https://www.youtube.com/watch?v=WC8YhQaTtNA
Monday, 8 April 2013
Monday, 23 July 2012
Roof Castor Upgrade
For several months now it's been apparent that some of the castors on the roll-off roof have been getting worn, even to the point of complete failure:
When I originally chose the castors, I was going to cover the roof with corrugated plastic roof sheet, but then decided to go for the much more impact-resistant Onduline. But Onduline is *much* heavier than plastic roof sheet! So anyway after replacing a couple of the castors like for like and seeing that these also quickly showed signs of wear, I decided the best course of action was to upgrade the castors/channelling completely. I looked around and found these 50mm castors from Screwfix:
As you can see they're a lot beefier than the old ones, so changing to these should mean that they will hopefully last the lifetime of the observatory. I also bought some wooden lats from B&Q to replace the aluminium channelling which I think was one of the causal factors for the failure of the original castors:
I had to wait several weeks for a weekend of good weather, as I didn't want to run the risk of a sudden downpour on my unprotected 'scope.
So last weekend I enlisted the help of the BADAS Secretary, Terry Devon, and went about dismantling and removing the roll-off roof.
So first the exterior side panels had to come off:
Then the Onduline roof panels, which came off in one big piece, as they were all glued together with roof sealant. Zac took the opportunity for a quick sunbathe before the Onduline came off!:
Once the Onduline was off, Ziggy (who only visits a part-time basis) had a feel of the new pavement over the gravel:
Terry and I then lifted the roof off and put it on the ground. We then turned it over, and we removed all the old castors and replaced them with the shiny new ones.
I drilled holes in the lats so that they could easily be screwed into place to form the new U channels for the castors to run in:
Once these were fitted Terry and I lifted the bare roof back up to check that it rolled OK - and it did :-)
The castors look much more up to the job than the old ones did... :
However with the new castors being so much taller than the old ones (~60mm) it means that there is only a tiny gap between the warm room roof and the obs roof when closed, so that needs to be addressed as I want a bit of an air gap so nothing starts to rot:
Also the motor, limit switches and roof closed/open sensors all need to be re-positioned for the new level of the roof.
When I originally chose the castors, I was going to cover the roof with corrugated plastic roof sheet, but then decided to go for the much more impact-resistant Onduline. But Onduline is *much* heavier than plastic roof sheet! So anyway after replacing a couple of the castors like for like and seeing that these also quickly showed signs of wear, I decided the best course of action was to upgrade the castors/channelling completely. I looked around and found these 50mm castors from Screwfix:
As you can see they're a lot beefier than the old ones, so changing to these should mean that they will hopefully last the lifetime of the observatory. I also bought some wooden lats from B&Q to replace the aluminium channelling which I think was one of the causal factors for the failure of the original castors:
I had to wait several weeks for a weekend of good weather, as I didn't want to run the risk of a sudden downpour on my unprotected 'scope.
So last weekend I enlisted the help of the BADAS Secretary, Terry Devon, and went about dismantling and removing the roll-off roof.
So first the exterior side panels had to come off:
Then the Onduline roof panels, which came off in one big piece, as they were all glued together with roof sealant. Zac took the opportunity for a quick sunbathe before the Onduline came off!:
Once the Onduline was off, Ziggy (who only visits a part-time basis) had a feel of the new pavement over the gravel:
Terry and I then lifted the roof off and put it on the ground. We then turned it over, and we removed all the old castors and replaced them with the shiny new ones.
I drilled holes in the lats so that they could easily be screwed into place to form the new U channels for the castors to run in:
Once these were fitted Terry and I lifted the bare roof back up to check that it rolled OK - and it did :-)
The castors look much more up to the job than the old ones did... :
However with the new castors being so much taller than the old ones (~60mm) it means that there is only a tiny gap between the warm room roof and the obs roof when closed, so that needs to be addressed as I want a bit of an air gap so nothing starts to rot:
Also the motor, limit switches and roof closed/open sensors all need to be re-positioned for the new level of the roof.
