Rudder Pedal Shaker

[Xpendable]

The Harrier has a RPS system, or rudder pedal shaker, which I think it is relatively unique to the Harrier. It was developed to warn the pilot in slow speeds during hover or transition to or out of hover, from excessive sideslip. If the sideslip becomes to great, it can result in loss of control and a crash. Early AV-8A's did not have this but it was added in the late 70's. The AV-8B also has the SAAHS which helps keep the aircraft stable and is less prone to the excessive sideslip but it could still happen. Anyway, the mission computer with activate the RPS when one of the following conditions occur when lateral acceleration is 0.6G or greater and any of the following conditions exist:
* Gear down and STOL flaps selected
* Gear down and Flaps set to Cruise or Auto and speed less than 0.3 mach
* Gear up, STOL flaps, speed less than 0.3 mach
* Nozzles greater than 10 degrees down

When this happens, the mission computer switches on an electric DC motor with an eccentric weight on the pedal that should be pushed to correct for the sideslip, which causes it to shake.

This isn't modeled in the Razbam Harrier, but I figured out that I can probably replicate it using Dcs-Bios, an Arduino, and 2 vibration motors. From Dcs-Bios I can read the value of the slip ball. I can't read the value of lateral acceleration but I wonder if I could probably calculate it using other values such as AOA, airspeed, lat and lon (and difference based on delta over time), etc. I just ordered a pack of vibration motors from Amazon for $10. The plan is to 3d print a bracket to hold a motor and mount it to the backside of each pedal. The Arduino will switch on the motors when needed, possibly via relay to protect against the current draw of the motor. Alternatively I could use flyback diodes and transistors. Should be a fun little project. There is also a RPS test switch which I can read that should turn on the motors when pressing full rudder while taxing.

Edit: I keep forgetting that the Harrier has a weather vane on the nose specifically to tell the mission computer the angle of side slip. I need to see if the position of that weather vane is readable by dcs-Bios.

[Xpendable]

Hmm, the weather vane is not currently available in dcs-Bios. I may have to dig into the code and implement it.

[Xpendable]

Actually the SAAHS uses the INS to get the lateral acceleration. The weather vane is not hooked up to anything and is just a visual aid. I think the lateral acceleration can be computed using data exported from DCS - not necessarily via DCS-BIOS, but data that would also be needed by motion platforms.

[Cr33p3r]

Very cool thing to simulate in your home cockpit! You can also tell your children to watch your airspeed gauge and grab you and shake you when you get too slow!

I've been trying to get my Logitech FIP's to work with DCS and researching that but many dead ends (or they freeze after a small period of time).

[Trichome]

That sounds pretty awesome. Good luck with that.

I'm starting to build a bit of a racing sim here (got the seat and measurements so far) and I've been watching lots of diy rig videos on YouTube and I've seen a few that have little motorized seat belt tensioner so when you shift or turn the appropriate belt is pulled to give you that immersion feeling....

I'm not doing it but your experiment reminded me of that. Pretty neat the things people are doing now with DIY stuff.

[Xpendable]

Update on the RPS project. The RPS system is supposed to use lateral acceleration from the INS in combination with the various parameters in my previous post. If inside one of those parameter sets, and lateral acceleration exceeds 0.6G, the RPS activates. DCS-BIOS does not natively expose lateral acceleration. What to do? Modify DCS-BIOS to add lateral acceleration, of course! And that's exactly what I did. I found out that DCS has a Lua function called LoGetAcceleration() which returns an object that has x, y, and z values. X = lateral acceleration, and Y = longitudinal acceleration, or the G value the plane experiences. So I was able to add support for lateral acceleration in DCS-BIOS by writing some Lua code and editing a JSON file. Now I have access to that value. I have written all the code for the Arduino to fully support all of the RPS logic. That's the good news. The bad news is the lateral acceleration values I am getting do not seem to match much what I think should be happening in a sideslip, for example. I have compared the values against a couple of other modules and the results seem to be consistent at least. So where to go from here?

I am thinking that I need to apply some sort of math to the raw value, coupled with perhaps some other piece of data so I know whether the left pedal or right pedal should shake. There is next to do info about the lateral acceleration in DCS but I do know that it is used in motion rig software. I may need to reach out to Eagle Dynamics and/or other devs that have written software against this value. More to come.

[Trichome]

So much of this is over my head but I hope it all works out and I cant wait to see this setup once its complete

[Xpendable]

Test of the RPS ground-test mode:

[Hammer]

I just gotta say your dedication is way, way over the top! I have nowhere near the time, and not even the dedication.

[Xpendable]

RPS installed. Still not done with the coding.

[Trichome]

That looks cool... look forward to hearing how it a works out once you're done the coding.