motor-speed at turn-on, (unlike commercial ESC's) it is all easy changed in the Arduino IDE.

Once you have your radio, all you need to do is upload the code to your Arduino, plug in the 2 channels that you want to use from your radio receiver into Digital pins 2 and 3 of the Arduino (these are the 2 external interrupt pins on the Arduino) and you are ready to control whatever you want. If you don't have a batter pack for the receiver, you can run jumper wires from the Arduino +5v and GND to the R/C receiever for power, you only need to supply a single channel with GND and +5v (it is not necessary to power every channel).

Upload the code using the Aruino IDE (I am using version 0016 on Ubuntu).

I started by controlling 3 LED's with 1 channel on a breadboard. I wired a red LED to be Forward (digital pin 9), a yellow LED for Reverse(digital pin 5), and a green LED for Neutral (digital pin 12). This allows you to adjust the code to fit the needs of your radio system. You will have smooth 0-100% PWM control of both LED's and the neutral light will turn on when the control stick is centered. If needed, you can widen the deadband for Neutral, but doing so will increase the speed at turn-on (which starts at 0%, so that would likely be desirable). See pictures.

----------------------------------------

The code has 4 PWM outputs for motor control:

channel 1 Forward = Arduino digital pin 9
channel 1 Reverse = Arduino digital pin 5
channel 2 Forward = Arduino digital pin 10
channel 2 Reverse = Arduino digital pin 6

2 outputs for Neutral indicator lights:

channel 1 = digital pin 12
channel 2 = digital pin 13

The 2 INPUTS from the R/C receiver should go to:

channel 1 = digital pin 2
channel 2 = digital pin 3

---------------------------------------

If you are interested to see your readings, turn on your Serial Monitor in the Arduino IDE (set to 9600bps) and you can see the actual real-time pulse readings for each channel, they should read:

full forward = 2000 (2 milliseconds)
center = 1500 (1.5 ms)
full reverse = 1000 (1 ms)

These readings reflect the number of microseconds that the pulse signal from the R/C receiver stays HIGH (or at 5v). The typical Servo signal that comes from an R/C receiver is a pulse whose length varies from approximately 1 ms to 2 ms with 1.5 ms being Neutral (which should also be the position that the control stick returns to when you let it go). The transmitter reads the position of the control stick and sends that pulse length about once every 20milliseconds. So it is constantly updating for precise control (for more info, look up PPM on wikipedia).  If you push the transmitter control stick forward, the reading should go up to 2000, if you push it backward it should go down to 1000. You can also use a voltage meter at this point to see that Digital Pins 5, 6, 9, & 10 will be changing from 0-5v depending on the position of the control sticks on the R/C transmitter.

If you care to know, the code uses the Arduino's 2 external interrupts to capture when the Rx signal pin changes states (goes from HIGH to LOW or vice versa), when it does at the beginning of each signal, it calls the interrupt function which reads the digital state of the pin and if HIGH, it records the microseconds value on the Arduino system timer0. It then returns to the loop until the pin goes LOW, at which point it subtracts the previously recorded microsecond value from the new current microsecond value to determine how long the pulse stayed HIGH (which tells us the position of the Transmitter control stick). It then does that over and over really fast.

I have the values constrained from 600-2400 in the Arduino code to keep things simple. Once it receives the signal and constrains it, it maps that value to be proportionally between 0 and 511, where 255 will be Neutral. The code then determines when the value changes and uses a function to determine the appropriate 0-255 PWM value in the appropriate direction and each direction has it's own PWM output pin to control the H-bridge.

On a side note:

To make things easier, I built an Arduino-based breakout board using Radio-Shack perf-board, a 28pin DIP socket, a 16mhz oscillator, and a bit of wire. I also added a set of female-headers in such a way that I can plug my R/C receiver directly onto the breakout board. For secure connections while mowing grass, I added screw-terminals on each Output pin and each of the 6 channels from the receiver. It also has a built in 5v regulator to power both the Atmega168 from the Arduino and the R/C receiver (which gets power when you plug it onto the breakout board). So you just route jumper wires from the channels you want to use on the receiver, to the Atmega digital pins 2 and 3. I also added 2 LED lights that are hard wired to the digital pins 12 and 13 for the Neutral lights for each channel so I can easily see when I am in neutral.

Since this bot is a Tank steer setup with 1 drive motor on each wheel, the coding is very straightforward where the left stick controls the left motor and the right stick controls the right motor. Both sticks forward means lawnmower goes straight forward, both backward and it goes in reverse. If you push the left forward and the right backward, it does a zero-turn circle. As you can imagine, mowing the grass is really fun now.



