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Old 2011-10-04, 11:41   Link #1
DonQuigleone
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Join Date: Dec 2007
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Electric motors

This is a pretty weird place to ask this, but I figure one of you here will be able to at least set me in the right direction.

I'm doing a small projectm and as part of it I need to be able to control an electric motor. I figure the best and easiest way to do so is to have a computer do it, IE either have some kind of computer controlled amplifier hooked up to the motor, or just plug the motor directly into my computer.

Problem is I've never done it before. If one of you guys can help me out, or even point me to another forum, you'll have lots of gratitude from me.

Basically, I need to find a small electric motor/controller combo that I can plug direct into a PC.
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Old 2011-10-04, 12:07   Link #2
Sides
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Try googling for robotic forums.
But from what you describe you want a controller with serial/usb port for a DC motor, correct? Just google for "DC motor controller +usb". Pretty sure you can build one on a breadboard, but gathering the components can be a hassle unless you have access to a lab.
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Old 2011-10-04, 13:19   Link #3
Vexx
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There's a real time computer controller my son bought for his EE robotics work. I can't remember the name of it so I've sent him a query. You access it through a USB cable to program.... that may be overkill. Unless the motor has a control unit built-in with a USB or serial port, its unlikely you can just hook it to your computer directly there needs to be some kind of DAC (digital-analog-convertor) and then possibly an amplifier to step up the power to something the motor will recognize.

Here's an interesting article I googled up on building your own system for a stepper motor with the parallel port as a control conduit.
http://channel9.msdn.com/coding4fun/...-Stepper-Motor

Depending on why you need to change the motor speed (what are the feedback criteria), you might be able to build a simple analog feedback circuit as well that doesn't require a computer at all.

How you proceed just really depends on what your current skills are and what you want to take time to learn.
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Old 2011-10-04, 16:12   Link #4
Jinto
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What size is the electric motor?
Is it a stepper motor or a spindle?

For large sized motors you will need a frequency inverter additonally to the control unit. For small sized stepper motors the control unit is sufficient.

How much money do you want to spend? Which precission are you aiming for (with or without taking into account the motor characteristics)?
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Old 2011-10-04, 19:09   Link #5
DonQuigleone
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Well, I'm looking to rig up a propeller to a cheap electric motor, and so be able to control the lift it produces. Once I've done that I'd like to be able to make a feedback control where the propeller will produce more power depending on how it's angled, IE so I can tilt it at any angle and still maintain the same level of vertical "lift".

Obviously the latter part is a whole other problem, but the first thing is just having an electric motor I have some semblance of control over.

What I think is the easiest solution is to have some kind of electric motor I can power off my computer, and be able to tell my computer to turn it on and off rapidly to create an ad-hoc PWM amplifier.

For this project, the electric motor would be pretty much always attached to the computer, so it doesn't need to be able to store information.

Likewise, the controls required for this project are not going to be simple (as propellers do not have linear behaviour), so an analog controller isn't going to cut it. Plus I'm used to programming with Control Theory.

So I think what I'm going for is a DC motor, low price point, consistent behaviour, good power to weight ratio (needs to be able to life itself), and that I can somehow control from a computer in a cheap manner. I don't mind getting down and dirty and messing with my computer, but I do need to be able to control it from a computer program.

Propellers are cheap, I can get one for less then 5$, and Motors can be pretty cheap too, but I don't want to get the wrong one. I'm coming from an engineering background, so I know the mathematics and theory, but not a lot about the practicals of different motor types.

Given that my power requirements are going to be 10-50 watts(so low), I would think that if you could somehow have the motor directly draw power from the computer would be the way to go. That way the computer can directly change how much power it's giving the motor, either by directly changing the voltage or current, or through PWM. Given that a computer already powers fans and hard drives and whatnot, it shouldn't be beyond the realms of possibility.

You guys seem to know your stuff, so I hope the extra details helps.

@Vexx: I did see that link previously, but I wasn't sure whether or not it's the best way forward, and I wanted to ask around a bit first before I tried messing with my ports. I also wasn't sure if a stepper would be the best type of motor for this purpose.

Last edited by DonQuigleone; 2011-10-04 at 19:22.
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Old 2011-10-04, 19:21   Link #6
TheFluff
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It sounds like you need a Arduino board (costs around 25 EUR).
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Old 2011-10-04, 22:16   Link #7
Vexx
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Quote:
Originally Posted by TheFluff View Post
It sounds like you need a Arduino board (costs around 25 EUR).
Ah THAT's the board I was trying to remember the name of... its a fabulous little board, more fun than the Lego Robotics system. He took it with him back to school.

but yeah if you have a fan connector on your mobo that isn't being used for other purposes and you can control the speed via software then you could plumber's-nightmare something from that
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Old 2011-10-05, 02:51   Link #8
Jinto
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Quote:
Originally Posted by DonQuigleone View Post
Well, I'm looking to rig up a propeller to a cheap electric motor, and so be able to control the lift it produces. Once I've done that I'd like to be able to make a feedback control where the propeller will produce more power depending on how it's angled, IE so I can tilt it at any angle and still maintain the same level of vertical "lift".
Typically if you need reliability you'ld need a real time system, like a cheap PLC logic controller to do the analysis of the gyro sensor data and the controling of the motor.
You can do it on the PC too, but if the PC is very busy with something you cannot guarantee the processing of the data.

