Page 3 of 5 FirstFirst 12345 LastLast
Results 21 to 30 of 43
Like Tree13Likes

Thread: Drive system help

  1. #21
    AustinPSD's Avatar
    AustinPSD is offline Super Moderator
    Points: 56,828, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 2.0%
    Achievements:
    200+ Posts Achievement!First 1000 Experience PointsGot three Friends20+ Friends Achievement!5+ Referrals Achievement!
    Join Date
    Sep 2009
    Location
    McDonald Observatory, Mt. Locke
    Posts
    6,921
    Points
    56,828
    Level
    100
    Thanks
    743
    Thanked 5,863x 3,113 Posts
    Blog Entries
    1

    Default



    Rather than defer any longer awaiting the resolution of some annoying infrastructure problems, I'm going to post the remainder of this mount/drive material incrementally, in sections. As Gus (the admin) will be enabling a new article section in the mid-term, I'll consolidate, edit and refine this material into a single coherent article at some later date.

    With that being said, my intent is as follows:

    - discuss the real-world design of a German Equatorial Mount, complete with a mechanical prototype, including the necessary engineering drawings, solid model, bill-of-material, and finite-element model (FEM)
    - the mount design parameters are such that the finished mount is capable of a working, or live load of 80Kg (176 lbs.), and a total load of 160Kg (353 lbs.). The working load includes the counterweight, or "dead" load
    - discuss the motor drives, gearing/reduction system for the mount
    - discuss a complete control system, including schematics, bill-of-material, and control system interfaces
    - the end result should be a working, high-precision, high-capacity mount that a sufficiently skilled individual could fabricate using minimum machining, and where necessary low-cost machining services
    - the end result should "scale" up, or down in terms of total working load by a factor of at least two

    Those are the high points of the design center and goals.

    With that, the basic mechanical design of this mount uses several principles:

    - short mechanical coupling; that is to say shaft lengths are kept to a minimum, so as to reduce mechanical moment, leverage, and torsion loads at all points, particularly bearing surfaces and rotating joints
    - this also reduces mechanical resonance in the mount, damping wind or drive induced vibration as completely and rapidly as possible
    - maximizes use of standard size, off the shelf components, including pillow-block bearing housings, taper, roller, and ball bearing assemblies, shafts, fasteners, and flat plate materials
    - the above reduce the amount of welding, machining and custom fabrication, keeping cost lower and making fabrication simpler
    - machining operations are largely constrained to what can be done using a metal cutting bandsaw, a drill press, and simple mechanics hand tools
    - the mount is intended to be installed on a pier, although it would be straightforward to adapt to a tripod and wedge (if a sufficiently heavy-duty tripod/wedge are obtained)

    Most amateur class instruments are well within the live load design target for this mount, and no de-rating of the mount's specified capacity is necessary.

    Key Design Element: Plate & Pillow-Block Construction

    The use of pillow-block bearings is an cost-effective approach for constructing equatorial mounts.

    Advantages are as follows:

    • Ease of assembly
    • Self-aligning pillow blocks seek their own center-line. This insures smooth operation, reduces binding and torsional loads, which in turn reduces required drive motor torque
    • Once the center-line is achieved parallelism of both axes is maintained by the flatness tolerance of the sub-plate to which the pillow-blocks are mounted
    • The pillow-block/sub-plate construction insures that the RA axis is perpendicular to the DEC axis within a few seconds or arc
    • Concentricity of the bearing to shaft and pillow-block bearing to its housing insure a combined concentricity of plus/minus .0015".
    • The pillow-block bearings use roller-tapered rod bearings for thrust, and roller ball bearings for radial loads, resulting in equal load handling for both radial and thrust loading.

    The use of pillow-block bearings also reduces costs, as the sub-plate/pillow-block assembly does not require a cast/machined or machined housing. A simple sheet enclosure can provide protection for the shaft/bearing mechanism, as no load carrying or stressed member construction is used in this design.

