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Mounting Conundrum, Revisited
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Tim Wescott
Nov 13, 2012, 2:28:04 PM11/13/12
to
OK, here it is again with more pictures and explanations. Sorry for
starting a new thread, but it seemed reasonable given that I did such a
poor job of getting the design problem stated in the last one.
I'm building a gizmo, which, for lack of a better name I'm calling a "fan
trainer". It consists of an arm about 30" long with a small DC motor and
propeller on one end, and a pivot and counterweight on the other. The
thing is pivoted on a frame which has a controller circuit board. The
controller monitors the motor current and the arm position, and drives
the motor voltage.
This isn't an executive toy that you sit back and watch move (that would
get old very fast). Rather, it is a platform to provide a series of
exercises for a student to tune the control system, and to do it in a way
that you can see and feel it working. I'd use it in conjunction with
seminars, and perhaps make it part of a "seminar at home" package.
So my larger problem is to manufacture this in small quantities (20 to
100 a year), and sell them at a reasonable price without losing my ass.
"Not losing my ass" translates to a total bill-of-materials cost of $50
or so, and if I could get it way lower then I'd just sell it for less and
increase my potential market.
My immediate problem is that the potentiometer that senses the arm
position is getting punched off of the board in shipping. The
potentiometer has a hole, through which you pass a 4mm shaft with a flat
milled into it. If you mill the flat so that you can easily pass the
shaft through the pot then the control is not smooth -- the arm hunts
across the rotational slop caused by the shaft rotating within the pot.
If you shim the flat for a snug fit (very very light press fit?) then
when you chuck the thing into a box and fly with it in checked baggage,
the pot gets punched off of the board, apparently by getting hit from
behind.
The shaft on which the arm pivots is restrained in the housing by a
couple of model airplane wheel collars. On the trip out, both of these
collars, and the arm, loosened on the shaft, and the pot was punched
out. On the return trip I loosened the arm and tied it to the back plate
of the frame -- the wheel collars were fine then, but the pot was still
punched out.
I really like that pot: it costs less than $2.00 for onsies (less,
obviously, in higher quantities), it has undetectably small friction, it
isn't noisy, and because it's board mounted it saves me from needing a
bunch of brackets which would just drive up my BOM cost. So any
alternative that involves not using the pot has to compete with that
price, and being practical to do in small quantities in an environment
where labor is not free.
So I'm thinking at this point that perhaps I just need to be happy with
what I have, and to warn people not to drop the thing off of a table or
to ship it without disassembling it first. But it would be nice if there
was a way to make it more robust (by isolating the pot from the shaft
somehow).
The best suggestion I got from the other thread, assuming that I can do
it cheaply, is to put a slit in the end of the shaft, so I basically have
a D-shaped shaft with some spring. I would like that idea a lot if I
knew what it would cost to have a batch of 20 shafts made with the slit,
vs. without, and if that cost wasn't much greater than just making the
shafts.
The second-best suggestion is to use a flat coupling. This would require
(essentially) two shafts and the coupling, which is clearly going to
drive up the BOM cost, but I'm still toying with how to make it cheap.
Several people suggested reinforcing the mounting of the pot to the
board: it probably doesn't show in the pictures, but it is clear from the
construction of the thing that this would just result in _part_ of the
now-destroyed pot remaining on the board.
Here's a general arrangement shot:
https://docs.google.com/open?id=0B5lSHlBBxGvjX0MxMEM3b1l2c0k
And the thing in action:
https://docs.google.com/file/d/0B5lSHlBBxGvjX0MxMEM3b1l2c0k
And, finally, a close-up of the potentiometer in question:
https://docs.google.com/open?id=0B5lSHlBBxGvjcTBCc3VzWDYxZ0E
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
starting a new thread, but it seemed reasonable given that I did such a
poor job of getting the design problem stated in the last one.
I'm building a gizmo, which, for lack of a better name I'm calling a "fan
trainer". It consists of an arm about 30" long with a small DC motor and
propeller on one end, and a pivot and counterweight on the other. The
thing is pivoted on a frame which has a controller circuit board. The
controller monitors the motor current and the arm position, and drives
the motor voltage.
