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I'm designing a bot for a TDP(Team Documentation Profile) for a competition which is supposed to throw a rugby ball. Since the deadline is closing in soon, I can't test things out myself.

After going through multiple ideas, I settled on using two wheels throwing mechanism.
The mechanism

Can I implement the above-shown mechanism without using rotary encoders for the two motors?

Basically I just want to ask if the two BLDC motors have any difference in angular velocity even when powered with the same voltage.

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  • $\begingroup$ Welcome to Robotics Utkarsh Verma, but I'm afraid that Unbounded Design Questions are off-topic because there are many ways to solve any given design problem. We prefer practical, answerable questions based on actual problems that you face, so questions which ask for a list of approaches or a subjective recommendation on a method (for how to build something, how to accomplish something, what something is capable of, etc.) are off-topic. Please take a look at How to Ask & tour for more information on how stack exchange works. $\endgroup$
    – Mark Booth
    Jan 27 '20 at 15:34
  • $\begingroup$ @MarkBooth Is this question okay now? $\endgroup$ Jan 29 '20 at 2:25
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Yes. Motors of the same type, by the same manufacturer, driven by the same voltage may still have different angular velocities (and different torque curves and any other parameter). There are a variety of reasons for this: manufacturing tolerances resulting in different amounts of internal friction or mass, different magnet strengths, differences in winding, differences in internal resistance of the copper winding, the list goes on. Furthermore, a motor's characteristics may change over time too as mechanical parts wear. Depending on the quality of motor, these differences may be large or small.

Typically in robotics, this manifests as "why doesn't my robot go straight"? When people simply provide the same voltage to both wheel motors without a velocity controller.

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