I am going to try a quad. Yeah…I know! My question is the placement of the servos. I have seen all of the different designs of the hexapods and instead of keeping all of the servos close to the first degree of freedom and in close to the body, most of you (Jim, Zenta, etc.) are placing an individual servos at each joint.
Why?
Is there a lot of power lost using pushrods and rod ends? Or is it the extra weight of the pushrods and rod ends? It just seems that if I used small ball bearings at the joints and kept the servos as close to the body as possible it would help keep the weights closer to the center of gravity. This seems to be the largest obstacle to overcome, the weight of the overhung leg that is off the ground and moving forward wants to make the quad fall over to that side. If the weight (the servo weighs a lot more than a small pushrod and a ball end) were kept closer to the COG …you see where I am going.
I think you may be underestimating the mechanical complexity of building a 3DOF apendage that is completely pushrod / connecting rod driven. If you use a direct connection to a servo for the horizontal pivot, the other two servos would need to be attached to the leg not the body. I’m open to suggestions, but I don’t think it’s feasable.
I am experimenting with 2DOF legs with indirect drive and using ball link connecting rods, and it’s complex enough.
And if you have mechanical advantage or disadvantage built into the pushrod mounting distances, it changes the legs position relative to the servo position.
You would have to factor this into your programming if you are using inverse kinetics.
Here is an example of a 2DOF leg with mechanical advantage and connecting rod. It keeps the two servos as close to the body as possible. It actually works very well.
Adding the 3rd DOF to the leg would be challenging.
