DIY Slider (Inspired by Spider Trax dolly)

I threw this little video together to show the slider I built in a little more detail.
This slider ended up costing me around $45-$50, and I think it has some pretty cool features that a lot of other sliders don't.
The basis for this design is the Spider Trax dolly, which has quite a few variations around the internet, but these are the videos that I based mine on:

The dolly - https://vimeo.com/13696165
The rails - https://vimeo.com/13949623

I'll probably end up tweaking things here and there as I use it and figure out what works the best in practice, but this design seems to work pretty well as is. I LOVE the versatility of the "turnable" dolly, something that the vast majority of the DIY sliders I looked at didn't have. This design is a little heavy, but I think it's still compact enough to be pretty portable. I don't have to worry about it breaking in my hands like some designs.

Things I may eventually change:

Dolly platform - After I put it all together, I realized I really didn't need to make the dolly
platform as big as I did. If I come across some extra time or a material
as easy to work with and light as wood, I'll at least make it shorter, as
that would give me a little more length of motion.
End Legs - I may end up needing to revise how the end legs are attached. The
current way works great for most things, but when using the rails at an
angle, the legs can't swing to remain perpendicular to the ground. The
current attachment points were just the easiest way we could find.
Wheels - These wheels work well, but they can have a tendency to slide
sideways a bit on very smooth surfaces. I may try to find some made
of a bit softer rubber. These bearings also have quite a bit of friction,
but I'm actually quite pleased with that, as it makes it easier to hand
push the dolly at an even rate.
MOTOR! - That's right! I may eventually add a motor. As I built this I kept thinking it wouldn't
be terribly difficult to make it motorized with a couple pulleys, something to stretch
between them and grip a wheel or two, and a motor at one end. And if not a motor,
at least a little hand-crank, right??

Put any questions in the comments below!