Help on Inertia Dyno Project

[oldskool]

Heya all,
Appreciate some advice on finishing off my dirt dyno. So anyone on here been down this road before?
Thoughts on getting a clean signal from the spark plug? Plenty of circuits online but would like to hear thoughts from guys with real experience, not armchair theorists.
I've got the data acquisition module and a nifty optical sender, just gotta find someone with a bit of programming skills to build the app to do something meaningful with the data.
Also.. comments on whether running a hose from muffler into 44gallon drum of water would give inconsistent readings if runs were say 1 week apart. If readings were consistent, what sort of insulated hose could I use?
Here's it running today.

[bogan]

That's well cool I'd be too scared of knobblies flying everywhere to put mine on a dyno like that! How long does it take to go through the rev range?

Haven't done much with that sort of thing myself, but know a few who have and could ask them if you give a bit more info on where you plan on getting the signal from, and data aquisition module details etc. You going with an inductive pickup, low voltage side of coil connection, or something else?

Either way it should be fairly simple to program something up, as long as you got the right dll's and that sort of BS sorted.

[schrodingers cat]

Prolly stating the obvious but best you get that knobbly off there and fit a nice sticky road tyre...

Getting a clean spark trace is difficult. Personally I would go down the road of fitting a crank angle sensor. Essentially a Pull up or Pull down 5v frequency generator (ABS wheel speed sensor)

Build a water spray box to exhaust into. You can't afford to restrict the muffler in any way whatsoever

[oldskool]

That's well cool I'd be too scared of knobblies flying everywhere to put mine on a dyno like that! How long does it take to go through the rev range?

Haven't done much with that sort of thing myself, but know a few who have and could ask them if you give a bit more info on where you plan on getting the signal from, and data aquisition module details etc. You going with an inductive pickup, low voltage side of coil connection, or something else?

Either way it should be fairly simple to program something up, as long as you got the right dll's and that sort of BS sorted.

Hey there,

The DAQ is from here
http://labjack.com/u3

DLL info is here
http://labjack.com/support/u3

I have opened up a thread here
http://forums.labjack.com/index.php?showtopic=5166
They've been very helpful so far but some of it is beyond me

And just in case, I also have a frequency to analog converter for the engine rpm should I need it, from here
http://www.oceancontrols.com.au/KTA-245.html

Basically my thinking is 10 second runs wide open throttle from say 2000rpm up to wherever it goes.

The drum weighs 150kg give or take...this should be an editable variable in the code anyway, as a certain fudge factor may need to be tweaked. Maybe some model data could be used to get a certain degree of accuracy. If the inertia model isn't going to cut it an AC motor (eddy) could be included for a bit more friction.

Dirtbikes don't go much beyond 50 horses so I doubt if knobblies will go flying...maybe with a yzf450 or such like.

I'm looking for consistent readings to track tweakings in the low to medium rev ranges, I'm not aiming for accurate HP readings (if there is such a beast).

I'm open to debate.

[jonbuoy]

Maybe I´m missing something but can´t you just use a tiny tach or something for engine RPM? Why does it need to be super accurate and logged?

[schrodingers cat]

And just in case, I also have a frequency to analog converter for the engine rpm should I need it, from here
http://www.oceancontrols.com.au/KTA-245.html

The drum weighs 150kg give or take...this should be an editable variable in the code anyway, as a certain fudge factor may need to be tweaked. Maybe some model data could be used to get a certain degree of accuracy. If the inertia model isn't going to cut it an AC motor (eddy) could be included for a bit more friction.

If the logger doesn't accept frequency inputs then by all means go down the path of a converter

Bear in mind that the minimum sample rate you want to consider is 200Hz, preferably 500Hz.

I think the drum should be fine as inertial dyno's replicate 'real world' quite nicely.

I repeat tho that you seriously need to put a nice grippy smooth tyre on the bike. At maximum traction a tyre can be slipping up to 10% without you realising it. A speed sensor on the rear wheel and another on the drum will help you cross-reference. A knobbly will give inconsistent readings

Also, you will need some way of tracking atmospheric conditions - Air temp, Barometric pressure, Humidity (also altitude) and possibly a good sized fan to keep the temperature of everything consistant.

Although as you say, you are only playing with small power outputs, this increases the challenge more. At 50hp, 1 hp is 2%.

IS it possible to export the data file as say a *.css file? No need to write analysis software then - you could import it into antoher manufacturers software to allow you to manipulate the data

[oldskool]

If the logger doesn't accept frequency inputs then by all means go down the path of a converter

Bear in mind that the minimum sample rate you want to consider is 200Hz, preferably 500Hz.

I think the drum should be fine as inertial dyno's replicate 'real world' quite nicely.

I repeat tho that you seriously need to put a nice grippy smooth tyre on the bike. At maximum traction a tyre can be slipping up to 10% without you realising it. A speed sensor on the rear wheel and another on the drum will help you cross-reference. A knobbly will give inconsistent readings

Also, you will need some way of tracking atmospheric conditions - Air temp, Barometric pressure, Humidity (also altitude) and possibly a good sized fan to keep the temperature of everything consistant.

