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I am making a robot car with four wheels. Every wheel will be attached to a motor. If I use four motors and four wheels , will I get more speed then using two motors?(If all the motors rotate at same speed)

According to my thought, The speed should be increased after using four motors as more motors are rotating. But practically, I am seeing same speed whether I use four wheel or two. For balancing,I am using a ball caster at front.

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It depends on whether you are limited by the torque that each motor can generate.

If the friction is low, then the motor may end up running at its maximum speed (as a motor goes faster, it generates more back EMF until it equals the voltage applied).

When you add more motors, there is a risk that you draw more current from your power source, which drops the voltage available, and gives you lower speed.

It's also possible, if there is very low friction between the wheels and the surface, that you need to distribute the torque between the wheels to maintain grip; applying all the torque to two wheels only (especially front wheels) might cause slipping and reduce your acceleration.

So it really depends on details that you did not specify in your question - specifically, what factors are limiting your

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  • $\begingroup$ Probably , the friction between the wheels and the surface was very low. That's why I was getting same speed. But if I increase the friction, will the speed increase. if voltage remains constant? $\endgroup$
    – Abtahee Salekeen
    May 22, 2018 at 13:10
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Assuming simple DC motors and a constant voltage, the speed of motors and the car will depend on the load.

This is because the Speed ~ $EMF=(V-IR)$ and, since the current will increase with the load, the speed will decrease.

If the load, coming from the car, is insignificant, the current and the speed of all motors will be roughly the same and determined mostly by the characteristics of the motors. In this case, the number of motors would not affect the speed of the car.

As the load increases, the current increases as well to produce the necessary torque and, as a result, the speed decreases. In this scenario, assuming that the wheels don't slip and the load is evenly distributed between the wheels, adding more motors will increase the speed of the motors and the car, since the torque will be shared between more motors.

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