I have written these tech pages in the hope that it will encourage others to build walkers, and hopefully demonstrate that it is not perhaps as difficult as it would first appear. It just takes a lot of dedication and time.
We only had two weekends to build a battery powered walker, we did not think we could create anything that would be competive and so we thought we would try something which would be simple to build and intresting in the way it works. So we based it on a simple toy, a penguin which rocks it's way down a gentle slope.
Essentially Rita works like a pendulum, she rocks backwards and forwards at her natural frequency from one foot to the other. The foot which is loose pops out when she is near the end of the swing to the rear, hence moveing the rest of the body forward, as she rocks forwards again the main body drags the foot forward into it's starting position. To make her rock the weights rotate at a rate which is simelar to the natural frequencey. The following pictures show the walking action, when we took these pictures we did not have the rotating weights fitted. She will only walk forwards.
Rita Rocks is powered by a 400W motor which is geared down so that the arms can rotate at at a maximium of twice a second. We used a 4QD Pro 120 Speed controller and found that she would walked best at a rotation rate of around one turn every one and a half to two seconds. It did not matter which way the arms rotated she would still walk forwards, but in one direction she would walk more effectivly.
The weights on the arms where fire grates from an old water boiler each one weighs about 2.5Kgms.
It is intresting to note that Rita Rocks speed is smilar to Miss Struts. Rita powered by a 400W motor(She did not use that much power), Miss Struts about 4kW, umm......
Rita Rocks does not turn, she will only go in a straight line, but we did think if we put the piviot point of the free foot on a turn table we could rotae the table about 10-20 degrees and she would gradulally turn as she walks.
We have had a few problems with Rita Rocks, the rotational rate of the arms is very critical, if they are too slow she does not walk but just stands there rocking to and throw. If they arms turn too quickly she rocks too far and falls flat on her face. We controlled the rotational rate via our transmitter, setting the speed by limiting the maximium throw of the servo. This was okay, until we were in the studio for her actual race. Normally we sheild all our electronics in metal boxes, this is beacause we are uaslly using computers and so did not want to cause interference to our sleves and other robots. For Rita all the electronics are analogue so we mounted the electronics in plastic boxes. In the studio the level of RF signals is quite high and it got into the analogue circuits and made the arms rotaed too fast. We did not pin this problem down until we got home after Techno Games, were we fould if we held our transmitter close to the analogue circuits the arms would start rotaing much quicker. I think there is a lesson to be learned here. Apart from these she has proven to be quite reliable.
If you think there should be some other technical detail on these pages please EMail me at the following address and I may add the information to this page:-