RC Riding Lawnmower

This is my first attempt at an instructable . I have virtually no experience in electronics but at 80 years old I figure you are never too old to learn. Mowing the lawn was getting to be quite a chore so I decided to build an easy to use mower that I could either ride on or sit on my back porch and mow from there. I bought a used electric wheel chair on Craigs list for $100 to start the project off. After stripping wheels, motors, and battery box I mocked up the chassis with 2x2" lumber  This also allowed me to fit the donor mower to  the frame. I used the deck from an old Briggs  22" walk behind push mower. Once that was done I welded up the steel frame from 1 x 1/2" steel tubing. I tried building the electronics from a previous project in Make but I just didn't have the talent or experience. I decided to go with a Sabertooth 2x25. I already had the motor wiring and was set up for 24 volts. The folks at Dimension Engineering were a great help in advising me how to set up the DIP switch. I got a used 54 MHz. RC set up from a friend who fly's model airplanes. The Sabertooth is a no brainer to hook up. It even supplies the 5 volt power for the receiver. A switch, and fuse were all I needed to complete the job.

Step 1: Materials

STEP 1

Materials                                                                                     

Used Electric wheelchair                                                        $100.00
Steel Tubing                                                                              $25.00
Donor 22" mower                                                                      $ 25.00
Sabertooth 2x25                                                                       $125.00
Lawn mower batteries  (2)                                                          $68.00
Misc. Nuts, Bolts, Switch , and fuse                                           $15.00
Used RC TMX, AND RCVR                                                        $35.00

TOTAL                                                                                       $393.00

Step 2: DEMOLITION

Before taking the old wheel chair apart, look it over and see what you can use in the project. The motors came with a built in parking brake that puts the motors out of gear. This was handy for testing out the controls. The castoring rear wheels came with a nice bearing set up which saved a lot of work. The battery box was designed for U1 batteries and had a nice post mount for the removable seat. The chair came with a 24 volt charger, which I saved along with the charging plugs. I saved all the wiring from the motors to the batteries because they had very nice plugs and connectors with polarity indicators. I saved the joy stick and associated electronics for a possible future project that does not require a radio. The seat plugs into a pedestal built into the battery box. This makes it a riding mower complete with seat belts and arm rests.

Step 3: The Chassis

Building a wooden mock up of the chassis saves a lot of mistakes and wasted metal. My best friend did the welding for me. My eyesight doesn't allow me to see well enough thru a darkened hood. He did a great job with his TIG welder. The wheel chair originally had the drive wheels in the front. Remounting them in the rear was an easy task using the same mounting points with motor pointing backwards instead of forward. The donor mower deck was then put in place to set up the overall length and position the front castors. This was also a good time to position the battery box for clearance with the deck. The final step was to fashion an electronics deck in the rear.

Step 4: Suspend the Deck

A fresh coat of paint makes an old, rusty deck and motor look like new. Start  by positioning the deck where it won't interfere with the front wheels and the battery box. Raise the deck on wooden shims to the desired lowest cutting height. Set the wheel adjusters to the lowest point.
Fabricate four straps to hang the deck. The top is bolted to the frame, and the bottom connects to the old wheel mounting axles. This allows the height to be adjusted just as it did on the old push mower. .The deck tends to sway fore and aft, but once the desired height is obtained simply tighten the top bolts and it will be stable. If you have planned your mock up properly there should be ample room between the deck and the front wheels. Shorten the pull starter rope and be sure to dis-connect the dead man switch. I installed a small push pull switch to kill the motor.

Step 5: The Sabertooth 2x25

The Sabertooth 2x25 by Dimension Engineering is really a giant in a small package. It provides everything and more than I need. The DIP switches allow it to be programmed  to control the mower any way you choose. It has a built in fail safe that shuts down the system if you lose RC signal. The 5 vdc regulated power supply provides adequate current for most RC systems. The specs say that if you load it up with too many servos it may require additional power, but since I am not using any servos there is no problem. My Sabertooth is mounted directly to a steel plate and I have not noticed any heat build up. I am sure this unit is capable of much more than I am using. It comes with 4x40 mounting bolts for easy mounting.

Step 6: Installing the Motor Controller

Now comes the fun part!  It is a good idea to put in a terminal strip between the power and the Sabertooth 2x25. This isolates the on/off switch and the fuse from the controller. Connect the positive lead from the charger to the hot  side of the switch. This allows the batteries to be charged with the switch off. Hook up the power and motor leads to the controller. They are well marked . If the motors don't turn in the right direction, simply reverse the motor leads. My motors had an extra pair of leads that actuated an inner relay. I hooked these up to come on with the power switch. At this time you "MUST " set up the DIP switches . If you don't the unit goes nuts when you apply power. I set mine up for exponential steering. You can opt for tank steering . (Read the DIP switch instructions that come with the controller)

Step 7: Installing the RC Receiver

Positioning the RC receiver is critical. It must be placed as far away from any electrical interference as possible. If you have limited range on your mower move the receiver to another location. I'm not an RC guy, but I have been told that 12 inches should be enough. The standard servo leads come with 12 inch leads I think you can also wrap the receiver in aluminum foil to shield it. I mounted it to the frame using two sided foam tape. Try to keep the antenna away from electrical noise. I taped mine to a 36 inch x 1/8 dowel.

Step 8: Final Assembly

My chair didn't come with batteries. U1 wheel chair batteries are quite expensive. A trip to the local auto supply and I found heavy duty garden tractor batteries rated at 360 amp hours for $34 each. I have run for two hours or more and did not run out of power. The volt meter still showed 24 volts. I plugged the seat into the battery box and was ready to go. The blue led was not visible due to the cover plate . I hooked up an old 0-30 vdc meter and an old 24 volt light as a precaution to remember to shut off the main switch. I fashioned a 36"' dowel to attach my antenna behind the seat. I plan to add a pair of foot rests just for comfort.

