Author Topic: Friction drives. Potential problems?  (Read 1484 times)

unoritvie

  • Active Astronomer
  • ***
  • Posts: 120
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Friction drives. Potential problems?
« on: December 24, 2017, 03:21:56 PM »
Hi,

I am putting serious thought into purchasing a Mesu Mount 200.  It utilizes friction disk technologies, which I guess from the amount of users that have Mesu's, Fornax's and Gemini's G53F is still not fully understood concerning performance and behaviors with differing geographical locations (climate).

I work remotely (5hrs away) and while Friction Drives seem great on paper, the 1 thing that's preventing me from pulling the trigger is how the mount slides when off balance.  Not so much that I've troubles balancing, however, the idea of slipping.

My observatory is located in a cold, dry and windy climate.  Very cold in the winter (as I write this, it is currently -27*c and also feels just like -36*c down there).  I currently use my CGEM remotely there.  It and all of my other equipment have handled the cold quite well.  On these sharp ultra chilly nights, when seeing is spectacular, the mount has yet to let me down (brief of slewing electricity issues from a 120 cca Deep Cycle Marine battery that's hooked up to a trickle charger).

What happens when it is -30*c and the metal interior contracts?  Is it possible that the coldness can cause a slip and all of my gear smash into my dock, even when the telescope isn't in use?  Or I suppose that could require it to be away balanced?



obenanus

  • Active Astronomer
  • ***
  • Posts: 119
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #1 on: December 24, 2017, 05:10:22 PM »
<p>
Quote
Hi,
</p>
I'm putting serious thought into purchasing a Mesu Mount 200.  It utilizes friction drive technology, which I guess by the number of users who have Mesu's, Fornax's and Gemini's G53F remains not fully understood in terms of functionality and behaviours with differing geographical locations (climate).

I operate remotely (5hrs off) and while Friction Drives appear great on paper, the one thing that's keeping me from pulling the trigger is the way the bracket slides when off balance.  Not too much that I've troubles balancing, however, the idea of slipping.

My observatory is located at a cold, dry and windy climate.  Very cold in the winter (as I write this, it's now -27*c and also feels just like -36*c down).  I currently use my CGEM remotely there.  It and all my other equipment have managed the cold quite well.  On these sharp ultra cold nights, when viewing is magnificent, the bracket has yet to let me down (short of slewing power issues from a 120 cca Deep Cycle Marine battery that's hooked up to a trickle charger).

What happens when it's -30*c and the alloy interior contracts?  Is it feasible that the coldness could make a slip and all my gear smash in my pier, even when the telescope is not in use?  Or I suppose that could need it to be off balanced?

The friction required to turn a balanced head should in theory, be quite low.  Thus even contraction shouldn't necessarily affect its functionality.

That said, the bearing substance is likely to really make a difference.  Over time, there'll be wear resulting from the compression.  I suspect that certain sorts of aluminum could work out prematurely, whereas distinct sorts of steel would not.

Thus I would say a significant feature of any friction drive would be the capability to re-tension the joint as required (which ought to be quite in-frequent).  If the mount does not let you adjust this strain, or utilizes soft bearings, then the bracket will have a shelf life to it.

Kyle Styles

  • Active Astronomer
  • ***
  • Posts: 119
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #2 on: December 27, 2017, 02:15:26 PM »
I've had the same musings -- anyone remember the days of cassette tapes and the dreaded flat spot on the capstan roller? The folks who sell these mounts claim there are no issues with slippage or wear.

unexaric

  • Active Astronomer
  • ***
  • Posts: 102
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #3 on: December 28, 2017, 09:36:39 AM »
Quote
I've had the same musings -- anyone remember the days of cassette tapes and the dreaded flat spot on the capstan roller? The folks who sell these mounts claim there are no issues with slippage or wear.


Yea, and Celestron claims their mounts go thru QC 3 times.

Mark Patterson

  • Active Astronomer
  • ***
  • Posts: 117
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #4 on: December 31, 2017, 08:03:56 AM »
I'm pretty certain Lucas has carefully considered operating environment. One of the benefits of a friction roller drive is that lubrication isn't used (well, at the drive interface) and it will be "stiff" over a greater range of temperatures than a lubricated worm drive. Position and tracking accuracy should be more consistent. Perhaps it would be wise to ask about bearing lubrication and for a customer referral in a similar climate.

How about using a pair of solenoids to stop the axes in the event of loss of power to the motors? It would be easy enough to integrate a separate current-monitoring watchdog system if that worry keeps you up at night.

I wouldn't be too concerned with wear or at least any more than I would with a belt or gear driven transmission system. Mechanical items wear. That and manufacturing tolerances are why adjustments are provided.