This isn't an executive toy that you sit back and watch move (that would
get old very fast). Rather, it is a platform to provide a series of
exercises for a student to tune the control system, and to do it in a way
that you can see and feel it working. I'd use it in conjunction with
seminars, and perhaps make it part of a "seminar at home" package.
So my larger problem is to manufacture this in small quantities (20 to
100 a year), and sell them at a reasonable price without losing my ass.
"Not losing my ass" translates to a total bill-of-materials cost of $50
or so, and if I could get it way lower then I'd just sell it for less and
increase my potential market.
My immediate problem is that the potentiometer that senses the arm
position is getting punched off of the board in shipping. The
potentiometer has a hole, through which you pass a 4mm shaft with a flat
milled into it. If you mill the flat so that you can easily pass the
shaft through the pot then the control is not smooth -- the arm hunts
across the rotational slop caused by the shaft rotating within the pot.
If you shim the flat for a snug fit (very very light press fit?) then
when you chuck the thing into a box and fly with it in checked baggage,
the pot gets punched off of the board, apparently by getting hit from
behind.
The shaft on which the arm pivots is restrained in the housing by a
couple of model airplane wheel collars. On the trip out, both of these
collars, and the arm, loosened on the shaft, and the pot was punched
out. On the return trip I loosened the arm and tied it to the back plate
of the frame -- the wheel collars were fine then, but the pot was still
punched out.
I really like that pot: it costs less than $2.00 for onsies (less,
obviously, in higher quantities), it has undetectably small friction, it
isn't noisy, and because it's board mounted it saves me from needing a
bunch of brackets which would just drive up my BOM cost. So any
alternative that involves not using the pot has to compete with that
price, and being practical to do in small quantities in an environment
where labor is not free.
So I'm thinking at this point that perhaps I just need to be happy with
what I have, and to warn people not to drop the thing off of a table or
to ship it without disassembling it first. But it would be nice if there
was a way to make it more robust (by isolating the pot from the shaft
somehow).
The best suggestion I got from the other thread, assuming that I can do
it cheaply, is to put a slit in the end of the shaft, so I basically have
a D-shaped shaft with some spring. I would like that idea a lot if I
knew what it would cost to have a batch of 20 shafts made with the slit,
vs. without, and if that cost wasn't much greater than just making the
shafts.
The second-best suggestion is to use a flat coupling. This would require
(essentially) two shafts and the coupling, which is clearly going to
drive up the BOM cost, but I'm still toying with how to make it cheap.
Several people suggested reinforcing the mounting of the pot to the
board: it probably doesn't show in the pictures, but it is clear from the
construction of the thing that this would just result in _part_ of the
now-destroyed pot remaining on the board.
Here's a general arrangement shot:
https://docs.google.com/open?id=0B5lSHlBBxGvjX0MxMEM3b1l2c0k
And the thing in action:
https://docs.google.com/file/d/0B5lSHlBBxGvjX0MxMEM3b1l2c0k
And, finally, a close-up of the potentiometer in question:
https://docs.google.com/open?id=0B5lSHlBBxGvjcTBCc3VzWDYxZ0E
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Paul Drahn
Nov 13, 2012, 2:58:02 PM11/13/12
to
Paul
George Herold
Nov 13, 2012, 3:00:46 PM11/13/12
to
that is causing the failure... it gets pushed off the PCB. (lets call
it the Z-axis) Versus motion perpendicular to the rotation axis
which would push the pot in the plane of the pcb. So something that
allowed motion in Z-axis but coupled rotation... Will a spline cause
too much backlash? Maybe the right type of spring coupling two pieces
togehter... Something like the spring used in a retractable pen?
George H.