    The plate and sub-plate technique is mechanically simple. It has a number of advantages for use in constructing an equatorial mount:

    - Because the basic design avoids the use of welded joints, the use of aluminum plate material is possible, as no expensive or skilled TIG-welding is necesary
    - Aluminum plate is easier to work and fabricate than steel, even with thicker plate dimensions. This allows more readily available, and less expensive tools to be used in fabrication
    - The use of aluminum plate reduces the overall cost, as well as dead-load of the mount itself
    - The plate shapes require no complex machining, and provided cuts are dimensionally accurate and square, precise, stiff, and strong joints at facing plate surfaces are automatic and inherent in the design
    - It is easy and inexpensive to fabricate replacement parts, make changes in the basic design, or upgrade the mount because plates reduce the design complexity dramatically

    In summary, for this section:

    - Working, or "live load" = weight of the telescope OTA assembly, focuser, guide-scope, finder scope, imager, eyepiece, adapters, cable drag load, dew shield/dew heater
    - Dead load = weight of counterweights used to offset/balance "live load"
    - Total load = combined "live" and "dead" load

    The reference mount will be referred to as "Scale 1", abbreviated in the remainder of the document as S1. Its rated live load capacity is 80Kg, with a total load rating of 160Kg. From time to time, the half-capacity mount, "Scale 0" will be referenced, and abbreviated as "S0". This mount has a working load of 40Kg, and a total rated load of 80Kg. Similarly, the double capacity version will be referenced as "Scale 2", and abbreviated as "S2". This mount has a rated live load capacity of 160Kg, and a total load rating of 320Kg. The range of live load capacity in the Scale 0 - Scale 2 series of mounts is adequate to cover at least 99% of the amateur class, consumer telescope OTA's from 150mm up to approximately 1000mm aperture.

    More to come this afternoon....
    dynamo likes this.
    CGEM 800 HD, NexGuide, Orion XT8 Limited Edition, Oberwerk BT-100, Canon 20D/20Da/T3i/60D/5D Mk III, various eyepieces, adapters, geegaws, widgets, and tiddlybits

  2. The Following 6 Users Say Thank You to AustinPSD For This Useful Post:

    admin (01-14-2010),dynamo (09-28-2012),jonesy311 (03-11-2012),mikec (01-14-2010),saturn1970 (01-14-2010),tinkerer (01-02-2011)

  3. #22
    admin's Avatar
    admin is offline Administrator
    Points: 6,989,798, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 5.0%
    Achievements:
    First 1000 Experience PointsGot three Friends20+ Friends Achievement!5+ Referrals Achievement!100+ Threads Achievement!
    Join Date
    Mar 2007
    Location
    Sydney, Australia
    Posts
    13,481
    Points
    6,989,798
    Level
    100
    Thanks
    18,563
    Thanked 7,916x 3,807 Posts
    Blog Entries
    2

    Default

    Man Coyne, I actually got motivated due to your and many others amazing information and knowledge.

    I will post soon a link with login to the new area.
    Name: Gus OTAs: ED 100 PRO refractor, Orion ST80 (not the CF), 8" Dob stuck in Canada Mounts:HEQ5PRO Synscan mount, Manfrotto Tripod CAMS: Guidecam Philips SPC900 webcams (4), Canon unmodded-450D DSLR

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.


    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    |
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    | My Astronomy Blog

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.


  4. #23
    saturn1970's Avatar
    saturn1970 is offline Main Sequence
    Points: 9,379, Level: 67
    Level completed: 10%, Points required for next Level: 271
    Overall activity: 0%
    Achievements:
    10 Days registered365 Days+ Registered Achievement!First 1000 Experience Points750 Days+ Registered Achievement!1000 Days+ Registered Achievement!
    Join Date
    Nov 2009
    Location
    Oxford uk
    Posts
    66
    Points
    9,379
    Level
    67
    Thanks
    5
    Thanked 6x 4 Posts

    Default

    I really appreciate all the time and effort that you are putting into this.

    You are going into great detail and this will give me an opportunity to revaluate my mount at every stage.

    Here is a pic of the last mount i made - it is not the design I am going to work on now.

    It was made out of Mild Steel and I used pillow-block bearings and I tried to keep all materials and couplings to standard sizes to keep things simple.

