Andy.F

Discussion transferred from Scotland forum.

The rolling road at Star has a long run up time when compared to Well Lane, P Eng or G force. The run time/load is not representative of road acceleration rates and hence there are issues with cooling, boost control, heat soak etc.
I was suggesting a shorter run time would be more appropriate but the issue of reduced accuracy was raised.

Anyone aware of the specs of the MAHA rolling road such as logging frequency etc

quote:
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With a shorter run the data collected would be quantized to such a point that the values given would not be worth the paper they are printed on, due to the data sampling rate. Now can we put this one to bed ? As you and I know the only way the sampling rate can be increased is by the installation of a faster processor in the A-D converter along with more memory for the storage of the additional data, which must be an uneconomical option otherwise the dyno`s would be designed with this as standard (as this is not cheap machinery) or they would be available as a hardware upgrade
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Pete, with respect mate I think this is unlikely to be the situation.

Jims rollers were considered state of the art only 3-4 years ago. I can't believe that such an expensive (very) bit of kit would have a slow processor in it. Even my £150 AP22 can log at 100Hz and store IRO 2 minutes worth. Most processors are rated in MIPS so recording something as slow as 6 inputs from a 15 second dyno run is kids play. Even basic ADC's are unlikely to hold back the input for more than .01 of a second.

I think the inaccuracy introduced by holding back a powerful car and 'roasting' it will be of far more significance.

Remember, these rollers have the ability to control a standing start full throttle 0 - 60 mph run whilst simulating 'on road' loads dependant on weight input. This type of closed loop control is not possible without decent processing power. From what I seen of Dave Browns 4.1 second run, it was fully controlled and it also gave a power readout despite the short duration of the run.

Andy

john banks

Indeed a £3 microcontroller these days can do 6 channels of 10 bit ADC at 50 KHz plus run at 16 MIPS to process it all.


[Edited by john banks - 5/18/2003 11:59:29 AM]

ustolemyname??stevieturbo

iTrader: (1)

I know very little about rolling roads, but I wonder what other operators have to say. G-Force are making big claims about their rollers, and I have seen them post here a couple of times. I wonder what their opinion on the matter is????
Id also like to take a run over to their place sometime.

Pavlo

4 seconds is an eternity. To make the control loops work for constant speed PID control of the rollers, you're looking at a cycle time of about 2-5 milliseconds, and that was over 5 years ago.

You don't even need high cycle times to be honest, provided you know that when you collect any given piece of data, you know the exact time. The MAHA and dyno dynamics rolling roads don't use any data/time maths, as it measures load directly (unlike a pure innertia dyno).

The biggest problem is un realistic road conditions and poorly controlled heat etc.

Paul

Andy.F

That's exactly the point I was making paul, someone (who knows about r/roads) has suggested that reducing the run time from 30 seconds to 15 seconds would reduce the accuracy so far the result would be rubbish.

I maintain that you need a short run (like well lane) in order to control the heat build up, otherwise the result will definitely be rubbish, particularly on a high boost turbo car.

Andy

Anyone timed P/Eng or G force run times ?

Pavlo

Well, the said someone doesn't know much about rolling roads. Especially as identical rolling roads can be run in entirely different ways with different software. PE use the same software as Well lane, which is not the usual MAHA stuff that you see at Tuning Japanese and Star etc.

Even if the aquisition rate was only 4cycles a second for a 16 second run, if the 16 points sample RPM and Torqu together the results would be accurate. Even if there was a delay between RPm and Torque, if the times for each sample are known you can interpolate between. Indeed, you could interpolate between RPM points and torque points to get 32 points. Given that the errors are likely to be more than the noise that's smoothed out anyway, I think the errors would be minimal.

The thing is, and what Andy is eluding too is that different run times produce starkly different results, not just 1-2%, but nearer 10% in a given RPM zone.

The software I wrote for bench dynos used a sample rate of about 50hz overall across 6 channels and a counter, so that's a base rate of 300hz which was fine for measurement. It was pushed as high as 2khz base rate but that was for closed loop dyno control.

More to do with the actual load rather than recording the data I think.

Paul

Gerry Gaffney

Hi Guys,

Maybe the someone who is supposed to know about rolling roads is me?

I did mention to John that the Sun/Maha rolling road does have problems in accuracy & repeatability when the length of time taken to do a run is decreased. This has been my finding on quite a few of these machines (which I have upgraded to more modern systems) The thing you have to take into account is that the technology in these machines is actually late '80s early '90s (why else would you use a TV & ribbon printer) & that it uses basically a low level PC with it's own operating system to run the whole thing. Now many people will say that should be OK, but if you think about everything it it trying to do, you'll see that it is quite a lot to ask of any system (in fact our own dyno uses several processors dedicated to individual tasks to keep everything in order) you have loadcell inputs, speed inputs not just for speed but for also slip control, DAQ, printer control & GDI, you have separate PID control loops (very slow, but stable once it gets there) for front & rear rollers (& a PI loop to keep the load the same front to rear on 4WD) phase angle thyristor control, the list goes on. The problem appears that because you are relying on single processor to do this, it has to split it's resources as it see's fit. Now if you increase the ramp rate, you have so much more to do in a shorter time in the PID loop area, & the timing on these machines isn't great, so accuracy & repeatability start to slip. Don't take my word for it (even although I might be a little biased - we manufacture our own rolling roads ) try it, you can test very easily their PID loops, set the dyno to hold a constant speed of say 5000 rpm, put the car into 4th gear & plant the throttle, it will take quite some time to reach 5k, then it will overshoot by maybe 700rpm, them be pulled down to settle at 5k (also better to use an ECU output to determine rpm) now if it take this long to get a constant speed correct, imagine how hard it is to keep all of the above in tow. You can of course adjust almost every setting (I can scan in the variables, if someone can host them) but the problem I've found with almost every PID loop on dyno's (chassis or engine) is that you will get it right for that particular application, but then it is not suited to the next car you test (one of the reasons we don't use PID loops, but IMHO we are more stable, sensitive & repeatable than any other chassis or engine dyno I have tested)

