Is there a formula for determing lengths that the Femur and Tibia should be? Is it based up on the servos used and their torque? I am thinking that suspending a tibia of X amount of millimeters in length and weight, plus suspending the femur length plus weight of leg and servo corresponds to a oz/in thing that relates to the holding power of the servo in the hip. Is this calculated or is it just trial and error?
I am designing a quad and would like to have a long femur and tibia, but I know that “X” length will be too long and won’t work. I just don’t know how to determine what that “X” length is.
It’s for an arm, but it’s all torque and the math should work out either way you turn it. Just make sure your units match up (oh and his “acceleration” calculation seems to be off so just set it to 0 and then remember you’re going to need some extra juice to actually make it move) I think I used his excel version when I was poking around.
My best guess would be to use his arm model as essentially an upside down leg and go from there. Remember though: if you want your quad to move it’s going to have to have a leg in the air from time to time so you’ll need to divide your body weight by 3 not 4 (Admittedly, watching a walker fall over under it’s own weight is funny the first time, but it gets old VERY quickly when it’s your own project )
It’s that or bring out the trig and physics and go balance your torques like there’s no tomorrow.
Thanks jfavreau. An excellent resource and the tutorial is very educational.
And I never thought that with one leg in the air the other three would have to support the quads weight. I weighed everything on a digital scale and divided by four. Stupid rookie mistake.
(oh and his “acceleration” calculation seems to be off so just set it to 0 and then remember you’re going to need some extra juice to actually make it move) I think I used his excel version when I was poking around.
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