Tuesday, 29 November 2011
Automation Update - weather sensing
One of my goals in automating my observatory is to enable it to look at the weather and sky darkness conditions itself so that it can decide to make observations for me! I'm doing this with an eye on automated supernova hunting and comet/asteroid photometry. Prior to getting to that stage though, it needs to be able to check the weather to just safely park the scope and close the roof if it detects cloud/rain.
Cloud Sensor
After looking around on the Internet I found this and this which I found very intriguing. The Boltwood Cloud Sensors look great but seem very expensive for what they are (out of my budget anyway!) so I decided to have a go myself.
I used a Peltier thermoelectric cooler, purchased for a few £ on ebay, sandwiched between two small pieces of aluminium sheet. I used a small amount of thermal grease to make sure heat transfer would be as good as possible between the sheets and the cooler, which here works in reverse, i.e. the temp difference between the sky and the ground changes the potential difference generated by the Peltier device. The whole lot was held together with nylon bolts, mounted to the outside of the observatory and connected to a USB multimeter, purchased from Maplin for £20!
Cloud Sensor
After looking around on the Internet I found this and this which I found very intriguing. The Boltwood Cloud Sensors look great but seem very expensive for what they are (out of my budget anyway!) so I decided to have a go myself.
I used a Peltier thermoelectric cooler, purchased for a few £ on ebay, sandwiched between two small pieces of aluminium sheet. I used a small amount of thermal grease to make sure heat transfer would be as good as possible between the sheets and the cooler, which here works in reverse, i.e. the temp difference between the sky and the ground changes the potential difference generated by the Peltier device. The whole lot was held together with nylon bolts, mounted to the outside of the observatory and connected to a USB multimeter, purchased from Maplin for £20!
I used the provided software over several nights to calibrate the sensor - it was amazing to see the differences in the voltage generated by it changing as the cloud conditions changed.
I soon found though that rain did affect it - rain drops had the effect of cooling the top plate, but this usually changed the voltage much more than a normal clear night did, so is quite easy to spot. I did have a go with covering the sensor with cling film, but it didn't work for me unlike as mentioned in the second link above.
I soon found though that rain did affect it - rain drops had the effect of cooling the top plate, but this usually changed the voltage much more than a normal clear night did, so is quite easy to spot. I did have a go with covering the sensor with cling film, but it didn't work for me unlike as mentioned in the second link above.
It was a fairly simple matter to talk to the multimeter in my program using serial comms.
Rain sensor
So my program now had a good idea about the cloud condtions, and could react to them, but I felt like I needed a rain sensor as a sort of failsafe.
I tried a KEMO rain sensor (purchased from Maplins) but I kept having problems with it giving false alarms. I have read others having issues with these so I decided to make my own, with a view to possibly buying something else later.
I purchased a small piece of gold stripboard from Maplin and used that to make a simple rain sensor. Each alternate strip is soldered together, with a power resistor mounted on the underside to help combat dew and dry off the sensor after the rain has stopped. The sensor was linked up to a simple transistor circuit controlling a relay, which I wired in to be read as an input by the K8055.
This sensor works well, though I do have to wipe the stripboard with wire wool about once a month to get rid of oxidisation. For this reason I will eventually upgrade to another commercial unit.
Sky Brightness Sensor
In addition to the Peltier-derived cloud sensor and the rain sensor, I wanted the observatory to be able to check that the sky was actually dark.
I used an old LDR that I've had since er.. school (! - that's >20 years!), made a mount for it using bolts and bit of waste water pipe. I also put a small piece of thin perspex over the top to protect it from the worst of the weather.
Rain sensor
So my program now had a good idea about the cloud condtions, and could react to them, but I felt like I needed a rain sensor as a sort of failsafe.
I tried a KEMO rain sensor (purchased from Maplins) but I kept having problems with it giving false alarms. I have read others having issues with these so I decided to make my own, with a view to possibly buying something else later.
I purchased a small piece of gold stripboard from Maplin and used that to make a simple rain sensor. Each alternate strip is soldered together, with a power resistor mounted on the underside to help combat dew and dry off the sensor after the rain has stopped. The sensor was linked up to a simple transistor circuit controlling a relay, which I wired in to be read as an input by the K8055.