Clear skies,
Bill

galpaydabta

  • Active Astronomer
  • ***
  • Posts: 118
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #5 on: December 31, 2017, 05:55:36 PM »
I have just received a MESU 200. I can tell you that with power supplied and the system balanced it takes a decent amount of pressure to move (slip) the scope. With power off the setup still has some stiffness. Not as much stiffness as an AP Mach 1 with the clutches disengaged but enough to slow/stop momentum if a balanced system is in the middle of slewing when power is lost.

teoknoxparli

  • Active Astronomer
  • ***
  • Posts: 122
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #6 on: January 03, 2018, 10:18:17 AM »
Yes Lucas is very helpful and quick in answering questions! Honestly, I'm pretty much sold on this mount now. Even the SiTech at first seemed a little daunting, but the more I'm exploring it's features and capabilities the more I am liking. I like how its already wired for limit and home switches. It wouldn't be hard to rig up either as sitech has good information on their site with the parts necessary and everything.

Ryan Wilton

  • Active Astronomer
  • ***
  • Posts: 134
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #7 on: January 04, 2018, 01:37:45 PM »
I had/have 2 I had one of the first prototypes ... sold it to Olly who runs an astro B&amp;B ... not a single issue in I can't remember but about 4 years off heavy operation carrying an ODK 14 inch in the past and now dual tak 106 ...
The one we currently run remote has the sitech, not a single problem in years ...

/Yves

fucheatisu

  • Active Astronomer
  • ***
  • Posts: 105
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #8 on: January 09, 2018, 07:54:21 PM »
How does the drive deal with the cold, when the compressed friction drive sets, doesn't it leave a dent in the material?
Blueman

grumepinod

  • Active Astronomer
  • ***
  • Posts: 119
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #9 on: January 11, 2018, 03:37:02 AM »
I used my Mesu 200 at around -5C withouth any problem.

In the yahoo group, there is a user report using the mount at -36C without an issue.
https://groups.yahoo...ions/topics/161

Here is another user using the mount at very low temperature
https://groups.yahoo...ons/messages/13

If you send an email to Lucas, I think he will explain how he deals with the temperature.

Shawn Bush

  • Active Astronomer
  • ***
  • Posts: 112
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #10 on: January 11, 2018, 12:27:25 PM »
Quote
I used my Mesu 200 at around -5C withouth any problem.

In the yahoo group, there is a user report using the mount at -36C without an issue.
https://groups.yahoo...ions/topics/161

Here is another user using the mount at very low temperature
https://groups.yahoo...ons/messages/13

If you send an email to Lucas, I think he will explain how he deals with the temperature.

Wow! I would be surprised if lubricated mounts can handle -36C well.

Keith Dixon

  • Active Astronomer
  • ***
  • Posts: 128
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #11 on: January 12, 2018, 07:37:04 AM »
Quote
I have just received a MESU 200. I can tell you that with power supplied and the system balanced it takes a decent amount of pressure to move (slip) the scope. With power off the setup still has some stiffness. Not as much stiffness as an AP Mach 1 with the clutches disengaged but enough to slow/stop momentum if a balanced system is in the middle of slewing when power is lost.

I seem to remember reading that the Mesu has medium-resolution encoders, and they should negate any problems with slippage. Are the encoders standard, or is that an optional add-on?

brunenrizap

  • Active Astronomer
  • ***
  • Posts: 100
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #12 on: January 12, 2018, 09:51:45 AM »
I don't have the Mesu mount but I've looked at friction drive designs in detail. Most designs I have read about are steel on steel. Dry steel has a surprisingly high friction coefficient, something like 0.4 if I recall correctly. The key is that the drive roller is pre-loaded against the large driven wheel on the mount, and steel, being both stiff and elastic (in the sense of returning to its initial shape), will deform very slightly under the pressure contact. If you have 100 lbs of preload, then you'll thus have 40 lbs of frictional contact force at 0.4 friction coefficient. This is how a locomotive gets traction; you have steel on steel but there is just a huge preload of the wheel onto the track.The design needs to create and maintain the preload condition as temperatures change but that shouldn't be very difficult. They probably don't use a soft roller, because the problem you have there is that the effective contact radius will change as the soft material deforms.

Robert Farley

  • Active Astronomer
  • ***
  • Posts: 126
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #13 on: January 13, 2018, 05:29:47 AM »
@Homer - I have a Mesu 200 and I'm remotely operating it all the time. Never experienced slippage whatsoever due to temperature change.. but the lowest we get is 0*C in my place.

acoplochop

  • Active Astronomer
  • ***
  • Posts: 119
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Friction drives. Potential problems?
« Reply #14 on: January 21, 2018, 10:41:50 AM »
I am currently considering buying the G53f. I love that mount. Still wondering that there is hardly any mention of this mount here, and it seems as though no one has one.