My second project htis month after completing the Cheap Guidescope is a wedge for my DOB.
For those that know me I had already made an EQ Platform but the frustration on getting the diameters correct and the bearing to roll properly require special tooling which I successfully did and managed some nice images especially planetary stuff. The old EQ Platform had some problems though so I decided to make a more accurate version but all the special requirement to make them was frustrating.
Saw a couple although very few site displaying Wedges instead so for the fun of it I decided to see if I could start making one this weekend.
Well I am surprised, what an easy build. The photo on this link - https://plus.google.com/photos/10992...92392851058466 is an almost complete assembly (non driven) creation with stuff I had lying around at home, raided a few unsuccessful projects.
First in the photo you will notice 2 rods at the back, this provide latitude adjustment and using 2 of them provides good stability as well. These rod a stainless steel as I had some lying around, but the key to the build is the pivoting mechanism which uses the same SS rods. These rods are so strong they are highly accurate. I have used 4 x 20mm conduit clamp from Bunnings to attached the pivot rod to the V member and the bottom ply base board.
The conduit clamps are very sturdy and the downward pressure of the DOB prevents any form of the rod coming out of the clamps.
The V-Member turned out great, I have hinged them for portability, the based comes off the clamps and take up only slight more than a typical DOB base so there is no more room to take up in the car. The hinged V-Member can be folded away and compacted nicely to take up very little room in the car as well. The Hinges though are very expensive as I wanted good ones that have little to no play.
I have also designed the based so it can be removed and without any modifications can be used as a regular DOB.
Parts of the project that require attention are:
1 - Motor Drive, both Alt and AZ.
2 - Modifying the rear rod for full accurate adjustment (half way there already).
3a - Modify the bearings on the DOB to handle the angles for wedging.
3b - Modify the whole AZ mechanism to be easily driven (requires a new bearing system).
4 - The inevitable issues that arise when building things without a diagram .
So far no major issues have arisen so far but having an option of building a EQ platform to a Wedge - The wedge wins hands down. I already know there are some people against it though.
Since the post, i have made a design decision change for the latitude adjustment. I will be using various lengths of threaded rods 10mm for rigidity and use rod end bearing to mount them. I have to wait for the rod end bearing to come in first. Unfortunately for Australian supplier they cost 3 x more than overseas suppliers so i have to wait.
This is the only project at the moment i am willing to spend a bit more money on as the DOB has been awaiting use for a long time and i want to get back to planetary imaging and if stable enough narrow angle deep sky as well.
I don't want to be a wet blanket but making the "wedge" is the easy part.
The real problem will come when you need to redesign the azimuth (RA) and altitude (Dec) bearings. The Azm pivot is designed just to keep the "rocker box" central on the base. It will not form a stable pivot once you put a radial load on it.
I once modified a Dobsonian mount to make the azm a substantial bearing with a new pivot that had thrust races to draw the two sections together firmly and ball race wheels replacing the three teflon rub pads. This made a very rigid assembly for driving with a geared stepper motor and belt. However if mounted as an equatorial platform the flexure of the rocker box was a still problem.
The Declination bearing will present another problem. The existing arrangement won't be very suitable. You will need to make a proper bearing that will hold the optical tube and allow it to move at least from pointing at the pole up to the equatorial plane.
As a digressing here you have given me a couple of ideas. I have a LX200 10" classic set of forks or a LX 6 set of forks here that I could use to hold an 8" F4 dobsonian without too much trouble and mount it on a wedge like in your picture.
These forks have the gear drives and I have a set of electronics that will fit the LX200. It would be an interesting project even if not very practical as I would expect my HEQ5 pro to be a better proposition for photography.
You will find information on my modified dobsonian here:
I don't want to be a wet blanket but making the "wedge" is the easy part.
Can never be a wet blanket, I also love to explore areas of development to see what options can be explored. Love to get feedback as well as I go sometimes it can give ideas to work with.
