What Motor Specs Are Needed for a DIY Tennis Ball Launcher with a £100 Budget?

[noah1984]

Hey not technically a college student but i do have a problem aimed at this sort of level. I'm attempting to build a motorised tennis ball launcher using two counter rotating wheels. they are approx 15cm dia and compress a standard tennis ball two just over 3cm height. unfortunatly the motors are required to be DC fed from a 12V supply and i can't find any specs for what sort of speed or torque I'm going to need. please somebody out there must have had a similar problem. oh an my only real constraint is budget, limited to about £100 to get both motors. you can e-mail responses to noahj1984@hotmail.com

 

[Andrew Mason]

Hey not technically a college student but i do have a problem aimed at this sort of level. I'm attempting to build a motorised tennis ball launcher using two counter rotating wheels. they are approx 15cm dia and compress a standard tennis ball two just over 3cm height. unfortunatly the motors are required to be DC fed from a 12V supply and i can't find any specs for what sort of speed or torque I'm going to need. please somebody out there must have had a similar problem. oh an my only real constraint is budget, limited to about £100 to get both motors. you can e-mail responses to noahj1984@hotmail.com

The principle is simple enough. The wheels supply a force to the ball over a small distance (the product of which is the energy imparted). The kinetic energy of the tennis ball is equal to the work done on the ball (Force x distance).

The force on the ball is a little complicated because it is a combination of the torque of the motors and the compression of the ball (which causes the ball to push off against the motor wheels). Ultimately, though, the energy comes from the motors.

$$\frac{1}{2}mv^2 = 2\tau\Delta\theta$$

where $\tau$ is the torque provided by each motor and $\theta$ is the angle of rotation of the motor while the motor wheel is in contact with the ball.

Lets' suppose that $\Delta\theta$ is 90 degrees or $\pi/2$ radians.

$$\frac{1}{2}mv^2 = 2\tau\pi/2$$

$$\tau = \frac{1}{2\pi}mv^2$$

$$v = \sqrt{\frac{2\pi\tau}{m}}$$

The mass of a tennis ball is .057 kg and if you want a speed of 30 m/sec, you would need a motor that produces a torque of:

$$\tau = \frac{1}{6.28}*.057 * 900 = 8.2 Nm$$

which is about 6 foot pounds (pounds-force) of torque.

AM

 

[thepatientmental]

Hi there,

Thank you for reaching out to the college student community for help with your motorized tennis ball launcher project. While I may not have personal experience with this type of project, I can offer some suggestions and advice based on my knowledge of motors and budget constraints.

Firstly, it's important to determine the specifications of the motors you will need for your project. This will depend on factors such as the weight and size of your counter rotating wheels, as well as the desired speed and torque for launching the tennis ball. Since you are working with a 12V power supply, you will need to find motors that are compatible with this voltage.

One option could be to use gear motors, which are specifically designed for high torque and low speed applications. They can be found within your budget and with a little research, you can find ones that are compatible with 12V power supply. Another option could be to use DC motors and add a gear reduction system to achieve the desired torque and speed.

In terms of budget, it may be helpful to look for used motors or motors from discount suppliers to keep costs down. You could also consider reaching out to local universities or maker spaces to see if they have any spare motors that they could donate or sell at a lower cost.

Overall, my advice would be to do some more research on the specific specifications and requirements for your project and then look for motors that fit within your budget. Good luck with your project and I hope you are able to successfully build your motorized tennis ball launcher!