Accelerometers

[Jacko]

Just been looking at the race-technology Ap22 jobie
Does anyone have one of these or know if they are any good or not?



[This message has been edited by Jacko (edited 22-01-2002).]

[Spooky]

I know Tom_S14 has an accelerometer in his S14.

------------------
Peter - currently driving a non scrabbly black Cav SRi - 130.5 BHP @177K miles. Highest BHP holder at the rolling road event until they put a 200SX on the rollers...
Car now dearly departed except for...
Blitz FATT type S turbo timer and a black ally tax disc holder. Just got a traction control system now, all I want is a 200SX again...

[Tom_S14]

Yep, you'd be right. I do have one. So does Risky_Business, he even puts his in his plane !
So yep, they work pretty well. With an accelerometer you HAVE to be completely still before you start taking any measurements, this is because you can be travelling at constant speed and measure no acceleration.
The AP-22 is better than the AC-22 because it can measure acceleration every 1ms, if you integrate acceleration (ie measure it over time) you can get velocity, integrate again (ie. measure over time again) and you get distance. Each time you integrate you introduce a constant of integration, which in the real world translates to "integrator drift" which all real life integrators suffer from.
The AP-22 can measure acceleration for a couple of minutes before integrator drift becomes an issue, it's accurate to about 1 metre for a good minute's worth of data acquisition. It's got a good quality dual axis accelerometer in it, the board runs a PIC at 20MHz, enough memory to do a couple of minutes. RS232 port on the back so you can dump the data to your PC.
Alternatively you can just use it to give you acceleration (including cornering) on the fly. You can enter the weight of your car, and drag coefficient-Area product so it can reasonably well estimate power at the wheels...probably comparable to the errors you measure at a rolling road to be honest.
Take a look on my website the results aren't hard to find. I've tested my own car a couple of times, my brothers old 944 S2 before some theiving git stole it, and the piece de resistance... a 998cc A reg polo... well... why not eh ?
I've also got some results for a boeing 737, but they're not up yet http://300zx.co.uk/200sx/ubb/smile.gif
Nice blokes run the business, I'd recommend buying one. (I don't have shares).
In use, the hardest thing about using it, is you really have to have access to a nice straight flat road... where you can STOP. takes a couple of seconds to set the thing up, and tear off like a bastard. No good if police are driving around, no good on a busy dual carriage way, no good on a hill.

Tom

------------------
1996 Blue/Green S14 (manual)
K&N cone filter
2.5" Tube-torque Cat Back Exhaust.
TechTom MDM-100
Race-Technology AP-22
http://tom.marshall.tripod.com

[Billy]

Why no good on a hill? I would have thought acceleration would be the same regardless. Or is it to do with the apparent extra drag during uphill gearchanges screwing the rest of the calculations? I realise it would have to be zeroed on the level.

I'm curious, as "a flat bit of road" means somewhere you can put your foot down in the local parlance... http://300zx.co.uk/200sx/ubb/smile.gif

[Tom_S14]

no good on a hill because if the accelerometer is at an angle, lets say 45 degrees, then half the horizontal acceleration it measures will be down to the car, and half of it is gravity !
What it does do, is make a compensation for this effect before you start a run, it measures the acceleration due to gravity at rest, and can then compensate for this - assuming the angle of inclination stays constant throughout the run. More than a slight incline however, and the unit will give a tilt error because the errors will get too big. The other side of it ofcourse is charging down a hill ain't really a fair test ! You're going to accelerate loads quicker, and vice versa going up hill.

If you start the run on the flat and then go up a hill, the measurement "axis" of the accelerometer is the same as the car, but you're still measuring a vertical component due to gravity which you don't want to do. This is a real problem on a bike, they were working on a version for bikes but I haven't heard much about this lately.


Nice bit of float road.. yep a good mile is nice. You need somewhere to get up to whatever speed you want, not having to worry about people who might be turning out of side corners etc.

Tom

[Jez]

I've got the AP-22. Really good bit of kit.

