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It is a guide to select best Coreless motor. |
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| Application requested data: |
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Operating speed
Nr = 4000 rpm |
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Operating torque
TR = 1.4 mNm |
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Max. voltage supply
Umax = 10 VDC |
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Max. current supply
Imax = 0.2 A |
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Ambient temperature
Ta = 25°C |
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Motor type
DC Coreless motor |
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Max. motor length
Lmax = 35 mm |
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Max. motor diameter
max = 13 mm |
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| Consider motor technology and physical dimensions when seleting potential candidates from the catalogue. In this example, coreless motors up to SCL12-30 series ( = 12.5 x L = 32 mm)will be considered. |
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| Knowing the motor working point, NR =4000 rpm and TR = 1.4 mNm,select from datasheets all motors where the working point is inside the continuous operating area. In this example, SCL12-22(max. continuous torque 1.6 mNm) and SCL12-30 series will be considered(max. continuous torque 2.09 mNm). |
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| Verify whether selected motors are able to operate at the working point with the available maximum. current and voltage supply. |
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Current absorbed at working point, IR[A]
TF = Motor friction torqure [mNm], KM = Motor torque constant [mNm / A] |
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Motor voltage at woring poing, UR[VDC]
R = Motor terminal resistance at (25°C) [ω], KE = Back-EMF constant [mV / rpm] |
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Result of calculation
SCL12-2204 ⇒ IR = 0.46 A, UR = 3.1 VDC ⇒ IR too high
SCL12-2222 ⇒ IR = 0.18 A, UR = 7.4 VDC ⇒ OK
SCL12-3005 ⇒ IR = 0.30 A, UR = 3.4 VDC ⇒ IR too high
SCL12-3020 ⇒ IR = 0.15 A, UR = 7.1 VDC ⇒ OK
SCL12-3043 ⇒ IR = 0.14 A, UR = 10.4 VDC ⇒ UR too high
In red where motor current and/or voltage exceed power supply limits.
| Note: |
In this catalogue only standard coils are shown. If desired, Namiki can provide different coils to meet specific working points. Please consult our sales section for details. |
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| Once the motors that can operate at the working point have been defined, the performance around the working point can be calculated. |
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Motor output power at working point, Pout [W] |
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Motor efficiency at working point, [%] |
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Result of calculation
SCL12-2222 ⇒ Pout = 0.59 W, = 43 % ⇒ Second choice
SCL12-3020 ⇒ Pout = 0.59 W, = 55 % ⇒ First choice |
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| The described procedure is generally suitable for most of the cases.However, if more accurate calculation is required, then the thermal behaviour at the working point can be considered. |
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Motor coil temperature at working point, Tc [°C]
= 0.004 [K-1], Rth1 & Rth2 = thermal resistances [K / W] |
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Motor coil resistance at working point, Rwp [Ω] |
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By replacing R in [eq.2]with Rwp, repeat steps 3 and 4 considering the motor coil temperature. For safety, the coil temperature at the working point must not exceed the maximum coil temperature indicated in the catalogue.
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| If a motor-gearhead combination is requested, before proceeding with step2, calculate the working point at the motor output shaft. For gearhead selection, where life expectancy is concerned, it is important to choose a product with an output torque higher than that required by the application and to operate the motor, by selecting the appropriate reduction ratio, at a continuous speed lower than the gearhead maximum recommended input speed. |
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Speed and torque calculated at motor output shaft |
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| Nout |
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gearhead output speed |
| Nin |
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motor output speed(gearhead input speed) |
| Tout |
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gearhead putput torque |
| Tin |
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motor output torque(gearhead input torque) |
| i |
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gearhead reduction ratio |
| η |
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gearhead efficiency [%] |
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