Quote:
Originally Posted by Barrykgerdes
The real problem will come when you need to redesign the azimuth (RA) and altitude (Dec) bearings. The Azm pivot is designed just to keep the "rocker box" central on the base. It will not form a stable pivot once you put a radial load on it.
I agree this is going to be a challenge, I noticed in your drawing that you have used curtain roller. I am planning using the concept rollers although i will mount CAM Followers on an Ali bracket upside down to keep the base board flat as circles around.
Quote:
Originally Posted by Barrykgerdes
I once modified a Dobsonian mount to make the azm a substantial bearing with a new pivot that had thrust races to draw the two sections together firmly and ball race wheels replacing the three teflon rub pads. This made a very rigid assembly for driving with a geared stepper motor and belt. However if mounted as an equatorial platform the flexure of the rocker box was a still problem.
Yes I understand this, I have removed sections of the box and looking at re-enforcing sections to reduce flexure.
Quote:
Originally Posted by Barrykgerdes
The Declination bearing will present another problem. The existing arrangement won't be very suitable. You will need to make a proper bearing that will hold the optical tube and allow it to move at least from pointing at the pole up to the equatorial plane.
I agree declination is going to be a pain, but initially I will run this similar to an EQ Platform and fix the Dec as is and consider ideas slowly as they come. This section could prove to be the most comprehensive of builds but as EQ Platform do not have Dec adjustment then I am not missing anything in comparison.
Quote:
Originally Posted by Barrykgerdes
As a digressing here you have given me a couple of ideas. I have a LX200 10" classic set of forks or a LX 6 set of forks here that I could use to hold an 8" F4 dobsonian without too much trouble and mount it on a wedge like in your picture.
These forks have the gear drives and I have a set of electronics that will fit the LX200. It would be an interesting project even if not very practical as I would expect my HEQ5 pro to be a better proposition for photography.
It would be nice, unfortunately I don't have a spare set of fork here. Maybe that will come later if needed.
Photography wise, if I can get the same of better results as a very early platform version - http://mswhin63.waelect.com.au/Deeps...11_17_30PC.jpg then I will be happy.
Quote:
Originally Posted by Barrykgerdes
You will find information on my modified dobsonian here:
Hi All, managed to get more work done on this project with great results.
I have almost completed the polar adjust rods. The only thing left to do is to shorten the rods and make additions to extend the rods at different latitudes.
After that has been completed I intend to work on stabilising the base board with cam followers and for the interim will leave the standard base bearings as they are and will only consider replacing them if they play up with the design.
To save placing photos on different places I have place them for view on my Google+ album. Also details on each photo explains each step.
Another exciting instalment (for me at least) on the Wedge mount. I have completed the polar adjustment rods and was able to get threaded rod extenders that allowed me to shorten the rod to a latitude of 46 deg. So if I live, move down to the freezing zone called Tasmania then it will still work without modification.
I can now insert various lengths of threaded rod to the end of the main rod to extend latitude further north. The picture shown is for a latitude of 24 deg. So if I want to got further North again without modification. The conduits provide a nice stability to the threaded rods, although the rods are 10mm I gave it a bit more rigidity with the conduit. The other advantage of the conduit is the conduit clamps can be inserted and the lot can be clipped during transport and allow for the base board to be used as a regular DOB.
Baseboard stability
A question came up about the stability of the base board while rotating. This is a good point, I had a small thought on this but as a prototype please not my implementation is functional not pretty.
I have used bearings call CAM Followers which I was going to use on my second EQ Platform. I am using a simple levering system with steel bracket to compress slightly onto the base board, as the altitude raises I may increase of decrease the tension as required but so far it is performing really well.
Another note something I was not expecting. The compression of the bearing also smoothes out the bumps around the surrounding strip. Although not ideal it save the need for trimming which I have left for another time if at all.
There are 4 CAM followers fitted
Next step now is adding base board friction motors (initial).
Project is nearing completion and is now ready for general viewing ability. It is though not the most comfortable for viewing it is still possible. They are quite a few accidental benefit that have come from this.
