baberjaved

Heres' a picture of my Robotic arm.. Comments Please! I Still have to make the software for it and the End Gripper is also under construction at the moment. =)
Can anyone tell me how can I find out exactly how much torque would be required at any joint of my arm and see if my Stepper motor can provide that much torque or not... Otherwise as the weight is quite a lot maybe I'll have to use some other motor (or maybe I can use Gears? If yes I dun know how :s)

Marks256

Looks very nice! Let us know how it turns out! Also, please post schematics for your controller, and the software, if it is ok with you, of course.

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theinfamousbob

Here's a Wikipedia article on torque:
http://en.wikipedia.org/wiki/Torque

Basically, figure out how much your arm weighs and how far it is from the hub of the motor. Compare this to the torque rating on the motor and go from there. (Think I worded that properly; feel free to correct me. )

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ikalogic

hello,

Nice work.. however, if i was you, i would put all the motor in the base arm (the shoulder) and find out a way of transmitting power to the rest of the robot through wires. I did that last year, with bicycle brakes metallic wires, and it worked perfectly, we had a robot with movements controlled by 6 motors, and they were all in the base of the robot. This way you reduce inertia, also you need less power to move the 'end effector' of your arm.

good luck and keep us posted

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baberjaved

Well I'm tryin to Run this thing now and The torque provided by the motor is way too less to lift the arm up...ikalogic your idea is very good and I would like to implement it in my arm but now that its already made I don't know how can I? =/

Anyideas to solve this torque issue? I need the motors to move this.. but the weight is just too much =/

Nigel Goodwin

From the look of it you're trying to use stepper motors at the joints?, there's no way you can ever make that work, stepper motors are weak to begin with, and you're gearing them up a lot and making them MUCH weaker.

I can only suggest you scrap it entirely and start again, this time give some thought how to make one - and test before you build it.

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baberjaved

means there's no way I can add Gears and produce enough torque to make this thing work?

blueroomelectronics

Sure why not, but you're going to have do some radical changes to make it work. Pulleys / chains might be the way to go, High torque motors for the heavy bits (steppers won't do it, not cheap ones anyway)
Counterbalancing goes along way too.
Here's the old Armdroid1
http://www.senster.com/alex_zivanovi...roid/index.htm

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Nigel Goodwin

Like Bill says, you would need to rebuild it entirely - your existing model also looks incredibly heavy?.

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picbits

Timing pulleys and belts are the way to go here.

Not cheap though.

baberjaved

The ARM itself is not that heavy but the motors are...
you mean One Motor cannot even lift the weight of the rest of the motors?

blueroomelectronics

It's because it's a 3rd class lever, the fulcrum has to support the entire weight of the arm.
Take a yardstick and add a 1kg weight to the end and hold it out at arms length. Heavy isn't it. Welcome to physics 101.
http://www.phy.cmich.edu/people/andy...s/Chapter7.htm

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Krumlink

A Class 1 fulcrum usually has a Mechanical advantage of less than 1, 1 exactly, or more than 1. A class 2 Has A MA of more than 1 Always or Exactly 1, but never less. A class 3 Lever has a MA of 1 or less, but never over 1.

Wow I actually did learn something in HS so far

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Nigel Goodwin

No, because (as Bill's diagrams show) they are at a massive mechanical disadvantage, and steppers are only low power anyway.

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NightFalcon90909

Nice solid construction! In fact, from the sounds of the other comments, too solid!

Firstly, torque = force * distance, force = mass * acceleration, acceleration = the change in position divided by the change in time.

So you could do some measurements to find out just what kind of torque you were looking at here.

Secondly, as has been suggested, you should looking to gears and chains. You could have all your motors at the base, and using a series of chains or even simple strings connected to winch type deals, really decrease the amount of weight you are dealing with.

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