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# Motor sizing for an autonomous mower

I plan (one day) to build an autonomous mower. This page is dedicated to the motor sizing.
To size the motors, I need the following data:

## Number of motors

I plan to build a four-wheel drive mower, so I'll need **four motors**.

## Diameter of the wheel

I don't know yet, but I current have a Worx Landroid and
we'll assume the wheels will be the same size, about **21 centimeters**:

## Weight of the mower

As for the wheel diameter, I'll assume my mower will have approximatively the same weight
than my Landroid mower. Let's say about **12kg**:

## Maximum velocity

Not easy to estimate the maximum velocity of my future mower. As for the weight and
wheels diameter, I check on my mower. I'll take this opportunity to do the acceleration.

Here is the result. Blue points are the point measured
on my mower, the red line is the modelization.

The cruising speed of the mower is close to 0.4 m/s, let's take some margin, our goal
will be 0.5m/s.

## Maximum acceleration

We don't need a strong acceleration to avoid wheel slip. On the previous model, the
acceleration is 0.0125 m/s². Let's take some margin: 0.015 m/s² will be great.

## Maximum slope angle

Let's be ambitious! **45 degrees** seems a great goal.

## Motor sizing

Thank's to this wonderfull online motor sizing calculator,
we get the following specifications for our motors:

### Four wheels drive

- Velocity: 45.47 rpm
- Torque on wheel: 2.2 N.m
- Power: 12.9 W

### Two wheels drive

- Velocity: 45.47 rpm
- Torque on wheel: 4.4 N.m
- Power: 25.8 W

## See also

Last update : 05/26/2021