Tim Wescott
Nov 13, 2012, 3:50:14 PM11/13/12
to
The thing in action:
https://docs.google.com/open?id=0B5lSHlBBxGvjX0MxMEM3b1l2c0k
Tim Wescott
Nov 13, 2012, 3:50:34 PM11/13/12
to
https://docs.google.com/open?id=0B5lSHlBBxGvjX0MxMEM3b1l2c0k
Tim Wescott
Nov 13, 2012, 3:51:58 PM11/13/12
to
If I lucked out and found one, a spring that grips the shaft would be
easy to assemble; since the torque on the pot is low it may even work...
Paul Drahn
Nov 13, 2012, 3:55:03 PM11/13/12
to
circuit board so as to act as a second regular bearing and a thrust
bearing. Any "Z" motion of the shaft would be restrained by the dummy pot.
Paul
rangerssuck
Nov 13, 2012, 4:14:02 PM11/13/12
to
This is a pretty neat training gizmo for control loops. Sort of like the ball balancer, but better.
Tim Wescott
Nov 13, 2012, 4:47:14 PM11/13/12
to
For that matter, I really wanted to do an inverted pendulum -- but I
couldn't see how to do the mechanism cheaply.
The wheel collars stayed tight on the flight home, yet the pot was still
punched off the board. Not by as far -- but all leads broken is still
all leads broken. I suspect that any sort of collar that rides close to
the board to limit travel in that direction will either rub or have too
much play to be safe -- but I could be wrong.
At this point what I see is a choice between some rotational slop between
shaft and pot (which messes up the educational value of the thing), the
current setup (which leaves it fragile, but possibly manageably so), some
sort of a flex coupling or spring (assuming I can figure out how to do
that well and cheaply), or some sort of a spring-loaded means of holding
the shaft-pot joint to be snug in rotation, but still low friction to
axial motion.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Paul Drahn
Nov 13, 2012, 5:11:17 PM11/13/12
to
>>>
>>> http://www.wescottdesign.com
>>
>> I think you ought to focus on *why* the wheel collars loosened. I am
>> assuming that had they stayed secure on the shaft that the pot would
>> have survived. If that is a correct assumption, how about a dimple in
>> the shaft for the setscrew, or perhaps some loctite?
>>
>> This is a pretty neat training gizmo for control loops. Sort of like the
>> ball balancer, but better.
>
> I considered doing a ball balancer, but I figured this would cost less.
>
> For that matter, I really wanted to do an inverted pendulum -- but I
> couldn't see how to do the mechanism cheaply.
>
> The wheel collars stayed tight on the flight home, yet the pot was still
> punched off the board. Not by as far -- but all leads broken is still
> all leads broken. I suspect that any sort of collar that rides close to
> the board to limit travel in that direction will either rub or have too
> much play to be safe -- but I could be wrong.
>
> At this point what I see is a choice between some rotational slop between
> shaft and pot (which messes up the educational value of the thing), the
> current setup (which leaves it fragile, but possibly manageably so), some
> sort of a flex coupling or spring (assuming I can figure out how to do
> that well and cheaply), or some sort of a spring-loaded means of holding
> the shaft-pot joint to be snug in rotation, but still low friction to
> axial motion.
>
If this was "checked" luggage instead of carry-on, then suspect the bag
>>> http://www.wescottdesign.com
>>
>> I think you ought to focus on *why* the wheel collars loosened. I am
>> assuming that had they stayed secure on the shaft that the pot would
>> have survived. If that is a correct assumption, how about a dimple in
>> the shaft for the setscrew, or perhaps some loctite?
>>
>> This is a pretty neat training gizmo for control loops. Sort of like the
>> ball balancer, but better.
>
> I considered doing a ball balancer, but I figured this would cost less.
>
> For that matter, I really wanted to do an inverted pendulum -- but I
> couldn't see how to do the mechanism cheaply.
>
> The wheel collars stayed tight on the flight home, yet the pot was still
> punched off the board. Not by as far -- but all leads broken is still
> all leads broken. I suspect that any sort of collar that rides close to
> the board to limit travel in that direction will either rub or have too
> much play to be safe -- but I could be wrong.