    This was a proto-type. I decided to make it a very heavy observatory based mount. It was not my intention to include latitude adjustment at this stage. It does not show the drive system fitted.

    As I have said i am changing the design and making it a GEM I have worked out a lot of the problems but I am looking forward to your posts.

    Cheers Matt


  5. #24
    AustinPSD's Avatar
    AustinPSD is offline Super Moderator
    Points: 56,828, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 2.0%
    Achievements:
    200+ Posts Achievement!First 1000 Experience PointsGot three Friends20+ Friends Achievement!5+ Referrals Achievement!
    Join Date
    Sep 2009
    Location
    McDonald Observatory, Mt. Locke
    Posts
    6,921
    Points
    56,828
    Level
    100
    Thanks
    743
    Thanked 5,863x 3,113 Posts
    Blog Entries
    1

    Default

    Another segment of the mount mechanical design. N.B., I'll be replacing the screen-shot version of these drawings with the engineering versions as soon as I resolve my CAD infrastructure problem.

    A narrative description of the screen-shot/drawing:

    The Scale 1 mount is composed of four rectangular plate sections. Two plate sections for the RA and DEC axis bearing mount plates. Two additional, smaller plates form the shaft to sub-plate connection from the polar axis to the companion sub-plate, while the second smaller plate forms the dovetail attachment plate for mounting the OTA.

    Each of the axis sub-plates mount two pillow-block bearing housings, two pairs of tapered thrust bearings for each bearing housing, the axis shaft, and a U-shaped shaft tensioner/hold-down bracket assembly.

    There are no welded or permanently joined connections.

    The pillow-block bearing housings bolt to their respective sub-plate assemblies using one bolt on each end of the block housing. The two axis assemblies are connected using 8 bolts between the small shaft connecting plate and the axis sub-plate assembly.

    All the components are either complete, off-the-shelf, commercially available parts, or fabricated using simple techniques:

    - plate sections are 6061 T-6 aluminum plate
    - shafts are stainless nitronic 60 steel in standard diameter
    - pillow-blocks, bearings, fasteners (bolts/nuts, collars/set-screws) are all standard dimension, off-the-shelf components.

    None of the aforementioned components require any shaping or surface machining. The plate materials can be cut from larger sheets, but are sized to be obtained from a variety of suppliers as pre-cut rectangles. Similarly, the shafts are sized (length and diameter) such that they're available pre-cut to size, or may be cut to size from longer stock.

    If the plate and shaft materials are obtained pre-cut, the only machining operation required is boring holes in the plate sections.

    This mount is designed to be attached to a permanent pier, although it could be mounted on a wedge/tripod of appropriate size. The drive mounts don't appear in this particular cross-section, but will be shown in forthcoming additions.

    Here is the screen-shot/drawing for reference:
    Attached Images Attached Images
    dynamo likes this.
    CGEM 800 HD, NexGuide, Orion XT8 Limited Edition, Oberwerk BT-100, Canon 20D/20Da/T3i/60D/5D Mk III, various eyepieces, adapters, geegaws, widgets, and tiddlybits

  6. The Following 6 Users Say Thank You to AustinPSD For This Useful Post:

    admin (01-15-2010),dynamo (09-28-2012),jonesy311 (03-11-2012),mikec (01-14-2010),saturn1970 (01-14-2010),tinkerer (01-02-2011)

  7. #25
    saturn1970's Avatar
    saturn1970 is offline Main Sequence
    Points: 9,379, Level: 67
    Level completed: 10%, Points required for next Level: 271
    Overall activity: 0%
    Achievements:
    10 Days registered365 Days+ Registered Achievement!First 1000 Experience Points750 Days+ Registered Achievement!1000 Days+ Registered Achievement!
    Join Date
    Nov 2009
    Location
    Oxford uk
    Posts
    66
    Points
    9,379
    Level
    67
    Thanks
    5
    Thanked 6x 4 Posts

    Default

    Just for reference here is a pic of my current mount that i am using.

    It is a Beacon Hill mount. It is a bit rough and ready and i had problems with it but now it works well.


