Probably the mistaken presumption of a shared understanding that the role of
the gears in precisely positioning the work implies a free turning, backlash
free mechanism. ;) I think I would have just cut a hob on the knee mill and
made the plywood gears that way. Very little drawing or figuring involved,
obviating the obvious problems.
My apologies - I was experiencing an adversity/frustration overload and
shouldn't have posted anything anywhere...
...and MikeWhy was right that one of the headaches involved backlash in
a trough-type reflector tracking mechanism subject to (mostly)
unpredictable wind loading.
I haven't actually ever made a hob, but know of the general principles. If
your gears are non-metallic, wood or GRP, the problem might be even simpler.
Better still, if the geartrain is a worm gear, a simple tap -- the things
used to cut internal threads -- are perfectly serviceable hobs for cutting
the worm wheel.
Your suggestion is appreciated, but this thing needs to be thermally
driven (as opposed to motor driven) - and if I need to use a geared
approach, it will probably be a sliding rack with one or two simple spur
It's one of those problems that /seems/ like should have a simple and
inexpensive solution, but every attempt so far has led to unacceptable
complexity and/or cost.
Toothed belt? A la printhead on an inkjet? Bicycle sprocket
parts....VERY universal and cheap.
Those nodding oil pump things I see all over the country-side around
Your reciprocal motion on one end, the same, but fulcrummed (LOL) on
the other as a pump?
This comes closest to what I'm working on - except that that the power
source is solar heat. I think I can make it work with a flat panel, but
the efficiency (which translates into ROI here) goes way up if
high-temperature heat is used. That requires a collector aiming
mechanism to track the sun.
Recently I got a video of the first engine actually pumping water (not
doing a very good job yet, but still not bad for a first try) in Pakistan.
The sight glass on the piston shows the pump displacement, and the
pumped volume should match that. I think their problem is check valves
with too-strong springs.
The sun-tracker will, of course, need to make one (controlled) cycle per
day, and somehow (automagically) start out facing east in the morning.
That's an easy one. Expanding gas cylinder like the greenhouse people
use to open a vent. Hide it in the shadow of the collector itself, so
when the sun peeks around, it starts expanding till it creates its own
shadow again sortakinda like a wheatstone bridge but mechanical. When
the sun stops playing peek-a-boo with the cylinder at night, it is
brought home by its own collapse, perhaps helped by a counterweight/
The cylinder would sit lengthwise along the obvious edge. It could sit
in a slot in the collector itself for extra intensity. The mechanical
challenge is minimal.
Maybe something bi-metal?
I've been considering /two/ such gas cylinders (so that operation isn't
air temperature dependent) - one on each side of the collector, each
side connected to opposite ends/sides of a double-acting hydraulic or
pneumatic cylinder. That setup would allow for an eastward pressure bias
that would be overridden during the day, but would cause the tracker to
revert to east-pointing at night, pretty much as you describe.
The major drawback appears to be instability in gusty winds due to the
Maybe, but I think your first idea is a better match to the problem.
PV plus motor plus worm drive is certainly an attractive route, but too
expensive and not suited for local production and maintenance.
It needs to be really simple and so inexpensive that it's not worth
stealing. For context, rural Somalia might be one of the target "market"
Offhand I'm not sure how one would design such a thing but rather than using
shaft work could you pump water from one plastic bag to another, with
appropriate levers and paddles resting on top of the bags?
Maybe. I've been too involved in trying to help get the engine working
to worry about the tracking system until now. Nearly all of my past
experience with control systems has been digital, and I'm really in over
my head on this one.
It seems to me that if I can choose one side to pump to, then I should
be able to pump to a cylinder/piston linear actuator of some kind
(thinking of a reworked shock absorber or strut) to do that job.
Hmm - if I use robatoy's gas cylinder idea to control a valve to direct
part of the pump flow to one of your actuators, I might be on a better
track than I am now, even though I'll still need to figure out some
reliable way to make it face the morning sun without being vulnerable to
As though I/we needed taunting... ;) Give credit where credit is due. The
man's an obvious genius, and his workmanship is topnotch. I was about to
remark on replacing the gear drive with a DC servo motor, ground ballscrew,
and linear slides, but I see he already did one with a stepper. It wouldn't
take much to put a microcontroller on it to drive it without a PC. I have an
old AVR Butterfly sitting around unused...
Hmm - if you're going to do that, why not add a second motor to move the
stock over the blade too? Then you could do something else while it
makes the joint for you...
...and if you do that then you might as well add a third motor and build
so that it can make about any kind corner joint you can think of.
Pull out that Butterfly and a soldering pencil. :)
Everytime I see a Leigh jig, I think an X-Y table, and a router motor for
the spindle. One of these days, I'll actually do something about it. The
last time this came up, I ended up with a boxful of dozukis and waterstones
instead, which obviated the need (for the time being).
The single axis jig, as here in the box joint cutter, is a special case in
simplicity. It should work equally well on the router table, doing the job
of an Incra-style jig. The full set of Incra templates could reasonably be
stored in flash. The more I think about it, the simpler it seems and the
more generally useful (in the same way that an Incra jig is useful).
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