Quote:
Originally Posted by DonQuigleone View Post
Obviously the latter part is a whole other problem, but the first thing is just having an electric motor I have some semblance of control over.

What I think is the easiest solution is to have some kind of electric motor I can power off my computer, and be able to tell my computer to turn it on and off rapidly to create an ad-hoc PWM amplifier.
I don't know, that approach might create a lot of reactive power and could cause harm to your motherboard. MBs are not meant to be used as frequency inverters or rather since we are talking about transformation of direct current to direct current... a switched mode converter.


Quote:
Originally Posted by DonQuigleone View Post
For this project, the electric motor would be pretty much always attached to the computer, so it doesn't need to be able to store information.

Likewise, the controls required for this project are not going to be simple (as propellers do not have linear behaviour), so an analog controller isn't going to cut it. Plus I'm used to programming with Control Theory.
In that case you are better off with either a soft PLC for your PC or lab software. A real PLC is extremely expensive if you want to use it to control drives/motors with regards of their specific characteristics.

Quote:
Originally Posted by DonQuigleone View Post
So I think what I'm going for is a DC motor, low price point, consistent behaviour, good power to weight ratio (needs to be able to life itself),
How do you plan to stabilize it, so that it does not begin to spin around the propeller?

Quote:
Originally Posted by DonQuigleone View Post
and that I can somehow control from a computer in a cheap manner. I don't mind getting down and dirty and messing with my computer, but I do need to be able to control it from a computer program.
I guess that disqualifies the Arduino board, its programmed similar to a standard PLC.

Quote:
Originally Posted by DonQuigleone View Post
Propellers are cheap, I can get one for less then 5$, and Motors can be pretty cheap too, but I don't want to get the wrong one. I'm coming from an engineering background, so I know the mathematics and theory, but not a lot about the practicals of different motor types.
A stepper motor is certainly not what you are looking for. If you can get a motor that is typically used in helicopter modelling kits. Those should have a good power to weight ratio with as little as unecessary material as possible (this however means that the motor is not too efficient - less copper).

Quote:
Originally Posted by DonQuigleone View Post
Given that my power requirements are going to be 10-50 watts(so low), I would think that if you could somehow have the motor directly draw power from the computer would be the way to go.
10-50W is a lot of power for MBs, I remember USB 3.0 could provide 5W or something like that. With USB+ (powered USB) you could utilize up to 144W, but I don't think you can control the power output.

Quote:
Originally Posted by DonQuigleone View Post
That way the computer can directly change how much power it's giving the motor, either by directly changing the voltage or current, or through PWM. Given that a computer already powers fans and hard drives and whatnot, it shouldn't be beyond the realms of possibility.
If you wanted to extract a steady current (this what the MBs and the PSU is made for) you could utilize whats on the MB directly. But you want to turn it into something like a high power switched mode converter... I doubt the MB will fit for this.

Quote:
Originally Posted by DonQuigleone View Post
You guys seem to know your stuff, so I hope the extra details helps.
Unfortunately I do not know of any free soft PLC besides http://mat.sourceforge.net/... which is certainly not what you need to accompish your task.

What you need it is something with the capability of one or two analog inputs and one analog output with ms response times.

Well, if you have the money... http://sine.ni.com/nips/cds/view/p/lang/en/nid/201612

But you'ld still need a device that amplifies the analog output signals to drive the motor.
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Old 2011-10-05, 07:28   Link #9
SaintessHeart
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10-50 Watts? How many rpm are you aiming for? If you want to lift something, your propeller must generate enough downward force (air current) to lift it AND the motor.

My brain is a little fried on engineering and Physics related stuff, but if you have money problems trying to get parts or fuel, I can advise you on how and where to get them.

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Old 2011-10-05, 08:00   Link #10
DonQuigleone
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Quote:
Originally Posted by Jinto View Post
I don't know, that approach might create a lot of reactive power and could cause harm to your motherboard. MBs are not meant to be used as frequency inverters or rather since we are talking about transformation of direct current to direct current... a switched mode converter.
Why it's a good thing to ask about this kind of stuff before diving in...

Quote:
In that case you are better off with either a soft PLC for your PC or lab software. A real PLC is extremely expensive if you want to use it to control drives/motors with regards of their specific characteristics.
Software PLC seems best, but the real question is just interfacing with a motor.

Quote:
How do you plan to stabilize it, so that it does not begin to spin around the propeller?
It's going to be held in place, the actual lift will be measured using a weighing scale of some kind. It's not actually going to be lifting off, it's more of a "proof of concept" type thing.