1 - Height increased for general viewing scope. A problem I experienced some time ago and with my bad back was difficult to use. I used to place a crate under the DOB before and was only a little too high but more comfortable. The new height is almost perfect for viewing especially at Zenith.
2 - The wheels had to be changed many times to allow it to be wheel around the house and also fit in the van. The bonus is when I lift it into wheeling position, the DOB is soooo light I can maintain balance with only one finger (see not very good picture of me.) Not only that I can wheel it from both sides as well. One one side the wheels are permanently fitted although I can change it, The other side the wheels are removable and is important when I come to use it as a wedge mount.
Pictures:
1 - Shows the new bolts I created to allow the position of the wedge to be changed. I can remove the lower section and create other sections for different latitudes.
2 - Safety strap. This a marine grade locking pulley that i haven't used in a long time. I found when testing that when I raise the wedge past a certain point the centre of gravity would become unstable. Not by much but enough to make it difficult to hold the base and then insert the latitude bolts. So I created the safety strap to hold it past the COG while fitting the bolts. It can also act as a pulley system to load the DOB into the van.
back again, bit of a spell during the last post had to take a breather. Anyway further images:
1 - Four wheel running position, very stable and so easy to push.
2 - This is the wheelbarrow method and my ugly mug. If it is possible to imagine the ease of holding it, my fingers are loosely placed around the axle. This will also benefit the wedge because it is the rough position that the wedge will be when fully operational. I have good balance from about 20 - 70 deg incline. In any future builds or modifications, I may look closer at COG, but for the moment it was just a fluke.
3 - Very easy to roll it up onto the van ledge and as shown stay there, I have a slight incline in the driveway but not on the garage concrete. I will consider wheel chocks if I need to prevent the scope from rolling out, but is very stable and felt comfortable in leaving it to get the camera.
4 - Final position only just fits inside the van. Citreon Berlingo similar to the smaller VW, Renault and Holden Combo in size. If it was a problem I could remove the tube but glad I don't have to.
There are 3 primary tasks left to carry out, Motor drive RA only (making it very similar to a EQ Platform operatively), Feet for levelling (got that worked out but need certain type of feet) and forgot the last thing (age creping up )
Though this kind of wedge has been on my mind in the last fortnight, your new postings inspired me get up of my arse to do some preliminary testing
Taking off the UTA and Mirror cell meant I didn't need to build something and could just 'Wedge' the rockerbox on a stool
This is one of the few instances in astronomy where far northern or Southern latitudes are actually a bonus. 53ºN means my rockerbox is tilted 37º.
Seeing as I already have a Servocat Drive system (yet to be fitted) I would have no need for this for visual use but if I can find out whether a scope this weight on a side braced baltic birch rockerbox replacement can be made stiff enough for Astrophotography/Long integration Mallincam use then I would definately be interested in attempting this in the future. Preliminary enquiries with Gary at Servocat indicate that the servocat drive and Sky Commander combo can be operated in Equatorial mode and in fact the drive method for the Meade Lightbridge servocat kit arguably lends its self to this kind of use better than the regular direct drive/Alt cable versions used on premium dobs.
The lightbridge alt forks and bearings lend themselves to equatorial use in my case though if I was further south they wouldn't. The rims are helping to hold the OTA on the forks. Small versions of some of those socket ball bearings used on conveyors mounted in the fork against the rims of the alt bearings would keep the OTA from sliding laterally when pointed east and west while preventing binding of the 'higher' rim as it rubs against the 'higher' side fork.
