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Offline tipipliouTopic starter

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encoder
« on: September 13, 2010, 03:58:26 AM »
hi
i need an encoder and i found this one: http://www.lynxmotion.com/p-448-quadrature-motor-encoder-wcable.aspx
but i'm wondering if these encoders can be adapted to any kind of DC motors
and generally,can encoders be used with any kind of motors?
thanks

Offline waltr

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Re: encoder
« Reply #1 on: September 13, 2010, 07:13:32 AM »
Quote
can encoders be used with any kind of motors?
Yes. However, there needs to be a way to mount the encoder body and a way to attach the encoder 'wheel' to the motor shaft. Most motors have only one shaft extending out of the motor housing, The motors this encoder is designed for has a shaft out each end, one is to the gear box the other for the encoder.

What is your requirement for the encoder?

Offline Soeren

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Re: encoder
« Reply #2 on: September 13, 2010, 11:43:10 AM »
Hi,

It may be possible to mount it single sided, if the motor is just to drive a spur wheel, by using a coupler at the end to connect the axles.

Code: [Select]
-----+   __        +--------
      |__|_|__ ____|
 M    |______||____  E
      |  |_|       |
-----+   G         +--------

M = Motor
E = Encoder
G = Gear wheel
Just slip a coupler over the two (or perhaps just a piece of rubber tubing).
« Last Edit: September 13, 2010, 11:48:05 AM by Soeren »
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline tipipliouTopic starter

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Re: encoder
« Reply #3 on: September 14, 2010, 07:46:40 AM »
hi
Soeren : i'm not sure i understood you suggestion,what do you mean by a coupler?

Wltr :"What is your requirement for the encoder?"
a resolution of more or less 100 pulse/revolution


Offline Soeren

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Re: encoder
« Reply #4 on: September 14, 2010, 08:45:03 AM »
Hi,

Soeren : i'm not sure i understood you suggestion,what do you mean by a coupler?
A metal "tube" drilled from each side to fit the shafts and with a set screw each side.


Wltr :"What is your requirement for the encoder?"
a resolution of more or less 100 pulse/revolution
Are you sure that you NEED this high a resolution?
There's a wast difference between "want" and "need" and amateurs often go for the "the more the better" dogma, but there's nothing good in getting too much data, unless you dedicate a controller to handle this task and just report back when addressed.

With a gearing of say 30:1 between motor and wheels, you will have (more than) 3000 pulses for each revolution.
That means your controller need to spend more time capturing the pulses and that you will have superfluous data to consider if used for odometry, as driven wheels WILL slip every now and then.

One pulse each 5mm the 'bot moves is more than sufficient for most general apps (actually it's a bit of overkill, but within reason).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline tipipliouTopic starter

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Re: encoder
« Reply #5 on: September 14, 2010, 09:17:36 AM »
ok ,I see
I thought the encoder "turns" with the wheel,not the motor,so i'd have 100 pulse/revolution
is it possible to do it?  i'd have [motor+gears]-->[wheel]-->[encoder]
the encoder would be "outside"

Offline KurtEck

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Re: encoder
« Reply #6 on: September 14, 2010, 10:00:43 AM »
It could prove interesting to see how you mount these to other motors.  They currently are setup such that the wheel presses over the rear shaft, the electronics part is sized to fit on the back of the motors, and held in place with double face tape...  Yes if you could somehow attach the right size shaft to mount the encoder wheel on and somehow got something out there this is stationary (IE does not move with the wheel) you might be able to.  Probably easier inside the wheel....

As Soeren has mentioned, these encoders are typically attached to the other side of the motor, before it goes to the gear box.  I have a few of them connected to the Lynxmotion motors (12v 30 to 1 reduction, 200 RPM).  These encoders have 100 pulses per revolution (or 400 quadrature transitions per revolution).  So for each turn of the wheel you actually have: 400*30= 12000 quadrature transitions. 

If you were to run the motor at half speed, like 100RPM, you will have: 30*100/60*400=20,000 quadrature transitions per second. Needless to say that this can eat up a lot of processor power to count these...   On one robot I have, I have this handled by a Roboclaw motor controller by Basic Micro (http://www.basicmicro.com/Robo-Claw-2x10A_p_45.html)

Good Luck
Kurt

Offline waltr

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Re: encoder
« Reply #7 on: September 14, 2010, 10:10:33 AM »
Yep, putting the encoder on the output from the gearbox or on the wheel is the more common method for small Bots. The encode/motor you linked to has the encoder on the motor shaft.

There are a number of ways to do wheel encoders. Google will show a few that work well.
Here are some links:
http://www.acroname.com/robotics/parts/R332-WW-11.html
http://www.acroname.com/robotics/parts/R252-WW02-KIT.html
http://www.pololu.com/catalog/product/1218

These are just for ideas.  

 


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