I am working on robotic manipulator(articulated 6 DOF) and i want to apply gravity and inertial compensation for which i have to control the torque of DC motor ,so do you any method to do that or any tutorial.
@amesh Unfortunately we do not reply during weekends. If you provide only 1/3 of the required torque, you won’t be able to move the arm much past vertical; 13Kg-cm won’t work with the input parameters you provided. You will need to decrease the payload and/or decrease the weight of each joint and/or decrease the length of each joint (or choose a more powerful actuator).
@Awais Mughal Excellent question indeed - the equations used here do not factor in inertia, nor do they include torque control. You will need to update the “worst case” scenario and include a downward acceleration for all links and actuators, as well as the load. We currently do not have time to do this, but will certainly consider it for future articles.
So to lift a 300 lb person with a forearm of 15" weighing 10lbs would require an elbow servo with 5271Nm of torque?
@JM Since you only indicate one length, we assume you mean shoulder servo? You would need 300lbs*15in/12 = 375lb-ft = 508Nm This is why normally rotational actuators are not used for heavy loads - you might consider a linear actuator.
I would like to ask you how to calculate the torque if we use the newtons law F=mg & T=F . L so how can i find the torque as mass is not given meaning that when i go to to the workshop to implement the design
@Nasr You’ll need to estimate the masses of each joint and actuator in order to estimate the torque. If not, over-estimate the torque needed per joint and you will simply need to live with whatever weight the arm supports at the end.
I am working on a mars rover project for which i need to manufacture a robotic arm for that i also need to consider the centre of gravity before deciding the arm length. So is there any way to calculate the arm length on a moving rover??
@Venkatesh There are ways to calculate everything, but in your case, the size and weight of the base will have a huge impact on the reach and arm payload. Do a simple torque balance.
Hello Sir, I have a retractable robotic arm with 2 dof. the base is retractable, followed by a rotary joint, and attached to it is a gripper. How do I calculate the weight and robot specifications. Should I first take it to zero position?
@Asheeta See Unfortunately there’s not enough info to really help. Can you create a new topic on the RobotShop Forum and provide details and sketches, as well as dimensions? The more information you provide, the better we can help.
hello,
can i use the arm calculator for the legs also or do you have a different one? i am treeing to guess the motors toque for an 150 cm humanoid robot. (ar a legged robot like cassie, 150 cm just legs)
@Razvan Leg tutorial: https://www.robotshop.com/blog/en/robot-leg-torque-tutorial-3587 Unfortunately these are for “insect” legs only and not a humanoid. Unfortunately we have not yet looked into the equations for a humanoid. Most smaller humanoid manufacturers choose one powerful RC or smart servo and “get what they get” out of a design in terms of capability.
Hi, I entered the values and It says I require a 43 kg cm for the L3(shoulder) servo motor. I have 3 degree freedom (shoulder L3, elbow L2, wrist L1), but I only have 20kg cm torque servo motor. And I am using a ball bearing to hold the servo motor shaft. Will the use of ball bearing change the calculations? meaning I would think it would use less torque since ball bearing will be holding most of the weight(torque).
@vinay shivaiah No, the ball bearing will not really affect the calculations. It sounds like your arm is either quite long and/or is being used to lift a heavier weight.
Hello Sir,
Yes, the arms are long 50 cm each (L5 and L4). And I have L3 at 2 cm only. No L2 or L1. M4 and M5 are 0.1 kg each. A4 and A5 are 0.05 kg (weight of servos and its assembly). M3 : 0.01 and A3 = 0.3 kg (main weight to lift). At these values, its saying I need a 49 kg cm servo motor. So, do you have any recommendation of any good metal gear servos? (inexpensive ones)?
This website is awesome and has very useful information ! It kept me from guessing the required servo motor, since I did not know how to calculate the torque
Thanks
@vinay shivaiah A somewhat similar arm: https://www.robotshop.com/en/robotshop-m100rak-v3-modular-robotic-arm-kit-no-electronics.html
Ex: https://www.robotshop.com/en/servocity-tube-arm-gearbox-hs-785hb-servo.html (requires 785HB servo, sold separately)
Producing high torque is not “cheap” unfortunately, which is why larger robot arms tend to cost quite a bit.
for my project , i have to use the only L5 and L4 is required along with the base both L5 and L4 length is 60cm square steel or aluminium bar
in L4 my weight will slide horizontally in L4 and total weight 15 kg at 60cm length of arm to be lifted and rotated 360° and slide
please advice me each servo motor capacity for L5 and L4 or torque required for above weight
Thank you Sir,
So, you are suggesting that I can use the 5:1 tube arm-gear box to achieve the required high torque (say 200 kg cm) and I dont have to use a equivalent powerful servo motor to drive my requirement. In your link, the servo motor used hs785 has only 13 kg cm torque but the gear box mechanism will provide much higher torque end result.
@MURALI That’s the point of this tool - input the values you know and the system will provide an idea of the torque at each joint.