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293 comments
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May 17, 2012. 8:20 AMJurko says:
I need fuse specifications of the picture on Make magazine.....4A, 2A, 30A I don't know????? help please!!
May 12, 2012. 11:35 AMtma73 says:
Excellent job on your Lawnbot! :D
Thanks for also posting the code you used. I'm putting together a bot using parts from a wheelchair.
Also using a Spektrum Tx & Rx to drive it for now (using a Sabertooth2X25 motor driver).
I noticed in your code you have it setup for independent steering. Was wondering by ommitting the 'b' in motor 1 & 2 I could run it using differential steering.
Thanks,
Thomas
May 6, 2012. 1:56 AMJurko says:
Hello! I started this project with a little modifications.....I added tracks (tank) ((http://amando-abreu.webs.com/diytanktracks.htm)) and frame without tracks are about 50kg. I wounder if the motors will handle this weight with lawnmover and bateries...I have hilly yard so thats are tracks for...

I add some data fo my robot:
-Length: 120cm
-weight: about 100kg
-Width: 70cm (100cm with a tracks)
-height 20cm

I will post some pictures of progress soon as possible!!
May 11, 2012. 10:08 PMSamfordValley says:
I'd love to see some pictures, I'm building a larger one myself, don't think it's as large and heavy as that though, it is larger than the LawnBot400 but might not even be as heavy. I will try to get some measurements and photos too, I've just finished the frame.
May 8, 2012. 2:38 PMJurko says:
Hy! I have question. If I read right on board triple8 4inputs are listed in couples 5-10 L and 6-9 R? and thats it.....and I have my edition about triple8...little modifications on a little bigger plate and larger holes.....contact me and I will send U (anzejurkosek@gmail.com)
May 10, 2012. 9:07 AMlitehouse43 says:
Is there any "method to the madness" of picking wheelchair motors? I have found quite a few different types and also ran across brushed DC motors that appear to be very similar. I plan on using the sabertooth motor controller but have not really identified what I should be looking for in the motors. Am I just looking for anything high torque and low RPM?
May 6, 2012. 1:47 AMajurkoaek says:
(removed by author or community request)
Apr 24, 2012. 12:59 PMbrancilo says:
hello
I finished my project
http://www.youtube.com/watch?v=7Diwy08YR9Y

May 1, 2012. 7:13 PMSamfordValley says:
Very nice!
May 2, 2012. 1:27 AMbrancilo says:
Thank you :-))
Apr 17, 2012. 7:19 PMSamfordValley says:
I'm going to build something similar to this, but I'm going to make it so not only can I suspend the mower, but mount it on top for longer cut on rocky terrain.

I don't like the sprocket and chain system though, but I haven't done enough research or know for sure I can do it any other way. I'm worried the chain is too complex and something weeds and twigs will get caught in.

The main problem I'm having is I can't find these wheelchair motors for a reasonable price. I live in Australia and there don't seem to be any local cheap ebay auctions for these, and shipping on these suckers from the USA is $100-$200. I can't even find a cheap old wheelchair.

Is there a more... retail... kind of product I can use? Something like a servo/actuator I can order? I have no idea what I'd need to look for in terms of torque though. What sort of specs would I need to ensure in such a product to make it work with this project?

I need it to go up steep hills (30 degrees?) in long grass on rough ground. I'm already getting hardier wheels, larger drive wheels, and I found a company in Australia called Fallshaw that makes puncture-proof semi-pneumatic castors (though I can't find a price!), I will check out one of their stockists soon.

Because I need to mow my rocky terrain sooner rather than later, I might build the frame and use it like a push mower until I can get the motors and retrofit the electronics.

Any suggestions on alternatives to wheelchair motors would be appreciated.
Apr 24, 2012. 1:30 PMbrancilo says:
I was lucky motors of the wheelchair gave me one for free otherwise they are expensive but the best solution, as an alternative solution can be taken from the truck to 24v, scooter, such as John, but the best of the wheelchair
I was denied the money I worked 2 years but the project eventually end only needs to be persistent.
Apr 22, 2012. 3:19 PMniak32 says:
I'm also in Australia close to Ballina NSW, I hounded a local scooter shop about an electric wheel char they had on consignment for $380, eventually got it for $150.
If there are old people living near by (lol) there should be a scooter shop which will have parts. Batteries I got for $5 each (deep cycle) as they replace both batteries at once and one is normally "still ok".
Hope this helps
Apr 2, 2012. 3:25 AMbrancilo says:
Hi me again,

Can you give me the code for the arduino to duty cycle is less than 100% and the maximum without the relay, just an ordinary convert the signal from RC receiver in 4 PwM signal of 0-90% duty cycle, and where if necessary after I change the duty cycle?

Thanks a lot and I apologize for the inconvenience
Nov 20, 2009. 3:59 AMrcflyeriam says:
I have noticed that the your electronics are the highest part of the mower.  Maybe adding some sort of cage or box around it to keep bushes and shrubs from catching it and breaking things? 

