Jump to content

SkySurveyBanner.jpg.21855908fce40597655603b6c9af720d.jpg

Gina's Observatory Roll-Off-Roof Automation


Gina

Recommended Posts

This diagram shows the roof open.  It's a bit more accurate than the previous diagram showing the roof open :D  Pulleys and sprockets shown in black and grey, chain in blue and chain end attachments in red.  The roof toggle clamp is in light grey.  The "pull closed" chain section will go between the parts (I think).

post-13131-0-89956300-1419698241_thumb.j

I'll need to do some proper measuring up as a quick estimate comes out at just over 5 bicycle chains.

Edited by Gina
Link to comment
Share on other sites

Why not fix the chain to the top roof directly between the two red marks. Then the pulley would drive the roof open by engaging in the chain. The pulley could be sprung loaded to push up against the chain.

Now you could have the pulley on a torson bar to the other side of the shed where another chain and pulley are, like a sort of 'parallel motion', you now you have both sides driven.

A release of some sorts could be arranged to lower the pulleys to disconnect from the chain and allow manual closure/opening.

Link to comment
Share on other sites

Unfortunately that would not give quite enough movement of the roof, unless I can arrange one end or the other to go beyond the roof ends.  Also, that pulley is in the gap between the partition wall and the scope room south wall though it could possibly be two sprockets back to back with the second being driven by chain from the motor in a different position.

It was actually the first idea I had - to drive a chain (like a rack) fixed to the roof.

Edited by Gina
Link to comment
Share on other sites

Actually, 5 bicycle chains won't exactly break the bank :D

I think 5 would cover it - length of roof is 2.2m, so 3 times that is 6.6m then add a bit more for going round the pulleys etc.   If a chain is about 1.4 m then 5 of them would be 7m which leaves 400mm extra for the pulleys.  Link here

post-13131-0-42340400-1419704947_thumb.j

Edited by Gina
Link to comment
Share on other sites

I'm now printing out a 15 tooth bicycle chain sprocket to see what it's like - ah - finished :D  It's half scale I think :confused:

OK going again with scaling x2 :)  Looks better ...

post-13131-0-88040100-1419707670.jpg

Edited by Gina
Link to comment
Share on other sites

This sprocket actually looks somewhere near the riight size to be fitted to the winch drum.  It would need boring out to fit the bottom of the drum and cut in half to be fitted.  Alternatively I could dismantle the winch and use the lathe to remove one flange.  Then the sprocket would not need cutting in half - it could go straight on.  It could be bolted to the remaining flange with spacers.

Actually, I think I'll look into producing my own sprocket then I can make the boss bigger and longer and the hole bigger.

Edited by Gina
Link to comment
Share on other sites

Here are some photos of the winch and the drum.

post-13131-0-81094100-1419713665_thumb.j

Drum removed

post-13131-0-48337200-1419713672_thumb.j

Drum removed with knob replaced

post-13131-0-13336000-1419713669_thumb.j

Knob pulled out and turned to release the clutch

post-13131-0-63314700-1419713675_thumb.j

Dog clutch in disengeged position

post-13131-0-45310800-1419713680_thumb.j

Dog clutch in engaged position

post-13131-0-16905500-1419713685_thumb.j

Failed printout of the sprocket - too much curl but good enough to show the size.  Here shown placed on the winch drum.

post-13131-0-33035800-1419713690_thumb.j

Edited by Gina
Link to comment
Share on other sites

Well, if I could find a reasonably priced reversible motor I'd use it.  Maybe I'll measure the pull force required to move the roof tomorrow but it's nothing like that as I can quite easily move it by hand.  I would like to use a smaller and lighter motor (and a less noisy one!!).  Wonder if there's a stepper motor strong enough :D

Link to comment
Share on other sites

This NEMA 23 gives 12.6Kgcm torque which seems more than enough.  By my calculation, with the sprocket I've just printed of 3cm radius I should get a pull of 4.2Kg :eek:   That's ridiculous.