Like yourself, I would be raiding the parts bin of other unsuccessful projects. Specifically I have motors and threaded rods and various other bits and bobs from a JMI TNT Lightbridge drive system that never worked right on this dob. I'd been thinking about fast accurate polar alignment and remembered Tom Olpowski EQ platforms with his GLP polar alignment stalk. Seeing as I have to make my optical and tube axis coincident for a Rotating UTA mod anyway (which is even more of an imperative if I went ahead with this), I would set a stop for the OTA to perpendicularise it with the rockerbox at set up. So set up would be as follows:
Set up wedge and broadly align it with sprit level and compass and Alt scale. Affix rockerbox to wedge. Place OTA on rockerbox. Align GLP with high power Eyepiece on a bright star. Push OTA against stop. Now the GLP and Eyepiece are aligned with the axis of the wedge. This is where the JMI bits and bobs come in. While at the eyepiece use the JMI hand controller to make fine alignments adjustments to the wedge via the stepper motors till I am accurately poar aligned. No half hour of drift alignment On a sidenot, the JMI handcontroller performs dual use as a motorised primary collimation controller with the other two spare JMI TNT motors I have
I'll be using a 500mm VXB bearings lazy susan ring for my rotating UTA and funnily enough for my Rockerbox too. ie. replacing the MEade needle roller bearing lazy susan system. I needed to do this to be able to implement a powered groundboard system to get the heavy batteries out of the rockerbox which would unbalance the rockerbox in equatorial mode. The side benefit or maybe infact the main necessary benefit is that the Rockerbox would be kept orthagonal with the groundboard mounted to the wedge by this kind of lazy susan (400kg capacity) and the ring would take the strain off the central pivot too.
Having thought about this, there is not much about this plan that necessitates drastic changes to my particular scope or to other modding plans for it and in fact some of the required changes are beneficial to the scope even in Alt/Az mode anyway. So I guess I have nothing to lose except time and/or patience by trying this out regardless. If its good enough for Astrophotography, Great, if not I just wasted some time building the wedge but sure it kept me out of trouble for a while so it wasn't a complete waste of time
Funnily enough I am also doing a conversion from Truss to 3 strut like your flextube, I have a thread on CN about it) Those changes are going to give the scope the benefits of very quick setup at home like the Flextube while maintaining the ease of transport of a fully breakdownable OTA and smaller rockerbox of the Lightbridge compared to the flextubes. The shorter Lower OTA and longer poles however and greater propensity for pole flexure mean I will be implementing a string virtual truss system.
If I can pull this all off it will be pretty cool to have a big driven 400mm F 4.5 scope capable of private AP or public outreach mallincam video astronomy by simply attaching to my wedge or used in Alt AZ mode for private visual or public outreach visual use.
Fairly busy at the moment, so I am going through as I write so sorry for repeats.
Quote:
Originally Posted by Calibos
Hi Malcolm,
Though this kind of wedge has been on my mind in the last fortnight, your new postings inspired me get up of my arse to do some preliminary testing
I noticed the post has been fairly quiet so I thought there was a bit of hanging on to see if it was going to develop into something
Quote:
Originally Posted by Calibos
Taking off the UTA and Mirror cell meant I didn't need to build something and could just 'Wedge' the rockerbox on a stool
This is one of the few instances in astronomy where far northern or Southern latitudes are actually a bonus. 53ºN means my rockerbox is tilted 37º.
Seeing as I already have a Servocat Drive system (yet to be fitted) I would have no need for this for visual use but if I can find out whether a scope this weight on a side braced baltic birch rockerbox replacement can be made stiff enough for Astrophotography/Long integration Mallincam use then I would definately be interested in attempting this in the future. Preliminary enquiries with Gary at Servocat indicate that the servocat drive and Sky Commander combo can be operated in Equatorial mode and in fact the drive method for the Meade Lightbridge servocat kit arguably lends its self to this kind of use better than the regular direct drive/Alt cable versions used on premium dobs.
Well having a drive already is one up on me, The motor drive is going to be the biggest challenge financially for me and so I am starting with a very basic configuration. This will really test the system. Definitely higher latitude will make it easier, I suppose I was just purely lucky to get a good COG. Maybe this is the scope that I am using. I was thinking a bit more and noticed that the best COG for my scope is when the DEC/ALT bearing is directly over the pivot point. This which I am going to test more over time is the key to the ease of making these, so the base board could be created to allow the ALT bearing to be directly over the pivot.
