Has anyone ever heard of a (hobby sized) servo device that would let you, say
rotate a servo arm to close a pair of
grippers, then lock it in place mechanically so you wouldn't need to keep
powering the servo to hold an object ? Of
course, it would need a way to release it, preferably electrically.
I guess a better alternative would just be a lead screw setup, but I thought I'd
ask anyway. I have been wondering about
this for a while & figured you guys would know if anyone would !
Haven't seen one, but as such it doesn't take that much power to hold an
object, especially if the gripper uses leverage (most do). Most of the
power is consumed when lifting an object, unless the arm or other
mechanism is counter-balanced (most aren't).
If you look at the older gripper I have on my site it's actually made
from a ratcheting clamp. I remove the ratchet. One could leave the
ratchet in place, and release it by some means, such as a solenoid, but
I think it's overkill. Now you have the weight of the solenoid and the
releasing mechanism on the gripper, and power consumption goes back up
Anyway you can get these clamps at many woodworking outlets. Cost is a
buck or two.
Thanks Gordon. I actually copied your idea about a year ago and made one almost
identical to that one. I didn't think
about leaving the ratchet part in, though. And yeah I agree about adding the
weight of a solenoid - not really
Here's a photo for those that are interested:
Here are a few ideas to think about...
You could always spring load the gripper so the spring holds it closed.
That way, you only need power to hold it open. The spring would bias the
action of the servo making it stronger for closing and weaker for opening.
If you kept power applied, it could produce a stronger holding force, but
would still reduce the load on the servo and I assume reduce the power
drain as well.
Also, if you design it right, you should be able to make it hold by
friction of the parts alone. It's just a matter of using the correct gear
ratio or the equivalent created with a series of levers. But that might
end up creating a gripper that opens and closes too slowly for what you
want to do. Your lead screw idea is likely to produce enough leverage to
hold by friction alone.
If you are designing the gripper to grab one very specific size of object
which will allow the gripper to close to the same position every time, then
you can use the same trick that is used with vise grip pliers. You just
use levers that are the correct length so they lock into place when the
gripper is in the closed position. With the help of a spring between the
levers and the gripper, you could make it lock on to slightly different
Look up Toggle Clamps, or the more general 'over center mechanism'. Another
example is the Mole Grip. These all generate a large force which is
You will need some compliance (ie spring) to control the force applied to
the object, or it may get damaged ...
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