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March 29, 2024, 01:44:08 am

Author Topic: Torque & Force Time graphs of motor  (Read 1507 times)  Share 

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Matth3wliu

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Torque & Force Time graphs of motor
« on: June 05, 2020, 06:12:46 pm »
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Hey all,

Can someone please explain the answer for this question?

fun_jirachi

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Re: Torque & Force Time graphs of motor
« Reply #1 on: June 05, 2020, 09:06:55 pm »
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Hey there!

While not a proper explanation, an easy way to justify the answer to yourself is to consider the relevant equations \((F = BIL\sin \theta \text{ and } \tau = nIBA \sin \theta)\) and relate them to the graph + relevant theory.

We know that for every 180-degree turn, the current changes direction in the wire AB (when the area enclosed by the armature is perpendicular to the magnetic field). By the right-hand palm rule, the force also changes direction, every time the coil rotates through 180 degrees. The magnitude (or rather the distance on the graph from zero) remains constant because none of the variables change at any point - the sin is irrelevant here because the wire is always perpendicular to the field!

We also know that the torque is always greater than or equal to zero, but never negative - nowhere does the motor start spinning in the opposite direction! Keeping in mind that as the motor spins, and that none of the variables change apart from the angle, we see the absolute value of a sinusoidal curve. If it helps, try to recall where the torque is zero, and where it is maximised - or even substitute arbitrary values into the equation to convince yourself 'okay, this makes sense'.

Hope this helps :)
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Matth3wliu

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Re: Torque & Force Time graphs of motor
« Reply #2 on: June 05, 2020, 09:43:33 pm »
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Thank you, that was really helpful!