Hi, I have a problem. You see, I was being and idiot and ordered 2 DC Motors from Adafruit for $2 each. Well, I was expecting that $2 motors with a starting torque of 20 g*cm could move an RC car with a weight of 13.5 ounces. Yeah, that's not happening. Now that brings me to my next question. How much torque is required to move a 13.5 ounce mass using 2'-1/4'' diameter wheels continuously using the split voltage from a 2S 7.4V 800mAh battery? I have spent a long time researching this with no luck on figuring out the needed torque, although to simplify my question, will any of these motors below do what I am asking? If so, which one will do the bare minimum? Thanks in advance to those who respond!
Probably the easiest thing for you to do is look at bot kits similar in size you are planning to make and see what type/size motors the kits use. Almost all drive motors will have gear boxes to reduce rpm and increase torque.
The hard thing to allow for is friction, which depends on a lot of factors.
What you can do is calculate the torque required to climb an incline (discounting
friction) and/or the torque needed to achieve a given acceleration.
Do all you calculations in SI units for sanity - N-m for torque, radians/sec for angular
velocity, wheel radius in metres, etc.
Small motors always have small torque - the torque depends more-or-less on the
volume of the motor's rotor stack, this is a limit direct from the laws of physics.
The idea of using a small motor to drive a wheel directly is flawed, you need much more
torque and far less angular velocity - something like 10 to 50 fold reduction gearing is
normally used.
One tip, if you calculate the torque needed to climb a 1 in 10 incline then you're
probably going to have enough torque to overcome friction too unless your mechanical
system is very high friction.
Sometimes its convenient to use energy or power calculations - 1 N-m is also 1 J/radian
MarkT:
The hard thing to allow for is friction, which depends on a lot of factors.What you can do is calculate the torque required to climb an incline (discounting
friction) and/or the torque needed to achieve a given acceleration.Do all you calculations in SI units for sanity - N-m for torque, radians/sec for angular
velocity, wheel radius in metres, etc.Small motors always have small torque - the torque depends more-or-less on the
volume of the motor's rotor stack, this is a limit direct from the laws of physics.The idea of using a small motor to drive a wheel directly is flawed, you need much more
torque and far less angular velocity - something like 10 to 50 fold reduction gearing is
normally used.One tip, if you calculate the torque needed to climb a 1 in 10 incline then you're
probably going to have enough torque to overcome friction too unless your mechanical
system is very high friction.Sometimes its convenient to use energy or power calculations - 1 N-m is also 1 J/radian
Ok so if you say a 50 gear reduction is good, then would you say something like motor 4 with 50 fold reduction or would you think motor 2 is good with 100 reduction?
2 1/4" wheels are 5.75cm, or radius of 2.86cm.
The 50:1 ratio motor can push or lift 1kg at a 1 cm radius, or (1/2.86) .349kg at 2.86cm radius.
Your car is 13.5 ounces or .383kg.
So given that the car's 383g weight is almost equal to the 349g of force at the perimeter of the wheels, your car could almost lift itself up a vertical incline with those 50:1 motors.
Chagrin:
2 1/4" wheels are 5.75cm, or radius of 2.86cm.
The 50:1 ratio motor can push or lift 1kg at a 1 cm radius, or (1/2.86) .349kg at 2.86cm radius.
Your car is 13.5 ounces or .383kg.So given that the car's 383g weight is almost equal to the 349g of force at the perimeter of the wheels, your car could almost lift itself up a vertical incline with those 50:1 motors.
Oh I thought that it would push it on a flat surface wow okay so those would do me fine even on an incline?