# Calculating motor size for a project, help please

• Jogilvie95

#### Jogilvie95

Hello all,

I have a project in which i need to design a small vehicle which is able to carry 4kg for 10 meters. I have took it up to 5kg as the frame and wheels add up too 1kg. So the total weight will be 5kg.

Acceleration isn't a priority, but 0.5 m/s I would be fine with.

The wheel have a diameter of 6cm, they are made of rubber and they do have tread, it will go along a smooth surface.

I can only use electric motors, I was planning on using 2 motors attached to the 2 front wheels. I only have a budget of under £100 to cover the motors and battery to power the motors.

I am unsure on how to calculate what size motors i need and the power supply. Would anyone be able to help me with the equations that I need to use to calculate this please?

Thank you for reading and i appreciate any help! :)

Jack

Are you moving it horizontally? No up or down ramp? If so, and if acceleration is not important, then the power need depends only on friction. You can not easily calculate friction.

Why two motors rather than one?

Only horizontally,

The vehicle will have to travel in a straight line, I was thinking if I use one motor on a single wheel it would make this harder to keep straight.

Welcome to the PF.
Acceleration isn't a priority, but 0.5 m/s I would be fine with.
0.5 m/s is a velocity. An acceleration would have units of m/s^2.
The vehicle will have to travel in a straight line, I was thinking if I use one motor on a single wheel it would make this harder to keep straight.
Steering by only adjusting wheel drive and not wheel angle can be pretty problematic. I'd suggest just starting with something like a simple battery-powered radio-controlled (R/C) car, and implement the pieces yourself as the project...

https://sc01.alicdn.com/kf/UT8PYDTX74bXXagOFbX0/3709/UT8PYDTX74bXXagOFbX0.jpg

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jim hardy
To just move (without specified speed), motor with 0.1-0.2 N*m torque may be enough. This is typically 20-40 mm diameter motors without reduction gears.
Smaller motors are also ok, but they will need speed reduction gear.

Jogilvie95
To just move (without specified speed), motor with 0.1-0.2 N*m torque may be enough. This is typically 20-40 mm diameter motors without reduction gears.
Smaller motors are also ok, but they will need speed reduction gear.

Thank you, are you aware of any equations to use to calculate this?

To just move (without specified speed), motor with 0.1-0.2 N*m torque may be enough. This is typically 20-40 mm diameter motors without reduction gears.
Smaller motors are also ok, but they will need speed reduction gear.

Do you think it’s worth going for 0.3N*m motor just to be sure?

trurle
Thank you, are you aware of any equations to use to calculate this?
Tmin=M(vehicle)*g*R(wheel)*Kf=5*9.8*0.03*0.1=0.147 N*m
Total friction factor Kf through transmission is 0.03-0.1 for wheeled vehicles (0.05 is typical).

If you really want to you can build the little car and then put something on the vehicle to simulate the weight of the battery pack and motor. You can then attach a little Newton scale to the car and see how much force it takes to pull it horisontally. You then calculate the torque directly T=Force x 0.03, because the wheel with the drive motor will have to supply the force that you just measured. Very few people have a Newton scale lying around so it might not be possible for you to do this...The force might be so low that the Newton scale might not register it...