Encoder for DIY MPG Handwheel - How much PPR?

More
09 Mar 2023 09:46 #266187 by denhen89
Hello guys,
i am planning to build my own MPG Handwheel with some features to replace both MPG handwheels on my CNC Lathe.
The MPG Handwheels that i have currently installed on my Lathe are the standard 80mm chinese handwheels with 100 PPR.
They are working fine, but i would like to build my own, but i am a little bit confused to be honest.
100 PPR seems to make sense for a MPG Handwheel, because 100 pulses per round is easy to divide in the Metric system, but yesterday i saw a video where someone was turning that kind of MPG wheel fast and it was not couting every pulse.
My question now is, could i use higher PPR rotary encoders to have more precision or at least that no pulse will miss?
Another thing is, that the standard Handwheels are physically divided to have 100 fixed points - i believe inside there is a ball (bearing) on a spring that gets pushed into small holes (100 holes per round). What if i use a 1000 ppr encoder but i want a pulse everytime i move the handwheel to the next physical hole. Do i need to divide it in software? Does it then make sense to use higher resolution Encoder?

I would be interested to know what encoder is inside the standard chinese mpg handwheels.

I a hope you understand what i mean and be able to help me out with that. I believe i would just go for a 100ppr encoder if i could get one soon and not wait couple of weeks until it arrives from China.


Thanks in advance.

Please Log in or Create an account to join the conversation.

More
09 Mar 2023 14:44 #266212 by PCW
Losing counts depends on the counting hardware

On reason 100 PPR MPGs are used is that they typically have
detents so you can move a known distance by feel

Please Log in or Create an account to join the conversation.

More
09 Mar 2023 18:13 #266225 by denhen89
Thank you PCW.
I have ordered this kind of Arduino optical encoder ( global.microless.com/product/generic-mot...ition-control-lm393/ ) and will cut out a 100 cpr disc on my laser cuter. I am not sure if it will work as expected, but its the cheapest option.

Please Log in or Create an account to join the conversation.

More
09 Mar 2023 21:19 - 09 Mar 2023 21:20 #266236 by PCW
Note that you would need two of those for a MPG ( for A and B )
Last edit: 09 Mar 2023 21:20 by PCW.

Please Log in or Create an account to join the conversation.

More
09 Mar 2023 22:22 #266238 by denhen89
Thanks for that important information :D I have to order one more.

Please Log in or Create an account to join the conversation.

More
09 Mar 2023 23:35 #266243 by JPL
I'm not sure you understand how challenging it is going to be for you to come up with a working solution...

Consider the following:

- As PCW mentioned you will need 2 encoders like the one you chose (btw those are not really encoders but more like tachometers). One for phase 'A' the second one for phase 'B'. But consider that phase B also need to be 1/4 of a cycle behind (or ahead) of phase A. With  a 100ppr encoder this is 360 / 400 = 0.9 degree difference between A and B. Have a look here for more info about this: www.dynapar.com/technology/encoder_basics/quadrature_encoder/

- Also, another important feature feature of an MPG is indeed the tactile 'click'. But this is not only for tactile feedback. It is also to make sure there will not be unwanted change of position ( via extra pulses)... but again this need to happen at a precise position relative to phase A and B since if it is too near any of the 4 transition points there's a very high risk that the MPG will send an extra pulse if anything (vibration etc) change the position ever so slightly. Those 100 'clicking positions' must then ALL be perfectly aligned between the 1/4 cycles mentioned above...

- You will also need large 'knob' (ideally something like a thumb wheel) and of course a 'scale' around the knob with 100 divisions and marking for the 10th, 20th, 30th etc.

Well,I'm wondering why going thru all that since you can buy a fully working MPG like this for less than $20.00: www.amazon.com/Terminal-Aviation-Aluminu...tronic/dp/B07Q75KT49  .
 
The following user(s) said Thank You: denhen89

Please Log in or Create an account to join the conversation.

More
11 Mar 2023 10:05 #266390 by denhen89
I knew that it will not be a very easy task and i was aware that i needs to be pretty precize to work properly, but still its good that you mention it. That what i want to try out will be also possible with that kind of MPG Handwheel as you mentioned, but i want to learn a bit of Arduino and do some experiments.

You gave me some important information and it makes it more clear to not loose time on trying to build my own MPG, but i have no the parts so i think in free time i will play arround.

Please Log in or Create an account to join the conversation.

Moderators: cncbasher
Time to create page: 0.088 seconds
Powered by Kunena Forum