Ok, so what I did was run these cars on a treadmill, while tied to string, took the photos, and used an eraser tool to try and hide the strings(these photos are what I shot pre-edits)
It doesn't actually look too bad, I do wonder though, maybe a string color similar to the tread mill might make it easier to cover in post, thenagain, might be wrong. Still looks solid!
I did actually try a thin wire that blended in better, but the heavier cars (the NASCAR and Ferrari) were too heavy to handle it, and the hot wheels I used were too tiny to offset how stiff the wire was
And I know from experience that the wire wasn't enough because when I tried the wire on the ferrari... The tape holding the wire snapped and I had to catch it from crashing onto the floor
