Hi Coleman…I am doing a similar work of calculating the torques and forces when the end effector does a few sequences.I have linear movements available with me but i need to know how to back calculate.If you could please share your id by sending to my email id,that would be great.I could well explain in detail.Any help on this would be appreciated.
@Neelam Gupta The calculations need to be based around torque. If you have a specific setup, you need to know each length and each weight, and the center of weight of each object. You can then calculate the torque at each joint based on a variable angle. Unfortunately we do not provide design or consultation services so we cannot take a lot of time to develop the equations for you.
Hello Coleman, I got a doubt. Consider a robot arm at static position. Now the motor holding the arm at that position is applying certain force(torque) to hold it. Does Gear ratio plays its role here? Further how to convert this force to power?
@Anto Do you mean adding an additional gear ratio after the motor output shaft? If so, then yes, it will affect the torque required by the motor. You would obtain the power based on the motor itself; we strongly suggest searching for an appropriate motor based on the torque required, and then choosing a voltage. You will get the power from the motor’s specs.
Hello Coleman, i’m trying to design an articulated robotic arm, but only I can use some motors that i already have. So i’m looking for an equation that allows me to calculate the ideal length of the segments, from the max torque of the actuators, weight, and the desired total length of the arm.
I know is an strange way to calculate an structure, but there is no way to get other actuators, and i want to give the best use to these i have.
The max torque of each motor was 20 kg/cm (shoulder), 8 kg/cm (elbow), 3 kg/cm (wrist, one for rotation), I hope these torques are enough for an 40-50cm arm.
Sorry if i’ve wrote something wrong, or with a poor redaction.
Thanks in advance.
@Santiago How many degrees of freedom do you want your arm to have? Note that if you want anything greater than one degree of freedom, you’ll have quite a few unknowns and you’ll need to experiment with lengths and payloads. You can plug in the known values into the calculator to experiment: https://www.robotshop.com/blog/en/robot-arm-torque-calculator-9712 The calculated torque required will need to be less than what you have available.
Yes, I’m trying to make a 6 or 7 DOF arm, that puts the maths quite difficult for do the backward calculation. Thanks for the calculator and the quick answer 
i will do trial and error for not surpass my servo’s torque.torque.
@Santiago You will need to understand the principle of torque. The servos closer to the base will need to be the most powerful as they have to support the most load. As you move along the arm, the servos should be lighter / smaller.
Yes, i understand the principle. I’m thinking put the more powerful servo (about 25kg/cm and 120g weight) on the base. On the next articulation, i’ll put the 8 kg/cm servo with a weight of 55g. And on the next articulation a servo with 3kg/cm and 45g of weight. From this point to the end I have two servos with 1.5kg/cm and 30g each one, for rotate y open /close the gripper. Thanks for the reply, I hope will post the finished arm and his wheeled platform before the end of the year…
(Sorry if I misspelled something or with a poor redaction, I’m using google translate for do corrections, but my english it’s not the best ) Thanks a lot
hello mr.coleman
im trying to calculate torque of 6 degrees robot cuz i want to build it like CMA GR 6100
and i just want to know this formulas is that true for a big arm of robot ???
@khashayar The basic equations are valid for any sized arm. Note that if you are considering creating something that size, you might want to use more involved equations which take into consideration the efficiencies, inertia etc.
hello again mr.coleman thanks for answer
in that formula i mean w1 and w2 is that means half weight of link?
so what about the speed of robot for movement ???
@khashayar W1, W2 etc are the weight of each link section (not half). We assume the weight of the link to be halfway between the actuators (for simpler calculations). The speed is not factored into the equations - we are only considering static forces to get approximations.
thanks alot mr.coleman
i calculated t1 and t2 for my robot that is 447n.m t2 2157n.m
so if i take it double for each joint 894 & 4314 for the best work is it good?
@khashayar Doubling the value might be a bit overkill, but you would need a certain margin of error.
thanks alot mr.coleman
Dont you get upset if I ask one more question to you?
@khashayar We are happy to help, so do not hesitate to ask. We just try to avoid a lot of back and forth here in the comments section so if the questions are about a project you’re working on, we suggest creating a new topic on the RobotShop Forum.
hey, can you help me how to get the transfer function from this equations
@mohamed This article and the equations provided would not provide the transfer functions / IK directly.
Thanks for this tutorial its very help full
I just want to ask if we could contact because the robot arm is my graduate project
And i need to know more about it