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Topic: How fast can stepper motor turn? (Read 5728 times) previous topic - next topic

mellink

Hi all,
I'm looking to update a system that used turns of a cable and converts it into a speed. I wasn tto replace the cable with a stepper motor and drive the stepper motor.

My question is how fast ast the stepper motors? I never see the quoted rpms. I dont need that high rpm, but just wanted to check before buying one..

Where can i get one? I've seen many on ebay, but don't know which ones are compatible wiht http://arduino.cc/en/Tutorial/MotorKnob

Thanks for any advice.

Rob

PaulS

There are links on that page to places to buy the two kinds of chips needed to drive stepper motors. Follow the links and read the data sheets for the two kinds of chips. Figure out how much current each chip can supply, at what voltage. Then, choose a motor that needs less than that current at that voltage.

Or, save yourself a lot of grief, and buy a pre-designed motor driver shield/board, and get a motor that fits within that board's specs.

Once you have selected a motor, read it's data sheet to figure out how many steps per revolution. The driver data sheet will tell you how many steps/half steps/quarter steps per second the driver can manage. You use that and the steps per revolution to determine the maximum speed.

Of course, you can work backwards if you know what RPM you need.

Quote
I'm looking to update a system that used turns of a cable and converts it into a speed.

Sounds like a Harley speedometer used up to the late 80s.
The art of getting good answers lies in asking good questions.

mellink

#2
Jun 24, 2011, 05:58 pm Last Edit: Jun 24, 2011, 06:01 pm by mellink Reason: 1
Hi sorry,
yeah i could have explained the concept better.

I'm replacing a old speedo cable with a hall senor on the wheel.
and a stepper motor on the input to the speedo.

MAX rpm would be 50 revs i would say.

So the driving chip is the main gouverning factor? I'm wondering which is the decent keep option for the motor/driver.

(ok someone removed their post)

mellink

for example this motor...

http://www.hobbytronics.co.uk/motor-control/stepper-motor-200-rev

with this driver

http://www.hobbytronics.co.uk/easydriver-stepper-motor

I can see how many steps per rev...

I cant see anything about the top rpm, but will it be above 50rpm?

wildbill

What is the speedo on? 50 rpm sounds an order of magnitude too low for any motor vehicle

mellink

sorry rps.
rev per second. MAssive mistake again there.


PaulS

Top RPM is generally not a factor with a stepper motor. Stepper motors are use for precise positioning, not speed. However, 200 steps per revolution times 50 revolutions is only 10000 steps per minute, in single step mode, or 166 steps per second, which is very slow.

So, yes, 50 rpm is quite easy to achieve. Much higher speeds are possible, in single step mode, if 1.8 degree steps are satisfactory. If finer resolution is required, half, quarter, and eighth stepping is possible (0.9, 0.45, and 0.225 degrees per step). The tradeoff is that you won't be able to step as fast, since each step takes time.

Even at 1/8th stepping, 500 RPM should be possible - depending on voltage, current, and load, of course.
The art of getting good answers lies in asking good questions.

mellink

#7
Jun 24, 2011, 07:04 pm Last Edit: Jun 24, 2011, 07:09 pm by mellink Reason: 1
Hi when i put 50rpm i menat 50rps

so 3000rpm.

which is too high then. So how would i do this then? At low rpm it needs to be quite acruate to stop needle jumping ont eh speedo.

Senso

No, what you need is stable rpm values, not accuracy, it doesnt matter if you use a stepper or a dc motor, all you need is stable rpm values.

PaulS

Quote
At low rpm it needs to be quite acruate to stop needle jumping ont eh speedo.

You should be able to find a setting (half, quarter, etc.) that balances the need for speed with the need for accuracy. The speedometer itself should have some mechanism for preventing needle flicker. If not, the key is to smoothly step the motor - constant interval between steps. The stepper library manages this for you.

I'm not yet convinced that the positional accuracy of a stepper motor is what you need. Perhaps just a regular electric motor that you can control the speed of is what you need.
The art of getting good answers lies in asking good questions.

mellink

Hi,
all the DC motors ive ever used havnt been use to know what rpm they are turning at.
I dont want to have a 2 curcit like signal conditioning. Wher ei use another hall effect sensor to check what speed the motor is doing. I thought that using  a stepping motor was a easy way of being able to set a rpm.

Can i do this with a DC motor easily?

PaulS

Quote
I thought that using  a stepping motor was a easy way of being able to set a rpm.

It would be. What, exactly, are you trying to do? Use a motor to make a speedometer move, yes. But, for what purpose? Calibration? Just to run up mileage? Visual effects?
The art of getting good answers lies in asking good questions.

mellink

Im replacing the cable that usally drives the speedo.

Doing this for several reasons. At the moment I do data logging on the car using the arduino, but the speedo has always been slightly incorrect and i've had enough of it. its about 10% too optimistic because tyre size has changed so hoping to correct that with a small bit of code and a motor

Ie the motor will be connected to the speedo to drive it from data im collecting from the car.

PaulS

If you know that the speedometer is incorrect, and are already collecting information to know how fast the car is going, an LCD screen to show what you think the car's speed is would seem simpler to implement, to me.

Physically connecting the stepper to the speedo could be an issue. But, the stepper motor you referenced will step smoother, in single step mode, than a physically twisted cable will, and will be plenty fast enough.
The art of getting good answers lies in asking good questions.

mellink

It has to be the speedo. Its just easy to read.

So a stepper motor isnt going to work and a normal normal motor isnt going to be controll able?

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