|May17-10, 09:19 PM||#1|
DC motor design calculations, help?
1. The problem statement, all variables and given/known data
Hi, well my task is to construct a DC motor. With 25w rotational mechanical output power. It cannot draw more then 5A current, and has to have 3 or more poles in rotation. The motor must be brushed/commutated. There is a max of 30v D.C. input. The motor needs to be built and tested within a few days, so ill need calculations done by tomorrow (brutally tough i know)
2. Relevant equations
I was not given relevant equations for the question, this is half my problem, id like some advise on which equations i should be using to caluclate the necessary parts to build the motor which will acomplish the goals stated above.
3. The attempt at a solution
My attempt came up short when i came across the term 'back emf' or 'induced emf'. i found an equation:
Vo = IR + Ve
Vo = power supply
I = current
R = terminal resistance (is this calculatable for my question or do i need to build and measure this, and what exactly is this resistance? where is it found.. i thought it was the overall resistance of the motor)
Ve = Induced EMF (Back EMF)
Further continuation of this formual suggest substituing Ve = w Ke
w = angular velocity
Ke = Induced EMF constant (how do i determine this?)
In other attempts at solving this i came up with the following:
Pi = VI
Pi = power input (i assumed motor efficiency to be 50% as someone suggested this was a good idea, how does this affect other calculations, it should have more effect then just doubling the desired output getting an input power of 50w)
V = voltage
I = Current (as no more then 5A is allowed, i set this to 3A so im well within the boundaries)
therefore i get voltage:
V = Pi/I
V = 50/3 = 16.67 Volts
As a DC power supply is used to power the motor, this should not be a problem?
I then attempted to find the resistance of the motor, thinking i could calculate the number of coils i needed.. evidently this led me no where as i used 'V=IR'. Apparently this resistance value is the resistance of the motor when not moving, resistance changes? I know a section of my research said that the current drawn by the motor is reduced the faster it spins. I dont know how or what im calulating from here, can someone please help?
|May19-10, 03:52 PM||#2|
Can you reformulate your question to be a bit more clear and concise?
|May19-10, 08:04 PM||#3|
I would like to work out the number of coils i need to use in a 3 armature DC brushed motor, using AWG 24 wire, 3A ( can be up to 5 if needed), the magnets being used have B=1.25 T ( id also like to know if a stack of 4 would make 5T? ) The output of the motor must be 25W of mechanical rotational power (Power = torque x angular velocity)
|May20-10, 09:08 PM||#4|
DC motor design calculations, help?
Just updating, ive worked out how to calculate the Torque, and the Angular velocity. But to find the angular velocity i need the Back EMF, and im still unsure as to how i can find this theoretically before i find the angular velocity? Also to find torque i need a value called 'Field density at end of pole (or armature)' and i assume this is just the field density caused by the input current in the coil of the armature, but i havent been able to verify this yet.
so i ask, how do i work out the back emf, if i dont know angular velocity? or what other method can i use to find the angular velocity?
and when finding torque using 'T = Fr' where 'F = BIl', what is this B value and how is it calculated?
thankyou for helping!
|calculation, dc motor, design, induced emf|
|Similar Threads for: DC motor design calculations, help?|
|TORQUE calculations for Brushless dc motor.||General Physics||8|
|Gearbox design calculations||Engineering, Comp Sci, & Technology Homework||10|
|Rotary Vane Compressor Design Calculations||Engineering Systems & Design||1|
|induction motor design||Electrical Engineering||1|
|About Beakmans motor. design equation B, I, N, calculations or mathcad file?||General Physics||0|