RPM to output shaft speed

Support Motor controllers/drivers and motors
1

Hello!

I apologize in advance if this question sounds stupid. I am very VERY new to electronics/robotics and need to buy a 12V motor with an encoder for a project I am working on.
This is the current list I am choosing from:

Since the High-Power options are in the $50 range this is quite an expensive purchase for me and I want to clarify some things before I make a purchase.
For example, this “20.4:1 Metal Gearmotor 25Dx65L mm HP 12V with 48 CPR Encoder” (Pololu - 20.4:1 Metal Gearmotor 25Dx65L mm HP 12V with 48 CPR Encoder) is listed as having 500 rpm (no-load) but a 20.4:1 gear ratio. Does that mean the output shaft (the metal thing that will actually spin on the outside and turn things) is going to spin at 500x20.4=10,200 rpm?
The goal of the motor is to power an electric toy car (weighing 0.86 kg or 1.9 lbs) that will go very fast for ~8-10 meters and then stop fast as well. The motor is directly connected to a gear that spins the axle, so that is why I am trying to figure out the output rpm. My current motor completed an 8-meter track in 8.5 seconds, but I want to lower this time. I presume I want to increase torque to have more acceleration because it is such a short distance and time? Would this also mean I should pick a motor with a higher gear ratio (ex. 20.4:1 instead of 4.4:1)?

Thank you so much for any input!

  • Emerson
2

Hello.

The no-load speeds listed in our product page documentation is for the gearmotor output shaft, so for the 20.4:1 HP 12V gearmotor that you mentioned, the output shaft is going to spin at about 500 RPM when you power it with 12V. The gearbox is already taken into account, and that is why the no-load speed listed for each gear ratio is different.

For a given motor at a given voltage, a higher gear ratio will result in more torque (and hence higher angular acceleration) but a lower no-load speed, which you can also see in the performance tables for our different options. The optimal trade-off between acceleration and top speed will depend a lot on the specifics of your particular application.

- Patrick