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V012024 • © 2024 Portescap. Specifications subject to change without notice.Examples of DC Coreless Motor CalculationsThis section aims to provide all the information necessary to select a DC Coreless Motor and to calculate the values at the desired operating point.Example: Direct drive without a gearhead attached to the motor.For this application we are looking for a DC Coreless Motor for a continuous duty application. The application requirements are:Available voltage: 10 VdcAvailable current: 1 AmpMotor operating point: 2,000 rpm [n] desired motor speed 6 mNm [τ] desired output shaft torque 22° C [Tamb] ambient temperature Continuous operationMotor dimensions: 45 mm maximum allowable length 25 mm maximum allowable diameterThe Portescap DC Coreless motor 22DCP can deliver 6.21 mNm of torque continuously, and is a good starting point for our calculation.Let’s examine the motor series 22DCP 32G1 213P.1, which has a nominal voltage of 9 Vdc. The characteristics we are most interested in are the torque constant (k) of 8.48 mNm/A, the terminal resistance (R) of 4.3 Ω and the no-load current (lo) of 53 mA. For a load torque (τ) of 6 mNm the motor current is: I = τ /k + I0 [A] I = 6 mNm / (8.48 x10-3 mN/A) + 53 mA = 0.76 AThe current value obtained is just below the maximum continuous current of the selected product. Now let’s verify that to meet this working point, we have enough supply voltage (U). U = R × I + k × ϖ [Vdc] ϖ = 2π/60 × n = 2π/60 × 2,000 rpm = 209.44 rad/s [rad/s] U = 4.3 Ω × .76 A + (8.48 × 10-3 Nm/A) × 209.44 rad/s = 5.0 VdcWith 10V supply voltage available and only 5V required, the motor will be able to meet the required working point. We note that the current of 0.76 A is quite close to the rated continuous current of 0.77 A. This means the coil temperature reached at this current is likely to be very close the motor specified maximum coil temperature of 100°C. The below chapter explores thermal considerations applied to this case. 224Engineer’s Appendix