Paul:

I'll ignore your first sentence however I'd like to point out you are comparing different machines, both W.L. & P.E. use Sun Ram 12 machines, which is a fully analogue system (well developed & IMO, better suited to most tuners needs than an underdeveloped digital machine, just ask many of the people that have gone from a Ram 12 to 2000) the S.R.12 outputs a -12V -> +12V signal relative to BHP & a 0 -> 12V signal relative to speed, these go into an inexpensive ADC PC card & collect data via software (usually Superchips)

Please don't see this as a pop at any tuning company (I do have almost 50 R.R. tuners as customers) but purely an insight into why so many people find that they do not get the results they are expecting (other than wishful thinking)

Hope that shines some light on the matter.

Gerry

[Edited by Gerry Gaffney - 5/19/2003 9:42:17 AM]

john banks

Thanks Gerry for your valued input. Chris from G-Force (IIRC) had previously said similar on an earlier thread about the (competitor) rolling roads re run length and accuracy although in less detail.

ChristianR

iTrader: (1)

how much is a 4wd rolling road?

Pavlo

Very useful, thanks Gerry.

By "analogue" for the older RR systems, i take it you mean the control and possibly speed measurement? Given that both systems will use analogue torque input via DAC.

One aspect I hadn't considered is FR/RR roller balance, which could upset things, and be made worse with shorter runs if there isn't enough time to stabilise.

Edited to add. 5ms cycle time for PID loop was to control brake excitation current, this was the speed of the loop, rather than the time the P, I and D elements were measured over, they were independantly variable and this was another way of tuning the response.

paul

[Edited by Pavlo - 5/19/2003 11:32:23 AM]

Gerry Gaffney

Christian please see email.

Paul: The whole system is based mainly around op-amps (in some instances extremely clever usage) therefore there is no digital electronics in it, just some fudge factors, but they work really well. The later Ram 2000 still uses the same Ram 12 chassis (right down to VR pickups & analogue loadcells - no DAC needed on Ram 12) it's just the controller that is different. The front/rear roller balance is a real pain to get right, & hence why a lot of modern electronically controlled centre diff's (TT etc) get upset on certain 4WD dyno's

Gerry

Andy.F

Thanks for that Gerry

I have seen the TAT upgraded software advertised for the MAHA rollers which I assume would overcome most of the issues you mention ?

http://www.tat-rd.com/dyno_htm_e/mahadyno.htm

Andy

Gerry Gaffney

Hi Andy,

It is an improvement, but won't fix it completey, as the Ram 2000 has 2 DAC outputs, that you can assign to give a -10V -> +10V relative to anything it measures/calculates & feed it into the TAT, but you are still relying on the Ram 2000 to spit out the info correctly. Rudi @ TAT has carried out quite a lot of enhancements to the software specificly for the 2000, but there is only so much you can do.

Gerry

john banks

Spent a good hour and a half at Star tonight with Jim, Andy F and T-uk came along and we did about 10 different runs trying 15 second total run up time, which on my car is equivalent to 3rd gear acceleration. The car was very happy on the rollers using up to 1.8 bar boost. Temperatures, detonation and surge which were big concerns before are now well controlled. I don't have to do anything different to a road setup now to run on the rollers. Run to run is more consistent. The only downside is that because of the shorter run up time it is difficult to get a true impression of torque delivery by RPM. I'm not sure now how the results would compare to English rolling roads now - we'll have to see.

[Edited by john banks - 5/22/2003 9:34:56 PM]

Chris.Palmer

John,

Did you see the same levels of boost on the rollers as on the road?

Dare I ask what your Power @ Wheels & Power @ Fly results were?

Cheers,

Chris

R19KET

John,

"which on my car is equivalent to 3rd gear acceleration."

Sorry, does this mean that the runs were actually done in 3rd gear ?

Mark.

Pavlo

Mark,

the runs were equivalent in time length to an acceleration run in 3rd gear

Paul

john banks

Runs done in 4th, but I think if you used third the run time is fixed the same.

I think there are still issues with boost delivery, air temperature correction and loading, but all RRs have these. At least you can run a powerful car at Star without cooking it now. Earlier in the day short and long runs were done and the figures were very similar.

I'm still a fan of accelerometers, and not just because they give you higher figures Honestly, I am trying to question it all myself too.

I had a MAP hose off which was near the boost gauge tee, so the boost level appeared lower, but after that was sorted we'd already adjusted the boost control.

R19KET

John,

Sorry, didn't mean to come across as if I were questioning the figures, I'm not.

Given the turbo, boost, and car set up, the figures seem very realistic. I was just trying to benchmark the runs.

Mark.

john banks

That's fine Mark I know you are not. I think we both agree that all RR results need a rather large pinch of salt anyway as per our discussion the other day. The old dogma that you could use them to compare between cars on the same day I think is now somewhat out the window, and I think we are questioning even if they are useful for telling if you've gained anything less than 10% on the same car on the same day.