Suspension linear potentiometers

[Robert Taylor]

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0-5v, linear.

The other very relevant criteria is durability to the high frequency vibration and stress they are subjected to. For reliability and longevity they pretty much have to be military spec.

[Robert Taylor]

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These are priced from reasonably pricey to hideously expensive. I can understand why having an item like that that strokes at a high cycle rate, over millions of cycles, whilst still giving a clean signal, isn't the easiest thing in the world to manufacture, but it still surprised me a bit.

Any advice on places to find them? I really don't need to drop $600 a piece on Bosch Motorsport ones, to me the data will only be personal interest rather than mission critical, although I would give the traces to Ohlins dude when he revalves the bike.

I was just dredging through an automotive Ohlins parts price list for quite unconnected reasons, but came across a linear displacement sensor they sell for high end circuit race cars. 969 euro suggested retail plus local taxes.....

[bikaholic]

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0-5v, linear.

Had a ransack through the workshop, nothing as similar, plenty of rotary pulse encoders. A cheapo strain guage with a millivolt output could do the trick with a amplifier, otherwise a 10 turn potentiometer pot driven by a ratchet or gearing, or a sliding resistor but they have an accuracy of +- 20% but can be had for less than $20.

[bikaholic]

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The other very relevant criteria is durability to the high frequency vibration and stress they are subjected to. For reliability and longevity they pretty much have to be military spec.

Military use tacho-generators and resolvers for positioning, feedback and control. I use them for DC brushless servomotor control at US$975 each. All the run of the mill feedback transducers start at NZ$500 before fitting them to the appilication.

[Robert Taylor]

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Military use tacho-generators and resolvers for positioning, feedback and control. I use them for DC brushless servomotor control at US$975 each. All the run of the mill feedback transducers start at NZ$500 before fitting them to the appilication.

Indeed, its a high stress environment with incessant, destroying vibration and high frequency inputs. Only military spec stuff can long term survive in such applications.

[schrodingers cat]

Robert is right. High frequency is really important. As is resolution

First frequency -
Say your (front) wheel is dia 580mm = circ 1822mm or 1.822m

At 140kph you are travelling 38.89m/sec or 38890mm/sec.
At 100Hz you get a sample every 388.9mm or approximately every 1/4 turn of the wheel.
At 500Hz the sample is every 77.8mm
At 1000hz every 38mm

At the 100hz rate you may be able to see something about low speed trends (chassis moving on the wheel)
The data will be more believable the slower you go

At 220kph you're travelling 61.1m/sec
100Hz = sample per 611mm
500Hz = sample per 122mm
1000Hz = sample per 61.1mm

A lot can happen on the track in the first 5mm travel in between samples

Which brings me to resolution.
Resolution is basically the instruments lowest measurable difference. e.g. 0.1 v or 0.01 volt
Or since you're looking to measure travel/and rate of change do you get an output down to the nearest 0.5mm or 0.1mm, whatever?
Greater resolution brings greater 'believability'.
There will be an element of electrical 'noise' in the trace that will need to be filtered. Upon applying the filter to a low resolution instruments effectively 'thickens' the width of the trace line (believability range +/- raw signal)

Think of a digital tyre pressure guage. If it reads to the nearest PSI it is only accurate +/- 0.5 PSI. Intending to set a tyre pressure to 40psi the gauge will read 40 even if the tyre is down to 39.6 or up to 40.5
If it is has a readout to 0.5 psi then the accuracy will be +/- 0.25. So 39.76 - 40.25

String pots are a cute toy and so very easy to fit. However they are more accurate pulling the string out than retracting it. Also the string develops it's own harmonic relative to its extended length and introduces more noise and therefore less believability into the trace.

You are correct that some information is better than none so long as you accept and understand the limitations.
I think you'd see maximum travel events. If you're logging rpm you'd see wheelspin relative to bumps. Measuring both ends you'd see pitch. Squat relative to throttle application would show up.

You wouldn't get anything useful about the wheel's 'high speed' movement (wheel moving in the chassis).

