I see your post on Jan. 23 asking about weight considerations for a robotic
arm.. No replies though :( You might have your newsreader set up to ignore
posts you have read, and since there were no replies, you no longer see the
original message. If you are using outlook express, look under TOOLS then
OPTIONS and in the MAINTENANCE tab there is an option called "Delete read
message bodies in newsgroups" Make sure it is not checked.
Anyways, other than that, I don't think I have any useful advice for your
original inquiry other than to go to your local library and look up books on
traditional machines (like the windlass, inclined plane/screw, levers, block
and tackle, flywheels,etc...) as these will give you great ideas for machine
physics principles to apply to your design. Any good physics book (even my
crappy physics textbook) will be able to give you the formulae for torque
and potential energy/center of gravity. These are your friends when
determining the fulcrum point and required amount of force.
BTW, intuition (and a very crappy college physics course) tells me that your
counter-weight would be best placed at the top of the shoulder, so that it
ends up in the correct position to "counter" when the shoulder is moved.
Otherwise, it will help in one direction, but hinder in the other. It should
be balanced so that it will assist the joint. Also to properly balance with
a counter-weight, you will either need to have it at an equal distance to
the fulcrum (pivot point) or have a substantially heavier counter weight
(IOW: much bigger) if it must be closer.
Perhaps a counterwieght is not such a good idea afterall:
I do not know the technical term for this, but intuition again tells me that
it is not possible to use a counterweight without causing additional work.
In maintaining the position of the arm, it will need to work against all
forces applied. Although the counter-weight would be placed so that it
logically assists the motor, between pole reversals of the armatures of the
motor, the weight will be free-wheeling and the motor will need to catch it
and hold it (is this called backlash?). Something similiar to a flywheel or
pendulum in the gearing might be more efficient. I know I probably didn't
explain that right, so I am hoping someone else might offer a better
Perhaps (not something I have tried) the proper approach would be to build
the arm without the gearing and use a spring scale (or torque wrench) to
turn it and measure the amount of torque required to move the particular
joint. This will help you in choosing your gearing and motor, of course alot
of this will also have to do with what you are using for a power source. All
things are related...torque to work to watts to amps...etc..
There are so many variables that unless you already have the mechanisms
designed and have a pretty good idea about the length of the joints, size
and weights of objects expected to be "effected", and power availible, it
will be hard to give any direct advice. Perhaps this is why there was no
Anyways, I am not an expert on this in any way, but good luck.
P.S. Also googling for "mechanical advantage" should come up with some good
sources. Here is a link that may help you get started:
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