I'm a fan of
Automation Direct for stuff like this. They've always had good customer service, and tend to be on the cheaper end of industrial suppliers. I've used their CLICK series of PLCs on a number of projects and you can't
beat them on price vs capability.
One of my quarantine projects has been working on a design for pneumatic brakes. I went with the mindset that it's potentially a much more versatile approach than having to lift the whole
wagon on/off of its wheels. The only downside is that a loss of air pressure results in the brake being released... but that seems manageable by being careful about avoiding leaks in the
system. This is still a work in progress, but here's an idea of how it's looking:
It's based around
this cylinder, a couple pieces of t-track, some hardware, and one 3D-printed plastic part. Rubber on the bottom of the plastic
foot adds a decent amount of friction. It's small and cheap enough that you can sprinkle a couple of them around as needed based on the size and weight of the
wagon. The main thing I still need to figure out is how to shave off just a tiny
bit more height so it can be used under a 2x4 framed
platform with the casters we typically use (about 4.75" from the underside of the
platform decking to the floor). I started with a little simpler design using a
pancake cylinder, but I didn't like the way it put horizontal stresses on the rod & bushings. Plus that cylinder was about 3x the cost of this one...
Automation FX does have a similar product if you're looking for a less DIY solution:
AirPux 2 Friction Brake