I actually have a heap of logging equipment sitting at home. Trying to talk to people about the benefit of data logging is like banging your head on a brick wall - great when you stop bothering. Everyone wants it for free. No-one is commited to really learning the stuff and expect instant results. In cars data logging is universally adopted to a very low level in the sport. Spending the equivelent of a couple of sets of tyre saves a massive amount in the long run. Please don't tell me that car guys are made of money. At clubbie level they are doing it on wages same as bike guys.
Every free test day at the track there are guys flogging around and around wearing out gear. Practice doesn't make perfect - only permanent.
Data logging gives increased value to spend. An exception pilot can only relate 30% of what happened on any lap.
With logging the data is there in perpetuity to review. You can spend hours and hours looking and comparing. You get maximum value from your spend and get to be faster without needing to chuck parts at things. You still need to do the basics right but you start to chip out the last few percent you didn't even know existed.

[bikaholic]

What is the scan time of a typical datalogger ?

[schrodingers cat]

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What is the scan time of a typical datalogger ?

By scan time do mean sample rate?
If so, it varies. Most of the mid range systems will sample at a max rate of 200Hz. The channels can be configured (up to the maximum). Water temp or Battery voltage for example really only need to be sampled at 1 - 5 hz. Memory isn't an issue these days but over sampling serves no purpose.
MoTeC will sample at 1000hz. Some AIM systems log to 1000Hz. Race Technology is a max 200Hz system.
You gets what you pay for really

[bikaholic]

Yep, i do all a PLC's and they are measured in scan time update tables and logic execution, my desktype one has a scan time of 1.56 millisecs and a good one is 1 ms, i do alot of datalogging using MMI looking at refreshed data tables but dataloggers must be more task specific, hence faster. If i want something really fast a use a PID controller.

[schrodingers cat]

When connected to a display unit or through telemetery, usually the update rate is no greater than 20Hz (accelerometers, rpm). Only the onboard storage rates are higher.
There are stacks of devices out there now that record events and their magnitude against a time stripe.
The thing that makes a motorsport specific logger the better thing to use is the software package to allow you to manipulate the data quickly.
Generally the better systems have the best software.
It is possible to import data as a CSV but generally the traces get stripped out to no greater than 100Hz in the conversion/import

[k14]

The cheapest one I ever found was from xt racing here at current exchange rate they go for around $300-$400NZD depending on what length you need. I know of people in NZ that use them and don't think they have had any issues. I never got the balls to drop that much money on something I was unsure if I could use to make me faster.

[Brian d'marge]

What would the "average Clubbie " want to measure

Throttle /track position

Suspension ( to what degree? and cant this be done by reading the tyre?)

braking???

and to what degree, would a "basic" trace be ok , enough to give an "idea" of what is happening

Stephen

[schrodingers cat]

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What would the "average Clubbie " want to measure

The primary purpose of data logging is to identify where potential vehicle performance is under-utilised and to moniter performance parameters.

1. Lap time - Instant feedback on bike

2. Sector times - Because remarkably consistent lap times can be achieved with inconsistent sectors

3. Wheel speed (and therefore distance) - Speed is King. Closely linked to sector times. How have you achieved the faster time? A higher speed at a certain point down the track indicates a better exit from the previous corner.

4. RPM - Simply changing gear at the right time to maximise acceleration can add up to a few 10ths a lap. Speed compared to RPM can identify wheelspin. RPM and speed can identify gears/gearing/acceleration. Rear wheel locking under braking will show up. Start line technique can be nailed down - Launch RPM and 0 - 400m time

5. Longitudinal G - Braking performance.
Additionally connecting to the brake switch will indicate when the brake is applied and when it is finally released and will show much about braking technique. A better (more expensive) method is to measure brake line pressure.

6. Throttle position - tells volumes about rider confidence and the ability of the chassis setup to accept inputs


These are the first areas I'd be looking at.
In discussion with the pilot much can be explored about preferences and weaknesses in technique.

Most people will have 2 places on the track where they should focus their energies. Usually not the areas where they think they are weak.
By weeding out poor habits and reinforcing good technique the pilot will first become faster and secondly more consistent which is a massive gain over a race distance.

Performance parts wear out. Performance parts will make you faster but won't make you a better rider. Any investment in yourself is carried from machine to machine.

If buying a logger ensure that it has much more capacity than you first require. If you commit to using it as a performance tool it won't take long before you'll generate a whole heap more questions...