How to Find Your Dream Motor!

When choosing a motor, there can be so many numbers that it all gets too overwhelming! That's why FYDP group 49 has decided to create the end-all-be-all guide to find your dream motor!

What to Pay Attention To:

The first step toward finding your dream motor is to understand what your motor will be used for. In this case, we will be finding a motor to power this flywheel launcher system to launch a ball at 10m/s.

With this design, there should be minimal friction, and thus minimal losses, to the system. Let's also assume that both wheels take an equal load from the ball, and that there is no slippage between the ball and wheel. With that, let's get designing!

Finding Motor Speed:

With our system, we can find the motor speed by analyzing the following system:

The energy conservation formula of this system can be written as:

1/2 * I * w1^2 = 1/2*I*w2^2 + 1/2mv^2

With a known maximum ball velocity of v = 10m/s (see Motor Selection section), and the known relation between tangential wheel velocity and ball velocity:

v = 10m/s

w2 = v/r = 10/r, r = wheel radius

Thus the required rotational velocity of the motor can be made a function of the wheel's inertia, radius, and the ball mass!

Finding the Motor Torque:

To evaluate the required motor torque, let's now evaluate this system:

From this system, it can be seen that the wheels will compress the ball as the ball is pulled between them. By approximating the ball as a linear spring, the following formula can be used to find the torque required to compress the ball:

T = kxrsinθ

Where the two variables are the compression distance “x” and the contact angle . By numerically finding the maximum of this system for the angle range, the max torque exerted by the ball onto the wheels, and thus the motor torque required to compress the ball, can be found.

And simple as that, you can easily calculate your required motor specs! Make sure that you test the sensitivity of your system and choose the proper safety factor though!

Putting it All Together:

After testing lots of different parameter combinations, you should have a good idea of what forces and speeds are required from your system. All that's left is to search the web for your perfect motor! For us, it's the E-S Motor 3625BL-24. The specs are shown below, and they meet our demands perfectly! Hopefully you can find your dream motor to!

​Characteristic	Value
Rated Torque [Nm]	0.0686
Rated Speed [rpm]	6000
No-Load Speed [rpm]	8000
Rated Terminal Voltage [V]	24
Rated Power [W]	40