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Wheel Slip, PID, RPM sensor or strapping techniques

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(@rtattam)
Posts: 10
Member Customer
Topic starter
 

Hi Guys,

Wondering if anyone can help?

I have an old Vane VP950 chassis dyno with a Telma cc135 that I have updated using Yourdyno and a Sportdevices PWS3.2.

At the moment I'm struggling to get traction on the dyno with anything that has a fairly steep torque curve, the only cars that I have had on it are in the area of 300hp/300ftlbs and fairly light (datsuns).

Being a novice I'm not sure if its my PID settings, My strapping techniques or something going on with my rpm signal.

I'm really happy with everything at steady state and I can access all relevant areas of the map that I need to, it all seems to go awry when trying any of the PID related sweep functions.

I'll attach my settings and some recent tests at various PID settings.

If someone could take a quick look and let me know if there's something glaringly obvious that I've overlooked it would be greatly appreciated.

Cheers,

Rich.

This topic was modified 4 years ago by Datbeast
 
Posted : 14/09/2020 10:47 am
(@rtattam)
Posts: 10
Member Customer
Topic starter
 

https://drive.google.com/file/d/1hbLI9DBikD4t9hSfEVFO2tGfPsHl7lz_/view?usp=sharing

 

Sorry I couldn't find the attach file button so I linked it this way.

Cheers,

Rich.

 
Posted : 14/09/2020 12:36 pm
(@boz-race-engines)
Posts: 115
Member
 

it is all about how you tie the car down, alot of dynos dont have a proper vertical pull down system, if you look at dyno dynamics on youtube and you will see their rear bar pull down system, i went to that type of system and no more issues

 
Posted : 15/09/2020 4:36 am
(@mach_1)
Posts: 350
Member
 

I 2nd what boz race engines said about the way you strap the vehicle to the dyno. Did that back in  year 1995 no issues with big horsepower cars.

For chassis dynos DD's tie_down system works the best.

I have shared the information on here before easy to find do a few searches on here.

 

 

This post was modified 4 years ago by Mach_1
 
Posted : 15/09/2020 11:05 am
(@rtattam)
Posts: 10
Member Customer
Topic starter
 

Cheers for your replies.

I'm in the process of doing something similar to DD's method that you mention at the moment.

Any advice on strapping down decent powered IRS cars? This is also an issue for me I believe.

One more thing, can someone please shed some light on where the "attach file" button is on this forum?

TIA

Rich

 
Posted : 15/09/2020 11:17 am
(@mach_1)
Posts: 350
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(@admin)
Posts: 1397
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For wheel spin a (counter intuitive) trick is to use WD40 on the tires. Still need good tie down though. 

 
Posted : 15/09/2020 10:26 pm
(@mach_1)
Posts: 350
Member
 

WD40 = cheap PJ1 TrackBite sticky stuff

Select " chooce file " is what i use on my mobile telephone your display might be different.

IRS   is a bit tricker .... i have made various bolt_on brackets for the range of vehicles i have tested over the many years , only use it on high horsepower  vehicles. Still utilising the DD's tie down pull down method.

IRS rear ends are a pain in the but!  BUT still possible to control the traction on the rollers.

This post was modified 4 years ago by Mach_1
 
Posted : 16/09/2020 1:20 am
(@rtattam)
Posts: 10
Member Customer
Topic starter
 

Thanks to everyone for their input.

I will try a few things as suggested and report back.

Thanks again

 

 
Posted : 18/09/2020 4:42 am
(@rtattam)
Posts: 10
Member Customer
Topic starter
 

After doing some more testing and strapping correctly I have eliminated wheel slip as a problem, thanks all for the advice.

Can someone shed some light on the attached picture?

I'm getting RPM errors which seem to spike at the same time I have a torque/power dip.

I will also attach a .csv of the runs when I was testing, one of the runs was inertia only and the rpm errors were not present.

Any help would be greatly appreciated, I'm pulling my hair out atm.

Cheers

 
Posted : 09/10/2020 12:39 pm
(@rtattam)
Posts: 10
Member Customer
Topic starter
 

As mentioned above.

 
Posted : 09/10/2020 12:40 pm
(@admin)
Posts: 1397
Member Admin
 

Hi,

Just a clarification first. RPM error is not really an error, it is just the difference between the target RPM and the actual RPM. There will always be a difference, it is what drives the PID controller. We tune it to be as small as possible. 

A few observations:

You have a drop in power/torque between 4000 and 4200 RPM. Is this something the engine does? If not this looks like slip. The RPM vs time looks fine, so it is the load at the load cell that drops off. 

Your PID parameters seem a bit off. The RPM curve is without oscillations (unless masked by have heavy filtering, which filtering did you use). Kp is low I think, but it is hard to say without knowing more. What are your parameters? 

The RPM error you see is not really a problem for a Power sweep, as we only need a smooth sweep without oscillations. You don't get a better result when RPM error is less, it is much more important to have a smooth sweep. 

 
Posted : 10/10/2020 2:04 pm
(@rtattam)
Posts: 10
Member Customer
Topic starter
 

Hi,

Thanks for your reply, the torque dip at 4200 I'm pretty sure is not engine specific. I had another car on the dyno and similar issues were occurring at a similar rpm.

I will attach the config at the time of testing, I have tested so many different combinations of PID settings and I really am confused at this point.

The rollers and tyres are so grippy atm I really don't think its slip, that and the fact the car is on 8-9 psi it really is not making huge amounts of torque.

Thanks again for the help.

Cheers

 

This post was modified 3 years ago by Datbeast
 
Posted : 10/10/2020 10:25 pm
(@rtattam)
Posts: 10
Member Customer
Topic starter
 

Please see attached Power sweep to 5k

 
Posted : 10/10/2020 11:21 pm
(@rtattam)
Posts: 10
Member Customer
Topic starter
 
Posted by: @radics1

You can clearly see on the video,that under boost the car is coming out of the rollers and driving only the front. This will make a measurement error,because the inertia of the rear rollers become 0,but the software still calculates them. Do you have a rear strapping as well? 

Is that the case if they're unlinked idler rollers?

I only have a speed sensor on the load roller so I thought it was acceptable for it to climb a bit, as long as not to go past the apex of the roller.

I have replaced the speed sensor recently as I was using an encoder, I'm now using the gt101 hall effect and on closer inspection my trigger wheel may have a damaged tooth.

Does it look acceptable or am I better off getting a new one?

Cheers

 
Posted : 16/10/2020 8:10 am
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