Later...  Seems the bog standard NEMA 17 as used on 3D printers would be quite strong enough according to this link "Nema 17 Stepper Motor 4200 g.cm"

Edited by Gina
Link to comment
Share on other sites

I still say get the garage door motor with chain sprocket and clutch. It moves very slowly and works very well, and it is quite cheap. Also, no need to run the chain in a loop - one way will suffice. I'll ask Olly to shoot some images of our's when the weather clears.

/per

Link to comment
Share on other sites

Details? Motor, 18V DC, gearbox, total torque on 18V is 900 N, i.e. can lift around 90 kg. At 12V it is just right for roofs. Clutch, simple to operate, bicycle chain sprocket as final drive.

The garage door opener as a complete product is called the Sommer Marathon 1100. I simply bought the motor carriage as a spare part. The part was SEK 1862 and the freight to Olly's was SEK 280. If you buy from them you may need to pay VAT, but we can probably fix that for you. The price given is as per May 8th this year.

http://www.sommer.eu/en/marathon-sl.html

As you see on that page, the unit is available in three different "strengths". With our four pier, 4 x 5 m observatory, I figured the biggest. You can get the medium one. Check it out.

/per

Link to comment
Share on other sites

Details? Motor, 18V DC, gearbox, total torque on 18V is 900 N, i.e. can lift around 90 kg. At 12V it is just right for roofs. Clutch, simple to operate, bicycle chain sprocket as final drive.

The garage door opener as a complete product is called the Sommer Marathon 1100. I simply bought the motor carriage as a spare part. The part was SEK 1862 and the freight to Olly's was SEK 280. If you buy from them you may need to pay VAT, but we can probably fix that for you. The price given is as per May 8th this year.

http://www.sommer.eu/en/marathon-sl.html

As you see on that page, the unit is available in three different "strengths". With our four pier, 4 x 5 m observatory, I figured the biggest. You can get the medium one. Check it out.

/per

Thank you Per :)  Looks very interesting. 

I've just been out and connected up rope and digital scales to measure the pull required.  To start the roof from fully closed with the anit-lift pegs engaged it took 26Kg but a lot less once the pegs were disengaged.  Also, I expect to get the roof running easier.  As it's the maximum force required that matters, I didn't stop to measure the half open moving force but I can move it with one finger once it's moving. 

Looking at those garage opener motors, I would think the smallest at 550N would be quite adequate.  550N corresponds to about 55Kg, over twice the pull required for my roof.

Could you find out how much the 550N motor would cost, please?  Also, the dimensions.  The 800N garage door opener I bought is huge (300x220x100mm approx) though the motor itself is much smaller.  But it doesn't have a clutch :(

Overall, I think I would prefer to get the motor you suggest as it has a clutch and is 12v so much more convenient.  That is if you would be happy to arrange it :)

post-13131-0-67044900-1419781070_thumb.j

Edited by Gina
Link to comment
Share on other sites

I'll check it out tomorrow... But do take the middle one. The motors are 18V and run so nicely and calmly at 12V, albeit with somewhat less torque.

I am currently running H-bridge tests for roof motor control... Looking good!

/per

Edited by perfrej
  • Like 1
Link to comment
Share on other sites

Hi Gina,

Which ever way you do it incorporate circuit breakers/switches in the  winch power line. With any winch of that type it has a massive power or pull and could easily rip everything to bits if the controller stuck in the on position. So I suggest two microswitches at each end in serial. They can be change over types. If one fails because of damage or damp the other will cut the power. I once watched an overhead crane rip fittings off a tank for such a reason. Thousands of pounds damage! If you can get pressure sensitive strip even better as it should prevent finger/telescope damages.

Best of luck,

Derek

  • Like 1
Link to comment
Share on other sites

My H-bridge design is coming along nicely and I now have firmware for full motor control and am working on speed sensing. The idea is to make sure that the roof rolls at an even speed regardless of temporary fluctuations in load. I'll implement a PID, I think, to regulate everything.

/per

  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.