Calculating Stepper Motor Torque for a 4-Wheel Robot

[saleh2]

Hi everybody
I have 4 wheel robot like car .
2 stepper motors that one is in front and other is in rear of robot and these motors directly connected to wheels. so two of other wheels is not connected to motors.
this robot move straight and curve.

i want to find the formula that calculate torque of every stepper motor in straight and curve movement.

weight of robot: 4 kg
weight of load: 10 kg

 

[BvU]

Hello @saleh2 ,

!​

You will need a little more information, such as

What is the force needed to move the vehicle ?
What is the diameter of the wheels that are diven by the motors ?
Any friction ?

Do you have a sketch of the setup ?

$\$

 

[russ_watters]

I have 4 wheel robot like car .
2 stepper motors that one is in front and other is in rear of robot and these motors directly connected to wheels. so two of other wheels is not connected to motors.
this robot move straight and curve.

i want to find the formula that calculate torque of every stepper motor...

Can't you just look up a product data sheet for the motors?

...in straight and curve movement.

The torque required for flat, slow, un-accelerated motion is effectively zero, or rather is equal to the rolling resistance. It's generally not a useful thing to know. Is it really what you want? What are you going to use this information for?

 

[saleh2]

You will need a little more information, such as

What is the force needed to move the vehicle ?
What is the diameter of the wheels that are diven by the motors ?
Any friction ?

Do you have a sketch of the setup ?

$\$

Thank you for response.

diameter of wheel is 9 cm. robot's length is 25 cm , robot's width is 25 cm
robot must be move in surface like asphalt, wood, ceramic, concrete, etc... so friction Coefficient can be vary from 0.3 to 1.

stepper motors are driven by s109 stepper driver that have Tushiba IC and controlled by arduino mega 2560.

 

[russ_watters]

diameter of wheel is 9 cm.
robot must be move in surface like asphalt, wood, ceramic, concrete, etc... so friction Coefficient can be vary from 0.3 to 1.

Surface friction coefficient has almost nothing to do with the torque requirement. Do you understand why?

stepper motors are driven by s109 stepper driver that have Tushiba IC and controlled by arduino mega 2560.

Google tells me that's the controller, not the motor.

 

[saleh2]

Surface friction coefficient has almost nothing to do with the torque requirement. Do you understand why?

Google tells me that's the controller, not the motor.

can you explain it?
please correct my opinion:
F= umg
torque= F.r= umg.r
that r is the radius of robot turn some way.
centripetal force

stepper motor: Primopal 80 N.cm
driver: s109 (up to 4 ampere)
controller: arduino mega 2560

 

[russ_watters]

can you explain it?
please correct my opinion:
F= umg
torque= F.r= umg.r
that r is the radius of robot turn some way.
centripetal force

That equation calculates the maximum friction force the surfaces are able to withstand before slipping occurs. It has nothing to do with how much friction force is actually being applied (up to that limit).

[edit]
FYI, you can research "rolling resistance" for different combinations of surfaces/wheels, but again I'm not sure how useful that's really going to be to you.

 

[saleh2]

how much friction force is actually being applied

how much?

it is need for calculating torque?

 

[russ_watters]

how much?

At steady speed in a straight line, it's zero.

it is need for calculating torque?

No.

 

[saleh2]

if you want to buy 2 motors for 4 wheel robot, (according to my details) you choose which stepper motor ?

 

[berkeman]

weight of robot: 4 kg
weight of load: 10 kg

Did you read the information about Rolling Resistance yet? It's important that you understand that concept so you can apply it to your torque calculations.

How fast does your 14kg robot+load have to accelerate? Does it have to ascend or descend any inclines? This looks like a school project, so were you given any other specifications beyond the masses? What are your wheels/tires made out of? What kind of surface will you be driving it on (concrete, carpet, dirt, grass, sand)?

 

[saleh2]

Did you read the information about Rolling Resistance yet? It's important that you understand that concept so you can apply it to your torque calculations.

How fast does your 14kg robot+load have to accelerate? Does it have to ascend or descend any inclines? This looks like a school project, so were you given any other specifications beyond the masses? What are your wheels/tires made out of? What kind of surface will you be driving it on (concrete, carpet, dirt, grass, sand)?

yes, i read http://www.creativeworldindia.com/tutorials/e-learning/robotics/robotic-car/robotic-car.html, Torque T = ( F + 2R ) * r where r is radius of wheel , R is rolling resistance force, F is static friction force .
so T=(uN + 2*u'N)*r where u' is rolling resistance coefficient

this is my wheel , that made from aluminium.
max speed of robot is 0.5 m/s with no acceleration in many cases.
robot must be move in concrete, wood, ceramic, asphalt .

 

[BvU]

robot must be move in concrete, wood, ceramic, asphalt .

Can you build a prototype of teh same weight and drag it around to measure the force needed to move it (with a spring dynamometer) ?
Bumps, slopes ?