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About skybadger

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  • Birthday 09/02/69

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    Riseley Berkshire
  1. What makes you think synthetic hydrocarbons are less appealing than natural ones to things that eat them ? M
  2. Nose grease , just a smidgen is required. And it's free.
  3. I've used cement quite happily for a tile tool. Went off without a problem. I also used the tiles set side on for longer grinding. Using 1cm square tiles worked really well. Can't say I finished polishing it though.. Mike
  4. " Someone else said previously that if you have a candle 100m away and bring it to 6" away, is it brighter? No, just closer." I might regret this, but it is apparently brighter but not intrinsically brighter. It's brighter because it's closer and therefore by the 1/r^2 rule it must be brighter, there is more energy pouring into the same unit solid angle of the observers eye. If unresolved, the flame will just appear brighter, if resolved, the light might be smeared over more rods , so now you have 2 rods firing not just one. But the flame isn't burning any harder. for a telescope, the brightness increases by the light gathering area but decreases by the f/ratio, compared to the eye. That's because the image size and inversely , the brightness per unit area,scales by the f/ratio. cheers Mike
  5. "Depth really isn't that critical for a pad, as much as area. If I was laying one I would make it a meter square but perhaps only 150cm thick on a good base of well tamped down hardcore. We have the base for a summer house and the concrete is no more than 4" thick (over a sandy soil) and I would defy anyone to bother a scope set up on it with anything short of sledgehammer blows." I don't think I can agree with this. I had a similar large thick concrete apron around the back of my garage which is where I bolted the observatory and the mount. I could easily see every truck that went past 60 yards away in teh scope vibrations and that was a sturdy, heavy welded tripod mount. I have a double pass liquid mirror ronchi tester in the garage and I can see every breath I take while standing 3 feet away in that because its on a common thick concrete floor. Cheers Mike
  6. Doh! Thanks Nigel . The scope I built was mobile with some heft and the wheel barrow wheel at the front. Bet one night I hefted, ran into a bump and then it went over the top. So the mount is in bits while I replace the horseshoe disk. I'v taken the opportunity to move the CoG so should be able to remove some counterweights. I'll finish that one I've finished my ronchi double pass liquid mirror experiments... Alpollo, The idea seems really good. Have you thought about folding a slightly larger scope to keep your size down while allowing a larger aperture ? One of the projects on my books is a 15" f/8 that's going to be too long without folding... Regards Mike
  7. Hi Alpollo a 900mm aperture split ring? That's going to be some telescope. I built a 12" f/6 split ring some while ago and there were some lessons that had to be learnt: Design around the centre of mass from the start. You will be surprised how close your mirror and pivots are. It needs careful weight and distance measurement but its worth it in a simple spreadsheet. This means your trusses will be highly asymmetric. Ot that you might care to introduce a central rigid box and shorter trusses either end. I also found that the plywood top ring was very easy to build heavy - I built it as a rigid two-tier cake with focuser mount in-between. Then re-built it it with a single top ring and suspended focuser. Over time this has warped slightly. In other words it needs to be both very stiff and very light to not skew your balance and not go out of shape. There's some pictures here but I'm sur you have looked at lots already. Good luck Mike
  8. I have an upside down pyramid of concrete as my base, about a meter on a side at the surface, going down a meter to the clay line and just below. The pier it supports is 8' high so the intent was to prevent vibration by getting a large surface area and counteract the large fulcrum by having some depth. The load is about 100kg fully laden, so there will be two effects, that of a pendulum with fixed end and column resonance. The Column is 12" diameter so I'm not worried by flexure or resonance, so I just need enough of a damping mass at the end and to resist bending forces. It has been sufficient .... Mike
  9. Hi Gina. Fair enough but I assumed most of that, which is where the question is coming from. 13M ticks is a small fraction of an arc second per tick, so maybe it's a case of precision not resolution. Hi Hugh. I was looking at the product selector pages and also some motors on the bay from FHA. Assuming you behave as if the harmonic gear head is an exceedingly stiff planetary gear, typical ratios are still only 100:1, which means yet more gearing is required. So still looking for that understanding. Mike
  10. Hi all has anyone got any experience of fitting direct drive motors to a telescope mount, possibly replacing the worm wheel with a different drive train ? I'm looking at the catalogues and trying to work out what the likely cost and engineering effort mighth be and talking to someone who has already pursued this would be helpful. I am looking into converting my AE type B mount into a gearless mount driven from a direct drive motor on the botto of the RA shaft or belt driven at the top. The payload of the mount is typically around 30Kg and so I reckon a output of about 15Nm will do the trick, although higher for direct drive. I also read that direct drive with inbuilt encoder can do 13M ticks per rotation but the spec says the positioning precision is 90" - what does this mean ? Any thoughts ? Mike
  11. ah ok. in which case they really are 1/4"x20 threads per inch Whitworth or Unified Coarse. You can get them from ebay here <>for example for set screws and here <> for cap/Allen screws. Watch out for bolts with no threads... M
  12. They should be M6 for a chinese or japanese made mount. Different thread size. Its Metric 6mm and has a pitch of 1.0mm. M
  13. Hi all Im looking for advice on the idea of improving my mount by taking off the worm/dc servo and moving to a direct drive motor with built in encoders. The reason for this is that I get quite a large periodic error on the existing worm & wheel and have some options to address this. My kit consists of a 8 or 12" scope with 6" frac twin mounted and a pair of guidescopes, cameras, sun scope etc depending on season. So I'd like to be tracking well at 2m focal length and upwards of 30Kg payload. My thoughts on options are: Buy a new mount - rather expensive, even if second hand. Maybe £3.5K for a second hand Mesu 200 ? Replace the worm and wheel on the existing AE mount. Certainly do-able. Beacon Hill do a 11" worm for about £400. Are there any recommended suppliers for large worm/wheel sets? It coudn't exceed 11" diameter. Replace the entire worm and wheel for a direct drive motor attached to the bottom end of the RA shaft. This would also require a dedicated motor controller/driver and then an ASCOM driver. I have one of these I did for the SkySensor so the ASCOM part isn't that hard. This is probably the most expensive option but still less than £3.5K . Has anyone ht any experience of buying and fitting these direct drive motors in retrofit and what were the results ? An other option to be identified. What are your thoughts - is too long and painful to fit your own DD motor to a mount that its much more worthwhile to buy or should I perservere and sppend more time looking at the worm /upgrade the worm first for relatively small beans ? Cheers Mike
  14. For only £50 I put together this mount from two Mondeo rear hubs. Mind you, I had to prise the abs sensor housings off but once done and a decent dovetail mount added , I get a very smooth and solid head that will carry a sizeable load. I intend to add clutches and belt drive next using DC motors. Really I built it as a test stand from scrap for assembling and testing scopes up to 12" but it seems to work well enough for observing use...
  15. This is an old topic now but... the motor will need to be reversed on the worm - either by replacing with one which turns the opposite drection ( in teh case of an ac syncro motor) or by moving the motor to the other end of the shaft, reversing the motor direction that way. Or replace the whole motor with a stepper/dc motor and belt system for forward and reverse control. Good luck Mike