I'm running an evening class for wannabe machinists, starting in September. One of the would-be master craftsmen asked a question about Stirling engines, which then segued into the little beast shown above (click on the picture for a larger view). For those who know their Stirling engines, it's a 'Ringbom' type that uses air pressure to move air between the hot and cold sides of the displacer rather than running the two pistons off a common crank arrangement.Actually, it's probably a little complex to use for assessment pieces (not least because it's only around two inches high) - the qualification is at 'level 2' which is sort of equivalent to GCSE. That said, I'm hoping there'll be plenty of time available during the year and we can build one anyway. If we do, I'll re-engineer it (lets just say the person who designed it doesn't expect anyone trying to make it to have access to CNC machinery) for quicker manufacture.
Now back on with the car. I'm debating whether to install the spherical rod ends for the uprights in a pseudo-vertical or a pseudo-horizontal plane (by which I mean the axis of the hole). If I install them vertically, I'll have no issues with steering lock, but I might have articulation issues under bump. For a horizontal installation, it's vice-versa. I've been using the Aurora Bearings catalogue to try and make my choice and their rod ends would have around 35 degrees of articulation. If you look at yesterday's picture, you'll see that the joints are already relatively inclined, so I might have issues with wheel travel. I doubt that I'd need to use 35 degrees of articulation with turning. The tightest bend I know (the hairpin at Mallory) needs around 10 degrees of steering lock at the wheels to negotiate for a neutral steered car, which leaves plenty in reserve. I'll do some calculations and let you know the results.
2 comments:
So if even a basic Stirling engine would be considered advanced for the course, can you give an example of what would normally be produced?
(and there was me with a vision of a myriad of LTD engines being knocked out)
The assessment pieces include such things as your own tap wrench, a plumb bob, a mill stop, a pipe vice and some stepped blocks. It's not that the engine is beyond you, merely that you need a period of time getting the basics right and I couldn't guarantee that everyone would get the whole thing done in the time period. The course will equip you to make that on your own though.
BTW that one isn't an LTD - it uses an alcohol flame. The LTD ones are somewhat light on manufacturing...
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