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MS3x Traction Control in 240

shaved240

shaved240

Active member
Joined
Jun 6, 2003
Location
California
anyone know anything about traction control feature on MS3X? surprisingly I haven't found a lot of helpful info on msextra.com

does megasquirt need two vehicle speed sensors (VSS) for traction control to work? Also any ideas on a good pickup point for the sensor to read off of. I'm trying to stay away from the stock read diff speed sensor because its a VR type sensor and I would have to build a conditioning circuit for it to work in megasquirt.
 
Whats optimal location for a VSS sensor for traction control and would pulling the reading from my differential work out.

also if you only need one VSS sensor how does megasquirt determine when traction is lost if its reading it from the rear differential vs. reading it from the front. Or does it need both to work.
 
I think there was an early version which just looked at the RPM change and used that to determine if the wheels were losing traction or not. I don't think that worked all that well.

AFAIK the current one uses VSS, you'd need one from a driven wheel (rear axle on an old Volvo) and one from a rolling wheel (either of the front wheels). And,,, no massive stagger in sizes front to rear, heh.
 
You can use perfect run with one vss or percent slip with dual vss. Don't matter where the vss is, it's all programmed in megasquirt. Stagger doesn't matter either as speed will match in TS

I run it on my 2j volvo, effective and as of late, more datalog fields have been implemented to help with tuning

I run two vr sensors, front abs and tranny mounted. There being buffered by a dual vr board from JB perf
 
Pulling a reading from the diff works best because it's already a wheel-speed reading. Unless you enjoy making life overly complicated, adding a VR circuit would be the cheapest and easiest solution for a rear wheel reading.

Much like using RPMdot for the traction control, you can use just rear wheel speed and define an acceleration rate that would represent loss of traction. It works, however, the faster speed the car is going, the slower it accelerates. Using a single-ended acceleration strategy seems to only work well in lower gears. Once you get the car moving, unless experiencing a complete loss of traction, a single sensor doesn't work well since you can't detect slip percentage.

Using dual VSS, one rear wheel speed, and one front wheel speed, you can detect slip percentage and base your traction control off of slip instead of just acceleration rate.

What strategy works ideal greatly depends on your application. Drag applications I've found timed boost after launch works best. Slip percentage based on dual VSS is less than ideal, especially with cars that carry the front wheels the first few hundred feet. VSSdot works as well for lower power cars.

If your application is DD, then slip % based on dual VSS would work best. However, keep in mind the front and rear wheels in a tight turn will register a high slip rate, so there is some headroom you'll have to allow for percentage of slip.
 
I %slip vss on the wagon. Works really well unless I'm pulling a trailer in the rain (and it works well then too I suppose, just not as ideal). haven't noticed any issues in tight corners.

I piggybacked off the abs sensors for mine, using a jbperf dual vr card. There's not much to talk about because it's fairly straight forward to setup.
 
linuxman51 said:
using a jbperf dual vr card. There's not much to talk about because it's fairly straight forward to setup.
Click to expand...

This is basically what it comes down to. Anything beyond that is just added difficulty.

Implementation is easy, strategies are a different story.
 
Homer said:
ABS front struts and use the rear diff.
Click to expand...

that's what I'm thinking but will most likely have to ditch my coilovers for these struts and seems like too much work i'll have to come up with a better solution for the front.

gross polluter said:
Pulling a reading from the diff works best because it's already a wheel-speed reading. Unless you enjoy making life overly complicated, adding a VR circuit would be the cheapest and easiest solution for a rear wheel reading.

Much like using RPMdot for the traction control, you can use just rear wheel speed and define an acceleration rate that would represent loss of traction. It works, however, the faster speed the car is going, the slower it accelerates. Using a single-ended acceleration strategy seems to only work well in lower gears. Once you get the car moving, unless experiencing a complete loss of traction, a single sensor doesn't work well since you can't detect slip percentage.

Using dual VSS, one rear wheel speed, and one front wheel speed, you can detect slip percentage and base your traction control off of slip instead of just acceleration rate.

What strategy works ideal greatly depends on your application. Drag applications I've found timed boost after launch works best. Slip percentage based on dual VSS is less than ideal, especially with cars that carry the front wheels the first few hundred feet. VSSdot works as well for lower power cars.

If your application is DD, then slip % based on dual VSS would work best. However, keep in mind the front and rear wheels in a tight turn will register a high slip rate, so there is some headroom you'll have to allow for percentage of slip.
Click to expand...

thanks this was EXTREMELY helpful, also thanks to Kenny and Nathan too.
 
one more thing...

in terms of wiring I already have a zeal engineering dual VR conditioning circuit from another project lying around. How does the card interface with the MS3X daughter card? would it be mounted inside box or externally. since the pins come straight out from the db37 how to i interrupt the signal so that it passes through the VR circuit. In layman's terms how do i wire the dam thing in.
 
I went super easy and drilled a hole in the top of the case, ran the vr wires in like that. If you're not using the various SPR headers for anything, you can run the vr signals in there. or the iac wires
 
bringing this back from the dead....

I was looking at the 240 wiring diagram and noticed that the VSS sensor wiring from the differential goes directly into the speedometer. The speedometer also outputs the VSS signal to things like the overdrive relay and the cruise control module. Are the other outputs coming off the speedometer for the cruise control module still in VR form, or is there some sort of conditioning circuit that converts the signal to 12v so that the cruise control module can utilize the signal?
 
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not sure, i used the abs stuff for mine, spliced into the wiring at the abs ecu. no problems there
 
shaved240 said:
bringing this back from the dead....

I was looking at the 240 wiring diagram and noticed that the VSS sensor wiring from the differential goes directly into the speedometer. The speedometer also outputs the VSS signal to things like the overdrive relay and the cruise control module. Are the other outputs coming off the speedometer for the cruise control module still in VR form, or is there some sort of conditioning circuit that converts the signal to 12v so that the cruise control module can utilize the signal?
Click to expand...

I did my fuel pump the week and there's a box sealed up on the wires coming off the diff sensor in the back of the car. I didn't see it on any diagrams and couldn't find any info on it. It could be what you're talking about.
 
The Vss signal from the speedo board to the LH2.4 ECU is a square wave, after VR conditioning, with 1 pulse per tooth. It comes from an open-collector driver within the UAF2115 speedo chip. I expect the ECU includes a ~1K ohm pullup resistor but I'm not sure if cruise control does too.

See cleanflametrap's speedo page. His schematic shows pin 3 of the UAF2115 conditioner chip going to the ECU, with no pullup on the speedo board. If you surf for the UAF2115 datasheet, it describes pin 3 as a NPN open-collector driver for a taximeter.
 
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