>
> At this point what I see is a choice between some rotational slop between
> shaft and pot (which messes up the educational value of the thing), the
> current setup (which leaves it fragile, but possibly manageably so), some
> sort of a flex coupling or spring (assuming I can figure out how to do
> that well and cheaply), or some sort of a spring-loaded means of holding
> the shaft-pot joint to be snug in rotation, but still low friction to
> axial motion.
>
was x-rayed, and the inspector removed the items to play with it and
broke it. then replaced it in your luggage.
Paul
Tim Wescott
Nov 13, 2012, 5:46:49 PM11/13/12
to
I don't think I have any excuses there: it was a combination of my
design, my packing, and a normal level of knocking around from the
airline.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
George Herold
Nov 13, 2012, 5:49:12 PM11/13/12
to
>
> - Show quoted text -
I was thinking of your issue, (boring day at work...testing testing
testing) So it's always good to think about a problem, "from the
other side". Which in this case led me to think that if the pcb was
light enough, you could add some spings (in the z-direction) where the
pcb mounts to the resot of the apparatus.
George H.
Jim Wilkins
Nov 13, 2012, 5:55:15 PM11/13/12
to
"Tim Wescott" <t...@seemywebsite.please> wrote in message
news:qo-dna9a1_x_Ij_N...@web-ster.com...
http://www.dynapar.com/uploadedFiles/_Site_Root/Technology/White_Papers/Encoder%20Mounting%20WP.pdf
#3, Direct mount with tether. The tether might be the connecting
wires.
jsw
news:qo-dna9a1_x_Ij_N...@web-ster.com...
#3, Direct mount with tether. The tether might be the connecting
wires.
jsw
rangerssuck
Nov 13, 2012, 6:02:26 PM11/13/12
to
Tim Wescott
Nov 13, 2012, 6:04:58 PM11/13/12
to
assumptions: the pot _doesn't_ have bearings, and by construction its
designed to be soldered onto the board.
Tim Wescott
Nov 13, 2012, 6:06:29 PM11/13/12
to
surface-mount part, so mounting it as designed is very quick while
mounting it just about any other way isn't so.
George Herold
Nov 13, 2012, 6:29:41 PM11/13/12
to
>
> - Show quoted text -
How about a thermal thing for control loop education?
> - Show quoted text -
TEC, air fin heatsink, heater as variable load, maybe a couple of
sensors. It'd be nice to have variable thermal 'lengths' in the
system.
(More than $50 though I'd guess.)
George H.
mike
Nov 13, 2012, 7:20:32 PM11/13/12
to
On 11/13/2012 1:47 PM, Tim Wescott wrote:
>>>
>>> http://www.wescottdesign.com
>>
>> I think you ought to focus on *why* the wheel collars loosened. I am
>> assuming that had they stayed secure on the shaft that the pot would
>> have survived. If that is a correct assumption, how about a dimple in
>> the shaft for the setscrew, or perhaps some loctite?
>>
>> This is a pretty neat training gizmo for control loops. Sort of like the
>> ball balancer, but better.
>
> I considered doing a ball balancer, but I figured this would cost less.
>
> For that matter, I really wanted to do an inverted pendulum -- but I
> couldn't see how to do the mechanism cheaply.
>
> The wheel collars stayed tight on the flight home, yet the pot was still
> punched off the board. Not by as far -- but all leads broken is still
> all leads broken. I suspect that any sort of collar that rides close to
> the board to limit travel in that direction will either rub or have too
> much play to be safe -- but I could be wrong.
>
> At this point what I see is a choice between some rotational slop between
> shaft and pot (which messes up the educational value of the thing), the
> current setup (which leaves it fragile, but possibly manageably so), some
> sort of a flex coupling or spring (assuming I can figure out how to do
> that well and cheaply), or some sort of a spring-loaded means of holding
> the shaft-pot joint to be snug in rotation, but still low friction to
> axial motion.
>
How about this?
>>> http://www.wescottdesign.com
>>
>> I think you ought to focus on *why* the wheel collars loosened. I am
>> assuming that had they stayed secure on the shaft that the pot would
>> have survived. If that is a correct assumption, how about a dimple in
>> the shaft for the setscrew, or perhaps some loctite?
