Hello all. My name is Noah. im new to robots and to this forum. im doing a little research to find out whats right for me. after a quick search of the forum i didnt see an answer to a question i have. can the hexapods be programed to walk (even if its a ‘bad’ walk) on 4 legs, freeing up the ‘front’ two arms for other tasks?
ive seen the 4 leg stand during the ‘attack’ mode, but i mean actually walk
Hi
I have to say that I never tried to walk on 4 legs but the main thing about walking on 4 legs is balance. If you want to walk on 4 legs you need to keep 3 legs on the ground at all times. So what you need to do is shift the COG (Centre Of Gravity) between 3 legs. So there is no more weight on the fourth leg so it can be lifted.
Say you want to use the middle and rear legs to walk. Then you need to place the COG between the rear legs and one of the middle legs. I don’t know of this is possible… And even if you can pick something up with the first 2 legs because the COG will be shifted to the front.
I hope this helps.
Xan
If you are walking on 4 legs, you are basically imitating a quadropod. And many people have made them walk.
Mostly, you will find the people in this forum advocating various means of statically stable gaits. These are fine, however they have some serious limitations. In particular, if you want to simulate a damaged leg or two, Or if you are overhanging a large load off the front of the 'bot because you used the front legs to pick something up, you are not going to get that nice centered CG you need for a statically stable gait.
If your servos are fast enough, you can always look at dynamically stable gaits. These types of gaits will allow you to do just about anything if you can get them right. For instance, I have a dynamically stable gait* that allows my robot with three legs to walk. So it can most certainly be done.
Perhaps you are wondering about the weight? With 4 legs instead of 6 legs supporting the ‘bot, there is obviously more weight per leg. So either you put on bigger servos in some or all of the joints, or accept a reduced payload limit.
You certainly can just walk on 4 legs! All it takes is a little software… To that end, I suggest you study the quad gait, as explained elsewhere on this forum in a white paper (can’t remember where). I think it does a “body shiftâ€
thanks for the input guys. i guess you figured out my intention. i was thinking about making two of the legs with simple open/close pincer type claws… so i could pick something up or manipulate something. i wonder if thats easier or if it would be more practical to have some sort of arm system on top – johnny 6 style. ill have to keep thinking…
For the case of a hexapod walking on four, it is best if you design your bot with a COG between the middle legs and rear legs. It can be achieve with counter weight or simply shifting the battery (which takes most of the weight). Perhaps you can immitate insect anotomy; with a huge abdomen to counter the weight in front.
As for quadruped walking gait, designing a stable working gait is generally more challenging than hexapod. When using the front legs for lifting, you need to consider the COG shift, and your bot need some level of intelligence to compensate that.
unlike hexapod, quadruped walking gait (static and dynamic) is very sensitive to COG shift. Increasing the COG shift tolerance means the gait is becoming less efficient, in other words, smaller step.
