Explanations of maxon terminology: DC motor
Dimensional drawings Presentation of the views according to the projection method E (ISO). All dimensions in [mm]. Mounting in plastic Screwed connections on motors with plastic flanges require special attention. M A Max. tightening torque [Ncm] A torque screw driver may be adjusted to this value. L Active depth of screw connection [mm] The depth of the screw connection must be less than the usable length of the thread! Motor Data The values stated are based on a motor temperature of 25°C (so-called cold data). 1 Nominal voltage U N [Volt] is the DC voltage on the motor connections on which all nominal data are based (lines 2–9). Lower and higher voltages are permissible, provided set limits are not exceeded. 2 No load speed n 0 [rpm] ±10% This is the speed at which the motor turns at nominal voltage and without load. It is approximately propor- tional to the applied voltage. 3 No load current I 0 [mA] ±50% This is the typical current that the unloaded motor draws when operating at nominal voltage. It depends on brush friction and friction in the bearings, and also increases with rising speed. No load friction depends heavily on temperature, particularly with precious metal commutation. In extended operation, no load friction decreases and increases at lower temperatures. 4 Nominal speed n N [rpm] is the speed set for operation at nominal voltage and nominal torque at a motor temperature of 25°C. 5 Nominal torque M N [mNm] is the torque generated for operation at nominal voltage and nominal current at a motor temperature of 25°C. It is at the limit of the motor’s continuous operation range. Higher torques heat up the winding too much. 6 Nominal current I N [A] is the current that, at 25°C ambient temperature, heats the winding up to the maximum permissible tem- perature (= max. permissible continuous current). I N decreases as speed increases due to additional fric- tion losses. 7 Stall torque M H [mNm] is the calculated load torque that causes the shaft to stop at nominal voltage. Rising motor temperatures reduce stall torque. 8 Stall current I A [A] is the quotient from nominal voltage and the motor's terminal resistance. Stall current is equivalent to stall torque. With larger motors, I A can often not be reached due to the amplifier's current limits.
9 Max. efficiency h max [%] is the optimal relationship between input and output power at nominal voltage. It also doesn’t always denote the optimal operating point. 10 Terminal resistance R [ W ] is the resistance at the terminals at 25°C and deter- mines the stall current at a given voltage. For graphite brushes, it should be noted that resistance is load- dependent and the value only applies to large currents. 11 Terminal inductance L [mH] is the winding inductance when stationary and mea- sured at 1 kHz, sinusoidal. 12 Torque constant k M [mNm/A] This may also be referred to as “specific torque” and represents the quotient from generated torque and applicable current. 13 Speed constant k n [rpm/V] shows the ideal no load speed per 1 volt of applied volt- age. Friction losses not taken into account. 14 Speed / torque gradient D n / D M [rpm/mNm] The speed / torque gradient is an indicator of the motor’s performance. The smaller the value, the more powerful the motor and consequently the less motor speed varies with load variations. It is based on the quotient of ideal no load speed and ideal stall torque. 15 Mechanical time constant t m [ms] is the time required for the rotor to accelerate from standstill to 63% of its no load speed. 16 Rotor inertia J R [gcm 2 ] is the mass moment of inertia of the rotor, based on the axis of rotation. 17 Thermal resistance housing-ambient R th2 [K/W] and 18 Thermal resistance winding-housing R th1 [K/W] Characteristic values of thermal contact resistance without additional heat sinking. Lines 17 and 18 com- bined define the maximum heating at a given power loss (load). Thermal resistance R th2 on motors with metal flanges can decrease by up to 80% if the motor is coupled directly to a good heat-conducting (e.g. metallic) mounting rather than a plastic panel. 19 Thermal time constant winding t w [s] and 20 Thermal time constant motor t s [s] These are the typical reaction times for a temperature change of winding and motor. It can be seen that the motor reacts much more sluggishly in thermal terms than the winding.The values are calculated from the product of thermal capacity and given heat resistances. 21 Ambient temperature [°C] Operating temperature range. This derives from the heat reliability of the materials used and viscosity of bearing lubrication. 22 Max. winding temperature [°C] Maximum permissible winding temperature.
23 Max. speed n max [rpm] is the maximum recommended speed based on ther- mal and mechanical perspectives. A reduced service life can be expected at higher speeds. 24 Axial play [mm] On motors that are not preloaded, these are the toler- ance limits for the bearing play. A preload cancels out the axial play up to the specified axial force. When load is applied in the direction of the preload force (away from the flange), the axial play is always zero. The length tolerance of the shaft includes the maximum axial play. 25 Radial play [mm] Radial play is the bearing’s radial movement. A spring is utilized to preload the motor’s bearings, eliminating radial play up to a given axial load. 26/27 Max. axial load [N] Dynamic: axial load permissible in operation. If dif- ferent values apply for traction and thrust, the smaller value is given. Static: maximum axial force that does not cause per- manent damage when applied to the front of the shaft at standstill. Shaft supported: maximum axial force applying to the shaft at standstill if the force is not input at the other shaft end.This is not possible for motors with only one shaft end. 28 Max. radial load [N] The value is given for a typical distance from the front flange. As the distance increases, this value decre- ases. 29 Number of pole pairs Number of north poles of the permanent magnet. The phase streams and commutation signals pass through per revolution p cycles. Servo-controllers require the correct details of the number of pole pairs. 30 Number of commutator segments 31 Weight of motor [g] 32 Typical noise level [dBA] is that statistical average of the noise level measured according to maxon standard (10 cm distance radially to the drive, no load operation at a speed of 6000 rpm. The drive lies freely on a plastic foam mat in the noise chamber). The acoustic noise level depends on a number of fac- tors, such as component tolerances, and it is greatly influenced by the overall system in which the drive is installed. When the drive is installed in an unfavorable constellation, the noise level may be significantly high- er than the noise level of the drive alone. The acoustic noise level is measured and determined during product qualification. In manufacturing, a struc- ture-borne noise test is performed with defined limits. Impermissible deviations can thus be identified.
maxon DC motor
March 2021 edition / provisional data / subject to change
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