@bongza Those equations are beyond what we can offer here. You might contact a local university to see if they can provide some assistance / guidance. If it’s a custom project, try to measure the torque needed by hand, then choose a motor which can provide at least that torque.
This is very helpful! Just one question, how do you calculate friction?
@Joe Humpston You need the static and kinetic friction coefficient between the two surfaces. This has often been calculated based on experimentation, so you’ll have to do a search.
Hi. This page is really helpful - I’ve been using the equations here for completing a college assignment. I just wondered if you happened to know of any engineering textbooks or similar that could use as a reference for where the equations can be found? Thanks in advance!
This is an awesome post. Such a huge help. I have a question though. I am building a robot., roughly around 15-20 lbs, and I’m getting really low numbers in term of what 4 drive motors with 1.375 inch radius wheels would need to generate them to move them at a relatively slow speed on a completely horizontal surface. I was initially thinking somewhere in the ballpark of 20-25 kg-cm but the tool is telling me 0.079500 kg-cm. How can this be? ( Initially I used Torque = 8 x Coefficient of friction for wheels x Diameter of wheels x Weight )
@Martin On a horizontal surface, the robot does not (theoretically) need to fight against its own weight - just friction an inertia. This is why, under the proper conditions, you can even push a regular passenger vehicle on a skating rink. The tool does not factor in inertia or friction, so to get more accurate values on a horizontal surface, you need different equations which include friction coefficients (static and dynamic). We suggest at least a 2 degree incline for ballpark figures.
Ur post is awesome and it helps me understand some things… i thinking of automating my home’s front gate by fixing a dc motor operatable at 12v and controlling it by Arduino wirelessly, i cant able to decide the rating of the dc motor … gate(9ft×6ft) is swing type and thinking of fixing the motor at the bottom of the free end of the gate with a castor wheel. Gate weighs about 100kg.since motor is driving the wheel to swing the gate open or close , i cant predict the suitable motor. Help me
@Harish Two considerations: The motor’s rating, and the fact that it will be exposed to the environment. An easy approach would be to use a DC linear actuator, it’s just a question of making it weatherproof: https://www.robotshop.com/en/actuators.html
@Coleman thanks for ur suggestions…
Hi, what about sizing small 4-W nameplate DC motors to lift on lets with say a winch? Let’s say the winch diameter is 4-in. So torque arm 2" or 0.05-m. Let’s say we needed to lift a 2-kg or 20-N weight at a winch speed of 50-RPM or approx 5-radians/sec. Let’s say the stall torque and current of the motor are 1.7-Nm and 5-A respectively. How many motors should we hook to the winch directly? I.e no gearing to improve torque.
@Tad Ideally you would only need one motor with the right specs. Your minimum specs would be 5cm * 2Kg = 10kg-cm at 50rpm. You should choose a gear motor which can provide 12Kg-cm or more to be “safe”.
Hi. Why not calculate the friction coefficient? Most important ground to incline calculat !
Thank you
@Pouya We found that going into too much complexity in the calculations and require values created too many variables for new customers who just want an idea of the torque / RPM required when selecting a drive motor.
Hello
I think this formulw is correct !
T=[R.M(a+uk.g.cos(tetta)+g.sin(tetta)]/(N)
And this page is verry helpful
@Pouya We do appreciate the insight and will certainly take a look when we have time. T = [RM(a+(μk)gcos(θ) + g*sin(θ)] / [N]
Hi. How to calculat acceleration in robot ? Just put the number or calculate ?
@Barish That works the opposite way, knowing the mass of the robot, the wheels, and the specs of the motor. However, the acceleration is needed for this tool, so you would need to enter an estimate of the desired acceleration.
How estimate the desired acceleration ?
@Barish Think of how much distance you want the robot to travel from a velocity of zero, to get to its full speed and use the standard physics equations relating acceleration to velocity and position.