@jakimovska Interesting result. The equation used is:
VK = (100/VI) * VA * VC * (VG + 9.81*(Math.sin(3.1415926*VE/180))) / VB;
Seems to work out to 0.616?
Yes, you are right, I had a minor miscalculation in my excel sheet. Thanks!
@jakimovska Given that your calculations are EXCEL-based, free free to make it more accurate by including the moment of inertial of the wheels chosen, the weight of individual components (battery, frame, motors etc.), efficiencies of each component (motor controller, battery, motor, gearing), coefficients of friction etc.
Yes, I will definitely do that. For now I wanted to decide how many drive wheels the locomotion should have which some basic calculations. But from the results that I got I would definitely need four motors, as each motor needs a Torque of 0.301 Nm and Speed of 143.24 rev/m. I checked the motors in the comparison motor link that you shared, however, it was difficult to find one with such characteristics. The closest one I found was this one: https://www.robotshop.com/en/12v-165rpm-6805oz-in-precision-planetary-gearmotor.html#Specifications
Any suggestions on what I should do?
A 20Kg robot is very heavy indeed (44 pounds, or the weight of a 4 year old child).
Remember, you need to select the motor based on its maximum continuous torque, as opposed to its stall torque.
In your case, 0.616Nm = 84oz-in, which is acceptable for that motor (if you use four).
Keep in mind that 10 degrees is not a significant angle, so you’re designing for a relatively flat surface.
Yes definitely, the surface is indeed flat, therefore, I was I was even considering lowering the angle to 5 degrees in order to lower the torque required to around 0.3 Nm. But it would be ideal if I design it at 10 degrees for safety. Unfortunately, most of the dc brushless motors I looked at in the RobotShop website that have 84 oz-in do not have the required rpm needed. Initially, I was considering having 2 drive motors and 1 or 2 wheel(s) as support. However, due to the weight and the characteristics needed of the motor I decided to use 4 motors driving each wheel.
Could you please recommend me other acceptable motors that would be suitable, as I struggled in finding motors when searching?
Thank you for all your input so far, it is really helpful!
You’d be looking at a DC motor with planetary gearing, running at 12V or 24V.
https://www.robotshop.com/en/planetary-gearmotors.html
However, you might consider something like this:
To get an idea of mounting:
https://www.robotshop.com/en/maytech-dual-hub-motor-rear-aluminum-truck-e-skateboard.html
Electronics:
Yes, this is a skateboard hub motor, but we carry it because it’s easily used in robotics for heavier loads.
Thank you very much!
The MTO9055 motor has KV of 60. Does that means that if I use 24 V, “ideally” I would get 1440 RPM? Also how can I check that this motor meets the torque requirements?
Correct - that’s the theory. Good question about the torque - don’t see any specs, but it can provide up to 800W (don’t push it up to that for long though) and they are intended to move an adult male on a skateboard… If you need specs, I can transfer the post to a tech who can reach out to the manufacturer.
Yes, I would definitely want to see the specs of the motor before ordering it, if you could provide me with them I will be really grateful!
@jakimovska Unfortunately it seems the manufacturer does not have / provide additional information. Note that 800W = 1 horsepower.
Yes, it is quite powerful as I only need around 8 W. Since Power = torque * speed. If the power is 800 W, and speed 140 rpm (15rad/s). Which means I could get a torque of 53.3 Nm.
However, as each motor is almost 1 kg and I would need four per robot that is quite heavy. Do you have any motors that are lighter?
@jakimovska Anything in that range would be here: https://www.robotshop.com/en/planetary-gearmotors.html
Hi, I’m selecting 20 degree incline and 1hr operation in my inputs. Are the calculation based on the robot having 20degree incline 100% of the time (1hr runtime)?
@gmoney18 For the drive motor sizing tool, that is correct - the tool does not factor how long you plan to be moving up the incline. It’s simple, to provide an estime.
I have an inquiry from the robot calculations
Its deduced that I need
2 Drive motors
torque/motor = 87.5 N.m
Angular velocity = 4.5 rpm to have a speed of 0.0385 m/s
and based on supply voltage V = any value for instance 12 V
Running time = 72 hrs
How can I find the motor that would provide the specific torque & rpm as well as battery pack
@sh The maximum continuous torque your motors will need will be 87.5Nm at 4.5rpm (which is very slow). If you can only find DC gear motors which list the stall torque, then you might need to consider 4x that value.
https://www.robotshop.com/en/planetary-gearmotors.html
To get those specs, you’ll likely need a very high gear down and a fairly beefy motor.
Once you find an appropriate motor, see what the current draw is at maximum efficiency, multiply that value by the voltage to get an estimate of the battery’s “Watt hour” rating.
Again, given the info you provided, you might need to tweak the values to get something smaller, keeping in mind the calculator is simple and goes for a worst case scenario - accelerating uphill at whatever acceleration and angle you specified.
I have an inquiry to find a motor.
My required spec is
4 drive motors, robot travelling at 3.5m/s
torque for each motor - 2.01nm
angular velocity - 116.67rad/s
based on a voltage of 24v, mass 60kg and a running time of 8hr
Looking for the best motor for this application, preferably a geared motor.
Many thanks
Hopefully this will explain some of the limitations with the online calculator:
The torque calculation is to obtain the maximum required torque to move the robot up an incline, as opposed to what would be more “normal” operating conditions. Most motor manufacturers provide the stall torque for their motors, so look for a motor whose stall torque is 4x higher than the value calculated. The running time is also based on the worst condition - in that the robot is moving up an incline for 8 hours.
To get an idea of the type of motor you’ll need a small personal transport robot (like a Segway) can move an adult human up a small incline.
2Nm seems really low for a robot of that size - what angle and wheel radius did you enter?
With this calculation based on the worse case scenario to prevent stalling, is the power also calculated using the maximum force (ie the power up the slope) despite this only occurring of a maximum of 20% of the working time. Would it be wise to calculate the force of a flat slope as well and then scalar this (ie 80% flat, 20% incline) to work out the power?
The maximum slope working on was 13 degrees, and a wheel diameter of 30cm.
Ideally we require the motor to be as light and small as possible.