Excellent, and happy to help. If you follow the tutorial, you can see the limitations of the tool, but also how, if all of the values are needed beforehand, it becomes a bit of a “chicken before the egg” problem.
No problem, but would be nice to have some credit / link to the original, perhaps under the “project” field?
Updated added the link back to the original calc and write up in the project description and linked in the bottom of the calculator page too.
Appreciated. Feel free to expand on it, verify it, add additional functionality etc.
Thanks for the reply! Its working again the next day. Another question to add, may I know how the equations will differ if the robot were to pull (tow) some of the load? Or will it make no difference? Thanks in advance.
You would add the total weight of the trailer as added payload. You would not include the wheels for the trailer (idler wheels are not counted anyway). What it changes overall is that the robot itself would not need to physically support the weight on its wheels, though that is not factored into the equations.
Can you tell me why my result is different than yours?
Mass: 20 kg
Motors: 4
Wheel radius: 0.04 m
Velocity: 0.6 m/s
Incline: 10 deg
Acceleration: 0.3 m/s2
efficiency = 65 %
You get:
Torque =0.61646 Nm
I get:
Torque = (100/65) * ((20 kg) x (0.04 m) x (0.3 m/s^2 + 9.8 m/s2 *sin 10 deg ) / 4) = 0.260 Nm
Why is that?
I would really appreciate your help.
Thanks
@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