Community project to legalise race car seats for road use. (Australia)

Projects General Guidance
1

Hi all,

My task in this project is to collect the accelerometer data when a sphere strikes a race seat head rest as part of an approval process our Australian Government deems necessary.
The specifications are
2 x 600Hz (Edit - change to 6kHz) Accelerometers sampled 1000 times per second.
(and a speed sensor – more on that later)
(Edit - must be able to read greater than 80g)

I have a Bosch BMA180 sensor coming and I hope I can read it quickly enough. I have an Arduino (Uno compatible) processor (freetronics eleven) board to play with.
So I need to read and send the data to Excel. Sounds easy enough but my first series of tests indicate the 1000 reads per second might be too fast for the comm. port, even at the highest baud rate.
If this is the case, I might need to rethink the strategy somewhat and hence would love to hear for your thoughts on the best way forward.

SD card / buffer / compression algorithm / magic? All ideas welcome.

Dave

2

Just a quick update for the interested.

Some of my boundaries.

ISO 6487:2012 : Road vehicles - Measurement techniques (Class 600 = 600Hz response.)

http://www.comlaw.gov.au/Series/F2006L01377 Australian design rules for seats.

We have guys building the seat testing jig and the domed 6.8kg pendulum. Others are designing a few seats.

If I am successful in measuring the acceleration then we can engage local certified engineers during the build process.

1.2. Test apparatus
1.2.1. This apparatus consists of a pendulum whose pivot is supported by
ball-bearings and whose reduced mass ∗/ at its centre of percussion
is 6.8 kg. The lower extremity of the pendulum consists of a rigid
headform 165 mm in diameter whose centre is identical with the centre
of percussion of the pendulum.
1.2.2. The headform shall be fitted with two accelerometers and a
speed-measuring device, all capable of measuring values in the
direction of impact.
1.3. Recording instruments
The recording instruments used shall be such that measurements can be
made with the following degrees of accuracy:
1.3.1. Acceleration:
accuracy = + 5 % of the actual value;
frequency class of data channel: class 600 corresponding to
ISO Standard 6487 (1980);
cross-axis sensitivity = < 5 % of the lowest point on the scale.
∗/ The relationship of the reduced mass "mr" of the pendulum to the total mass
"m" of the pendulum at a distance "a" between the centre of percussion and the
axis of rotation and at a distance "l" between the centre of gravity and the axis
of rotation is given by the formula:

mr = m * l / A

1.3.2. Speed:
accuracy: + 2.5 % of the actual value;
sensitivity: 0.5 km/h.
1.3.3. Time recording:
the instrumentation shall enable the action to be recorded throughout
its duration and readings to be made to within one one-thousandth of a
second;
the beginning of the impact at the moment of first contact between the
headform and the item being tested shall be detected on the recordings
used for analysing the test.

3

The BMA180's highest measuring range is ±16g. Is that enough range for the testing that you want to do?

frequency class of data channel: class 600 corresponding to

Not 600 hz and sample rate is minimum 6Khz, see:

freq class

This defines the filter for the data channel.

4

groundfungus:
The BMP180's highest measuring range is ±16g. Is that enough range for the testing that you want to do?

Sample rate is minimum 6Khz, see:

Thanks. Looks like I have a lot more reading to do.

I have an old copy of the ISO code and I read it as this - Imgur: The magic of the Internet
But I trust the 6kHz value. Makes more sense.

As for ±16g - I have to apply a force of 37.3 daNm of 6.8kgrams at a speed of 24.1 km/h

By means of a spherical headform 165 mm in diameter an initial force
producing a moment of 37.3 daNm about the R point is applied at right
angles to the displaced reference line at a distance of 65 mm below
the top of the head restraint, the reference line being kept in its
displaced position in accordance with paragraph 6.4.3.2.

This requirement is deemed to be met if in the tests carried out by
the procedure specified in annex 6 the deceleration of the headform
does not exceed 80 g continuously for more than 3 ms. Moreover, no
dangerous edge shall occur during or remain after the test.

So it looks like I need to find a new sensor. :slight_smile:

I really appreciate your comments.

5

A quick update. June 2015

I have a few hobby car builders and engineers interested in the project. It is a joint open/share project.

I have not given the data collection much thought beyond streaming to a PC. Ideally Excel or another capture program would be good.

Any suggestions welcome -

I have to send a command to operate the servo and capture a stream of data from 2 Bluetooth HC-05's in a 5 second period and dispaly the results and show a pass of fail icon.

#############
The Problem

There are no after market seat meeting the current ADR Australian Design Rules. Our options are limited to seats (or head restraints) from production cars so let us test seats ourselves.

The ADR

From my research we need to test these specific items.

Head restraint deceleration.
Seat strength
Physical sizes

Head Restraint.

The speed of a 165mm diameter, 6.8kg Sphere at impact using the average of two accelerometers measuring deceleration.

Sphere speed at impact = 24.1km/h. Accuracy: + 2.5 % of the actual speed; Sensitivity: 0.5 km/h. Time recording – samples every 1msec.

Our rule of thumb is if the head restraint moves more than 30mm it should pass.

Seat strength

Mount seat vertically, load 20 times the seat weight, for more than 1 second, in all adjustable positions.

Physical sizes

ADR is clear but typically the seat needs to be around 900mm from the cushion to the top of the head restraint and openings and slots must not exceed 65mm (there are a few tricks to this)

Electronics –

Arduino Mega processor. It should be able to record the impact for about 3 to 5 seconds depending on how smart we can make the software.
Memory and data transmission rates are the bottlenecks.

Accelerometer – must read greater than 80g, more than 600Hz response.

Encoder to measure speed. Will require its own Arduino processor.

Bluetooth communications

SD (camera style) memory card

Servo release to initiate pendulum swing.

Hardware –

Sphere. I have a sphere to test with but I would love to get a local guy to manufacture these to ensure correct weight and ability to mount electronics.

Pendulum. A pendulum makes a lot of sense as the speed just prior to impact will not vary too much. The sphere suspended from an A frame, forklift or factory ceiling on some flat steel bar. A mechanism to capture the rebounding sphere?

The floor frame. Ideally a 50mm RHS with say a 6mm plate and tabs to bolt or secure to floor. We can secure chassis rails or seat runners to this frame.