Hatch control (1)- Alas the Windlass

As mentioned earlier lifting and lowering the main hatch manually proved difficult from the start because of the height of the roof and the poor mechanical advantage obtained when trying to drag the lid against gravity from its fully open position. Furthermore, controlling its free  descent to its closed position when past the meridian required a substantial braking force to counteract gravity once again.

My first attempt at mechanizing the main shutter employed a windlass and some heavy steel cable. In theory the cable would be attached to the shutter and conducted to a windup barrel in a continuous loop much like the old transistor radio sliding  frequency pointer used to have.  For this purpose I constructed a steel cylinder reel with two compartments and mounted horizontally on a frame inside roller bearings. . Turning this would wind the steel cable on one side of the reel while unwinding it from the other side thus enabling a controlled movement of the steel wire  anchoring point on the hatch. 

A temporary winding arm was added that would later be replaced by an electric motor .  Well so much for the theory…

In practice the device proved a frustratingly infuriating absolute waste of time!!!! Contrary to what you may think from reading these chapters I am not generally known for my patience and this infernal creation of mine nearly drove me to the brink! The steel wire showed no sign of cooperating and insisted on curling, knotting, twisting, crossing over itself, jumping lanes… you name it …it tried it! Another consideration was the hazard it would pose to the user (me!) should the steel cable or some anchoring point snap under stress!

Back to the drawing board, and this time I changed tack and decided I’d go for a chain-driven system that would allow forward and back movements controlled by motor driven sprocket wheels.  A visit to a friendly neighbourhood cycle shop rewarded me with two used-but-in-good-condition ½ inch 7-cog gear cassettes.

I dismantled one of the cassettes using WD40, heat and lots of  ‘axle grease’.  Naturally the individual cogs having been designed to fit over each other and around a common hub, needed to have their centres filled in before they could be used individually as cogwheels over a shaft. 

Having measured their internal diameter with a caliper I proceeded to cut circular discs  out of  a scrap piece of thick  steel sheeting to fit the inside of the cogs.  This was done using a metal jigsaw making sure the initial rough cut was somewhat larger  to allow for a more accurate sizing and shaping later.

An 8 mm bolt was driven through the centre of the discs and secured by means of a locknut and this was then mounted in  a slow speed vertical drill and  the final rounding off and size reduction performed with the drill turning and the edges rubbing against a hand held grinding wheel. (I must emphasise that this proced ure is fraught with danger and  it is very easy to injure oneself unless using full hand and eye protection as well as a suitable leather apron.  The spinning edges of the metal disc are as sharp as razor blades and fragments of grinder wheel can fly off and end up anywhere!! It provides a poor man’s alternative to a lathe but with proper care and precautions and frequent caliper checks of the diameter, one ends up with very acceptable steel discs complete with central bore. Indeed the discs were so well fitting that I had to actually hammer most of them in place! I repeated this for several of the cogs scavenged from the cassette and then proceeded to braze them in place using my trusty propane/oxygen torch and brass rods.

One of the smaller discs can be seen fitted inside one of the cogs of the set below.

2015-09-10 19.05.292015-09-10 19.04.49

This way, at budget price  I procured seven very usable cogwheels that provided me with an assortment of ratios to try out when it came to decide which ones to use to drive the canopy control.

I decided to buy the bicycle chain new and I resorted to a UK very comprehensive cycle store and got three full lengths of this sent 

http://www.chainreactioncycles.com/mt/en/kmc-z410-1-8-chain/rp-prod120670

I received these by post very rapidly and proceeded to test for proof of concept. I built a mount for a 12V DC low gear motor, one of several cheap chinese imports I bought on ebay and rigged this up. The other sprocket wheel in the picture was used as a free wheeling take up spool mounted on an 8mm shaft. A length of chain was strung up around the two gears and the system tested for traction.

Flying colours! 

2015-09-14 15.49.35

 

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