  8. #26
    AustinPSD's Avatar
    AustinPSD is offline Super Moderator
    Points: 56,828, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 2.0%
    Achievements:
    200+ Posts Achievement!First 1000 Experience PointsGot three Friends20+ Friends Achievement!5+ Referrals Achievement!
    Join Date
    Sep 2009
    Location
    McDonald Observatory, Mt. Locke
    Posts
    6,921
    Points
    56,828
    Level
    100
    Thanks
    743
    Thanked 5,863x 3,113 Posts
    Blog Entries
    1

    Default

    My goal is to release this work into the public-domain, under a GNU-like use license, including the mechanical design.

    I've been a long-term follower of the Alt-Az Initiative, the One-Meter Project, and EQMOD. My follow-on to this project (which includes fabrication and assembly of this mount in Scale 2 format) is an open-source CDK telescope design along the same lines, Scale 0, 1, and 2 at 1/4, 1/2 and 1 meter aperture respectively.

    The other companion conceptual aspect is the use of open-source and public domain tools for all of the design and modeling support, including MODAS for the optics, BRL-CAD for the mechanical design and solid modeling, and FEAP for the finite element work. As you'll see with respect to the control system, it is designed for integration with the existing open-source EQMOD platform.

    In combination, all this would hopefully allow an enterprising individual, or group at high-school, collegiate under-grad/grad level, or a club to develop and build their own open-source telescope and mount between 1/4 and 1 meter depending upon their ambition and budget.
    dynamo likes this.
    CGEM 800 HD, NexGuide, Orion XT8 Limited Edition, Oberwerk BT-100, Canon 20D/20Da/T3i/60D/5D Mk III, various eyepieces, adapters, geegaws, widgets, and tiddlybits

  9. The Following 6 Users Say Thank You to AustinPSD For This Useful Post:

    admin (01-15-2010),dynamo (09-28-2012),Lenbo (01-15-2010),saturn1970 (01-26-2010),sxinias (01-15-2010),tinkerer (01-02-2011)

  10. #27
    saturn1970's Avatar
    saturn1970 is offline Main Sequence
    Points: 9,379, Level: 67
    Level completed: 10%, Points required for next Level: 271
    Overall activity: 0%
    Achievements:
    10 Days registered365 Days+ Registered Achievement!First 1000 Experience Points750 Days+ Registered Achievement!1000 Days+ Registered Achievement!
    Join Date
    Nov 2009
    Location
    Oxford uk
    Posts
    66
    Points
    9,379
    Level
    67
    Thanks
    5
    Thanked 6x 4 Posts

    Default

    Hi there

    I would just like to say that i am enjoying your imput. I am looking forward to your next installment.

    I have just found myself a C9.25 which i am planning to design my mount around.

    Cheers Matt

  11. #28
    Sputnik57's Avatar
    Sputnik57 is offline White Dwarf
    Points: 6,782, Level: 57
    Level completed: 16%, Points required for next Level: 168
    Overall activity: 0%
    Achievements:
    365 Days+ Registered Achievement!First 1000 Experience Points750 Days+ Registered Achievement!2 Posts Achievement1000 Days+ Registered Achievement!
    Join Date
    Apr 2010
    Location
    Idaho
    Posts
    11
    Points
    6,782
    Level
    57
    Thanks
    0
    Thanked 0x 0 Posts

    Default

    I just added a post this a.m. related to a drive system for my GEM which looks very similar to what you were discussing last year. It's under "telescope mounts" " A large pillow block GEM".

    Did you continue the design/fabrication?

  12. #29
    saturn1970's Avatar
    saturn1970 is offline Main Sequence
    Points: 9,379, Level: 67
    Level completed: 10%, Points required for next Level: 271
    Overall activity: 0%
    Achievements:
    10 Days registered365 Days+ Registered Achievement!First 1000 Experience Points750 Days+ Registered Achievement!1000 Days+ Registered Achievement!
    Join Date
    Nov 2009
    Location
    Oxford uk
    Posts
    66
    Points
    9,379
    Level
    67
    Thanks
    5
    Thanked 6x 4 Posts

    Default

    Hi there

    I just responded to your post about your mount - it may help.

