Saturday, February 24, 2007

Lowboy Prototype

It's been way too long since my last post. It seems I'm taking the large chunks route instead of frequent small posts. Oh well.

For this past months, lots has happened in my Lego world. Firstly, building a robot for the Brickfest Competition has been soaking up some of my free time. The rest of the time I've been faithfully working on the Argosy! Changes: Basic pressure switch, more cab, doors, trailer!

The idea is to have an automatic pressure regulation system. This has been done before in Lego, using a polarity switch, a pneumatic cylinder, and some rubber bands. However, this is unacceptably large.

Instead I've been toying around with a normal 1cc syringe acting as a single-acting pneumatic cylinder. It stretches a rubber band when it extends, and when the pressure drops, it contracts and hits a 8mm square tactile sensor, turning on the motor. It is difficult to tune for the correct pressure range, but I just need to do more experimenting on it.

I've also started building the cab more, putting in windows, handlebars, and the other door. No pictures yet, as it looks odd with a shortage of tiles.

Thanks to, I've found some excellent large lowboy pictures. After seeing this trailer I knew it had to be the one. It has a detachable neck - meaning the hitch part comes off for loading and unloading. It's also got big hydraulic cylinders for raising and lowering the trailer height. Total capacity is 52 tons.

That gradually amassing pile of black Technic beams was beckoning, so I decided to take a break from the Argosy proper. Pictured is the first prototype. The neck doesn't detach, some colors are wrong, and the thrid axle isin't made yet.

To my knowledge there are three common types of supsension for trailers: leaf springs, spring-ride, and air-ride. I settled on the second, shock absorbers, - although a heavy load will max them out, it is easier to design and they cost about 1/20 the price of small pneumatic cylinders. With a 14M-wide vehicle, and 8 of those 14 used up by tire, there's not a lot of room left for suspension.

What I have is a straight-and-simple wishbone setup. It works ok, but the ground clearance in the middle is awful. If luck is with me tomorrow, I'll be able to change it slightly to lower the axles 1M relative to the wishbones. Yay! Need more shocks first.