Tripod Dolly with suspension

I wanted a way too shoot dolly like footage.
I saw these wheels for tripod online but they all had very small wheels and no suspension.

So I designed something, it was some time ago, if something is unclear, please ask.

the bolts are wood bolts with a rounded head and a square part.
I got the springs from rsonline, they may be a bit too stiff.
A bit of oil is required for a smooth suspension.

Steering is a bit akward and requires some practice ;-)

See it in action:
https://youtu.