BigCrawler

From TheRobotGroupWiki

The BigCrawler is a 2 legged 2 wheeled robot that crawls along on its front legs and drags the rear wheels which support the bulk of the battery weight.

First I built the main front legs assembly with a single screwdrive actuator (from a car's power seat) moving both legs in and out for side stepping motion and turning.

This actuator below powers the leg lift motion.

After going to a lot of trouble making nice machined adjustable pivot joints and linkages for the side step and leg lift I ran out of time so the leg stroke linkage got thrown together out of scraps of chip board but since the the motor mount was in the wrong place anyway I will fix both the mount which needs to be lower and make an adjustable nylon swivel linkage to go with it.

After getting all the parts mounted and wired up to test the motion I will strip it back down to just the body parts so I can give it one final coat of fiberglass with Kevlar in some key high stress areas. I needed to see how it would balance with the car battery on board but unfortunately the wheels will need to be extended further out and the battery moved further back so the front legs will be able to alternate lifting off the ground.

Also unfortunately I could not resist the temptation to see if I could get it to take a step by adding more weight to the back. It still wanted to lift the tail end, battery and all, so when I tried the side step action with both front feet still on the ground I ended up cracking the motor mount that was just the foam shape with no skin to handle the stress.

Fortunately it is easy to glue back together when I do the fiberglass skin.

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