MoTeC Global Forum

In a drag race application where the front wheels can't be used as a velocity source, what are people using for ground velocity input? Integrate the longitudinal accelerometer to calculate velocity? Laser? Would GPS have quick enough response? Or, do most just ignore ground speed and opt instead to look at engine or driveshaft accel? Any thoughts would be appreciated.

Would 20Hz GPS give you enough resolution?

Is this for Mx00 or SDL/ADL2?

I don't know if a 20hz GPS would work? This is for a M800+ACL setup.

Jamie mentioned that there is a GPS with Digital output, that will work on the ECU. Or you run the RS232 to the ACL and from there set up a Can template to send the Data you want to the ECU. There is a technote on sending data from ADL to M800, guess it must be the same from the ACL. Ive done this from an ADL,,,sending wheelspeeds for TC. Suprisingly the can bus is fast enough

Only problem would be if your GPS has lost satelites

There is also an inherent time delay with GPS systems which in my opinion makes them unsuitable for TC or Launch Speed channels.

have a look..


Gps vs drive

You can see the drive running away from GPS as there is more slip just before each shift, but the delay isnt too bad is it?

IDP & Martin (or others), I'd like to hear more on your thoughts re using GPS as a velocity source for TC/LC.

Martin, is the above graph using one of the Motec GPS modules, or something other? I know that GPS technology generally involves a latency time depending upon the system & satellites available, and that this can be compensated for during post analysis.

However, during live analysis & decision making, how big a deal is this? Can a person use either of the Motec modules live for such purposes, or would something like the RaceLogic V-Box be required (or some other product) for the purpose of fine TC/LC control?

What about going back to basics and simply integrating the longitudinal X-axis chassis accelerometer signal? Would that work adequately since we will be operating essentially along a horizontal plane and essentially along a straight vector line (hopefully)?

Again, all of this is related to a drag race application. "If you can still turn........you're not going fast enough"

It would be very handy to be able to start a timer with a driven speed, say timer1 on at >5kph. Then use timer1 as an axis along with driven speed in the Launch RPM table. And if we wanted to get really fancy add a Z axis for gear.

I'm currently using clutch position or clutch pressure via a pressure sensor and AT levels to start the timer, but these are somewhat inconsistent, starting the timer with driven speed would be more consistent.

Don't know about the rest of you but buying an extra module or two vs. a software solution doesn't compute.

Hi TOL

Yes it was with a 10Hz or 20Hz GPS module as sold by Motec. As you can see the channel that i used was an "obsolete" channel but that was just because the ADL sent the GPS data. As you know the ADL is a 16 bit device and not 32 like the ADL2, SDL etc...GPS`s arent fully compatible with the old ADL`s. The SDL, ADL2 are no problem.

Have a look at the logged data and then you decide if the latency is a problem....i dont think it is...From the ACL you can transmit up to 100Hz

I would definately try the GPS! Get the RS232 output from the GPS into the ACL and then you make a Custom data set and send the GPS speed channel to your M800 via Can bus. In my opionion Can bus if fast enough for TC and LC since ive done it with good results! GPS`s allready incorporate G sensors to decrease response time and increase position update rate. Novatel has really nice GPS`s with 200Hz Data output and up to 20mm accuracy but they are just too expensive. My sugestion is to try a 20Hz or even a 10Hz. Drag strips are usually open places with not much to block Satellite signals.

Are you familiar with setting up a can template? If not you can get a document discribing how its done.

Maybe someone from motec would also like to give an opinion on this subject?

HI guys !... I'm doing s TC too by Now... AndI just add a Speed sensor con a Rear Wheel for Ground Speed !.

Why can't you dothis?

Cheers.!

Gaston