>>
>> This is a pretty neat training gizmo for control loops. Sort of like the
>> ball balancer, but better.
>
> I considered doing a ball balancer, but I figured this would cost less.
>
> For that matter, I really wanted to do an inverted pendulum -- but I
> couldn't see how to do the mechanism cheaply.
>
> The wheel collars stayed tight on the flight home, yet the pot was still
> punched off the board. Not by as far -- but all leads broken is still
> all leads broken. I suspect that any sort of collar that rides close to
> the board to limit travel in that direction will either rub or have too
> much play to be safe -- but I could be wrong.
>
> At this point what I see is a choice between some rotational slop between
> shaft and pot (which messes up the educational value of the thing), the
> current setup (which leaves it fragile, but possibly manageably so), some
> sort of a flex coupling or spring (assuming I can figure out how to do
> that well and cheaply), or some sort of a spring-loaded means of holding
> the shaft-pot joint to be snug in rotation, but still low friction to
> axial motion.
>
http://www.chinajiaho.com/6-in-1-diy-educational-robot-solar-kit_p1763.html
Start with the configuration that rotates around the vertical pole.
put two solar cells back to back. It should track a focused light
source around the circle. If the dead zone is too big, put the cells in
series in a bridge and the motor in a full-bridge and chop the power into
a fan voltage that nulls the input bridge.
Costs you $8 for the toy and the one you stole the other solar cell
from. Free shipping.
If you can stand the dead zone, you have a very tight visual coupling
between the sensor and the positioning mechanism. And you don't need
batteries or electronics or nothin'. It just works.
There will be balance issues.
Lots of other possibilities with all the kit parts.
Use the car configuration for your inverted pendulum.
The pot thing is a loser until you use one with a bearing that can
support the weight and the abuse of shipping and students.
I'd try to put the fan on the bottom, out of harm's way and use
something light, like a soda straw out the top for an indicator.
Are we having fun yet?
Tim Wescott
Nov 13, 2012, 7:26:42 PM11/13/12
to
On Tue, 13 Nov 2012 15:29:41 -0800, George Herold wrote:
> How about a thermal thing for control loop education?
>
> TEC, air fin heatsink, heater as variable load, maybe a couple of
> sensors. It'd be nice to have variable thermal 'lengths' in the system.
> (More than $50 though I'd guess.)
>
> George H.
I'm thinking of doing something like that next. There's not much visual
> How about a thermal thing for control loop education?
>
> TEC, air fin heatsink, heater as variable load, maybe a couple of
> sensors. It'd be nice to have variable thermal 'lengths' in the system.
> (More than $50 though I'd guess.)
>
> George H.
interest there (unless I can do something cool with liquid crystal
thermometers), but I think I could get it below $50 and it'd be of
interest to someone who happens to be living and breathing thermal
control when they set out to learn the stuff.
Dennis
Nov 13, 2012, 9:56:30 PM11/13/12
to
"Tim Wescott" <t...@seemywebsite.com> wrote in message
news:ptSdnWNU6KzZAj_N...@web-ster.com...
rubber / nylon beverage tube / or even a tight wound light spring to couple
the shaft into the pot.
rangerssuck
Nov 14, 2012, 12:12:23 AM11/14/12
to
On Tuesday, November 13, 2012 6:06:29 PM UTC-5, Tim Wescott wrote:
> On Tue, 13 Nov 2012 15:02:26 -0800, rangerssuck wrote:
>
[trimmed]
> On Tue, 13 Nov 2012 15:02:26 -0800, rangerssuck wrote:
>
>
> > How about mounting the pot semi-ridgedly on kinked or s-bent pieces of
> > bus wire? Pretty much free (except for 30 seconds or so of extra
> > assembly) and easily repairable. If the pot really has very low
> > rotational friction, the wires shouldn't bed in normal usage, but will
> > give enough to prevent damage. You could even try some springy piano
> > wire.
>
> Hmm. Good thought, but it'd take a lot more than 30 seconds. It's a
> surface-mount part, so mounting it as designed is very quick while
> mounting it just about any other way isn't so.