    Yes I have continued with my mount - although I had a baby which has taken up a lot of my time - a my business has been demanding too.

    I have almost completed my mount, I brought the gears although I had to redesign the worm gear bracket. I also bought the drive system.

    I am hoping to have it completed in the next couple of months - time allowing.

    Cheers Matt

  13. #30
    Art Bianconi's Avatar
    Art Bianconi is offline Banned
    Points: 7,670, Level: 61
    Level completed: 40%, Points required for next Level: 180
    Overall activity: 0%
    Achievements:
    First 1000 Experience Points200+ Posts Achievement!400+ Posts Achievement5+ Referrals Achievement!365 Days+ Registered Achievement!
    Join Date
    Dec 2010
    Location
    Delaware River Valley, Western New Jersey
    Posts
    328
    Points
    7,670
    Level
    61
    Thanks
    91
    Thanked 198x 106 Posts

    Default !

    Quote Originally Posted by saturn1970 View Post
    I am making a very heavy German Equatorial mount and i looking some help and advice for a drive system for it. I want it to be used for astrophotography for a 12" Newtonian Reflector. It needs run on 12 volts, have a simple hand controller, with drive in RA and Dec.
    Thanks Matt
    Been there done that. Trying to collect sundry parts and making them all work together harmoniously can be daunting.

    I have a GEM mount that was made from 1/2" cold rolled boiler plate steel and which takes 3 men to lift and install on the pier. a four inch steel pipe with pipe flange fittings.

    The flanges allow me to connect the pier to a similar pipe buried 8 feet deep in a column of cement that took 20 bags of cement to fill only to have light pollution worsen and compromise the whole effort.

    So, before I address the mechanical issues let me caution you to take a serious look at the skies under which you will be erecting this mount.

    I wait for an total overcast night to check the sky. "What!?" Yes. . . . . overcast!

    When the sky is clear you can't see how badly the sky-glow is from ground based light sources. With a cloudy sky you can easily see it reflecting off the base of the clouds from 20, 30 miles away.

    I also urge you to check local zoning boards and boards of adjustment to see what building permits have been requested or already approved.

    You won't be very happy setting up the scope for First Light only to find out too late that a shopping mall or car dealer has set up brilliant mercury vapor lights with no horizontal cut-offs, a quarter of a mile away. I check those resources regularly and when I see evidence of potential light source, I show up and demand use of known lighting standards, not as an astronomer but as an environmentalist. I am NOT a tree-hugger but they don't know that. They view astronomers as one of many special interest groups whom they are inclined to ignore. Environmentalists are better organized than us and they get heard.

    As for the mount itself, if you are absolutely certain that it's never ever going to moved while you live at that location, then I suppose it won't matter much how much the base unit weighs.

    The pillow blocks on mine weigh 18 pounds EACH! There are four altogether: two for the RA axis and the other other pair for the DEC. The two shafts and the pillow blocks add up to 100 pounds and we've not even begun to build the head. (see photos)

    After so many years of doing the GEM "over the top" dance and having been spoiled by fork mounts, I've chosen not to ever build a scope again for anything but a fork unless circumstances dictate otherwise.

    The moments of polar inertia for a big GEM mounted scope are considerable. My 12.5" F-8 took five 15 pound barbell weights to balance the system with the scope on and it was so well balanced a breeze would move it with the dampeners loose. But. .. . . the effects of polar inertia on the system was a bummer. "Things in motion tend to . . . . ." Remember?

    A Hurst 120 VAC geared synchronous motor drives the system through a 12" worm and sector gear set and while it was frightfully expensive when available and well made it still exhibits periodic error to some slight degree and the tracking while very close is not quite up several hours of unattended long exposures with a DSLR.

    Still this set up continues to be the simplest drive environment I have ever used and while it worked well with warm, wet eyeballs, I am not sure how it would fair for long duration imaging.

    The flaw in that ointment is that the gearing, as good as it is, does not track as well as the stepper driven system in my ATLAS EQ, an older first generation drive system.

    A really excellent drive system IMO is the one offered by Mel Bartels that uses two Pittman geared motors and integrated encoders. He uses Sidereal Technologies solid state fully integrated system that only needs a computer once: to establish the mechanical drive ratios in the final drive. Then you put the lap top away forever if you want or set it aside for use with your imaging system.

