At 3:34 PM +0000 8/31/07, dan michaels wrote:
>--- In SeattleRobotics@yahoogroups.com, Rich Chandler <rchandler@...>
>> Actually, One thing I'm interested in is an improved mechanical
>> design that avoids supporting the weight of the robot via the force of the
>> servos. And from there, I'm interested in programming the motion so that
>> there isn't any sideways force on the feet as it walks or turns. Those
>> things interest me.
>The easiest way to do the former is use "upright" or rotated-under-
>the-body leg design, rather than sprawled leg design.
No, that's not quite what I'm talking about. Although I suppose in a way,
it's related. Way too many folks design the legs so that the entire torque
of the horizontal "Thigh" is directed through the servo, with the servo as
the pivot point. My idea is to design the leg so that the thigh is lifted
and lowered by the servo, but a) the pivot point is not the servo and b)
that when the leg is supporting weight, there's no torque on the servo. So
like the leg you're talking about, the force against the servo is radial to
the axis of the servo, like a locked knee. (Alternatively, I was thinking
a spiral cam for raising and lowering the leg, which would never torque the
servo in any position).
>Regards the later comment, you will observe that a certain amount of
>sideways force on the feet is necessary in order for the frame to
>have stability. Rbt Full calls this "lateral self-stabilization", and
>it's a MAJOR factor in reducing the amount of processing power [ie,
>brain power in animals] required to produce stable locomotion.
On this point I'm talking about the kinematics of the foot end of the leg,
because so many designs (other than that cool five-legged robot we've seen
at various meetings) don't pay enough attention to the tracking of the foot
on the ground, and tend to slide or drag their feet while turning. For
that I'm looking at the lower leg (shin?) being able to track in and out.
And again, I don't plan to support the weight through the servo, which
should significantly reduce power consumption.