Is there a way to attach a speed sensor, slotted or reflective, to this motor?

Thread Starter

Xavier Pacheco Paulino

Joined Oct 21, 2015
728
Many motors brings a physical spot for a speed sensor, either a slotted disc or reflective IR. I have this old motor which doesn't have that spot, but I would like to measure the speed with a little of precision. Are there on the market any physical structure that I could attach to this motor? Any trick or idea for this?
@MaxHeadRoom , you once told me something similar, but I don't remember.



 
Last edited:

jpanhalt

Joined Jan 18, 2008
11,087
Something like a white stripe or dot on the flywheel will give you a reflective signal. In fact, the cast "ribs" in the end of the flywheel may offer enough reflective difference to work without any modification.
 

dendad

Joined Feb 20, 2016
4,503
A Hall sensor and magnet placed to trigger fron the ribs on the flywheel is another way to sense it. If you place a couple just right, you could get quadrature output too and add direction info as well if you need that.
 

shortbus

Joined Sep 30, 2009
10,049
If you're going to keep working with motors, you might want to get something like this - https://www.amazon.com/Digital-Photo-Laser-Tachometer-Contact/dp/B001N4QY66 I got one from Ebay for less. They even included a couple of strips of reflective tape that you can cut and place on the shaft or flywheel.

If you do something measuring off of the 'ribs' on that flywheel, don't forget to divide the resulting RPM by the number of ribs on the wheel.
 

Reloadron

Joined Jan 15, 2015
7,580
What kind of speeds do you anticipate? I would clean up the flywheel and go with reflective tape and depending on the anticipated speed I might use more than a single strip for example two strips 180 degree spaced or even 4 strips 90 degree spaced. Then do the math in however you read the sensor. Also if this has a high RPM which it does not look to have keep the dynamic balance of the flywheel in mind.

Ron
 

shortbus

Joined Sep 30, 2009
10,049
What kind of speeds do you anticipate? I would clean up the flywheel and go with reflective tape and depending on the anticipated speed I might use more than a single strip for example two strips 180 degree spaced or even 4 strips 90 degree spaced. Then do the math in however you read the sensor. Also if this has a high RPM which it does not look to have keep the dynamic balance of the flywheel in mind.

Ron
That's the nice thing about the optical tach I referenced, it only needs one piece of tape. Before buying one I used to use an analog mechanical tach.



 

DickCappels

Joined Aug 21, 2008
10,246
Just get a stroboscope and adjust the frequency until the the spinning motor appears to be standing still. Painting a single white dot or stripe would make the measurement less ambiguous on a symmetric surface.

upload_2018-10-20_21-33-59.png
 

MaxHeadRoom

Joined Jul 18, 2013
28,830
Many motors brings a physical spot for a speed sensor, either a slotted disc or reflective IR. I have this old motor which doesn't have that spot, but I would like to measure the speed with a little of precision. Are there on the market any physical structure that I could attach to this motor? Any trick or idea for this?
@MaxHeadRoom , you once told me something similar, but I don't remember.
I have used the slot opto and also the QRE1113 retro-reflective sensor, the latter is OK if you require coarse count and it is in a contamination free area.
What resolution are you after? There are slot optos and slotted disc on ebay from 10p/rev to 100p/rev.
Is that a fan on the rear or a flywheel?
For many applications using a ex T.M. motor, it is often advantageous to remove the flywheel. This also would give a rotation area for a detector.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
28,830

Thread Starter

Xavier Pacheco Paulino

Joined Oct 21, 2015
728
The motor is actually in a treadmill. It has a single magnet and a reed switch in the tread pulley, but the signal I get is really awful. No worth dealing with debounce. Maybe a hall effect works much better. I actually like the idea of putting reflective strip in the flywheel ribs. They are 6 ribs, so 6 pulses/rev. A microcontroller will process this speed signal. The ratio of the gears is 3.

 

MaxHeadRoom

Joined Jul 18, 2013
28,830
If it has magnet you could use a Honeywell ss400 series of min. hall effect proximity switches.
The QRE1113 is a miniature retro-reflector that can be picked up on ebay etc, the SparkFun version is already board mounted.
Max.
 

MisterBill2

Joined Jan 23, 2018
19,466
Ading a magnet to that flywheel will upset the balance and lead to excessive vibration. So an optical pickup is the best choice. You can paint half the distance around the outside of the flywheel flat black and the other half white and then use a reflective type pickup to get one pulse per revolution, which ought to be good enough. But if you are intending to use it for a speed control circuit then an inductive pickup sensing the ribs on the flywheel would be a better choice.
I see that it is a brush type DC motor and so it probably has a wide range of speeds.
 

MaxHeadRoom

Joined Jul 18, 2013
28,830
One other consideration on the resolution is if it is just for RPM monitoring/indication or RPM control is considered, if the latter, then closer control is achieved using a multi count/rev method.
If using a one/turn retro-reflector, use a single small white paint stripe or tape, not half the wheel.
Also I have tested the QRE1113 I used for any effect of incidental light that might be present, but I did not detect any detrimental effect from the sources I used.
Max.
 

Thread Starter

Xavier Pacheco Paulino

Joined Oct 21, 2015
728
One other consideration on the resolution is if it is just for RPM monitoring/indication or RPM control is considered, if the latter, then closer control is achieved using a multi count/rev method.
If using a one/turn retro-reflector, use a single small white paint stripe or tape, not half the wheel.
Also I have tested the QRE1113 I used for any effect of incidental light that might be present, but I did not detect any detrimental effect from the sources I used.
Max.
I want to do RPM control. I will make use of the six ribs in the flywheel.
 

MaxHeadRoom

Joined Jul 18, 2013
28,830
I have used the retro reflector similar to that, I going this route, I would paint the recesses black before making the ribs white, high gloss paint etc.
I have not tried glitter paint which could be an alternative also.
Max.
 
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