DC Motor Type Selection

Learn about DC motor type selection with Dr. Urs Kafader of the maxon academy.

Transcript

00:00:01 [Music] hi I would like to show you how you can find suitable DC motors for your applications in this tutorial we focus on the speed and torque requirements for the selection of the right DC motor type once you have found the motor size you will have to determine the matching winding please refer to a separate tutorial for winding selection

00:00:32 darting point for motor selection is the motion of the load in the application the necessary operation cycle speed profiles and friction result in speed and torque requirements the motor has to fulfill in case of mechanical transformation think of gears and screws the values at the load have to be converted to the motor output shaft in our standard diagram with motor speed as

00:00:57 a function of torque this can be represented as points of operation for example there can be a constant operation at the given torque and speed there might be an operation at higher speed but at lower torque or maintaining a position against some external force at zero speed another possibility is speeding up with some mass inertia to overcome usually

00:01:22 that's where the highest torque occur regarding torque which contains all the operation points in a few key values the average RMS load torque and the extreme operation point let's first look at speed we need a motor with a speed limit that is high enough to cover all operating points the speed limit of maximal just corresponds to the upper limit of the operating range diagram

00:01:50 however it is essentially the required torque that defines the motor size we have to select the motor that on average can produce the necessary torque hence we need a motor with the nominal torque larger than the RMS average load torque short load Peaks as during acceleration may be located in the short term operating range the maximum permissible speed of Maksim motors can be found in

00:02:17 line 23 of the motor data it is related to bearing and brush life considerations the torque capability of the motor type is given as the nominal torque in line 5 of the torque data it is a characteristic parameter for a motor type and size it limits the continuous operating range essentially it's given by a temperature limit up to this torque the motor can be loaded continuously

00:02:45 without overheating on the standard conditions a good overview of the nominal torque of Maxim motors offers the selection guide in the catalog direct bars indicating the torque capabilities with respect to the scale at the bottom you can also find here a lot of additional information such as possible combinations with encode the skiers and

00:03:07 controllers higher torques the nominal are possible but only a limited amount of time how long an overload situation may last depends on the amount of overload torque and the motor type as a rule the larger the motor the longer the overload can be typically overload can last several seconds as indicated by the thermal time constant of the winding roughly speaking a motor can support two

00:03:37 to three times the nominal torque for periods up to this thermal time constant in addition to this considerations about torque and speed there are other questions related to the selection of motor size that need to be addressed the first one being the mechanical interface what is the maximum diameter and length that is possible how is the motor going to be fixed are there any restrictions

00:04:03 concerning the size of mounting flange and how about the shaft diameter and length in case a Maxim gearhead has been selected previously we have to respect the maximum system for the possible motor types in combination with this particular gear head and at last service life and motor temperature might also have an influence on the selection of the motor type sometimes it is advisable

00:04:30 to select oversized motor to enhance the life of the brushes or to keep the housing temperature low that's it a short introduction on brushed and brushless DC motor selection don't forget the starting point for a good selection is the knowledge of the speed and torque of your application put some effort in it to find out at least approximate of values and good luck

00:04:56 during selection [Music]