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Dome Motorisation


Project Leader: Keith Rickard
Members: Martin Crow, Andy Barber, Steve Floodgate


Synopsis
Our new observatory's dome needs to be motorised to maximise members' enjoyment of using the telescope. A goal is to keep the cost below £500.

The first task is to make it easy for the dome to be rotated. Currently, 10 of 12 rollers have very rusty bearings which need to be replaced. The dome will have to be raised for this to happen. Also, the upper shutter section needs to be worked on to allow it to be slid open easily and smoothly.

The second task is to make the dome rotate in sync with telescope so that when it slews, the dome will turn with it ensuring that the telescope will always point through the dome's slit.

The third task is to motorise the opening of the upper shutter section. This will make it easier members to open the shutter without the need to climb up a step ladder and precariously lean over the telescope while doing this.

The task will require making the use of Arduinos, motors, electrics, electronics, and creating the necessary hardware.

Ideas are already flowing, which incorporate using car windscreen motors, duplex chains, sprockets, 12v batteries. To find out more, please speak to Keith Rickard or read about the progress below as details start to appear.



Dome1070917.jpg

PROGRESS

Thursday 3 July 2015

Andy Barber and Keith Rickard finished installing the remaining dome wheels. All 12 wheels are now in place and the dome now rotates far more easily. Although this is a success, more improvement can be made in two areas.

  • Castors

    The load bearing castors have rubber tyres and poor axles (can be seen in picture below). As the dome rotates, the rubber tyre resists changing direction, making a loud skid noise as the dome turns and creates an unnecessary force to overcome this. Also the castor wheels axles are very worn and are not up to the job.

    Keith is to look for alternative castors which have both a nylon wheel and a ball race bearing for its axle. www.blickle.co.uk have such wheels which can support 150kg! Replacing them with this type of wheel will reduce noise, friction between the wheel and the surface of the dome ring is far less as they change direction, and this wheel will turn more easily about its axle.

  • Dome ring surface

    The dome ring is made up of 4 quarter circle segments. The castor wheel runs on the top surface of the ring but where the segments join there is a bump due to a difference in heights of the segments. Although the wheel can negotiate these bumps with some force, it prevents the dome from running smoothly and potentially make it difficult for the drive motor to move the wheel over the bump if the wheel starts next to it.

    These bumps need to be levelled out by filing or packing out with some kind of epoxy filler.

Martin Crow took some measurements and offered up a spare piece of dome ring upriser under the top surface of the dome ring to assess how a duplex drive chain can be fixed so that a sprocket connected to motor can run along it to pull the dome round. He hopes to produce a pattern so that pieces of wood could be cut to achieve this.

Saturday 20 June 2015

A team of members successfully helped remove the old wheels and replace them with new ones. This was achieved by having four people lift the dome whilst two others placed two planks across the dome ring, allowing the dome to be placed on them and so provide an excellent platform to work on the wheels.

All 12 of the old wheels were removed and many were in a sorry state. They either had a rusty bearing or had their spindles bent, in some cases so bad, that the wheel was in contact with the dome wall and so unable to turn.

One of the old wheels can be seen fixed to the dome in the photo below (the lower small horizontal one).

Domes Wheels -old.png

The new 40mm diameter wheels (RNP40) were obtained from www.rollingcenter.co.uk.

Dome Wheels.png

Here is a picture of one of the new wheels installed. 35mm M10 stainless screws, nylon nuts and washers from Screwfix were used for fixing them.

Dome NewWheel.jpg

Only 5 were installed as 7 wheels were still on back order and had not arrived on time. Still, with the 5 installed wheels, the dome was much easier to turn and it was clear that a motor should be able to turn it. However, with so few wheels, the dome was flexing a lot and it was obvious that all 12 wheels would need to be installed, so another similar session will be required.

Many thanks to Honor Wheeler, Andy Barber, David Grist, David Freed, Steve Goldson, Janice McClean, Diane Clarke, Bob Byrne and Keith Rickard for all their help.

Click here to see more photos of the day.

(22 June 2015)


Current Ideas

DM001.jpg

Resources on the Internet

Here is a DIY solution which could be useful for us: http://geoastro.co.uk/dome_warn.htm

external image newdomerot0.jpg

A wiper motor is an ideal choice for rotating the dome - see this video:



Lots of ideas can be drawn from here:

http://www3.telus.net/northstar_observatory/services.htm







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CMHASD - Dome Motorisation