March 10, 2010
Okay, I broke the rules. Yes, I'm ashamed. But I don't give up. Hopefully this is the right place for this article...
TSWLhexaPOC? Well, Two Servo Watt's Linkage hexapod Proof Of Concept would have been a bit too long for a name, wouldn't it? I stumbled over a few hexapods controlled by three servos. Well, it should be possible to walk over a plane with only two of them. If this is possible using some simple gear it would save money when building small robots. How did I find a solution?
I had a closer look at the usual mechanism of those three servo hexapods then you will notice that one servo tilts them while the other servos move two legs in a bow while the thirs one is not the center of these bows. This makes their feet slip and slide a little when moving. Can we improve this? First idea was to use Watt's linkage to move them linearly. Or some other straight line linkage - there are lot's of them. While digging the net I found out that Watt's linkage only moves approximately linearly in the middle and also produces bow movement in the ends. This gave me the idea how to get rid of one serve.
In the image you see the first concept. One servo exchanges the three standing feet by tilting the bot. the other servo moves three feet through Watt's linkage with the third foot coupled to the other two. Yes, the third one will also slip in this construction. One reason for the POC in its name. If the servo only turns a small angle around the center this bot will move a straight line. I the servo turns a small angle near to one end it will turn to one side, if the servo turns near the other end the bot will wurn to the other side. cute, isn't it? As a side remark, if the servo turns the whole way the bot will make large straight steps. However, take care that the linkage doesn't turn the wrong way.
So far for the idea. A number of improvements are still necessary. The tlting meachnism in th eimage is not really feasible. Has to be done better. Hey, I'm a software guy! Extremely creative with electronic and mechanic knowledge. My current problems are that I don't have enough spare time to work on it - and robot construction is not my primary job - and that I am still thinking about the materials for a first prototype. Well, I have a few servos lying around, a propeller demo board, a few PICs, some transistors and other discrete electronic parts but I am not yet sure what to use for the body, the gear and the legs. Cardboard? Wood? Plastic? Metal?