MegasquirtnSpark-extra Firmware for megasquirt

< < BACK

This feature is designed to take action if the engine accelerates beyond a set limit (MSD call this slew rate.) In development Phil found that his maximum acceleration on dry tarmac in 1st gear was 2500rpm/second. If the engine accelerates faster than that there must be wheelspin. This is the basis of this feature.

No extra hardware is required if you use the RPM based selection.

Please Note: This is in the early stages of development, it works as it is described, but it has a fair way to go. Anyone testing this out, please do not expect miracles from it, it is very crude at present and may remain that way.

On the General menu you can find Anti-Rev

  RPM Based System

When the Anti-Rev system is selected ON and RPM Based is selected, the rate of change in engine RPM is monitored every 0.1Sec. If the rate of change exceeds the RPMdot Threshold setpoint the system will try to slow down the engine by retarding the ignition and or enriching the fuel mixture to bog the engine and or cut a spark or 2 if using MSnS. The system will also turn off the NOS system if you select it, when the threshold is reached. The values are all interpolated so if it detects an increase of 3500rpm then it will give a retard angle of 15 degrees in the above example and a 9mS increase in the PW to try to bog the engine down. The effectiveness of the system will depend on how well your engine reacts to retarding the ignition and by adding fuel to bog down the engine. The maximum spark cut allowed is 2 sparks, as this could cause the engine to suddenly slow down, causing a dangerous situation, so please be careful with this setting.

There is also a setting to keep the traction active untill the RPM is stable again, or for xx amount of engine cycles, the engine cycles can be set as above and they are interpoled depending on the amount of slip is detected.


VSS Based System

When the Anti-Rev system is selected ON and Vehicle Speed Sensor Based is selected, the MS takes in 2 x 0-5V signals related to the speed of an undriven wheel and a driven wheel. Here is a circuit we have come up with that can produce the voltages required for the system to work.

Please NOTE: For V3 pcb's X6 = JS4 and X7 = JS5

The code reads the driven wheel's input and works out what speed the un-driven wheel should be. The speed is worked out by mulitplying the voltage of the driven input by the ratio you enter in the Sensor Differential % box. If it calculates that the speed is higher than the driven wheel by the amount of slip allowed then the traction system cuts in. There are 3 interpolated systems that try to reduce the engine's power: Ignition Retard, Enrichment of Fuel and Spark Cut. These are interpoled from values you enter for 5, 15, 30 and 75% slip.

To find the Differential percentage drive down the road with the sensors hooked up and measure the voltage from both the circuits at a constant speed. Adjust the pots so as the driven circuit gives a slightly larger output than the undriven. Its best to adjust the voltages to around 2.5V at around half your top speed then you will have the ability to use it through out your entire speed range. So if you have 2.5V from the driven and 2V from the undriven at a constant speed the differential would be 2 / 2.5 x 100 = 80%

The system will work at a different threshold depending on the speed of the vehicle. The low speed setting is for anything under 2.5V input from the undriven speed sensor and the high speed threshold works when above 2.5V. We have also added a minimum and maximum voltage input that the system will work at, so if you dont want it to work at high speed then enter the voltage in the Max Undriven Speed that you want the system to stop working at.

< < BACK