This sensor works well, though I do have to wipe the stripboard with wire wool about once a month to get rid of oxidisation. For this reason I will eventually upgrade to another commercial unit.
Sky Brightness Sensor
In addition to the Peltier-derived cloud sensor and the rain sensor, I wanted the observatory to be able to check that the sky was actually dark.
I used an old LDR that I've had since er.. school (! - that's >20 years!), made a mount for it using bolts and bit of waste water pipe. I also put a small piece of thin perspex over the top to protect it from the worst of the weather.
This was then mounted to the same pole as my electronic weather station.
I have found that the LDR is great for not just detecting day/night, but also clouds! As I live in a light-polluted area, the sky's light level at night changes depending on whether it's a clear dark night as opposed to cloudy. So I now factor this in to the decision-making as well as the Peltier cloud sensor.
Weather Station
I use a Maplin (that shop again!) USB "Professional" weather station along with Cumulus software, which re-generates a text file every minute which my program uses to check if there's been any rain in the last hour (which I class as "bad", in case of showers and to allow the cloud sensor to dry out a bit) and for high winds. I have to check the file is both present and current to ensure the data is up to date, so no old data is used.
Still lots to do - mostly programming, working on the logic for coordinating imaging while it's clear and dark. But I have a few updates pending still on this blog. Keep an eye on my Twitter account @cho_web too for updates on this project.
I have found that the LDR is great for not just detecting day/night, but also clouds! As I live in a light-polluted area, the sky's light level at night changes depending on whether it's a clear dark night as opposed to cloudy. So I now factor this in to the decision-making as well as the Peltier cloud sensor.
Weather Station
I use a Maplin (that shop again!) USB "Professional" weather station along with Cumulus software, which re-generates a text file every minute which my program uses to check if there's been any rain in the last hour (which I class as "bad", in case of showers and to allow the cloud sensor to dry out a bit) and for high winds. I have to check the file is both present and current to ensure the data is up to date, so no old data is used.
Still lots to do - mostly programming, working on the logic for coordinating imaging while it's clear and dark. But I have a few updates pending still on this blog. Keep an eye on my Twitter account @cho_web too for updates on this project.
Automation Update - Power
Well a lot has happened since the last my last post in April on this project.
Having fitted sensors to the roof so that the software I'm writing can tell the status of the roof (open/closed/part open), I now needed to control the power to my mount and CCD camera.
I have built a simple relay box which controls the power to the mount and CCD. This is shown below. The relays are switched on/off by the K8055 and they turn on/off mains power to my two PSUs. Simple but effective!
I also have a webcam pointing at the PSUs so I can check for power lights if I ever need to.
Having fitted sensors to the roof so that the software I'm writing can tell the status of the roof (open/closed/part open), I now needed to control the power to my mount and CCD camera.
I have built a simple relay box which controls the power to the mount and CCD. This is shown below. The relays are switched on/off by the K8055 and they turn on/off mains power to my two PSUs. Simple but effective!
I also have a webcam pointing at the PSUs so I can check for power lights if I ever need to.
Sunday, 25 September 2011
Possible new lunar webcam
While still firmly stuck underneath a blanket of cloud and rain, I decided to modify a webcam that I had lying around for use as a possible lunar and planetary imaging camera.
The camera is a Logitech HD Webcam C270 capable of 1280x720 video, with USB2.0:
Modification was very simple.
First I removed the fascia:
I undid the three small screws that hold the front part of the case on and removed it. I then used a drill to increase the size of the hole in the front part of the case to accept a Mogg adaptor I had spare.
I put a little piece of black insulation tape over the LED on the camera board and unscrewed the supplied lens from the sensor housing.
I put the case front and fascia back on and then screwed the Mogg adaptor into the hole I made. I used a little superglue to secure it.
Et voilà!
The proof of course will be as they say in the pudding when I get chance to test the camera with my scope. It's likely that the video the camera produces will be compressed but I will experiment with the settings, and see what old faithful K3CCD Tools can produce with it.
The camera is a Logitech HD Webcam C270 capable of 1280x720 video, with USB2.0:
Modification was very simple.
