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'[EE]: What is the estimated torque ?'
2002\08\06@221900 by Pang

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Hi,

Thanks for suggestions and questions. It shows I have not been thinking
thoroughly on the method of implementation. First of all, the application I
will be building is going to be a tilt sensor. If you still recall, there's
a few thread on this subject not too long ago and someone actually suggested
using a potentiometer to measure the tilting by attaching a certain amount
of weight to the shaft. I think the name 'tilt sensor' is misleading.
Tilting here is not a 180 deg upside-down turn. It is meant to be installed
in an automotive to detect towing. As such, I think an angle sensor will be
a more appropriate name.

Thanks for highlighting  the different aspect of torque calculation. What I
intend to do is to attach a weighting to the shaft. The potentiometer is
fixed to a flat board. Whenever the board is raised at either side, the
weighting will move the shaft. The  weight that is atttached to the shaft
must be concentrated to a certain direction only, something like a pendulum.
Or let say the weighting is in the form of an arrow. The shaft will be
attached to the beginning of the arrow while the arrow will always point to
the gravity, assuming the end of the arrow is heavier than the beginning.

phew.... i hope you guys understand my kindergarden level of description...

I have enquire things like rotary encoder, position sensor, optical sensor
and angle sensor. But most of them are either costly or that they cannot
withstand much load to the shaft. It seems that the life of the ball bearing
will be greatly reduced. I am quite limited in my mechanical knowledge,
otherwise there are lot's of method of doing it.

> What will be turning the pot?          The weighting attached to the shaft

> Will it turn the pot directly, or is there a
> knob/attachment/lever/belt/pulley/etc on the pot?

The weighting will turn the pot directly ( that's the easiest method i could
think of )

> How much force is going to be applied to the point at which they (the
> pot and the other object) meet?

?

> Are you also going to be dealing with friction/slipping?
>
I was thinking that the weighting will be attached permanently to the shaft,
the weighting will not slip but the shaft will be turn according to gravity.

I have been searching for quite some time for a cheap solution (USD5 for the
potentiometer) but it seems not possible. The only way is still using the
accelerometer.

Thanks for the explanation of the fan, the torque and the different force
required.

Best rgds,
Pang

{Original Message removed}

2002\08\07@043242 by Dominic Stratten

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use a slotted disc (strip down an old mouse - there are the slotted discs
and phototransistors). Use the weight idea and just sense when the disc
moves. To make is less sensitive, use code or block up some of the notches.
I buy mice for less than a dollar wholesale so this is a much cheaper way of
doing it. Also consider using the speed pulse sender (if fitted - most
modern cars have them) on the car. The slightest movement of the wheels is
enough to give a pulse from one of these.

Just my 2 cents worth

Dominic

{Original Message removed}

2002\08\07@053906 by Roman Black

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Pang wrote:
>
> Hi,
>
> Thanks for suggestions and questions. It shows I have not been thinking
> thoroughly on the method of implementation. First of all, the application I
> will be building is going to be a tilt sensor.
> It is meant to be installed
> in an automotive to detect towing. As such, I think an angle sensor will be
> a more appropriate name.
>
>The potentiometer is
> fixed to a flat board. Whenever the board is raised at either side, the
> weighting will move the shaft.
> I have enquire things like rotary encoder, position sensor, optical sensor
> and angle sensor. But most of them are either costly or that they cannot
> withstand much load to the shaft.


I have a solution that is cheap, small, reliable and
"zero" torque. The only down side is that it will need
a calibration table in software.

Use a IR pair, a transmit/receive reflective pair as
found in VCRs etc. (Some are only about 3mm cube size)
Like this:

                      pin
                       *
                       |
                       |
  ,-------,            |
  |       |            |
  | IR    |==========> | White
  | pair  |            | surface
  |       |<========== |
  |       |            |
  |       |            |
  |       |            |
  '-------'            |
                 ,-----*-------,
                 |   Weight    |
                 |             |
                 '-------------'
             <----- swings ----->

(all under a light proof cover!)
The IR pairs can be attached to a PIC very easily, you
run the led at about 5mA and set the receive diode as
half of a voltage divider, and it will give an analogue
voltage somewhere between 0-5v as the device is tilted.
The voltage output is not linear, but can be calibrated
in software to give an easy 32 positions etc, which is
probably plenty?
:o)
-Roman

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2002\08\09@102836 by M. Adam Davis

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I would suggest the a pot is not the way to go then.  When the car is
accelerating and stopping the weight is going to swing.  The pot is
going to wear out very quickly.

As a proof of concept it is a good idea, but ultimately you'll want to
replace it with something which suffers less wear.

If you just want to measure tilt, use a slotted disc sensor with a
weight (easy o build).  When the car gets turned off the microcontroller
should save the current setting (in a slot or out).  If the car is
tilted then the weight will change the setting.

The nice thing about this is you don't have to remember analog voltages,
or even deal with what happens when you park the car on a hill.

-Adam

Pang wrote:

{Quote hidden}

>{Original Message removed}

2002\08\09@121159 by Olin Lathrop

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> If you just want to measure tilt, use a slotted disc sensor with a
> weight (easy o build).  When the car gets turned off the microcontroller
> should save the current setting (in a slot or out).  If the car is
> tilted then the weight will change the setting.
>
> The nice thing about this is you don't have to remember analog voltages,
> or even deal with what happens when you park the car on a hill.

Until one day when you park it and the edge of a slot is right at the
sensor, then a bird lands on the car.  The problem with this method is that
there is no upper limit on the sensitivity.


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2002\08\11@213451 by Pang

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Hi,

Is a slotted disc sensor available as one unit? Can you suggest one? Or are
you just suggesting that I can built a tilt sensor out of a slotted disc
with a pair of optical sensors?

Quite a number of piclisters has suggested to built something similar to the
mouse mechanism, but I think, eventhough it is workable it may not be that
practical as a product. Nevertheless, will get an old mouse and try to built
one. :)

Thanks

Rgds,
pang

{Original Message removed}

2002\08\12@043040 by Dominic Stratten

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Strip down an old mouse - they have slotted sensors in the majority of them
and can be picked up for pence (cents)

Dom
{Original Message removed}

2002\08\12@112035 by M. Adam Davis

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Look for motor encoders and rotary encoders.  Motor encoders often have
only one output (which is what you need) rotary have two (one 90 degress
out of phase with the other so you can detect which way it's turning,
and increase the resolution by four).  If you use a rotary encoder you
can ignore one output, or put them through an exclusive or gate to
double the resolution.
http://www.ubasics.com/adam/electronics/doc/rotryenc.shtml is a short
into into basic rotary encoder use.

They both come in many types.  I'd suggest using optical for wear and
tear.  Cars are physically hostile environments and mechanical encoders
are likely to wear quickly.

Good luck!

-Adam

Pang wrote:

{Quote hidden}

>{Original Message removed}

2002\08\12@132001 by Brendan Moran

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> They both come in many types.  I'd suggest using optical for wear
> and tear.  Cars are physically hostile environments and mechanical
> encoders are likely to wear quickly.

Until a few months ago, I also would have suggested optical encoders.
But recently, I had quite a bad experience with an optical encoder.
It stopped producing proper quadrature outputs.  On one portion of
the rotation, it started to produce glitches rather than a pulse.

I suppose that the likely thing is that it was subjected to
mechanical impact, and the high magnetic field that it was in
couldn't have helped, but having it kick the bucket like that was not
helpful, and we've modified the design to remove it.

- --Brendan

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