Hi, Ralph,
The existing RELS Arduino sketch is set up for 1800 pulses per spindle rotation, though that can be changed.? Have you thought about how you will affix the encoder to the spindle?? It might be more convenient, and easier to find a low-cost encoder, if you can increase the encoder speed and use a lower pulse per rev encoder.? John and I both (because I basically duplicated his implementation) used 600 PPR, belt driven with a timing belt at a 3:1 ratio, resulting in 3 encoder revolutions per spindle rev and 1800 pulses per spindle rev.
There are several factors you have to consider.? (BTW, I spent 33 years working for a company that manufactures encoders. Besides working on applications, I also sometimes wrote specs for how they were supposed to perform.)? The most critical ones here are:
RPM - All encoders have a maximum mechanical rotation rate. If the maximum spindle speed is 2500 RPM, and you are driving 1:1, then your encoder must have an RPM rating higher than that.? If driving 2:1 in the same example, the encoder will be running 5000 RPM at a 2500 RPM spindle speed.
Output Frequency - The pulses are sent out of the encoder via a digital system, and this system has a maximum frequency.? Say that your encoder is 600 PPR and is turning at 2500 RPM.
600 P/R X 2500 R/M X 1/60 M/sec = 25,000 pulses/sec
Or, 25 kHz.? So you need to decide on PPR, and gear or belt ratio between spindle and encoder, before you can calculate the maximum frequency rating you need.
Radial Bearing Load - The bearings in an encoder are only rated for a certain number of rotations.? This number decreases rapidly with radial bearing load. There is also a maximum radial load the bearing can take at all. In large, industrial systems, this is carefully calculated, but in our application, just use the lowest load you can. In my photos below, I used the weakest springs that I could while still keeping the belt fully engaged.? BTW, don't be fooled into thinking that a flexible coupling eliminates this problem.? They only work correctly within a very small specified range.? Outside that range, they apply substantial loads to the encoder shaft.
Below is a photo of my encoder installation, "borrowed", as I have said, from John Lindo's design.? I hope this helps...
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Regards,
Charlie
New Jersey, USA
MURPHY'S CONSTANT:?Matter will be damaged in direct proportion to its value.
