DIY Radio ControlLED Lawnmower

– MECHANICALS –

 

A TRUE DO-IT-YOURSELF Radio Controlled Lawn Mower!

all material here is copyright Terry Creer 2007

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DISCLAIMER - THE METHODS OF CONTROLLING AN UNMANNED VEHICLE DETAILED BELOW ARE POTENTIALLY LETHAL. YOU CAN KILL SOMEONE, AN ANIMAL OR A ROSE GARDEN IF YOU ARE NOT CAREFUL. I ACCEPT NO RESPONSIBILITY FOR LOSS OF LIFE, BEER PRIVILEGES OR SEX FOR CONSEQUENCES THAT ARE BEYOND MY CONTROL. IF YOU DECIDE TO BUILD A MOWER LIKE MINE YOU DO SO AT YOUR OWN RISK. BY BUILDING THE PROJECTS STATED BELOW YOU ARE ACKNOWLEDGING THAT IT IS ONLY YOUR FAULT IF SOMETHING GOES WRONG.

 

Introduction

 The purpose of this section is to detail the mechanical construction of the Lawnmower’s mounting frame and how the lawnmower and wheelchair parts are mounted to it.

 This is intended as a guide to build your own RC Mower, however I won’t be posting up CAD plans for a few main reasons:

  • Your mower will probably differ to the one I used.

  • Your wheelchair (parts) will also probably differ to those I’ve used.

  • There aren't any plans.

What IS here is a detailed description of the frame design and construction to provide plenty of ‘inspiration’ for your own creation.

Part 1 - Donor Machines:

 

The Mower:

The mower chosen for the job was a Murray low profile mulching mower powered by a Briggs n Stratton 5hp 4 stroke motor.

It was purchased off ebay for a measly $200 and was in pretty good condition.

I felt it was a great starting point for the mower project as it was low profile (no catcher - plenty of room for batteries), powerful, mechanically simple and had a large cutting area (20" if I recall).

I runs like a charm and I think I made the right decision.

To convert it over, no irreversible modifications were done to it at all. If desired, I could easily convert it back to it's original form, but why the hell would I want to do that???

 

       

  • The first pic shows the low profile of the mower with the wheels off.

  • The mower is quite wide and in the 2nd pic you can  see the beefy 5hp Briggs & Stratton 4 stroke (it's BIG!).

  • Lastly is a shot with the handle removed (I just unhooked the cables and removed the 2 locking pins securing them to the body)

  • Notice the 4 wheel independent height adjustment... This later turned out to be a pain in the ass but I think I have a solution.

Dismantling the Mower:

Here are the mods I had to do to the mower to get it ready for the 'transplant':

  1. Firstly the wheels disappeared.

  2. I removed the handles and carefully unhooked the engine cut and accelerator cables from the motor.

  3. Lastly I removed the two rear height adjusters (secured by a single nut and bolt) and reversed them to they faced the same way as the ones on the front (see pics below). This was done so I could fit the wheelchair motors & Wheels as close to the body as possible.

       

 

...And that's all I did to the mower!

 

The 'Chair:

The chair was acquired from a mate of my Dad's who sells and services wheelchairs and scooters. This old thing had been retired and needed a make over so we picked it up for $150.

It even had a charge in it. I kept it together during the testing stage of the Radio Control to Joystick converter I built (see the ELECTRONICS section). Once I was happy with that I pulled it apart!

       

(I forgot to get pics of it 100% complete - whoops!)

  • In these pics you can see the controller box (it happens to have my prototype RC interface sticking out of it), motors and wheels.

Not really much to tell apart from saying I stripped all the electrical gear out of the frame:

  • Batteries and battery boxes

  • Complete Motor, bracket and wheel assemblies

  • Front swivel wheels

  • controller box

  • Wiring loom

NOTE -  When you remove the wiring loom, mark where each plug goes with a pen or sticker for easy assembly later on!

The left hand motor assembly (with wheelie bar removed):

 

   

 

... And that's all for the wheelchair. I didn't need to modify anything apart from the Radio Control interface, so now it's on to...

 

Part 2 - Frame Construction:

MAIN CHASSIS

Ok, first step of the frame was the main rectangular chassis rails. 

Material used was a square steel 25mm tube (20mm inner diameter). To build the entire frame, I used approx 5.5metres of the stuff.

When determining what the width should be, I made mine so that the overall width of the chassis rails is the same width as the distance between the base of the axles for the wheels on the lawnmower. See 5th pic below.. HOWEVER, check if this width will also clear the mower motor and other accessories. Mine cleared nicely.

