Monday, March 25, 2013

Steering with parallelograms

It wasn't clear in the beginning how we would actually steer our kart. We started with a slightly more normal rotary steering column in CAD. We considered the design for  awhile but realized that because we were using a twist grip throttle there was the possibility of inadvertently accelerating as we went around a corner. We ended up opting for a parallel linkage. This will keep the handbars horizontal, even while we turn. The down side to this type of steering is it's a bit less sturdy and somewhat more difficult to make. When we made our preliminary work plan on Sunday we had all our steering machining and assembly slated for Tuesday  Well, here it is, Monday evening and we've finished our steering linkage.

The lower plate connects to the very front of our frame. The middle, gold-ish colored parts are ball joints. They will allow our pushrods to change angle with respect to the arms and uprights. The top bar will have thin tubular extensions that will become the handlebars.

 This piece was machined from 5/8" aluminum tubing with about 1/8" wall thickness. We need to buy some longer bolts, the ones that we are currently using are just barely threading onto the nuts. I used the aptly named tinylathe and minimill to thin the ends and cut the slot. The machines are indeed tiny and thus do not have a huge capacity. This means I had to do a lot of passes which wasn't fun, mainly because the bench they're mounted to is actually a tool chest on casters. Lots of rattling noise and the workpiece was at roughly the height of my belly button. My neck and back were sad. Moving on.

 The washers that look like pennies here are actually made of a special porous bronze impregnated with oil and little bits of teflon. That means the steel bars they're squeezing should be able to rotate nicely even with the bolts fully tightened. Things are starting to look good.

Until next time.