Step 9: RoadTest

Now is the time that I wish I had spent more time playing video games. It takes a little practice to get a smooth turn and a steady straight run both forward and reverse. I have the DIP switches set up for exponential steering. That lets me control the speed and direction with one joystick. This is the way most wheel chairs are set up. The way my  transmitter is set up, the left joy stick is used for the throttle and has a ratchet built in. This was confusing when  I tried to use tank steering. I did try to use the left stick for forward and reverse and the right stick for direction. This seemed to work okay but I am more comfortable using just the one stick. The really nice thing about the Sabertooth is that you have the option to configure it any way you choose. My radio is very old and requires a long antenna to assure adequate range. My yard is 200 feet long and I had no problems once I moved the receiver away from the wheel motors. If I had a larger budget I would buy a
2.4 GHz system. These new systems only require a very short antenna, and are far more tolerant of noise. The new Spektrum 5XDE is available for $99.00.
This was a fun project and is attracting a lot of attention from my friends and neighbors. The model airplane club that donated the radio is having a ball running it up and down the grass runway. The surprising thing to me is the way young kids can zip it around with little effort. I don't however, let them ride on it for safety reasons. Except for the welding I would considerthis an easy project. The wooden mock up chassis would have worked just as well, but I don't think it would have held up over time. I will add a video as soon as I can borrow a movie camera. Feel free to contact me any time.
mickeydee

Comments

[mikej1290]

Did you leave the battery wiring factory with fuses (if factory installed) as is, with no modifications? Could you please detail what each wire connects to on the terminal strip. Thank you

[WarriorInnovations]

How are the rear motors mounted and do you have dimensions for the tubing?

[RichardW235]

How do you have the switches set on the sabertooth? I am currently building something very similar and it is 'pulling' to the side.

[nickr6]

This may seem like a silly question, But will this only drive forward or will it go in reverse as well?

[kylerelay]

the mower will move in all directions similar to a electric wheelchair

[eda3]

[Thejersey]

I am trying to build a rc wheel chair n i am looking to see how the wiring hooks up to the chair to the remote do you have a diagram?

[Partybot]

The sabertooth seller has diagrams, but the only "chair wiring" you use are the power leads off the batteries and motors. You eliminate the onboard controller and joystick.

[BoyWonder620]

Awesome! Like "Honey I Shrunk The Kids!"

[mjhill434]

I have a perfectly good heavy duty power chair that everything works! I wonder how hard it would be to just put a deck up in there?? But it has the joy stick and all that work Great! I just can't sell the dang thing so i might as well build something with it! BTW! Great Job!!.. :)

[jjagtiani]

Hi mickydee,

great project. I made one myself. How did you make the kill switch with RC - what type of switch and hookup did you use. I have a futaba radio similar to yours connected to 12v deep cycle battery to power the mower - works great just need a kill switch. any info you can provide will be helpful. thx -jj-

[ProfessorJWN]

Powerwheels drives work well for some things. I built a robot using one and used H-Bridges and mixer from Carl at Diverse Electronics + 75hz Futaba controller.

[teknohawk]

Amazing!

[mickydee]

I put the 30 amp fuse in series with the positive lead just in case a direct short should occur I used the terminal block for easy connection of accessories such as charger and voltmeter. It keeps things neat and tidy. The only way to destroy your Sabertooth is to hook up the 24 volts backwards On my new version I am building I am using two 350 watt 24 volts Chinese geared motors. They should pull 14.6 amps.
(350 / 24) I have that circuit fused at 20 amps. inline with the positive terminal to the Sabertooth. I try to protect the controller in any way I can.
I used a 30 amp fuse because It was handy.
.

[osstekz]

I have 2 -12vdc35aH in series w/ positive going to a master switch, then straight to Sabertooth positive terminal. I assumed Sabertooth would handle amp surge so i dont have your 30amp fuse & terminal strip solution. Can you explain the need for 30amp fuse and exactly how it's wired? Thanks for a great DIY learning experience!

[fireplace]

what about electric brakes how do you wire them to make them work.

[mouse0079]

I have an electric wheel chair base with motors but I would like to know where you got your Sabertooth contorller from and as far as a radio goes I can get one from Ebay. I also have a twin blade mower deck that my chair base will be pulling and I plan on puting it on here when I'm done with it. Thank you for your answers.

[Lazygardener]

Hi mickeydee,

Great instructable, I have been inspired, and nearly have all the parts!

I managed to pick up a cheap wheelchair on eBay that actually had two fantastic batteries that hold a good charge. The seller thought that they were flat and useless! The problem is that after charging the chair and testing it out for power, I am doubtful if the two 180w motors will push the RC mower up a hill (I am not building one with a chair, and hence it will not be carrying a passenger up hill). What do you think? What size motors are you using, and would it make it up a 30 degree hill? I am not sure if the motors will be too weak, or if the wheelchair motor controller is limiting power.

Your advice would be much appreciated.

[mickydee]

Hi there!
Sorry about the delay, I have been traveling.
I don't think you will have any problems with power if you are using wheelchair motors. I am using 13 amp motors on mine. That equates to 312 watts..(Volts times amps = Watts. Using that formula it looks like you are using 7.5 amp motors. That seems a little light for a wheel chair.
I don't think you will have a problem though. I hope you will be using the Sabertooth 2 X 25 . It delivers smooth power to the motors even at very low RPM.
Let me know how you are doing
Happy building
Mickydee

[artxty]

hi, i've been inspired to do likewise after i saw this project.
btw, can i use a 4 channel remote radio for this project? or it should be 6 channel radio transmiter?

tnx