Although as you say, you are only playing with small power outputs, this increases the challenge more. At 50hp, 1 hp is 2%.

IS it possible to export the data file as say a *.css file? No need to write analysis software then - you could import it into antoher manufacturers software to allow you to manipulate the data

I believe the LJ U3 will easily clock 200hz sample rates. It also has enough digital and analog inputs to cover peripherals later down track. Yes I'm pretty sure txt file exports are possible, but hardly real-time. The LJ U3 also marries nicely to a 3rd party called DAQFactory. Supposed to be a dummies charting dragNdrop.

There is a surprising amount of traction on the smooth drum. Failing that I could try and coat it with some sort of vulcanised rubber compound.

My goal is to keep it fairly simple so the boys can bring their bikes around for a bbq and dyno run. Removing tyres and magneto covers or tapping into the coil I'll leave as last resorts.

I like your idea about adding a spd sensor to the wheel. The drum already has one, wouldn't be too hard to get a reading off the wheel too. This data could be used to smooth out any spikes.

[schrodingers cat]

There is a surprising amount of traction on the smooth drum. Failing that I could try and coat it with some sort of vulcanised rubber compound.

I'll say it a third time cause it really matters. Tyres generate their force by slipping. If they didn't they would never wear out.
Grip is a combination of molecular cohesion and friction. Maximum tractive force occurs around 10% slip. This is not recognisable as 'wheelspin'
To minimise the slip increase the contact patch.

Have fun

[bogan]

I'll say it a third time cause it really matters. Tyres generate their force by slipping. If they didn't they would never wear out.
Grip is a combination of molecular cohesion and friction. Maximum tractive force occurs around 10% slip. This is not recognisable as 'wheelspin'
To minimise the slip increase the contact patch.

Have fun

You're assuming it has the power to get to maximum traction though, in top gear (generally what inertial dynos are run at) I'd be very surprised if the tyre got even halfway there. Saying that, I'd still be bloody careful just in case some knobs come flying off.

I had a brief look at the U3 Labjack, looks like you should be able to get that set up all good, easiest way would be off the coil's low voltage side. But an inductive pickup in the plug lead would be somewhat more versatile, probably require a little bit more circuitry though.

[schrodingers cat]

You're assuming it has the power to get to maximum traction though, in top gear (generally what inertial dynos are run at)

So what slip value will we assign it because it is slipping...?

I had a brief look at the U3 Labjack, looks like you should be able to get that set up all good, easiest way would be off the coil's low voltage side. But an inductive pickup in the plug lead would be somewhat more versatile, probably require a little bit more circuitry though.

Yes it is easy to get some sort of signal from the coils low voltage side. No it isn't accurate - too much noise. You can filter it of course but then what is the point. Crank angle is the way forward.

[bogan]

Maybe I´m missing something but can´t you just use a tiny tach or something for engine RPM? Why does it need to be super accurate and logged?

If it's accurate enough you wouldn't need to measure the drum speed, and how quickly the rpm changes could be used to calculate the power. Course you'd still need to know the gear ratio over the drum to calculate it. In which case it may be easier just to measure the drum speed with a photo-interupter and plug in the gear ratio to work out hp. Then again, if you measure the speed of both you don't need to know the gear ratio at all

[bogan]

So what slip value will we assign it because it is slipping...?

I'd go with none, the slip will be negligible unless the knobblies start the rear bouncing around.

Yes it is easy to get some sort of signal from the coils low voltage side. No it isn't accurate - too much noise. You can filter it of course but then what is the point. Crank angle is the way forward.

By crank angle sensor you mean the CDI pickups? would probably be nicer, but would have to watch what you put on so it doesn't induce timing errors, and harder to get to than the coil. The coil is noisy, but you can be pretty brutal with how much you can filter out, all you need is pulses, a 500hz low pass filter would probly do it. Then just run it through a counter Personally I reckon sorting an inductive pickup for the plug lead is the way to go.

[Brian d marge]

there is a Kiwibiker who has been down this path and built his own dyno

do a search , as I cant remember much else ,,,,

Also check out

this site http://www.sportdevices.com/

they have circuitry

Stephen

[schrodingers cat]

I'd go with none, the slip will be negligible unless the knobblies start the rear bouncing around.


By crank angle sensor you mean the CDI pickups? would probably be nicer, but would have to watch what you put on so it doesn't induce timing errors, and harder to get to than the coil. The coil is noisy, but you can be pretty brutal with how much you can filter out, all you need is pulses, a 500hz low pass filter would probly do it. Then just run it through a counter Personally I reckon sorting an inductive pickup for the plug lead is the way to go.

Everything is easy when you underestimate the true nature of the problem.

I suspect you are suffering from the fruits of a good education. When I need a fruit educated I will let you know.

I shall depart from this post now. My experience and knowledge are obviously redundant in the face of your confidence

[oldskool]

Personally I reckon sorting an inductive pickup for the plug lead is the way to go.

Would using RF be a silly idea? Read somewhere online a post refering to using an AM radio off station.

I have a circuit, read closely some references from a picaxe forum and thought about hacking an old timing light for parts. Where else could I source a purpose built inductance clamp?