JoaoCaldeira
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| posted on 29/10/08 at 02:38 PM |
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Linear Potentiometer
Hi all.
I was thinking about using this
linear
potentiometer as a brake position sensor (BPS).
The idea is logging this data along with the rest of the sensors to join with the in board camera image and later see how I preformed (and could
improve) at a trackday.
More data on this sensor here
Questions:
1) Am I using the right component for my needs?
2) how is it wired? (red / green / yellow)
Thanks in advance,
Joao
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BenB
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| posted on 29/10/08 at 03:06 PM |
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Sounds like the right thing for the brake position. The datasheet shows it's
red wiper
green retracted
yellow extended
by which it likely means the wiper is @ the green terminal when its fully retracted and its at the yellow terminal when fully extended. The main issue
you may have is the throw of the pot vs the relatively small movements of a brake caliper....
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Davey D
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| posted on 29/10/08 at 03:10 PM |
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a linear potentiometer would work quite well in this application. i doesnt matter about it being linear or not because the resistance will always be
known for the corresponding amount of pedal movement.
usually the pins are laid out with 1 in the middle, and one on either end of the movement area.. you just need to use 1 wire attached to the middle,
and one to one end. you can then test the resistance change with a multimeter when you turn the pot
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BenB
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| posted on 29/10/08 at 03:13 PM |
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Still think the problem is going to be the 10mm range of the potentiometer.....
Personally I think measuring brake force would be better... brake movement is more likely to be a noisy signal and might get effected by things
expanding etc. Then again I suppose brake force might get effected by brake fade....
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02GF74
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| posted on 29/10/08 at 03:38 PM |
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quote:
Originally posted by Davey D
you just need to use 1 wire attached to the middle, and one to one end.
I can't seewhy that won't work but data sheet specifically says not to use it like that but as a potential divider.
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MikeRJ
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| posted on 29/10/08 at 03:40 PM |
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quote:
Originally posted by BenB
The main issue you may have is the throw of the pot vs the relatively small movements of a brake caliper....
Isn't this to log the movement of the brake pedal rather than the caliper?
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JoaoCaldeira
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| posted on 29/10/08 at 03:53 PM |
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Yeap... log the movement of the pedal... like "how was I behaving..." vs "how should I behaving"
Sorry for my (huge) ignorance, but how would it be wired? Usually (IIRC) this sensors receive a +5v, a ground and the other is for output.
I dont understand how should I wire this 
Thanks FOR ALL! 
Joao
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JoaoCaldeira
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| posted on 29/10/08 at 03:56 PM |
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quote:
Originally posted by BenB
Sounds like the right thing for the brake position. The datasheet shows it's
red wiper
green retracted
yellow extended
Sorry for the ignorance, but in terms of voltage, what should be connected to what?
positive, x volts, negative, ...
Cheers
Joao
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02GF74
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| posted on 29/10/08 at 04:19 PM |
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To use as a potential divider and log the variable voltage you would wire like this:
red wiper - to logger unit
green retracted - 5 Volts
yellow extended - 0 Volts
I have put 5 Volts but of course you can use higher or lower voltages - it depends on what the input to your logger unit is.
The green and yellow can be wired other way round;
it depends on whether you want the voltage to go from 0 to max as the plunger is extended or go from max to 0 V (is wired like this above).
Also since your logger unit is just reading voltage, you should use a potentiomenter between 1 and 10 K ohm value.
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JoaoCaldeira
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| posted on 29/10/08 at 04:22 PM |
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MANY MANY thanks!
Joao
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JoaoCaldeira
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| posted on 29/10/08 at 04:23 PM |
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Sorry, but one last doubt...
"0 volts" is the same as ground? Or has a special meaning?
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Davey D
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| posted on 29/10/08 at 04:40 PM |
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quote:
Originally posted by JoaoCaldeira
Sorry, but one last doubt...
"0 volts" is the same as ground? Or has a special meaning?
that is correct
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02GF74
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| posted on 29/10/08 at 04:54 PM |
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^^^ for car application yes.
if we were talking home electronics, e.g. HiFi, then ground and 0 V would not necessarily be the same.
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paulf
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| posted on 29/10/08 at 07:51 PM |
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Could be connected to the brake pedal and would show pedal operation but may not be able to show the actual force as once the pads are in contact
there should be little further movement of the pedal for increased brakingforce just pressure.I would think a pressure transducer plumbed into the
brake line would be better but not lowcost.
Paul
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JonBowden
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| posted on 29/10/08 at 09:23 PM |
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quote:
Personally I think measuring brake force would be better... brake movement is more likely to be a noisy signal and might get effected by things
expanding etc. Then again I suppose brake force might get effected by brake fade....
I tend to agree, but how about using an accelerometer to measure acceleration and deceleration - you could measure cornering force too.
I thik Farnell used to sell them
Jon
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JoaoCaldeira
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| posted on 30/10/08 at 05:24 PM |
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I'll be adding a MQ200-PRO so the accelaration part is already covered.
Well... it will be pedal travel rather than pedal pressure... it's not a pro thing... it's just to give an idea of what I'm doing
wrong...
Cheers all,
Joao
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Rob Lane
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| posted on 1/11/08 at 09:14 AM |
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Mount it away from pedal with a crank arm fitted to the pot spindle to extend the working range.
Then use a direct connection from crank to pedal using lightweight material, say perspex or plastic.
This will increase the wiper range if done correctly.
There are linear pots available as 'piston' design. Similar to the gas lifters for hatchbacks but much smaller and obviously a linear
pot.
See here http://www.celesco.com/linearpot/?gclid=CPrDqsfS05YCFRqH1Qod9zCb2g
http://www.transducersdirect.com/HeleoCart/Products/Default.aspx?sq=IxtvrI6BZNJ%2faC0J6KsW2T2eIH4lJzR0DffVgCfMFuw%3d&category=In+Cylinder+Lin
ear+Transducers
Hope that makes sense.
Personally I would go for a pressure transducer in brake line.
[Edited on 1/11/08 by Rob Lane]
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