First I removed the fascia:
I undid the three small screws that hold the front part of the case on and removed it. I then used a drill to increase the size of the hole in the front part of the case to accept a Mogg adaptor I had spare.
I put a little piece of black insulation tape over the LED on the camera board and unscrewed the supplied lens from the sensor housing.
I put the case front and fascia back on and then screwed the Mogg adaptor into the hole I made. I used a little superglue to secure it.
Et voilà!
The proof of course will be as they say in the pudding when I get chance to test the camera with my scope. It's likely that the video the camera produces will be compressed but I will experiment with the settings, and see what old faithful K3CCD Tools can produce with it.
Friday, 16 September 2011
Boundary layer fan mod
Something I've been wanting to have a go at for ages was installing a fan to help with cooling the primary mirror and especially a side mounted fan to hopefully eliminate the boundary layer of warm air that sits over the mirror that can affect seeing - see here. The normal way to minimise this effect is to just try to cool the mirror as close as possible to the ambient temperature. The problem with this though is that it does need to be very close indeed to the ambient temp which is difficult to achieve with fans blowing on the back of the mirror alone.
I did have a try using a Peltier cooler and fan combination but this still struggled to cool the mirror to ambient and I think would have needed a lot more engineering to go on around the mirror cell for it to be really effective. Anthony Wesley in Australia has done a lot of work on this using multiple fans and Peltier coolers, but his mirror cell (and the whole scope) is custom built and beyond my expertise and budget. My Orion Optics SPX250 already has a small cooling fan in the mirror cell, to which I have already added a baffle (made out of a rubbery Ikea placemat), to stop the air from just coming straight back out of the cell again and instead go to the edges of the mirror and up the tube. I also have an indoor/outdoor thermometer velcroed to the OTA to measure the ambient and mirror temps.
Baffle
Indoor/Outdoor Thermometer
A small, side-mounted fan can gently blow away the layer of warm air that sits above the mirror. Run at full speed and suitably filtered, it can also help with cooling the mirror itself.
So I set about removing the primary mirror and cell, and marking and cutting the necessary hole in the OTA.
I fitted the fan, oriented so that it blows air into the tube, and covered it with pc fan filter foam and made a grill to secure it out of an old oven-chip crisper. This was all secured by four small nuts and bolts. I added a 3.5mm sound jack (rescued from an old 56k modem) and wired it to the fan.
Fan inside
Fan outside
I have the fan plugged in to my 12V supply via a variable resistor so I can adjust the fan speed - full to help with the initial cooling, down to a gentle whisper across the surface of the mirror for observing.
12v Supply and speed control
The primary is back in the scope, it's all collimated again so I need some clear sky now to test it.
I did have a try using a Peltier cooler and fan combination but this still struggled to cool the mirror to ambient and I think would have needed a lot more engineering to go on around the mirror cell for it to be really effective. Anthony Wesley in Australia has done a lot of work on this using multiple fans and Peltier coolers, but his mirror cell (and the whole scope) is custom built and beyond my expertise and budget. My Orion Optics SPX250 already has a small cooling fan in the mirror cell, to which I have already added a baffle (made out of a rubbery Ikea placemat), to stop the air from just coming straight back out of the cell again and instead go to the edges of the mirror and up the tube. I also have an indoor/outdoor thermometer velcroed to the OTA to measure the ambient and mirror temps.
Baffle
Indoor/Outdoor Thermometer
So I set about removing the primary mirror and cell, and marking and cutting the necessary hole in the OTA.
I fitted the fan, oriented so that it blows air into the tube, and covered it with pc fan filter foam and made a grill to secure it out of an old oven-chip crisper. This was all secured by four small nuts and bolts. I added a 3.5mm sound jack (rescued from an old 56k modem) and wired it to the fan.
Fan inside
Fan outside
12v Supply and speed control
Tuesday, 26 April 2011
Roof Position Status
I've added two magnetic reed switches (of the type used in alarm systems) to the roof and wired them into two digital inputs on the K8055 unit. This has enabled my program to detect whether the roof is closed, fully open, or somewhere in between.
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