I am looking for some advice on part of a project i am doing. Last year for my dissertation I used 4 ADXL335 analog accelerometers and an arduino due to measure the acceleration of suspension components on a motorcycle that went over a specially designed mathematical speedbump and the response compared to a simulink model.
The results didn't match up as closely as i wanted them to so at the beginning of this year i'm going to redo the experiment but with different accelerometers. To determine which accelerometers will be the most accurate i'm going to perform a test of 4, maybe 5 accelerometers to determine which has the highest accuracy to the actual acceleration value. The 5 accelerometers i will be testing are below;
Datron 2D 1 or 2 axis (Benchmark) - http://2d-datarecording.com/Downloads/D ... -DINA4.pdf
As said above, the datron accelerometer is probably going to be the benchmark at a retail price of around £100 as these are the same accelerometers used on MotoGP bikes. However, i dont know 100% that it would be the most accurate. So, why not test it?
My plan is to find an oscillating source (we have a suspension dynamometer at uni which is my first thought as it can run at repeatable frequencies, though will have to check the accuracy of IT'S sensors) and attach all the accelerometers to the source, so that the axes are all facing the same way to as high a precision as i can. Then run the source at multiple frequencies, compare the results of each accelerometer to each other and the known acceleration of the source.
However, this is where i've had issues before. When using the arduino, the highest sample rate i could achieve was around 180Hz (even though the bandwidths of the ADXL335 are up to 550Hz for the Z axis, and 1600Hz for the X and Y). I'm unsure whether this was down to my code, or limitations of the arduino. So, i bought the raspberry pi in the hope i could achieve faster sample rates.
The issue with using a pi is that it doesn't have analog inputs, So i'll have to use an ADC. I already had an adafruit ADS1115 and just bought an ADS1015. What I'm concerned about is if using an ADC will slow down the sample rate. This concern is because when using it with the arduino, as i originally had an ADS1115 connected for a fifth ADXL335 on the due, the sampe rate dropped from 180Hz without the ADC to 28Hz with the ADC. However, i was completely clueless and looking back over the datasheet, it seems that the default setting of the ADS1115 is to use single shot mode (ADS1115 datasheet, pg 21, section 220.127.116.11) and i may have not been using code that allowed it to run at it's maximum sample rate.
So that is my description of my current project and the background. My questions and requests for advice are as follows (bearing in mind that the end goal is to have the accelerometers measuring suspension dynamics on a racetrack);
1. Any preferences on whether to use analog or digital?
2. Any suggestions on which Accell/ gyro module to use? or suggestion on one i haven't considered?
3. Would i be better using the ADS1115 (16 bit, up to 860 sps) or the ADS1015(12 bit, up to 3300 sps), or another i haven't considered?
4. If using the adafruit ADC's, would it be better to use single-shot mode with ALERT/RDY pin active, or continuous mode?
5. Would i get much better signals using differential inputs or is single ended accurate enough (considering possible noise)?
6. Any other suggestions?
Sorry for the long post, but thought i would try to tap into the massive collective knowledge and experience on here.
Thanks in advance