# Thread: robot arms

1. just i couple of qs about robot arms,
if a robot arm was 1m in height are ad had a 1m reach would the arm have stepper motors or just dc motors with gearboxes with some kind encoder to tell it where it is. because i was thinking would the stepper motor be able to hold the arm up on its own, if not would a gearbox bo needed, what sort of power do stepper motors go up to.
adam

2. To get any meaningful torque/control, you would need to use gearboxes of some kind.

3. as m_c suggests..

a 1m lever need 1Nm of holding torque per 100g of mass it has to hold up (including the mass of the arm). So for an arm able to lift and hold 50kg you'd need 500Nm of torque. On a 2.5Nm motor that would require a 200:1 gearbox. Assume the arm has 90deg of travel, that would require 10000 steps, about 5 - 10sec of movement... a bigger motor would need less gearing so could move faster (excluding inertia effects, which I have left out of the calc but are significant as well).

Could be done with steppers and screws, steppers and gearing, servos (motors with feedback), hydraulics, etc... will probably need some sort of positional feedback whatever drive mechanism is used...

4. Originally Posted by irving2008
as m_c suggests..

a 1m lever need 1Nm of holding torque per 100g of mass it has to hold up (including the mass of the arm). So for an arm able to lift and hold 50kg you'd need 500Nm of torque. On a 2.5Nm motor that would require a 200:1 gearbox. Assume the arm has 90deg of travel, that would require 10000 steps, about 5 - 10sec of movement... a bigger motor would need less gearing so could move faster (excluding inertia effects, which I have left out of the calc but are significant as well).

Could be done with steppers and screws, steppers and gearing, servos (motors with feedback), hydraulics, etc... will probably need some sort of positional feedback whatever drive mechanism is used...

thanks for that makes a more sense now. ive been looking all day but cant find anyone thats made a heavy duty robot arm they all seem to be small hobby ones, has anyone got any links for a robot arm build its just something thats intreased me.
adam

5. Robot arms are used in industry, but I don't think I've ever seen one for sale, and they probably go by a different name.

6. Originally Posted by m_c
Robot arms are used in industry, but I don't think I've ever seen one for sale, and they probably go by a different name.
I saw one not so long ago at university. It was pretty amazing - about 2m tall, lots of rotary axis' with servos and very stealthy. The guy operating it let me have a go, just pressing the jog buttons. Fun :) ! Good to watch when it just moves in a straight line since none of the axis are linear. I think it was 6 axis iirc.

7. I threw one in the skip a couple of months ago at work. Still worked perfectly well but we didnt use it anymore. It was a six axis Motoman robot used for gas cutting beams.
Anyway mosr robot arm are servo driven through gearboxes with brakes engaging when the motor power is off. Also encoders are used to indicate the position of the arm.
There is also a chrome plated one I think at the xscape centre at Breahead in Glasgow. I think it is called the Robocoaster and has two seats attached to it. A new idea for rollercoaster types I think.

Ian

8. Originally Posted by m_c
Robot arms are used in industry, but I don't think I've ever seen one for sale, and they probably go by a different name.
m_c, There now appears to be a fairly large market for second hand six axis robots. Take a look at http://www.globalrobots.com/. Not cheap though starting at £3,000 +vat. (This is my first post but I promise I am not affiliated to these guys in any way!)

Web Goblin, I have seen that beast at Braehead looks like fun but if you do a search in Youtube for '6 axis robot' the first video that comes up is some loonies strapping themselves on to a car seat mounted on the end of one of these things.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•