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Topic: Encoder question (Read 189 times) previous topic - next topic

jucasan

I need to attach an encoder to the shaft of a motor and was wondering about what kind to use.

I have this one but I'm wondering if this can take 4-5000 RPM.

https://www.addicore.com/rotary-encoder-knob-p/ad267.htm

Any sugestion?
Thanks

jremington

#1
Nov 20, 2017, 03:29 am Last Edit: Nov 20, 2017, 03:35 am by jremington
Quote
I'm wondering if this can take 4-5000 RPM.
Of course not. It is intended for a hand-twisted knob.

You will need a ball bearing, industrial quality shaft encoder, intended for operation at high RPMs. Here is one selection guide. eBay sometimes has good deals on used ones.

You will need to decide the angular resolution of the encoder (how many counts per shaft revolution), keeping in mind that the Arduino is not very fast.

jucasan

They are probably too expensive and big for what I need. What would be the best option if I want to make my own. Infrarred, reflective, photoresistor?? I don't need anything super precise. Probably can laser cut a wheel and even use a reduction. If I can get a pulse every 4-5 turns of the DC motor is more than I need.

Thanks

krupski

They are probably too expensive and big for what I need. What would be the best option if I want to make my own. Infrarred, reflective, photoresistor?? I don't need anything super precise. Probably can laser cut a wheel and even use a reduction. If I can get a pulse every 4-5 turns of the DC motor is more than I need.

Thanks
Are you looking to read RPM or control RPM via a servo loop?

If so, why not just color 1/2 of the shaft black (like with a paint pen) then just use an IR led and IR photo detector to pick up one pulse pre rev?

If you build an encoder wheel then use a reduction, you end up cutting your resolution by the reduction factor!

Say you make an 8 segment wheel and gear it down by a factor of 8. That turns it into a one pulse per rev encoder!


Gentlemen may prefer Blondes, but Real Men prefer Redheads!

jremington

If you can attach a slotted wheel on the shaft, it is easy to use an optointerrupter to count pulses. These have an LED and photodiode or phototransistor to detect the slot.

example

jucasan

#5
Nov 22, 2017, 09:34 pm Last Edit: Nov 22, 2017, 09:47 pm by jucasan
I'm thinking about drilling a small hole in the motor shaft and make an infra red encoder.

Found this
infrared LED

The question is. Can I connect the emiter straigh with a resistor to the 5v and the receiver straigh to the arduino input pin just like a photoresistor, or need some sort of circuit to make it work.
Thanks

MarkT

Drilling a hole in a hardened steel shaft isn't doable with normal tools - but you may be lucky and
your motor's shaft isn't hardened.  Surely a non-destructive method is easier - paint the shaft white one
side and black the other?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

jucasan

I have access to heavy duty equipment so drilling the shaft is not a big deal. My concern is the electronic part that I'm not really good at. You mentioned paint the shaft, and probably is an option, but how can I pick the signal.

Do you think if I paint the shaft and put the emiter and receiver next to each other is going to work? But like a said. I'm more concern about how to connect the LED's to the arduino than the mechanical part.

jremington

#8
Nov 22, 2017, 11:58 pm Last Edit: Nov 23, 2017, 12:01 am by jremington
Use a reflectance sensor to easily discriminate between the black and white portion of the shaft.

There are various other types that work over a range of distances, but they are much slower to respond than the one linked above.

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