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.
@vinay shivaiah A 785HB servo can provide up to 13.2Kg-cm (max), therefore 13.2*5 = 66Kg-cm (far from 200Kg-cm). The largest, most powerful normal RC servo we carry can provide ~110Kg-cm. You would need a Dynamixel Pro Smart Servo which are several thousand dollars each: https://www.robotshop.com/en/dynamixel-smart-servo-motors.html
I have one doubt sir. How to calculate the continuous torque required and axial load on actuator?
@Raja K For more precise calculations, you need to include inertia, which means you need to know the components you are going to use. Calculate for a “worst case” scenario of the arm having to decelerate from maximum speed against gravity (for each joint). This is hard to do at this step since the idea behind this tool is to give ballpark figures before a design is even started. Axial load calculations also requires the weight of each actuator and link. If you need to do these calculations, you’ll nee a basic course in forces, torque and dynamics.
Thanks for the information @coleman benson . I have another one doubt. In Robot Arm Torque calculator i put the values like mentioned below
L1=20 cm , M1= 2 Kg , A1(Include actuator and payload)= 8 Kg, then i got T1= 180 Kg cm . Now i going to put the values for LINK 2 like mentioned below
L2=20 cm , M2=2 Kg , Now how to put values for A2?
A2(Only actuator weight) = 2 Kg
or
A2(Actuator A2 + Value of A1 + M1) = (2+8+2)= 12 Kg - like this?
@Raja K The specs you provide will require very powerful actautors. ‘A’ stands for the weight of the actautor only. A2 is not calculated - it’s just the weight of that actuator at that joint. To see the calculations, take a look at this page: https://www.robotshop.com/blog/en/robot-arm-torque-tutorial-7152
@Coleman Benson Thanks
@Coleman Benson How to calculate an extra torque required to move the joints based on speed(rpm)?