Even more importantly is to choose the overall length of the chassis rails VERY CAREFULLY. Consider the following points when designing yours:

  • At all times/height adjustments the front swivel wheels must not touch the body of the mower

  • The height adjustment on my mower was 70mm from top to bottom, but at the half way mark, it also shifted the mower back 15mm. Make sure this does not interfere with the rear drive motors or the front wheels

  • Make sure you add a little extra to stick out the back. The motors end up sticking way out, so it's better to have too much than too little. I made a bit too short and ended up having to cut out the rear bar and welding it on top of the rail (see pics later).

                   

 

FRONT WHEEL SUPPORTS

Next up was to fix the rear wheels in place using clamps and weld the two upright swivel wheel supports to the main rectangular chassis.

Yes my welding skills are crap (self taught, gasless MIG - whaddaya expect???). Yes there is a nasty lean on the left hand wheel support. No - I don't really care.

These were welded slightly back from the front edge of the frame for no particular reason. It would be better to put them as far forward on the frame as possible to get best usage out of the chassis.

After these are attached, all that's required to fit the wheels is to drill holes in the new mounts to match the existing holes in the swivel mounts - easy!

       

 

MOWER SUPPORT STRUTS

Next I needed 4 identical fixed struts extending down from the main chassis which would somehow attach to the stub axels of the mower.

I wanted to be able to remove the mower from the frame if I needed to so I came up with the following setup:

                   

Pics (left to right)

1 & 2:    4 of these brackets were cut from 20mm tube steel. The brackets had two 5mm holes drilled on one face (for the bolts) and the other face had a single 12mm hole to fit the axle on the mower.

3:    Illustrating how the rig attaches to the mower's axle assembly

4:    how the brackets attach to the upright struts (which will be welded to the chassis)

5 & 6:    Fitting them to the chassis.

 

SOME CHASSIS ADJUSTMENTS

By now the chassis was coming along nicely. It was now that once I started test fitting everything, I decided that I needed a bit more room to shift the wheelchair motors back a bit, so I had to remove the rear horizontal bar and replace it with a slightly longer one (50mm longer) which sat across the top (see 1st pic below).

Then I trimmed the mower support struts to be flush with the chassis:

   

 

MOTOR MOUNTS

The last structural addition I felt this frame needed was and extra bit of bracketry so I could use all 3 bolt holes on the wheelchair motor mound brackets. They were 3 in a triangle pattern and I felt that the motors would flex too much if I only used two to mount them to the frame.

So, copying the same angles as the bracket, I made these on the underside of the chassis at the rear (again ignore the piss-poor welding - I'm am amateur dammit!):

       

MUCH better! But... there's something missing...

 

BATTERY TRAY

Now all we need is something in the back to hold those 2 huge SLA batteries, so here's what I did:

                

Pics (left to right)

1:    First I welded another horizontal bar across the tops of the rear support struts (make yours longer so they cover the top of the support strut - not like mine!)

2:   I cut 2 x 20mm flat bar steel to length and bent the ends up at right angles.

3:   Then I welded them into the frame between the rear horizontal bar and the new one I welded in the 1st pic. Make sure the mower is at it's maximum height setting before you do this!!!

4:   I cut 2 more 20mm flat bar pieces to length and bent the ends up at right angles, but they didn't go up as far as the first 2.

5:   Finally, I welded those to the first two flat bars perpendicular to them. Voi la! A place for the batteries.

PLEASE MEASURE YOUR BATTERIES TO MAKE SURE THEY'LL FIT BEFORE YOU GO DOING THIS TO AVOID DISAPPOINTMENT.

As it turns out, everything JUST cleared with about 5mm to spare on either side, but please - measure twice - weld once!!!

 

Part 3 - Final Assembly:

 

Ok, so now that all of the fabrication work was done, it was time for a nice shiny red paint job! I ground my crappy welding flat and cleaned the oceans of splatter with the angle grinder :)

           

 Beautiful! Then I went to the hardware store and picked up some 20mm furniture end caps (40c each). They fit perfectly and with a gentle tap with a hammer, seated into the end of the tube nicely.

       

Nice. Then I put the wheels and motors on.

Then it was time to stick the mower under the frame and attach it to the axles with our custom made adaptors. 2 bolts per adaptor.

I was amazed at how rigid the setup was. no sideways movement from the mower at all!

           

Batteries sit nicely in their cage and don't foul on anything at any ride-height setting:

   

Then finally, the wiring loom and electronic control box go on (see the electronics section for an updated pic with the receiver mounted inside the control box)

   

 

JOB DONE!!! A video of it in action is available in the downloads section...