Quote:
Originally Posted by Calibos
The lightbridge alt forks and bearings lend themselves to equatorial use in my case though if I was further south they wouldn't. The rims are helping to hold the OTA on the forks. Small versions of some of those socket ball bearings used on conveyors mounted in the fork against the rims of the alt bearings would keep the OTA from sliding laterally when pointed east and west while preventing binding of the 'higher' rim as it rubs against the 'higher' side fork.
Mentioned before if the baseboard is altered to allow the ALT bearing to be over the pivot then it could be possible to make it for different latitudes easily. Still more testing to confirm. The concept is that the scopes COG will prevent issue with binding etc. But one thing I need to test is any other factors that may occur. I found the COG for the wedge requires the telescope to be completely set-up as the mirror adds the necessary weight to balance the scope.
Quote:
Originally Posted by Calibos
Like yourself, I would be raiding the parts bin of other unsuccessful projects. Specifically I have motors and threaded rods and various other bits and bobs from a JMI TNT Lightbridge drive system that never worked right on this dob. I'd been thinking about fast accurate polar alignment and remembered Tom Olpowski EQ platforms with his GLP polar alignment stalk. Seeing as I have to make my optical and tube axis coincident for a Rotating UTA mod anyway (which is even more of an imperative if I went ahead with this), I would set a stop for the OTA to perpendicularise it with the rockerbox at set up. So set up would be as follows:
Set up wedge and broadly align it with sprit level and compass and Alt scale. Affix rockerbox to wedge. Place OTA on rockerbox. Align GLP with high power Eyepiece on a bright star. Push OTA against stop. Now the GLP and Eyepiece are aligned with the axis of the wedge. This is where the JMI bits and bobs come in. While at the eyepiece use the JMI hand controller to make fine alignments adjustments to the wedge via the stepper motors till I am accurately poar aligned. No half hour of drift alignment On a sidenot, the JMI handcontroller performs dual use as a motorised primary collimation controller with the other two spare JMI TNT motors I have
I mainly raid the parts bin because I need to clean the garage. My wife is getting insistent to clean up and make more space. It is working. I agree that polar alignment will be theoretically a lot easier with this set-up mostly before DOB is the equatorial axis. I think this will need to be tested but in thought look good.
Quote:
Originally Posted by Calibos
I'll be using a 500mm VXB bearings lazy susan ring for my rotating UTA and funnily enough for my Rockerbox too. ie. replacing the MEade needle roller bearing lazy susan system. I needed to do this to be able to implement a powered groundboard system to get the heavy batteries out of the rockerbox which would unbalance the rockerbox in equatorial mode. The side benefit or maybe infact the main necessary benefit is that the Rockerbox would be kept orthagonal with the groundboard mounted to the wedge by this kind of lazy susan (400kg capacity) and the ring would take the strain off the central pivot too.
Really solid, I am still using the original bearing and will continue so until I decide to head for a more accurate a strong bearing/drive system. That is my ultimate intention but a long way off.
Quote:
Originally Posted by Calibos
Having thought about this, there is not much about this plan that necessitates drastic changes to my particular scope or to other modding plans for it and in fact some of the required changes are beneficial to the scope even in Alt/Az mode anyway. So I guess I have nothing to lose except time and/or patience by trying this out regardless. If its good enough for Astrophotography, Great, if not I just wasted some time building the wedge but sure it kept me out of trouble for a while so it wasn't a complete waste of time
Funnily enough I am also doing a conversion from Truss to 3 strut like your flextube, I have a thread on CN about it) Those changes are going to give the scope the benefits of very quick setup at home like the Flextube while maintaining the ease of transport of a fully breakdownable OTA and smaller rockerbox of the Lightbridge compared to the flextubes. The shorter Lower OTA and longer poles however and greater propensity for pole flexure mean I will be implementing a string virtual truss system.
If I can pull this all off it will be pretty cool to have a big driven 400mm F 4.5 scope capable of private AP or public outreach mallincam video astronomy by simply attaching to my wedge or used in Alt AZ mode for private visual or public outreach visual use.
