Posted by Wade
As we learned during our attempt to scale up TrotBot, not all robot's legs will walk by pushing or pulling the robot. When we pushed TrotBot Ver 0 with its more rectangular-shaped footpath, the cranks would initially rotate, and then the linkage would freeze and the feet would skid on the pavement. Instead, we had to manually rotate TrotBot's cranks to make it walk:
The same thing happened when we tried to push our LEGO Klann walkers with the motors disengaged - the feet would skid and the cranks would not rotate. In both cases, this was due to the linkage being at a sort of reverse Dead-Point. As you can see in the image of Klann's linkage below, pushing Klann's feet at this point in the crank's rotation would not cause the crank to rotate. Instead, pushing the robot would only cause the legs to bend and the feet to skid.
Notice how the outer leg's connection to the crank is parallel with the crank, a tell-tale sign of a dead point.
If the crank is rotated past the dead point, then pushing Klann's legs will cause the crank to rotate:
If another pair of legs were added to each side of Klann, as done in the simulation of Strider below, then maybe its legs could be driven by pushing the robot (although one of Klann's feet would still skid at the corner of the foot-path, so it may not work so well - maybe adding feet that could slide or rotate a little would help?)
Here's a test to see how easily this linkage variation #6 of Strider's mechanism can be driven by an external force - gravity in this case:
Notice how the robot wavers slightly to the left and right as it descends, due to the foot-speed varying a little. Linkage variation 7 below has more consistent foot speed, and waivers less
Strider's legs can also be driven by pushing the robot when built in an 8-leg version, although not nearly as efficiently as 12-leg versions, and the ramp's slope had to be increased to get an 8-legged Strider to walk below:
Dead-Points part 1 is here.
Welcome to DIYWalkers! I'm Ben Vagle, and I've been building mechanical walkers since I was 11 years old, both big and small. I started this blog to share what I've learned, and to collaborate with you. Let's see if we can take walkers to the next level!