If you mount the pot on a separate little board, it would be easy. If you're making printed circuit boards, just add the little pot board to the layout with either a score line or a tab route separating them. If you're going to breadboard this (as in your photos), just make up a bunch of little boards that hold nothing but the pot and four mounting wires.
> > How about mounting the pot semi-ridgedly on kinked or s-bent pieces of
> > bus wire? Pretty much free (except for 30 seconds or so of extra
> > assembly) and easily repairable. If the pot really has very low
> > rotational friction, the wires shouldn't bed in normal usage, but will
> > give enough to prevent damage. You could even try some springy piano
> > wire.
>
> Hmm. Good thought, but it'd take a lot more than 30 seconds. It's a
> surface-mount part, so mounting it as designed is very quick while
> mounting it just about any other way isn't so.
IIRC, you were talking about small (20-100/year) quantities. Even if it took an extra three minutes per assembly (which it won't), you're only talking 1 - 5 hours PER YEAR. I personally have probably a half hour into this project already, between reading and writing.
Just sayin'
George Herold
Nov 14, 2012, 10:12:32 AM11/14/12
to
On Nov 13, 7:26 pm, Tim Wescott <t...@seemywebsite.com> wrote:
> On Tue, 13 Nov 2012 15:29:41 -0800, George Herold wrote:
> > How about a thermal thing for control loop education?
>
> > TEC, air fin heatsink, heater as variable load, maybe a couple of
> > sensors. It'd be nice to have variable thermal 'lengths' in the system.
> > (More than $50 though I'd guess.)
>
> > George H.
>
> I'm thinking of doing something like that next. There's not much visual
> interest there (unless I can do something cool with liquid crystal
> thermometers), but I think I could get it below $50 and it'd be of
> interest to someone who happens to be living and breathing thermal
> control when they set out to learn the stuff.
Yeah, I have no 'showy' thermal thing to control. But that's not so
> On Tue, 13 Nov 2012 15:29:41 -0800, George Herold wrote:
> > How about a thermal thing for control loop education?
>
> > TEC, air fin heatsink, heater as variable load, maybe a couple of
> > sensors. It'd be nice to have variable thermal 'lengths' in the system.
> > (More than $50 though I'd guess.)
>
> > George H.
>
> I'm thinking of doing something like that next. There's not much visual
> interest there (unless I can do something cool with liquid crystal
> thermometers), but I think I could get it below $50 and it'd be of
> interest to someone who happens to be living and breathing thermal
> control when they set out to learn the stuff.
important from my perspective. I’d be more interested in the control
details, different control loops, different source detector distances
(materials) So that thermal diffusion effects could be seen.
It would be really nice to have different cooling sources.
(TEC and air fins and then a heater and some sort of cryogen. But the
cryogen part looks more expensive.. (CFC’s are out), or dangerous,
(boiling water)
Do you mind if I ask whom you think you might sell this to?
Add on labs for your book? Engineering schools?
Does the $50 include all the electronics?
(you can always reply in private... gherold@teachspin (dot) com)
George H.
Tim Wescott
Nov 14, 2012, 4:54:58 PM11/14/12
to
language wunnerful?
When things are going well, the pot does not support the shaft in any way
-- there are bearings that support the shaft. The pot should only be
there to read position.
DoN. Nichols
Nov 14, 2012, 7:48:41 PM11/14/12
to
On 2012-11-13, Tim Wescott <t...@seemywebsite.please> wrote:
> On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:
>
>> On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:
[ ... ]
> On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:
>
>> On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:
>>> Several people suggested reinforcing the mounting of the pot to the
>>>
>>> board: it probably doesn't show in the pictures, but it is clear from
>>> the
>>>
>>> construction of the thing that this would just result in _part_ of the
>>>
>>> now-destroyed pot remaining on the board.
