Is this Equation Correct

[Mad Cows]

So I have been trying to work out an equation for the maximum weight a robot can hold. Does this look right?
https://drive.google.com/file/d/0B8z...ew?usp=sharing

T is torque of one motor, Mn is number of motors on one side, Wn is number of wheels on one side, Wr is wheel radius, Fs is static friction, rps is revolutions per second, m is mass.

The robot is a tank drive, with chains linking all wheels on each side to the motors.

[Jared]

Originally Posted by Mad Cows

So I have been trying to work out an equation for the maximum weight a robot can hold. Does this look right?
https://drive.google.com/file/d/0B8z...ew?usp=sharing

T is torque of one motor, Mn is number of motors on one side, Wn is number of wheels on one side, Wr is wheel radius, Fs is static friction, rps is revolutions per second, m is mass.

The robot is a tank drive, with chains linking all wheels on each side to the motors.

Likely not.
If nothing on my robot is moving, then rps = 0, and my robot can hold no weight, according to that equation.

The weight which a robot can hold depends on the strength of what supports the weight.

Why do the number of wheels, strength of drive, or speed at which the robot is travelling have anything to do with how much weight can be held?

What units are you using for torque? For wheel radius?

[Caleb Sykes]

Originally Posted by Mad Cows

So I have been trying to work out an equation for the maximum weight a robot can hold. Does this look right?
https://drive.google.com/file/d/0B8z...ew?usp=sharing

T is torque of one motor, Mn is number of motors on one side, Wn is number of wheels on one side, Wr is wheel radius, Fs is static friction, rps is revolutions per second, m is mass.

The robot is a tank drive, with chains linking all wheels on each side to the motors.

Your units do not work, which should is an easy sign that something is wrong. You have torque*distance/force/time = distance^2/time on the left side, and mass^2 on the right side.

Additionally, I'm having trouble understanding what you are trying to solve for in this equation. Is it the maximum mass that the robot can have before the wheels can't spin because they stall?

[Katie_UPS]

A quick search (admittedly, by searching Ether's posts) found me this white-paper, which might be useful:
http://www.chiefdelphi.com/forums/sh...d.php?t=119442

While searching is not as glamorous, I'm certain you could find a lot of good resources related to this topic.

[MrBasse]

Originally Posted by Jared

Likely not.
If nothing on my robot is moving, then rps = 0, and my robot can hold no weight, according to that equation.

The weight which a robot can hold depends on the strength of what supports the weight.

Why do the number of wheels, strength of drive, or speed at which the robot is travelling have anything to do with how much weight can be held?

What units are you using for torque? For wheel radius?

Number of wheels would determine how weight is distributed to the ground. Actually, that would only be number of wheels in contact with the ground. Four 3/8 axles can support far more than one.

[Mad Cows]

Ok. So here is my new equation:
https://docs.google.com/file/d/0B8zt...p=docslist_api
Problem is, this equation does not factor in speed needed. How would I add that to the equation?

[Nate Laverdure]

Originally Posted by Mad Cows

Ok. So here is my new equation:
https://docs.google.com/file/d/0B8zt...p=docslist_api
Problem is, this equation does not factor in speed needed. How would I add that to the equation?

It looks like you are trying to solve a dynamics problem. Have you first completed steps 1 and 2 (PDF link)?

[Ether]

Originally Posted by Mad Cows

Ok. So here is my new equation

Would you please answer the questions posed by the previous posters?

Originally Posted by Jared

What units are you using for torque? For wheel radius?

Originally Posted by inkling16

I'm having trouble understanding what you are trying to solve for in this equation. Is it the maximum mass that the robot can have before the wheels can't spin because they stall?

[Caleb Sykes]

Originally Posted by Mad Cows

Ok. So here is my new equation:
https://docs.google.com/file/d/0B8zt...p=docslist_api
Problem is, this equation does not factor in speed needed. How would I add that to the equation?

Your units still do not check out unless you happen to be using a unit system which makes some terms unneeded (e.g. a unit system where the acceleration due to gravity g is 1). Additionally, I still can't help you if I don't know what you are trying to solve for in this equation.

[Mad Cows]

Ok. So we fixed the equation, just remove the RPS. Our we are solving for W (Which is maximum stalling weight in newtons).
The last thing needed is how to add in a minimum top speed.
Radius is in meters, torque is Nm, everything is metric.

[Ether]

Originally Posted by Mad Cows

Ok. So we fixed the equation, just remove the RPS. Our we are solving for W (Which is maximum stalling weight in newtons).
The last thing needed is how to add in a minimum top speed.

The quality of the help you get will be proportional to the effort you expend to clearly explain what you are trying to accomplish.

"maximum stalling weight" as a function of "minimum top speed" is not a completely unambiguous description. Here's a case where more words would probably be better than fewer.