| Axles and Sprockets |
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This section will cover the types of axles and sprockets I use.
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Gokart Jack Shaft Kit – This is what I used to start making the engine drive axle. The axle is 3/4 inches
in diameter with a keyway. I did not use the sprockets that came with this kit because they did not fit on my
wheelchair motor output shaft or chain that I was using. However, everything else was used. I purchased this
kit at www.northerntool.com.
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Weld on Hubs – These are the key to mounting your lawnmower wheels to the rear axle. They are called weld on
hubs and they are used to mount sprockets and pulleys. Get the ones that have a round bore size of 3/4 inch and
it should have a keyway and two set screws. I purchased mine at www.tractorsupply.com.
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Here is what the hubs look like mounted to the metal rims. You remove the bearings from both sides of the wheel
and the machined lip of the hub will fit right into the hole. Before you weld them to the wheel be sure to insert
both hubs into the rim and then insert the axle and axle keys. You want to make sure both hubs will line up with
the keyway on the axle before you start welding.
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This is what the complete rear axle assembly looks like. Note there are some spacers on the axle. These are
short pieces of PVC pipe that I cut to fit between the various parts. The idea was that if I needed to make a
quick repair in the yard I could just pull all the parts off, fix what I needed, then put it all back together
again without having to re-measure or adjust anything.
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Actually finding the right sprocket to fit my wheelchair motor was difficult. The motor had a 17mm output shaft
and I could not find an off the shelf sprocket to fit. 17mm equals .669 inches which is just under 11/16 inches
(.6875 inches). I first bought a 17mm drill bit and tried to enlarge the hole of a 5/8 bore sprocket. Even using my
drill press I could not get a hole that was centered. I then got lucky and came across a tin cigar tube that I cut
to make a shim. This shim was wrapped around the axle and filled the gap to make the 11/16 bore sprocket fit snug on
the motor output shaft. I purchased my sprockets and chain at www.tractorsupply.com.
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Finding the right sprocket ratio. I knew I wanted my train to travel about the same speed as a power wheels kids car.
I mounted my motor and axle to a board and connected the two with a chain. I turned on the motor and while the wheels
were spinning in the air, I held up a power wheels motor and wheel next to my lawn mower wheel to gauge the speed.
I adjusted my sprocket ratios until I got a close match in wheel RPM. This was a very crude setup but it worked out great.
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