Good luck with your end, I do not propose this to be a super duper EQ system but as I have managed decent photos with the past EQ platform I have no doubt this will provide an equivalent but easy build. I mainly considering planetary work for this set-up and with reasonable Frame Rate accuracy is not a major problem. But if it works better then happy days
On another note, found the lower latitude (higher degree) there is a limit to how low in the north sky you can see. I have removed the eyepiece board on the front of the DOB to allow complete range of movement, but still have limited view North but not much fortunately.
I think it is important to mention this because this may affect peoples intention to build this and may find it better to build an EQ platform for a more complete view.
As you said in your opening post this wedge idea is arguably easier to DIY than an EQ platform and the beauty of it is that like an Eq platform a single highish torque motor with a simple Pot is all you need for tracking really and yet you don't have to worry about resets after an hour.
With Alt/Az tracking already sorted I am coming at this from the Field Rotation angle and I just love a project
I think I read elsewhere about the importance of having the COG over the wedge platform pivot. Looks like we both got lucky. Shorter forks relative to scope size on mine but the shallower wedge angle means my COG would still be roughly over the pivot.
Your thread really focussed my mind and the more I thought about it, the more I realised that I am particularily lucky with the Lightbridge which seemed to lend itself to equatorialisation and required minimal adaptation and such adaptations as were needed were beneficial in ALT AZ mode too. Again, after further thought, maybe its a forlorn hope that it will be good enough for true AP but then again even when I had the money I feared to tread in the AP waters. Its bad enough when the inevitable dew or cloud shows up here in Ireland puts a halt to a visual session. My frustration levels would go through the roof if a 30 minute sub was ruined or something like that. I suppose thats why I have always been interested in the Mallincam. Some pretty amazing near LIve views can be had with that device but field rotation limits Alt/Az scopes to 27 second integrations. Whatever about this mod being good enough for AP, I think its definitely still worth doing for future Mallincam use because I think worse case scenario its going to be capable of up to 120 second integrations.
Luckily for me most of the expensive stuff I need to make this a reality are already sunk costs if thats the correct phrase. Stuff I already spent money on for better or worse. This is really just going to cost me the cost of the wood and a few other small bits and pieces.
Although I am going to order a replacement baltic birch Lightbridge rockerbox (with some custom changes for this mod) and that is going to be a few huidred dollars, I don't consider this as a cost of doing this mod because this was something I was going to buy anyway. the only difference now is, is that I will specify side braces to beef up the side forks and ask for a removable section of the 'Eyepiece Panel' as you called it. Some threaded wood inserts and knobs will make for quick removal or reinstallation of this panelk depending on whether I am going to use the scope in Alt/AZ or equatorial mode.
Can't wait to see your finished project. Would love to see videos of it in action when its done.
Good luck again, just one point when working on the replacement panel, look at rotation balance. Your is not as bad as mine but this could be an issue with speed continuity for a full rotation (another plus compare to EQ Platform more rotation!)
Mine is way out of balance, but I am going to leave it for the moment because I prefer to see if high torque motor will negate the problem, and if not I hope to design an electronic torque adjustment which will automatically re-adjust power to the motor to compensate for minor fluctuations in rotation.
The project is now officially on hold, there was some issues that I can't resolve in my financial capacity at this stage but the problem now is entirely the drive mechanism. I require to fabricate a bearing/drive system that can contain the weight in the latitude I want. The system is not completely dead though as it will still works, the friction drive I tried was functional but the weight in the position caused too much slippage.
I can get driven bearing off the shelf but are quite expensive so will motorise it for ALT/AZ operation until I can get the right finances to complete it.
I am though considering another alternative, seeing the bearing is quite expensive I am considering building an EQ mount for the the 12" and possibly above instead. I am looking at a simple box design instead of crafting a thing of beauty I will go for a thing of functionality instead. I have plenty of stainless steel rod with 10mm taps on each end I will consider this option over the year.
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