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I have a 550 DC motor of 12V, 45W and 10K RPM installed on a wheel, which is not causing the wheel to turn fast enough when the motor is connected to a 12V battery. I replaced the motor with an older DC motor which I had, having the same specs of the replacement, however with 9K RPM (I thought it would be slower).
Sarcastically it generated more speed to the wheel than the 10K RPM one. Some electrician told me to ignore the labeling on the DC motors outside since they are not accurate.
I wasted plenty of time trying to fix the issue by following the book higher RPM means higher speed. I first thought that the gear train inside the gearbox was the issue, but I used the same gearbox for the older 9K RPM motor and still it gave higher speed. I am willing to buy additional DC motor but I need to generate even higher speed, I am confused to whether I should buy a higher or lower RPM DC motor for this purpose.

The following are the full specs of the project:
MOTOR1
Power:20-45W
Voltage:12 V RPM:10,000

MOTOR2
Power:20-45W
Voltage:12 V RPM:9,000

each motor was individually attached to gear train having the following teeth:

Motor1 turns a 10 teeth pinion, which turns a 52 teeth cylinder C1, attached to C1 is a little cylinder C1' having 10 teeth again, C1' turns a cylinder, C2, having 48 teeth, attached to C2 is C2' having 9 teeth, C2' turns a the last cylinder C3 having 38 teeth, connected to a wheel. After doing some calculations, the final output for the gear train would be 100RPM

Motor2, before replacement, had the following installations:

Motor2 turns an 11 teeth pinion, which turns a 56 teeth cylinder C1, attached to C1 is an 11 teeth cylinder C1', turning a 45 teeth cylinder C2, C2 is attached to C2' 11 teeth cylinder, C2' is turning a 42 teeth cylinder C3, C3 is finally attached to the wheel. The final output of motor2 in the above gear train would be 112RPM

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    \$\begingroup\$ What is a "550 DC motor"? 550 watt? "... higher RPM means higher speed." That's true because RPM is a speed measurement. Please edit your question add links to the datasheets for the two motors. The datasheet should give details on speed versus load. "No datasheet? No sale!" \$\endgroup\$
    – Transistor
    Sep 6, 2019 at 6:01
  • \$\begingroup\$ Possible duplicate of provide higher speed to a power wheel \$\endgroup\$ Sep 6, 2019 at 6:07
  • \$\begingroup\$ No 550 is the size of the motor, the DC motor is of 45W , 12V, i will add photos similar to the combinations I have. \$\endgroup\$
    – koki
    Sep 6, 2019 at 6:21
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    \$\begingroup\$ RPM is Revolutions Per Minute => rotational speed. More means more. Whether a datasheet for any given motor is accurate is another matter. Unfortunately, some manufacturers lie about what their product does. This tends to happen more at the cheaper end of the market, as people who buy on price alone tend to be more gullible, and tend not to have the right equipment to verify wild claims. \$\endgroup\$
    – Neil_UK
    Sep 6, 2019 at 6:21
  • \$\begingroup\$ @Neil_UK, I was actually astonished when the electrician told me to ignore the labeling on the DC motor, I mean I have been working on the project for a week off and on taking, connecting wires adding batteries. That's the only explanation "manufacturers lie about products" \$\endgroup\$
    – koki
    Sep 6, 2019 at 6:31

1 Answer 1

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DC motor RPM is highly dependent on load. Motors sold for industrial usually have specifications that provide RPM at rated load. Motors sold for hobby use often state the no-load RPM. Sellers of motors for hobby use often don't pay much attention to accuracy, clarity and completeness of specifications. I suspect that the problem is not so much that manufacturer's lie but that some manufacturers sell junk.

A gear that reduces the motor speed from 10,000 RPM to 100 RPM represents a significant percentage of the motor's load. Differences an the quality and age of the gears may have a significant impact on the output speed of a 45 watt motor.

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  • \$\begingroup\$ Thanks for the input, the majority of the colleagues here who are working on similar projects are trying to manipulate the voltage of the input to control/add speed to the wheel, I will try to do that differently by manipulating the cylinders inside the gear and/or motor. Thank you all for the comments \$\endgroup\$
    – koki
    Sep 6, 2019 at 11:29
  • \$\begingroup\$ If you want to have a specific speed with changing load, temperature, wear of components etc., an electronic speed controller is essential. \$\endgroup\$
    – user80875
    Sep 6, 2019 at 11:37
  • \$\begingroup\$ ok, I have to check it out \$\endgroup\$
    – koki
    Sep 6, 2019 at 12:43

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