I've tested it in a number of situations for measuring my max power (at the wheels) and 0-60 times. Seems pretty accurate.

Another explaination of why you need to use a flat bit of road is that if you are stationary on a hill the AP-22 thinks you are accelerating...

Worth getting one IMO.

------------------
Red S13
294bhp @ 16psi
www.Horsham-Developments.co.uk (http://www.horsham-developments.co.uk) - S13 ECU performance upgrades

[Jacko]

Cheers guys.
Just had alook at your website tom - nice http://300zx.co.uk/200sx/ubb/smile.gif



------------------
Jacko
http://300zx.co.uk/200sx/rides/jacko/sig_pic.jpg

[Tom_S14]

cheers http://300zx.co.uk/200sx/ubb/biggrin.gif

Tom

[Jacko]

Justa couple more quick things, where do you mount the box in the car? and do you have a problem with it not being backlit?

[Tom_S14]

Hi,
Yeah the lack of back lighting is a right old pain in the arse. I suggested it to them, but it's not on their list of priorities unfortunately.
I blutak mine slap bang in the middle of the dashboard, with the back of it touching the windscreen. That way you make sure it's nice and straight.

Tom

[risky business]

I also stick mine on the dash, straight in front of the driver. To get it level, I've carved out a mount from a block of polystyrene which mates with the top of the coaming and blue tacked it all together. As Tom and Jez said, setting it up well is imperative. At Santa Pod its 1/4 mile time was out by 0.03s and it gave a pwr figure 4hp greater than that of a rolling road session done about a month later.

BTW what's most lateral G you guys have pulled? My best is .83g @ 72mph on 195's.


------------------
Black S13 with asymmetric body styling

[Billy]

Originally posted by Tom_S14:
no good on a hill because if the accelerometer is at an angle, lets say 45 degrees, then half the horizontal acceleration it measures will be down to the car, and half of it is gravity !
What it does do, is make a compensation for this effect before you start a run, it measures the acceleration due to gravity at rest, and can then compensate for this - assuming the angle of inclination stays constant throughout the run. More than a slight incline however, and the unit will give a tilt error because the errors will get too big. The other side of it ofcourse is charging down a hill ain't really a fair test ! You're going to accelerate loads quicker, and vice versa going up hill.

If you start the run on the flat and then go up a hill, the measurement "axis" of the accelerometer is the same as the car, but you're still measuring a vertical component due to gravity which you don't want to do. This is a real problem on a bike, they were working on a version for bikes but I haven't heard much about this lately.


Nice bit of float road.. yep a good mile is nice. You need somewhere to get up to whatever speed you want, not having to worry about people who might be turning out of side corners etc.

Tom
But surely, if you accelerate up a 45 degree slope then the car will accelerate half as fast, so the result will be the same. It doesn't use one axis to measure acceleration and one to measure gravity, but the sum of both (all three?).

Or was Einstein wrong? http://300zx.co.uk/200sx/ubb/tongue.gif

Or is it just a crap bit of design. http://300zx.co.uk/200sx/ubb/frown.gif

[mambastu]

Originally posted by risky business


BTW what's most lateral G you guys have pulled? My best is .83g @ 72mph on 195's.


------------------
Black S13 with asymmetric body styling

.98g on 215/40 ZR 17's (crappy Falken GRB's) in the dry :D

[Filmidget]

Hmmmmm nevermind the AP-22 what about that Race Technology DL90!?!

That is one nice bit of kit. Looks like it has a GPS output as well - just what I need to plug into my Palm to run the Trafcam speed camera warning kit...

Gets around the problem of 'non-timed' trackdays as well :)

But 500 quid!?! OUCH!

Anybody fancy a trying to organise a REALLY heavily discounted group-buy!?!

Cheers, Phil

[stuee69]

I'm looking for one at a reasonable price:D

[risky business]

Originally posted by mambastu


.98g on 215/40 ZR 17's (crappy Falken GRB's) in the dry :D


RESPECT! :cool:

[mambastu]

Originally posted by risky business



RESPECT! :cool:


I thank you :D