DIY all-terrain Robotic Lawn Mower part 1

This is part 1 of a series of posts to outline my DIY all-terain open source robotic lawn mower.  I currently own two robot mower.  A Robomower RL800 and a Lawnbott Evolution by Ambrogio in Italy.  Both are great machines, but I like the Lawnbott better.  It has automatic docking and charging and it does better on rough terrain.  However, both of these machines are no match for backyard!  My number one design requirement for the DIY robot mower is having the ability to handle almost any terrain presented to it!  I created 3D model in OnShape.   The majority of the parts will purchased parts, but for the wheels I had trouble finding spiked wheels, so I decided to go with 3D printed custom wheels.   Here is my first version 3d printed on a PlasticScribbler Asterid 3D printer:

It looks great and I think the spikes would give great traction, but I was worried about the durability of it, so I redesigned it.   Here’s a screenshot of one of the drivetrains:

The 3D printed spikes have been replaced with #4-40 socket-head cap screws and lock nuts.  The wheel is driven by worm-gear 7rpm gearmotor with 8mm diameter output shaft.  The spiked wheel is attached to two shaft couplings which is secured to a 8mm shaft with set-screws.  I used the robot wheel speed calculator to calculate the expected robot lawn mower speed:

FPM = (8)*(3.14159) * 7  =Cf * WRPM (wheel RPM * circumference in feet = feet per minute) = 175.9 FPM
FPM * 60 = FPH (feet per minute * 60 minutes = feet per hour) = (175.9)*(60) = 10,555.74 FPH
FPH / 5280 = MPH (feet per hour / 5280 feet = miles per hour) = 10,555/5280 = 1.999 MPH

I know 2 mph is pretty slow.  A normal human walking speed is 4 mph, but I wasn’t going for speed.  I wanted as much torque as possible.  So the loss of speed was a compromise on the design.  I also went with 4-wheel drive for this robot

I own a Bolens 125cc push mower.  It’s the cheapest mower you can buy, but it will go thru anything.  The DIY all-terrain robot mower was designed around this standard push mower.  It would be easy enough to mount the RobotMower RL800 instead of the Bolens internal combustion engine driven mower, but for right now I’m planning on using the Bolens gas driven engine as the grass cutting portion of the DIY robot mower.



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