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### Author Topic: Arm Designs  (Read 10969 times)

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• Supreme Robot
• Posts: 11,703
##### Re: Arm Designs
« Reply #30 on: February 03, 2008, 05:31:45 PM »
its actually weight multiplied (not divided by) distance

for example:

torque = weight * distance

if distance = 0, torque is 0

or another way to put it,

torque/distance = weight

as distance approaches 0, weight it can carry goes to infinity

#### gamefreak

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##### Re: Arm Designs
« Reply #31 on: February 03, 2008, 06:07:00 PM »
so then I could take a 60 rpm 47 oz in servo, and rotate any mass(assuming minimal friction)

I always though it was weight over distance
ie, 67 oz in can carry 67 oz over 1 inch, but 33.5 oz over 2 inches....
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• Supreme Robot
• Posts: 11,703
##### Re: Arm Designs
« Reply #32 on: February 03, 2008, 07:18:49 PM »
Quote
so then I could take a 60 rpm 47 oz in servo, and rotate any mass(assuming minimal friction)
If there is no counter forces, then yes, any mass. Well, almost . . . there is also dynamic forces to account for such as rotational momentum. Check wikipedia for equations . . . So no, you can't rotate the earth on a motor

Quote
I always though it was weight over distance
ie, 67 oz in can carry 67 oz over 1 inch, but 33.5 oz over 2 inches....
if you plug those into the equation, you will see which equation is correct

#### gamefreak

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##### Re: Arm Designs
« Reply #33 on: February 03, 2008, 08:46:32 PM »
I think your giving me the required torque of the motor, and im giving the actual torque of the motor...

Alright looking up rotational momentoum brought me to angular momentum, I believe they are the same..., but since I havent taken physics I dont understand it, So im going to go the lazy mans way and use two of the same servo for this purpose that way I get double the torque.

Yay for random robot parts laying around
« Last Edit: February 03, 2008, 08:59:04 PM by gamefreak »
All hail Rodney, the holy 555 timer
And Steve said: "Let there be lead!"

#### gamefreak

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• Posts: 543
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##### Re: Arm Designs
« Reply #34 on: February 13, 2008, 10:16:54 PM »
Alright, being bored and reading through one of my six or seven robot books(not counting the progamming ones, im a nerd), I started reading about muscle wire, nitonal, BioMetal, or as they are generically called SMA's, Would it be feasible to run the arm using these, as the event is Electronic Research and Experimentation, maybe use a transistor to power it from the microcontroller?

It says it will contract by 2 to 4 % of its length, which seems to be very little, an 8 inch wire when heated, with 4 percent contraction, turns into 7.68 inch, which is a contraction of .32 inch, almost a third.
« Last Edit: February 13, 2008, 10:20:21 PM by gamefreak »
All hail Rodney, the holy 555 timer
And Steve said: "Let there be lead!"

• Supreme Robot
• Posts: 11,703
##### Re: Arm Designs
« Reply #35 on: February 14, 2008, 05:50:59 AM »
Nope, in short, SMAs suxor.

Just do the math on the force and contraction specs, and you will see.

(there are exceptions to this in micro/nano robotics, due to scaling laws . . .)

#### gamefreak

• Supreme Robot
• Posts: 543