Quote:
A stepper motor is certainly not what you are looking for. If you can get a motor that is typically used in helicopter modelling kits. Those should have a good power to weight ratio with as little as unecessary material as possible (this however means that the motor is not too efficient - less copper).
Quote:
10-50W is a lot of power for MBs, I remember USB 3.0 could provide 5W or something like that. With USB+ (powered USB) you could utilize up to 144W, but I don't think you can control the power output.
Take my power estimate with a grain of salt, I'm not absolutely sure how much power will be needed, just decided to err on the side of higher.



Quote:
What you need it is something with the capability of one or two analog inputs and one analog output with ms response times.

Well, if you have the money... http://sine.ni.com/nips/cds/view/p/lang/en/nid/201612
Money is unfortunately an issue.


Quote:
Originally Posted by SaintessHeart View Post
10-50 Watts? How many rpm are you aiming for? If you want to lift something, your propeller must generate enough downward force (air current) to lift it AND the motor.

My brain is a little fried on engineering and Physics related stuff, but if you have money problems trying to get parts or fuel, I can advise you on how and where to get them.
My power estimate wasn't particularly thought out, I just erred on the side of higher. I'm not actually sure how much power will be needed.


When we consider that a computer is already capable of driving fans and hard drives, there must be a capability in there to drive a motor outside the machine. If you want to, it's fairly easy to use hard electronics to change the speed an electric motor operates at, after all your average RC car can operate at different speeds. Why is it difficult for a computer to do so?
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Old 2011-10-05, 10:00   Link #11
Sides
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Quote:
Originally Posted by DonQuigleone View Post
When we consider that a computer is already capable of driving fans and hard drives, there must be a capability in there to drive a motor outside the machine. If you want to, it's fairly easy to use hard electronics to change the speed an electric motor operates at, after all your average RC car can operate at different speeds. Why is it difficult for a computer to do so?
Try dissembling an old fan, you probably would be surprise what is inside. HDDs and cooling fans all have controllers build in. And that is what you need, a controller, which allows you to manipulate the voltage (or current?). The computer is always limited to the interfaces or hardware it has. However you probably could simulated your idea, with the right programs.
Do you have a pic or avr programmer? I am pretty sure you can build a simple controller with some further parts, best is to ask a electrical engineer or mechatronics buddy. They could probably draw/design a suitable circuit for you, assembling should be easy and besides the fun part.
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Old 2011-10-05, 10:25   Link #12
DonQuigleone
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Quote:
Originally Posted by Sides View Post
Try dissembling an old fan, you probably would be surprise what is inside. HDDs and cooling fans all have controllers build in. And that is what you need, a controller, which allows you to manipulate the voltage (or current?). The computer is always limited to the interfaces or hardware it has. However you probably could simulated your idea, with the right programs.
Do you have a pic or avr programmer? I am pretty sure you can build a simple controller with some further parts, best is to ask a electrical engineer or mechatronics buddy. They could probably draw/design a suitable circuit for you, assembling should be easy and besides the fun part.
So is that controller directly capable of controlling the current/voltage the fan receives? And is that controller receiving an input from the machine itself that can be somehow accessed elsewhere?

In which case, can I attach the controller to any other electric motor?
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Old 2011-10-05, 12:54   Link #13
Jinto
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@Sides,

Those controlers inside those simple devices are often analog controllers... .e.g. temperature of sensor goes up... resistance of voltage divider goes down... voltage for fan goes up... speed of fan goes up.

As far as I understood DonQuigleone, he wants to be able to digitally influence the controller - i.e. use an algorithm on his PC to control the motor.

@DonQuigleone,

if you really want to control the motor in real time on your PC you will need some sort of analog input/output with moderate cycle times.

However, this approach will be quite expensive (at least to my knowledge). The Arduino board in combination with a highly responsive power amplifier e.g. op-amp (audio equipment output stage? - might need an additional resistor)... might be the next best solution. You cannot control the motor directly with your PC though but with the programmed controller board (I don't know if the program can be stripped down enough to fit on the controller though... or if the cycle times of the controller are sufficient).
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Old 2011-10-06, 03:02   Link #14
Sides
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Quote:
Originally Posted by Jinto View Post
@Sides,

Those controlers inside those simple devices are often analog controllers... .e.g. temperature of sensor goes up... resistance of voltage divider goes down... voltage for fan goes up... speed of fan goes up.

As far as I understood DonQuigleone, he wants to be able to digitally influence the controller - i.e. use an algorithm on his PC to control the motor.
I was just highlighting out that without extra components he will not be able to control the speed of a motor, aka you cannot alter the voltage if you hook up a dc motor to a computer directly.

Quote:
Originally Posted by DonQuigleone View Post
So is that controller directly capable of controlling the current/voltage the fan receives? And is that controller receiving an input from the machine itself that can be somehow accessed elsewhere?

In which case, can I attach the controller to any other electric motor?
Quick answer, no. Longer one, depends on the circuit and if the chip is rewriteable.
It is better to get a programmable kit, since it is more flexible, and you can reuse it for later projects. How much is the preassembled Arduino anyways?
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Old 2011-10-06, 06:11   Link #15
TheFluff
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Quote:
Originally Posted by Sides View Post
How much is the preassembled Arduino anyways?
Around 20 GBP/25 EUR for the Arduino Uno.
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