Thursday, August 11, 2016

Bicycle Trailer ep. 3 - Trailer Hitch

I realized from the internet (and by observing homeless people) that there's really no right or wrong way to build a bicycle trailer hitch, so here's my story:
I was considering using a bicycle head tube and fork combined with the swivel castor I bought in the first post, but not having any spare bikes to take apart, I figured the steering mechanism from my scooter would work just as well. It was a great relief to finally destroy this thing after crashing on it at least once per day during my first week of college. Those small wheels just can't handle pavement deviations!
destroying a scooter
Video explaining the design:

Firstly, drilling a hole for the bushing.
drilling a hole in scooter part for bushing
I used a flat end drill to avoid having the slot throw it off center.
using a flat ended drill
Then, to maximize the turning radius, I cut off the excess steering tube shaft.
cutting excess scooter steering tube
I guess I was too lazy to go to the hardware store to get a 1/2"-20 bolt to make the bushing from, so I decided to thread one myself. I think I had a grade 5 bolt, but it was too hard to drill through.
machining a 1/2"-20 bolt
Then for some unnecessary precision, reaming the hole to match the castor axle.
reaming a hole in hitch bushing
And I guess I was too lazy to get a 1/2"-20 jam nut too, so I drilled and tapped one from some hex stock.
machining a 1/2"-20 jam nut
Here's a poorly drawn diagram to explain how the bushing and castor fit together:
For the plate to mount the castor on, I first drew some hole locations on a piece of steel.
designing a plate to mount bicycle trailer hitch on rack
Then drilling the holes. Remember, always hold the clamp on the left side so it doesn't come around and hit you!
drilling mounting plate
 Mounting the castor with the scooter part.
hitch assembled
Drilling some extra holes for attaching the linkage later.
drilling trailer mounting holes in hitch
For the aluminum piece, I figured I'd mill some slots to help it index with the rack tubes so the hitch wouldn't slide out of alignment. Using a protractor to match the angles.
designing bracket to attach hitch plate to rack
Then using a ball end mill to cut the slots while the vise was tilted at the corresponding angles.
using ball end mill to cut indentations for rack rails
Perfect fit!
lining up bracket with rack
Then after cutting off the excess material and bolt length.
completed trailer hitch assembled
For some extra rigidity, welding some material on the scooter "fork".
welding extra support to trailer hitch scooter fork
Drilling a hole for a hitch pin.
drilling hole for hitch pin
The hitch completed. I ended up not using the hitch pin (probably since I drilled the hole too low on the axle causing it to be too tight) in favor of the lock nut. Even though this isn't "proper", I never had a situation with it falling off.
hitch with hitch pin
*insert Will Smith "Hitch" reference here

Part 1 Part 2 Part 4 Part 5 Part 6 Part 7 Part 8

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