Hi i have a BLDC moter https://www.banggood.com/350W-48V-DC-Brushless-Motor-Geared-Ebike-Tricycle-Kit-Engine-Electric-Scooter-p-1419702.html?akmClientCountry=NL&rmmds=cart_middle_products&cur_warehouse=CN And need to find how much kg it can drive and how fast please help me


  • \$\begingroup\$ In practical terms you should discuss this with those having light electric motorocycle experience to get a sense of what sort of rating is actually suitable for your application, whatever that is. This is not the place for either the topic, or for discussion. \$\endgroup\$ – Chris Stratton Apr 11 at 17:01

This is a mechanical engineering problem.

The motor specification sheet provides:

  1. The rated output power. That is the mechanical power that the motor can deliver to drive the load continuously.

  2. The rated speed. That is the motor speed at which it can deliver the rated output power.

  3. The rated torque. That is the torque that the motor will be providing when operating at rated speed and power. The motor can probably provide the same torque down to zero speed when controlled by a well designed speed controller. The maximum time of operation will be determined by the motor cooling system.

Mechanical output power in watts is equal to the speed in RPM multiplied by the torque in newton-meters divided by 9.549.

The maximum speed of the vehicle will be determined by the driving wheel diameter and the speed ratio between the motor shaft and the wheel. The speed may also be limited by the torque available to overcome the load.

The load presented to the motor by the vehicle consists of rolling friction, drive train friction, aerodynamic drag, force required to accelerate inertia at the desired rate and force required to raise mass up an incline.

Friction is a constant retarding force or torque that doesn't change much with speed. It is the coefficient of friction multiplied by weight or force.

Aerodynamic drag is the retarding force of the vehicle moving through air. It is proportional to speed squared multiplied by a drag coefficient.

The force required for acceleration is mass multiplied by the rate of acceleration.

The force required to raise mass up an incline (climb a hill) is determined by the force of gravity acting on the mass and the angle of incline.

There are handbooks and online sources that may be able to provide coefficients of friction for various types of driving wheels, bearings, chain drives etc. Drag coefficients may also be available.

The basics of applied mechanics - statics and dynamics can be found in text books, course notes and online tutorials.

Working out the details is a problem that is too broad for this forum. It is also off-topic for the electrical engineering section except that is is useful for an electrical engineer to understand the basics and the general principals as outlined above.

  • \$\begingroup\$ My wheels are 39 cm x 9 cm and it ways around 25kg \$\endgroup\$ – jojo osinga Apr 11 at 17:08
  • \$\begingroup\$ See above additions to my answer. \$\endgroup\$ – Charles Cowie Apr 11 at 17:24

There is a rated torque of 1.19 N.M, and a rated speed of 2800 revolutions per minute (3100 RPM with no load). Your question cannot been answered as you think: the motor does not drive Kg but torque; that means that the product of the radius of the heel with the force orthogonal to the radius should be at most 1.19 N.m. For example, suppose you transmit the force of the motor with a belt around a single heel that is supposed to elevate a weight of 1.5 kg. Now, suppose the radius of the heel is 10 cm = 0.1 m. Then the torque is 1.5 x g x 0.1 (where g is the gravity of earth constant, approximately equal to 9.8), that is, torque = 1.47. So the motor can drive it at a speed of somewhat more than 2800 RPM (since 2800 RPM is apparently for the maximal torque = 1.19 N.m.)

In other words, to know if your motor can do the job, you have first to derive the needed force orthogonal to the radius of the axis of the motor, and to know what is the radius of the heel that the motor has to rotate, then to multiply one by the other and to see if this is in the rated limit.

Notice also that with multiple heels of different radii, you can move even a very heavy thing with a weak motor: but of course, the price you have to pay is that this will be done very slowly. This is the basis of the concept of "work" and energy in physic: the product of the speed by the force, equal to the power, remains constant.

I cannot offer more help since the computations depend upon the way you transmit the power of the motor to your load.

  • \$\begingroup\$ My wheels are 39 cm x 9 cm and it ways around 25kg \$\endgroup\$ – jojo osinga Apr 11 at 17:08
  • \$\begingroup\$ That means nothing: you need to specify what the motor is supposed to do (is it for a bicycle ? if so, the maximal weight will also depend on the slope of the road the bicycle is traveling on) and how the motor transmits the power to the load (the exact mechanism). Unfortunately, this really becomes a mechanical engineering problem and it is not the place to ask these questions here. Try the "physic forum", and specify exactly the mechanism. \$\endgroup\$ – MikeTeX Apr 11 at 17:17

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