# FIT0186 Torque calcution

I am trying to find a strong motor which can deliver a torque at least 0.2Nm and around 130RPM. While trying to find a 6mm shaft geared motor with feedback,the required torque and rotational was already hard enough(at least for me), I've managed to find one very cheap and ROHS certified. According to the FIT0186 datasheet, (https://media.digikey.com/pdf/Data%20Sheets/DFRobot%20PDFs/FIT0186_Web.pdf) it has a nominal voltage is 12VDC, reduction ratio of 43.8, no-load of 251 rpm and a nominal current of 350mA.

However, there is no mentioning of continuous torque and how much current it will draw. It only states a stall torque of around 1.8Nm and a stall current of 7A...

I am planning to drive the motor with a SN754410(http://www.ti.com/lit/ds/symlink/sn754410.pdf) which supports a continuous current of 1Amp and peak of 2Amps. Since there is no diagram, is it calculatable? I don't know if the nominal current, stall current and torque has a some kind of relation(i.e. linear characteristic). Am I able to drive this motor with this current setup? X2 is the input coming from the MicroChip, X3 is the motor.

Sorry for this potentially silly question.

• Yes, current vs torque is linear (to a close approximation, you lose some torque to friction). So 1.8Nm at 7A implies 0.18Nm at 0.7A or a torque constant of 0.25Nm/amp, and you'll meet your spec somewhere comfortably under 1A. – Brian Drummond Apr 22 '18 at 18:37
• @BrianDrummond Thank you so much! I've been looking for this kind of motor for quite a while(many are so expensive, without even a sensor). I wasn't sure if it had a linear function but your explanation is assuring. – Capt. Frost Apr 22 '18 at 19:08
• You may need to add a heat sink if starting frequently of some other soft start means – Sunnyskyguy EE75 Apr 22 '18 at 20:30
• Also solve the Energy Conversion equations and account for losses – Sunnyskyguy EE75 Apr 22 '18 at 23:15