Got to love the RC stuff, without them, where would we be.  Keep up the good work and happy flying .... ooooops, mowing.
Nov 22, 2009. 7:06 AMadamvan2000 says:
Just had an interesting idea....

What about hooking the remote up to a pc and programming some sort of app that calculates mowing pattern so that it does it all automatically.  You could even set it to vary the patterns so that they're never the same, and you'll always have a nice looking lawn.

~adamvan2000
Mar 26, 2012. 6:49 PMaol1044 says:
This is a nice idea. You may want to do another instructable or add on to this instructable and develop a downloadable program for that. Other than that, cool idea, may be a project for summer for me.
Feb 26, 2012. 2:20 PMGunther45 says:
Love this but a few comments and not complaints as I think it brilliant.

1) Does the Lawnmower work? I see the gas engine on top but no vids of it cutting grass.
2) If you could lay out a grid of you property could you use coordinates of where you needed it to go? It seams easy enough to control but automated is better ( I have seen Arduino based UAV's , GPS might not be accurate enough for this ) but just a though more on the lines of cutting grass but it looked like you had you garden beds situated so if it could just turn and stop at say 4 points for every garden bed you would be set in the hauling aspect.

I don't Property or I would definitely be into this project. But much Props! I like it.
Feb 24, 2012. 10:12 PMnathanielg says:
Ohhhhh, I just realized that looking at all the schematics and thinking what would be connectd where i realized that everything has a common ground and that the 4 leads are all positive
Feb 24, 2012. 9:55 PMnathanielg says:
I am so confused on how the reverse on the h bridge works.? I dont understand how this works because the pwm signal is always positive and you only have 2 positive leads comming from the arduino going to the controller. Wouldn't this only be able to control 2 gates???? I do not understand how it can go in reverse from an always positive signal only using 2 wires (and 2 for ground). Please help and Great Instrustable
Feb 16, 2012. 8:36 PMjeremydial1981 says:
Also, this is a noob question but here goes anyway. lol Looking at the pictures it looks like there are only 4 wires coming from the arduino clone to the motor controller. Now if my understanding is correct each 3 mosfets in parallel are 1of the 4 legs/switches in each h-bridge, that makes 8 switches to control 2 motors. How exactly are you controlling 8 switches with only 4 wires. Am I missing something? I am still a little new.
Feb 17, 2012. 1:44 PMjeremydial1981 says:
Ok great, makes perfect sense now. 1 more noob question because I understand the "how" but I feel like I need to know the "why" of each step to further my learning. What exactly is the function of the capacitors on the motor driver. I don't see any diodes in the schematic for the triple 8 that you show on a few of the h-bridges in your book to protect from back emf, so am I correct in that the capacitors are "absorbing the back emf?
Feb 18, 2012. 3:37 AMjeremydial1981 says:
Ok, thanks JD. Makes perfect sense now.
Feb 17, 2012. 9:20 AMbrancilo says:

Hey
goes from arduino for each mosfet, tending one way out of the arduino ide two mosfet on the high side and low, can any another logic level, because the output is 5v arduino which is insufficient to completely open standard mosfet.
Here's a picture:
http://www.dodaj.rs/f/Q/4J/2EuyX78E/fda89k9g1qwb96j.png
http://www.dodaj.rs/f/1b/Gf/3VPVduTf/h-most.jpg
Feb 17, 2012. 12:08 PMbrancilo says:
I have TSC7000K (2N7000) I do not know whether the logical level. Everything is the same as you in datashet
Nov 30, 2011. 9:07 AMwazeem1 says:
hi john,

i want to design a motor drive circuit for driving 2, 5A 22v DC motors. Motors will be used in an electric wheel chair, i also want to control the speed of motors with PWM. Can you provide me with any help
Feb 16, 2012. 6:30 PMjeremydial1981 says:
Do I have to use the 2n7000 logic level mosfets or can I just use more of the 52a 60v n-channel mosfets for controlling the p channels?
Feb 19, 2012. 5:52 PMbrancilo says:
Hello all,
I want to make this controller with arduino
but there is a problem, because can not find this anywhere MOSFET FQP47P06 FQP50N06L and 2N7000L
I have MTP50N06 n channel 8 pieces, they were in the control unit of the wheelchair that is broken can not be repaired, and they are fine
whether there is a solution that they use no driver like HIP4081
because I do not have much money.
engines are the same of the wheelchair
I ask for your help
Feb 16, 2012. 11:35 AMbrancilo says:
Thank you John for their advice.
I'm going to do this most cheaper option, and then I get this when MOSFET
Thanks again for your prompt reply, it means a lot to me.
Feb 11, 2012. 2:14 PMDavid97 says:
Whats the rpm of the motoors. I need to know quickley i have a auction I want to win for thee motors.thanks.
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I have always been one to take things apart to figure out how they work, so most of what I own has been dismantled. If it can't be taken apart or hacked, i'd rather not have it. And I like to do thing...
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