1. Topics
  2. Renishaw Encoders

Renishaw Encoders

Bruce Howard
 

I currently have Renishaw encoders on both axis of my cassegrain. However they only have about 1 arc second resolution.
I want to upgrade the read head from .5 Micron to 40 nm resolution. This would give me about 16 million counts per rev and that would allow me to use the cascade option. The Renishaw literature offers clocking rates from 1 Mhz to 50 Mhz.. I would like to know what the appropriate rate would be for the Servo II controller.

Bruce Howard
Russell R
 

Hi Bruce,

I use Renishaw incremental encoders at 64.8M on the RA and 40M on the Dec. running a ServoII.  The Renishaw rep. set me up with 8Mhz and it works fine slewing at 3° per sec.  I don't remember the clock speed of ServoII.  It can handle 8m to 10M ticks per second.
One important thing is to keep your encoder wires short, less than 6 feet to controller.  Longer than that, you might need a RS422 to TTL converter and try not to run the wires next to the motor wires.

I hope this helps you,
Russell R.


 
Bruce Howard
 

 

Russell,

 

Which variety of encoder do you use? Tonic?

 

Bruce

 

 

Sent from Mail for Windows

 

From: Russell R via groups.io
Sent: Monday, October 3, 2022 7:01 PM
To: Sitechservo@groups.io
Subject: Re: [Sitechservo] Renishaw Encoders

 

Hi Bruce,

I use Renishaw incremental encoders at 64.8M on the RA and 40M on the Dec. running a ServoII.  The Renishaw rep. set me up with 8Mhz and it works fine slewing at 3° per sec.  I don't remember the clock speed of ServoII.  It can handle 8m to 10M ticks per second.
One important thing is to keep your encoder wires short, less than 6 feet to controller.  Longer than that, you might need a RS422 to TTL converter and try not to run the wires next to the motor wires.

I hope this helps you,
Russell R.


 

 
Russell R
 

Bruce,

Yes, Tonic, with dual readheads.

Russell
Bruce Howard
 

Thanks for the information.

How did you convert the RS422 differential signal to the single ended input on Servo II?

On my existing encoder setup I just used one of the two outputs. This works but I don’t think this is the correct way.

 

Bruce

 

Sent from Mail for Windows

 

From: Russell R via groups.io
Sent: Monday, October 3, 2022 7:53 PM
To: Sitechservo@groups.io
Subject: Re: [Sitechservo] Renishaw Encoders

 

Bruce,

Yes, Tonic, with dual readheads.

Russell

 
Russell R
 

Bruce,

You just use A+ and B+ of the interface, leaving A- and B- unconnected. 
This is why you keep the wires less than 6 feet and avoid the motor wires, it is more susceptible to electrical interference than the differential wiring method, but we work with what we got.

Russell R.
Dan Gray
 

You can alway put in an RS422 to TTL converter.  USDigital sells them.  THen you can have a long encoder wire.

On Tue, Oct 4, 2022 at 9:01 PM Russell R via groups.io <rem.64=yahoo.com@groups.io> wrote:
Bruce,

You just use A+ and B+ of the interface, leaving A- and B- unconnected. 
This is why you keep the wires less than 6 feet and avoid the motor wires, it is more susceptible to electrical interference than the differential wiring method, but we work with what we got.

Russell R.
Bruce Howard
 

Dan,

 

Yes. This sounds like exactly what I need as my cables have 14 feet of travel.

Russel uses the 8 Mhz clock rate. I am going to buy new read heads from Renishaw that will deliver

31,488,000 counts per rev using my existing 200 mm rings. My slew rate is only 1 degree/second. Is 8 Mhz a suitable clock rate for my application?

 

Bruce

 

Sent from Mail for Windows

 

From: Dan Gray
Sent: Wednesday, October 5, 2022 9:42 AM
To: Sitechservo@groups.io
Subject: Re: [Sitechservo] Renishaw Encoders

 

You can alway put in an RS422 to TTL converter.  USDigital sells them.  THen you can have a long encoder wire.

 

On Tue, Oct 4, 2022 at 9:01 PM Russell R via groups.io <rem.64=yahoo.com@groups.io> wrote:

Bruce,

You just use A+ and B+ of the interface, leaving A- and B- unconnected. 
This is why you keep the wires less than 6 feet and avoid the motor wires, it is more susceptible to electrical interference than the differential wiring method, but we work with what we got.

Russell R.

 
Russell R
 

Hi Bruce,

I enjoyed the article in AA magazine on your mount and telescope using the SiTech controller.   The craftsmanship is outstanding.  I also like the fact you use tapered roller bearings.  Although they are easy to incorporate into a build, most folks don't realize how much "slack" is in a new ball bearing hidden by the seals and grease.  When I use tapered bearings, I buy one cup and two cones, taking one cone and honing out the ID a couple thousands. This makes assemble and disassembly easy until the final assembly using the original size cone.  Did you make the worm and gears yourself? 

Well done!

Russell R. 
Bruce Howard
 

Russel, 

I use a slight press fit on the cup in the housing and also on the shaft to the front cone. Usually when I am using them back to back I use a slightly smaller bearing on the side away from the load. For this cone I use a transition fit and a little heat from a hair dryer.  All the assemblies on the telescope are done this way. I bought the gear sets from Byers as he was closing his business under doctor’s orders. 

Bruce


On Oct 30, 2022, at 12:13 PM, Russell R via groups.io <rem.64@...> wrote:

Hi Bruce,

I enjoyed the article in AA magazine on your mount and telescope using the SiTech controller.   The craftsmanship is outstanding.  I also like the fact you use tapered roller bearings.  Although they are easy to incorporate into a build, most folks don't realize how much "slack" is in a new ball bearing hidden by the seals and grease.  When I use tapered bearings, I buy one cup and two cones, taking one cone and honing out the ID a couple thousands. This makes assemble and disassembly easy until the final assembly using the original size cone.  Did you make the worm and gears yourself? 

Well done!

Russell R. 

Dan Gray
 

Russel, could you point me to that article?
Thanks,
Dan


On Sun, Oct 30, 2022 at 11:13 AM Russell R via groups.io <rem.64=yahoo.com@groups.io> wrote:
Hi Bruce,

I enjoyed the article in AA magazine on your mount and telescope using the SiTech controller.   The craftsmanship is outstanding.  I also like the fact you use tapered roller bearings.  Although they are easy to incorporate into a build, most folks don't realize how much "slack" is in a new ball bearing hidden by the seals and grease.  When I use tapered bearings, I buy one cup and two cones, taking one cone and honing out the ID a couple thousands. This makes assemble and disassembly easy until the final assembly using the original size cone.  Did you make the worm and gears yourself? 

Well done!

Russell R. 

Russell R
 


Sure can, Amateur Astronomy Magazine. It comes in print or electronic PDF, four times a year, issue# 116 (the latest), page 14.  This is my favorite astronomy periodical.
https://amateurastronomy.com/

Bruce done a fine job on this project.

Best,
Russell R.
Dan Gray
 

yes he has.  His mount model he recently made is 2.4 arc seconds RMS!
Dan


On Wed, Nov 2, 2022 at 11:46 AM Russell R via groups.io <rem.64=yahoo.com@groups.io> wrote:

Sure can, Amateur Astronomy Magazine. It comes in print or electronic PDF, four times a year, issue# 116 (the latest), page 14.  This is my favorite astronomy periodical.
https://amateurastronomy.com/

Bruce done a fine job on this project.

Best,
Russell R.

1 - 13 of 13