What formulas can you use?

FIRST General Forum
1

I am making a C++ program with all the formulas i can find that people in robotics will need. please post any i can use!

i am looking for formulas or instructions for the following:

co. of friction
torque output
speed output
gear ratio
mechanical advantages u got
just anything really

i have some of these and more but i want to check these.

2

Umm…huh?

3

Basically he’s making a Robotics calculator.

Good idea! Sounds useful :slight_smile:

Anyhow, I suggest that you read the white papers and get a physics/pre-engineering/engineering dynamics book! It will help you more than someone telling you and then you regurgitating them into a program… :wink:

And one little pick: Can you change the name of this thread to “What formulas do you use” instead of ‘can’? It’s just a grammar pick… :frowning:

4

please give me some

5

It sounds like you are trying to make a program where people can input data and get numbers out. For many of the instances you want equations for, you just cant do this. I would not want people to be misled. If this is not what you are trying to do, then disregard the rest of this post and let me know.

There’s a reason Engineers exist, because engineering is about having a set of constraints and a goal, and figuring out how to come to a solution. No one solution is right, and many times there will be many more than one solution. Most of the time one solution will be more right than others due to factors completely unrelated to the problem.

I’ll give you an example. Let’s consider gear ratios, and apply it to first. The goal is to create a lightweight gearbox that accepts an input of 5000RPM and outputs 250 RPM. Since gear ratios are expressed as input : output or input/output, the gear ratio is 20:1.
The simplest, and most logical, way to do this is to have the motor have a pinion of 1" in diameter mated with a gear with a diameter of 20". Closer analysis reveals the option of having a two stage 5:1 and 4:1 reduction or a three stage 5:1 and 2:1 and 2:1 reduction. Which is more right? Well, a number of external factors have to be considered, such as cost, and more importantly weight. If each of these gears are 1" wide, the first solution would have a weight of 89lbs (steel has a density of 0.283 lb/in^3) (plus that of 1 shaft we’ll assume each shaft is 1/2" in diameter and is ~4 in long, being 1 lb). The second solution would yield a weight of 11.5lbs and the third 11lbs. However, the cost and time (extra shaft and 2 extra gears) might be more important than the half pound so the 2nd solution might be considered the best.

That was only a slightly realistic example, but it does prove my point. There are simply too many variables to be considered to make one answer more right than others. For example, to save on weight you might choose a less dense material such as aluminum. However, aluminum has a rather low tensile strength compared to steel and you’ll have to use larger gears (or accept the risk of fracture).

Simply said: No computer program can replace an engineer. There’s simply too many variables to take into account. Typically, when programming you assume various things. However, in engineering nothing can be assumed.

Other than that, most of the equations are so basic that using a computer program to solve them would be purely a waste of time.
Most of the whitepapers around the Chiefdelphi (click up top “whitepapers” and read them) have all the equations one would need.

6

*Originally posted by Jnadke *
**
Simply said: No computer program can replace an engineer. There’s simply too many variables to take into account. Typically, when programming you assume various things. However, in engineering nothing can be assumed.
**

Being an engineer is knowing what assumptions are OK. Being a scientist is making no assumptions and proving everything.

7

Now, if you are making a C library to handle math problems… that could be rather useful. For example, it may include a function that you can use like this:

status = quadFormula(a,b,c, &x1, &x2);

So you would use the above like this: status = 1 when the answer is non-real. If there is a real answer, it would be stored back into x1 and x2 :wink:

A library like this could be useful :ahh:

8

All of this can be done by a standard graphing calculator already (including solving a quadratic). Also, the physics equations used for robotics that u mention (gear ratios, coefficient of friction, etc.) are very simple and it would be ultra super duper overkill to use a computer program to solve them.