Rick
05-24-2007, 08:28 PM
I called the California AIM office and spoke with one of their guys who works on development of the AIM products. I've also spoke with someone from a local AIM dealer. The information I received is somewhat conflicting. The local dealer seems to believe that accelerometers are the way to go. The guy from AIM did not. He believes combining both is the best way to go.
The guy from AIM told me that GPS is the way to go now. The reasons for this are:
1. no need for a beacon.
2. more accurate track maps.
3. more accurate speed.
4. z axis mapping (some glitches)
5. you still have accelerometer data anyways
6. you can pick and choose your start/finish and set your own sectors via software.
In the past, accelerometers were considered superior due the limitations of GPS technology and primarily because of lack of precision. This was primarily due to the low sampling rates coupled with the built in noise in non-military GPS receivers. For example, TraqMate's receiver operates at 4Hz. But, high frequency and more resolution is not the holy grail.
According to the guy I talked to, more frequency can actually be bad. This goes for both the GPS and accelerometers as well. In fact, he told me that the accelerometers sample no where near 1000Hz. If it did, it would record too many minor vibrations. In practice, the AIM accelerometers sample somewhere around 10Hz. This explains why it can record more data that what I had originally calculated/guessed. I was assuming at least 2 bytes per data point. 1 byte for the value and 1 byte for the timestamp (and perhaps some data to specify the type of data). 1MB = 1,024,000 bytes. 1,024,000 bytes/2 bytes per data point = 512,000 bytes. 512,000 bytes/1000Hz = 512 seconds of data. 512/60 = a little over 8 minutes. At 10Hz, it makes more sense. 800 minutes is a little over 13 hours for one sensor operating at 10Hz and with no dead band. Add in a temp sensor and RPMs and it's more feasible to fit 8 hours of uncompressed data into 1MB. But then again, I'm not accounting for the extra memory that is activated by adding the E-Box. So there is actually more memory available.
With the improvements in GPS technology and their internal software development, AIM is using a GPS receiver capable of receiving both "carrier phase" and "code phase" signals and smooth out the signals and correct errors. The preferred signal is "carrier phase". The software is written to utilize the less accurate "code phase" signals when "carrier phase" signals are not clean enough. The sampling rate of the receiver is around 10Hz. The MyChron 4 is also compatible with the AIM GPS unit. The GPS unit costs around $599.
Another interesting topic is memory. The MyChron 4 actually has 8 or 16 MB of physical memory in the unit already. Only 1MB is "activated" when the display unit is used by itself. As more and more AIM products are daisy chained, more memory is activated. They are also working on a solution to store enough data to so we can record the entire 24 hour race. They are trying it out at a MX-5 Cup race soon. We will have to wait for firmware upgrades in order to be able to do the same thing.
Rumor has it that they are also working on a new sensor that measures blood alcohol content of the driver. :evil_lol:
It's also important to note that most professional race teams are still primarily relying on the accelerometer technology. Only some teams are using GPS. Some pro karting teams are also using the GPS units with the MyChron 4.
For more info regarding carrier phase and code phase GPS signals see: http://webmail.nicolet.k12.wi.us/~Jason_Huber/FOV2-00014049/FOV2-00019020/FOV2-00019037/FOV2-00019039/codevscarrier.html (http://webmail.nicolet.k12.wi.us/%7EJason_Huber/FOV2-00014049/FOV2-00019020/FOV2-00019037/FOV2-00019039/codevscarrier.html)
The guy from AIM told me that GPS is the way to go now. The reasons for this are:
1. no need for a beacon.
2. more accurate track maps.
3. more accurate speed.
4. z axis mapping (some glitches)
5. you still have accelerometer data anyways
6. you can pick and choose your start/finish and set your own sectors via software.
In the past, accelerometers were considered superior due the limitations of GPS technology and primarily because of lack of precision. This was primarily due to the low sampling rates coupled with the built in noise in non-military GPS receivers. For example, TraqMate's receiver operates at 4Hz. But, high frequency and more resolution is not the holy grail.
According to the guy I talked to, more frequency can actually be bad. This goes for both the GPS and accelerometers as well. In fact, he told me that the accelerometers sample no where near 1000Hz. If it did, it would record too many minor vibrations. In practice, the AIM accelerometers sample somewhere around 10Hz. This explains why it can record more data that what I had originally calculated/guessed. I was assuming at least 2 bytes per data point. 1 byte for the value and 1 byte for the timestamp (and perhaps some data to specify the type of data). 1MB = 1,024,000 bytes. 1,024,000 bytes/2 bytes per data point = 512,000 bytes. 512,000 bytes/1000Hz = 512 seconds of data. 512/60 = a little over 8 minutes. At 10Hz, it makes more sense. 800 minutes is a little over 13 hours for one sensor operating at 10Hz and with no dead band. Add in a temp sensor and RPMs and it's more feasible to fit 8 hours of uncompressed data into 1MB. But then again, I'm not accounting for the extra memory that is activated by adding the E-Box. So there is actually more memory available.
With the improvements in GPS technology and their internal software development, AIM is using a GPS receiver capable of receiving both "carrier phase" and "code phase" signals and smooth out the signals and correct errors. The preferred signal is "carrier phase". The software is written to utilize the less accurate "code phase" signals when "carrier phase" signals are not clean enough. The sampling rate of the receiver is around 10Hz. The MyChron 4 is also compatible with the AIM GPS unit. The GPS unit costs around $599.
Another interesting topic is memory. The MyChron 4 actually has 8 or 16 MB of physical memory in the unit already. Only 1MB is "activated" when the display unit is used by itself. As more and more AIM products are daisy chained, more memory is activated. They are also working on a solution to store enough data to so we can record the entire 24 hour race. They are trying it out at a MX-5 Cup race soon. We will have to wait for firmware upgrades in order to be able to do the same thing.
Rumor has it that they are also working on a new sensor that measures blood alcohol content of the driver. :evil_lol:
It's also important to note that most professional race teams are still primarily relying on the accelerometer technology. Only some teams are using GPS. Some pro karting teams are also using the GPS units with the MyChron 4.
For more info regarding carrier phase and code phase GPS signals see: http://webmail.nicolet.k12.wi.us/~Jason_Huber/FOV2-00014049/FOV2-00019020/FOV2-00019037/FOV2-00019039/codevscarrier.html (http://webmail.nicolet.k12.wi.us/%7EJason_Huber/FOV2-00014049/FOV2-00019020/FOV2-00019037/FOV2-00019039/codevscarrier.html)