> The wheel collars stayed tight on the flight home, yet the pot was still
> punched off the board. Not by as far -- but all leads broken is still
> all leads broken. I suspect that any sort of collar that rides close to
> the board to limit travel in that direction will either rub or have too
> much play to be safe -- but I could be wrong.
that it is not actually the lever's mass which is the problem, but
instead the length and spring constant of the leads, and the mass of the
pot, happening to resonate at a frequency which matches that of
vibration present in the aircraft. Just for the fun of it, try a second
pot on the board with no lever attached during transist.
Good Luck,
DoN.
--
Remove oil spill source from e-mail
Email: <BPdnic...@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Tim Wescott
Nov 15, 2012, 1:11:08 PM11/15/12
to
On Thu, 15 Nov 2012 00:48:41 +0000, DoN. Nichols wrote:
> On 2012-11-13, Tim Wescott <t...@seemywebsite.please> wrote:
>> On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:
>>
>>> On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:
>
> [ ... ]
>
>>>> Several people suggested reinforcing the mounting of the pot to the
>>>>
>>>> board: it probably doesn't show in the pictures, but it is clear from
>>>> the
>>>>
>>>> construction of the thing that this would just result in _part_ of
>>>> the
>>>>
>>>> now-destroyed pot remaining on the board.
>
> [ ... ]
>
>> The wheel collars stayed tight on the flight home, yet the pot was
>> still punched off the board. Not by as far -- but all leads broken is
>> still all leads broken. I suspect that any sort of collar that rides
>> close to the board to limit travel in that direction will either rub or
>> have too much play to be safe -- but I could be wrong.
>
> Hmm ... one possibility which I have not yet seen mentioned is
> that it is not actually the lever's mass which is the problem, but
> instead the length and spring constant of the leads, and the mass of the
> pot, happening to resonate at a frequency which matches that of
> vibration present in the aircraft. Just for the fun of it, try a second
> pot on the board with no lever attached during transist.
The pot is plastic, probably weighs less than a gram, and it's surface
> On 2012-11-13, Tim Wescott <t...@seemywebsite.please> wrote:
>> On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:
>>
>>> On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:
>
> [ ... ]
>
>>>> Several people suggested reinforcing the mounting of the pot to the
>>>>
>>>> board: it probably doesn't show in the pictures, but it is clear from
>>>> the
>>>>
>>>> construction of the thing that this would just result in _part_ of
>>>> the
>>>>
>>>> now-destroyed pot remaining on the board.
>
> [ ... ]
>
>> The wheel collars stayed tight on the flight home, yet the pot was
>> still punched off the board. Not by as far -- but all leads broken is
>> still all leads broken. I suspect that any sort of collar that rides
>> close to the board to limit travel in that direction will either rub or
>> have too much play to be safe -- but I could be wrong.
>
> Hmm ... one possibility which I have not yet seen mentioned is
> that it is not actually the lever's mass which is the problem, but
> instead the length and spring constant of the leads, and the mass of the
> pot, happening to resonate at a frequency which matches that of
> vibration present in the aircraft. Just for the fun of it, try a second
> pot on the board with no lever attached during transist.
mount, so the leads are short and stiff.
I think there'd be other things falling off the board in vibration severe
enough to cause problems with the pot.
Baron
Nov 15, 2012, 5:54:49 PM11/15/12
to
Hi Tim,
Interesting concept :-)
Just an idea.
Mount the boom in the center of a thin, broad flexible strip of spring
steel. Make a quadrant with a line of perforations on the edge and use
a pair of slot photo detectors, a bit like the slotted wheel in a ball
mouse to detect the movement. This would do away with the pot and a
cheap mouse IC could do the rest. You could even use flexible pcb on
the strip of spring steel to provide power to the fan motor.
--
Best Regards:
Baron.
Interesting concept :-)
Just an idea.
Mount the boom in the center of a thin, broad flexible strip of spring
steel. Make a quadrant with a line of perforations on the edge and use
a pair of slot photo detectors, a bit like the slotted wheel in a ball
mouse to detect the movement. This would do away with the pot and a
cheap mouse IC could do the rest. You could even use flexible pcb on
the strip of spring steel to provide power to the fan motor.
--
Best Regards:
Baron.
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