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Author Topic: the robotic arm tutorial  (Read 6923 times)

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Offline MarwanTopic starter

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the robotic arm tutorial
« on: April 24, 2008, 02:48:31 AM »
Hi,

After I read the robot arm tutorial, I asked myself: what could prevent the vertical arm from leaning? (the attached picture can clarify my point). I looked at the robot arm calculator but I didn't find anything mentioned about that. I did some math and I want to review it with you:

TL = (W0 * Sin (theta) * L0/2) + (W1 * Sin (theta) * L0) + (W2 * Sin (theta) * L0) + (W3 * Sin (theta) * L0) + (W1 * Cos (theta) * L1/2) + (W2 * Cos (theta) *(L1 + L2/2)) + (W3 * Cos (theta) * (L1+L2+L3/2))

= (W0/2 + W1 + W2 + W3) * L0 * Sin (theta) + (W1 * Cos (theta) * L1/2) + (W2 * Cos (theta) *(L1 + L2/2)) + (W3 * Cos (theta) * (L1+L2))

I neglected the weight of motors in order not to make the equation complicated, but Im going to consider them later in my equation

TL: Torque around the fixed point.
W0, W1, W2, W3: The weights of the vertical, first, second linkage and load.
L0, L1, L2: The lengths of vertical, first and second linkage
Theta: leaning angle.

Do I miss something?
Now I want to get the optimum lengths of linkages that do not make the arm lean, if Im given the weights and theta is 1 or 2 degrees, how can I continue?



If you can't see the image, please follow the link:
http://img301.imageshack.us/my.php?image=armleanyn5.jpg

Offline Admin

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Re: the robotic arm tutorial
« Reply #1 on: April 25, 2008, 09:01:31 AM »
When you say leaning, about which joint/link do you mean?

The minimum required calculated torque about that joint is the torque needed to prevent it from 'leaning'. Also, you don't need any trig here - everything should be perfect 90 degree angles if there is no 'leaning' ;D

Also, the equations basically determine an effective moment (torque), so you wouldn't need to do any trig until after you have your 90 degree angle solution done.

Offline MarwanTopic starter

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Re: the robotic arm tutorial
« Reply #2 on: April 26, 2008, 01:27:23 PM »
When you say leaning, about which joint/link do you mean?

Please make a look on the image to get what I mean



alright, I'm gonna make theta = 0 "from the drawing that means no leaning". I may choose the suitable motors with suitable torques but the group may be too heavy to be carried by the vertical arm.

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Re: the robotic arm tutorial
« Reply #3 on: April 26, 2008, 01:47:36 PM »
Hmmmm your image is a dead link :P

Offline izua

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Re: the robotic arm tutorial
« Reply #4 on: April 26, 2008, 02:02:04 PM »
imageshack kicks (its own) ass.
Check out my homepage for in depth tutorials on microcontrollers and electronics.

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Re: the robotic arm tutorial
« Reply #5 on: April 26, 2008, 02:17:04 PM »
One way to counter that leaning torque is to put a heavy counter-weight on the other end of the arm, as I did on this bot:
http://www.societyofrobots.com/robot_arm_card_dealer.shtml

(notice the yellow batteries)


Offline MarwanTopic starter

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Re: the robotic arm tutorial
« Reply #6 on: April 27, 2008, 01:09:22 PM »
Thank you guys  :-*

 


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