    The Mel Bartels system allows for a second pair of encoders so that if the drive units loose registry, the shafts will signal the system for the appropriate correction.

    I dare not try to enumerate the capabilities of his system. It would take too long. I asked Mel a while back if his system could track fast moving objects like the ISS and he said yes, "provided you download the latest software"! I watched someone do that once.

    He dialed in a satellite's name, punched in the change in slewing speed and hit a button. The scope came alive, swung into position just a few degrees below the horizon and stopped.

    We waited what seemed like an eternity. Suddenly the two drive motors came alive and the scope started moving. We caught the satellite after it broke the horizon. But, not the scope. It had the target nailed before it cleared the trees and stayed right with it, right across, thru zenith and beyond.

    I paid Mel half the purchase price and periodically sent him checks. When the system was all wired up and tested, he sent it. I think it came to about $750. I'm not sure, it's been a long time.

    The system is bulletproof and tested when you get it. If you think you are handy with a soldering gun you can order a kit and build it yourself. I know how to do that stuff but know better than to start it. Debugging even the slightest mistake can take eons and I no longer have the time or patience for such mysteries.

    Another precious feature is the ability to define a collision envelope; areas where structure exists that the system should not go to. Who wants to see their Nagler Ethos get busted off the Moonlight while slewing?

    The list is endless and can only be appreciated by going to Mel Bartels web site which is BBAStroDesigns.com

    The question I ask you to consider is this: "what would you rather be doing.. . . . . building a scope or using one."

    I urge you to build it fast and to use as many previously integrated systems as possible so you are not faced with an eternity of debugging. As it appears here, you are destined to have to do that.

    As for the actual mechanical drive, there is a lot to be said for Gilmer type toothed belts, like the ones in your cars engine valve train. The drive is positive (no slippage) and indexing is always right on. My design calls for that in the fork tine for the declination inputs.

    The RA drive was originally made from the flywheel of a Corvette, whose teeth were ground off the ring gear on a precision cylindrical grinder and then the rest of the ring surface hardened. Then I found the weight to be objectionable so I changed it to a flex plate from an automatic transmission. Same geometry but dramatically lighter.

    The hardened pinion shaft from a golf cart gear box is held firmly against the ring gear and operates by friction, just like a railroad locomotive but without the slippage and with no periodic error.

    Tests thus far indicate perfection.I'll know for certain when the system is complete and under a full load.

    Attached are photos of the original GEM which now sits under a tarp and unused (no. . . it's not for sale). I've also enclosed a sectioned view drawing of the drive system in it's enclosure. The two bearings weigh something like 25 pounds EACH. Heavy though it is, the system is portable to dark skies in a van or station wagon.

    BTW, make sure you have Alt Az micro adjustments on the pier for polar alignment. Mine shifted while the cement was curing and I had on Hell of a time correcting the error.

    Lastly do not pour a cement walk around the pier that is any closer than ten inches to the vertical post lest you have every footstep vibrating the pier and the scope.

    Clear Skies

    Art

  14. The Following User Says Thank You to Art Bianconi For This Useful Post:

    tk1138 (03-23-2011)

 

 
Page 3 of 5 FirstFirst 12345 LastLast

Similar Threads

  1. Replies: 1
    Last Post: 05-21-2008, 02:41 PM
  2. Replies: 0
    Last Post: 04-30-2008, 12:24 AM
  3. Using an Autostar to control a large Dob drive system .(?)
    By Gary Heath in forum Amateur Astronomy Forum
    Replies: 1
    Last Post: 11-20-2004, 12:08 PM
  4. Ion drive
    By Fred Williams in forum General Astronomy Forum
    Replies: 0
    Last Post: 08-08-2003, 04:27 PM
  5. Ion drive
    By Brandon Siegel in forum General Astronomy Forum
    Replies: 0
    Last Post: 08-07-2003, 08:14 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Powered by vBulletin® Version 4.2.0
Powered by vBulletin®
All times are GMT. The time now is 02:25 PM.