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Project Apollo Beta 7.0 released!
http://nassp.sf.net/wiki/Installation
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| | | |-+  ECA committed (SCS manual and automatic control)
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Author Topic: ECA committed (SCS manual and automatic control)  (Read 2528 times)
dseagrav
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« on: March 24, 2006, 07:17:23 PM »

This enables SCS manual and automatic control. I think it works right. I have some tuning to do, mostly small things like the amount of pseudorate feedback, but I wanted to commit it before too long so others could see it, and to see if it works for everyone else.

Acceleration-rate mode, proportional-rate mode and automatic-rate mode, minimum impulse mode, deadband and rate limit switching, and pseudorate feedback all work to some extent, but I'm not sure if the numbers are exact.
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Christophe
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« Reply #1 on: March 25, 2006, 04:52:27 AM »

Sounds great Very Happy
Can't wait to try
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Tschachim
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« Reply #2 on: March 25, 2006, 12:39:13 PM »

Short and dumb question:  Wink

For the RJEC power supply you only check the SIGCondDriverBiasPower2Switch and not the 1-switch. Is that intended?

Cheers
Tschachim
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dseagrav
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« Reply #3 on: March 25, 2006, 02:57:13 PM »

No, I had meant to go back and add the other and I forgot to. They aren't identical though, #1 controls a second bias supply in the RJEC, and a signal conditioner in the EDA. I didn't know if these two were redundant supplies or if both were needed, and I forgot to look it up and correct that.
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Tschachim
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« Reply #4 on: March 27, 2006, 06:19:23 AM »

Thanks for explaining!

Can you also explain the new SCS features a little bit? Currently when I separate the CSM from the launch vehicle and have SC CONT to SCS the RCS fires permanently spinning the CSM around and I don't know why and how to turn it off...

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Tschachim
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dseagrav
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« Reply #5 on: March 27, 2006, 12:11:03 PM »

Sure thing.

The SCS has three major modes; ACCEL CMD, MINIMUM IMPULSE, and RATE CMD. These modes are selectable per-axis via the MANUAL ATTITUDE switches on the left side of the main panel.

In ACCEL CMD, when the RHC is out of center in any axis, the jet is fired continuously in the selected axis. That is, moving the stick left creates demand for left acceleration. The acceleration stops when the stick returns to  center.

In MINIMUM IMPULSE, moving the RHC out of center creates a one-timestep long pulse in the selected axis. To generate a second pulse, you have to recenter and then move the RHC.

RATE CMD is the complicated one, and the mode you were probably in.

When RATE CMD is enabled, the first thing the SCS does is find out if it has an operating BMAG or not, via the GDC. If the GDC is not working or the BMAG is rate-caged (or inop) you get zero attitude error, and are in RATE DAMPING PROPORTIONAL COMMAND mode. This works almost exactly like Airbus NORMAL LAW. Deflecting the stick a given direction creates a demand for rate in the given direction. The maximum rate is set via the RATE switch (next to TRANS CONTR PWR). Half deflection means half rate. Deflection is measured between the closing of the breakout switch and the closing of the direct command switch in the RHC. Additionally, SC rotation rates are damped down to maximum rates selected by the RATE switch. If the SC is tumbling, and you enter this mode, the SCS will un-tumble you. It works like killrot-to-within-limits.

If the GDC has attitude information and you are in RATE CMD, you are in ATTITUDE HOLD PROPORTIONAL COMMAND mode. In this mode, the SCS  tries to zero its error in the selected axis. With all 3 axes enabled, it basically flies to the attitude selected on the ASCP, using the GDC as reference. (So you have to have aligned the GDC for this to do anything meaningful). It considers its current attitude and rate, generates a target rotation rate to move toward its target, and fires jets appropriately. If you move the stick out of center. you get PROPORTIONAL COMMAND as outlined in the preceeding paragraph. When you recenter the stick it goes back to holding (or moving toward) the ASCP attitude. The attitude hold deadband is set with the ATT DEADBAND switch next to the RATE switch.

For both RATE CMD modes, if the LIMIT CYCLE switch is up, any thruster firing in any axis (except the SPS) generates a few impulses worth of additional "pseudo-rate" in addition to the current SC rotation rates. This has the effect of causing the jets to pulse on and off toward the outer edges of the rate deadband. This is supposed to conserve fuel.

It is worth noting that the rate deadband can extend to the opposite sign for values close to zero; That is, in proportional rate mode, if you are rolling fast left, and move the stick to command a slow right roll, the SCS will move to the left edge of the deadband, which may be a slow left roll.

Clear as mud, right?
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edmendduke
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« Reply #6 on: March 28, 2006, 01:46:17 AM »

So that's why in Apollo 13 (the movie), they press GDC align just before they begin docking
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Christophe
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« Reply #7 on: March 28, 2006, 02:53:48 AM »

I did cvs update but changes doesn't appear. I think new modules are necessary to get them.
While I still have a few problems to build with my free compiler, could someone post updated modules Very Happy
Thanks.
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Tschachim
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« Reply #8 on: March 28, 2006, 07:52:26 AM »

Hi dseagrav,

thanks for explaining! Additionally the member variables of the ECA were not properly initialized in the constructor, I fixed that together with the abs() calls.

I want to do some tests with the joystick and then I'll try to make new beta modules soon.

Cheers
Tschachim
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dseagrav
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« Reply #9 on: March 28, 2006, 08:50:06 AM »

Oh BTW, reason I missed the abs() mistakes - VS2003 does not generate a warning for that.
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