Hi
I'm currently building a Rotary speaker for a college project and I am struggling to find the right motor to use.
Essentially I need a dc motor, preferably 12volts that is capable of spinning a Polystyrene baffle (weighing around 110grams) at decently fast speeds (probably around 1000rpm is enough.)
The circuit that I am currently using is simply an L298N Motor controller hooked up to an Arduino Nano for speed control with a 12v 1.5A power supply giving power to the motor
I have tried several motors with varying degrees of success. An issue I have run into with two motors that I have tried is that the power supply cant supply enough current while the motor is under the load (the motor turns on for less than a second and then off and then on etc) this happens when the motor is connected directly to the power supply, when I use the motor controller the motor controller heats up very quickly.
I have tried using a 100rpm geared Motor, this worked fine but was quite noisy and slow.
Basically If someone could point me in the right direction in terms of finding the right motor/power supply I would be very grateful I'm fairly new to this sort of project and this is the first time that I have encountered this kind of issue
You seem to be ignoring the power supply problem you have described. Use a suitable power supply and try the motors again. Motors need a lot of current!
Paul
As well as a more capable power supply, many things will be better than that ancient L298 which can only handle low currents and wastes a lot of the input power as heat (as you've discovered). Have you measured the current that the motor takes?
Does the motor need to run in both forward and reverse directions? If not then a simple logic-level MOSFET circuit would work. If so then a more modern MOSFET based H-bridge driver would be good.
In reference to the power supply I imagine you are right and that I should use a more powerful one rather than a different motor, the power supply that I am currently using is 3 amps (I got this wrong in my original post.)
The motor that I would Ideally like to use is a 775 Motor (specifically this one Amazon.co.uk from amazon)
however I cant seem to find the current that I would need to run it with the load (if its any help it works fine with my current power supply with no load.) so I'm wondering if a 5 or 6 amp supply would be sufficient?
In terms of the motor controller no, the motor doesn't need to run in both directions so I will replace it with a different one would you know of any that would work for this?
The dimensions for the Polystyrene baffle are:
Height: 12.7cm (5in)
Width: 20.32(8in)
Its basically a cylinder with a cut-out about 4 inches deep, I have posted pictures below.
No need to wonder about the power needed by your motor. Measure the resistance of the motor wires. Use Ohm's law to compute the amps using your supply voltage. the answer is the current needed to start your motor movement.
Paul
It sounds to me like you are trying to build a Leslie speaker. If I remember correctly they were common starting in about the 30's . They were first introduced by Hammond Organ. They add the doppler effect to the music. I think you can find online how to build one, if so the work is done for you.
I have been doing some testing with the motor using a 9volt battery as well as the 12volt supply that I currently have and have found that , with the baffle connected the motor draws around 1.7A and with no load it draws about 0.25A.
I worked this out to be less than 24W at 12V, the power supply that I am using at the moment can apparently supply 36W however when I was measuring the current draw from the power supply I found that It would cut out at about 1.7A
I'm probably missing something obvious here and I'm sure the right power supply would solve my issue, I have listed the specs of the power supply that I am currently using below.
I found an old 12volt supply lying around witch works just fine, the motor draws 3.5A at 12V, the new power supply is only rated for 2A so I will get a new one rated appropriately to avoid breaking anything
as for the motor controller I found this one Amazon.co.uk on amazon witch will hopefully work well
Your supply needs to handle the stall current of the motor, not just the running current, otherwise
it will simply cut-out the moment you throw the switch. Measure the resistance of the motor to
determine the stall current. Battery power is easy as batteries handle brief overload gracefully (without
cutting out).
You can mitigate for large stall currents by ramping the drive PWM level gradually however, allowing
the motor to speed up at more modest currents and placing less stress on everything.
1000rpm is very fast for a Leslie speaker, it is the sort of speed that may shred some polystyrene
through drag forces however... Perhaps 500rpm is safer top speed?
Hi Mark
Thanks for the reply, ill certainly follow your advice on ramping the motor up slowly to avoid large currents as well as check that the power supply can handle them (the supply I have now works fine even under stall conditions witch it shouldn't ever have to deal with.) , in terms of the speed, I agree, I was planning on using software to control the max speed of the motor, this way I can tinker with what max speed I think works the best.
I wont be on the forum for the next little while so sorry if I don't reply to any messages.
Thanks again to everyone for all the help.
Hello
So I was trying to sort out the speed control and while doing this the pwm board I was using started to overheat, I measured the current the motor was drawing from my new 5amp supply and found that it was just over 6amps, more than what the board can handle.
I'm fairly sure that the motor that I am currently using is way overkill for my project anyway and I need to use one that draws less current, the baffle doesn't need to spin as fast as it is as Mark said.
I have tested a smaller motor with the setup and it works, spinning the baffle at a speed that seems adequate however I think that if I were to use this motor it would fail quickly as it heats up quite fast while spinning the load. I measured the current draw while it was connected to the baffle and it was around 3amps (this is with the same 5amp 12v supply I used for the other motor) I then held the baffle to stop it from moving and the motor drew around 3.5 amps, as I say I'm very new to this kind of thing but I think this basically means that I am running this motor at close to its stall current, as well as this I haven't yet tested this motor with the speed control so am unsure that It would operate at lower speed)
I would like to get this part of the project finished fairly soon so if someone could give me a specific motor that they think may work or a way of figuring this out for myself I would be very grateful, the specs of the two motors are below. (these are from the amazon listing so I'm sorry if they don't have all necessary information.)
I think I essentially need a motor that is somewhere in-between these two in terms of power.
Large motor:
775 Motor DC 12V-36V 3500-9000RPM Motor Large Torque High-power Motor
(amazon Link: https://tinyurl.com/n9bf8t3s)
Small Motor:
Rated voltage: 12V
Motor Body Diameter: 28mm/1.1inch
Total Length(Included Pin): 58mm/2.3inch
No-load speed: 10000 r / min
Shaft Size: 13 x 2.3mm/0.51in x 0.09in (L*D)
Motor Body Length: 37mm/1.46inch
(amazon Link: https://tinyurl.com/vd3brta8)
Thank You so much for your help
edit: I have tested out the Arduino circuit with the small motor and, although it works the pwm control board still heats up. As well as this the motor creates a high pitch whining noise. I have used a stand alone pwm board and this doesn't happen so I think I will need to replace the PWM board as well.
