Understanding the MCPX receiver chip

[coredump]

I agree. I was heading to the movie so I don't have time to detail my guessing.
My guess is that, those are receiver data 6 channel + 3 gyro + 3 servo position
+ main + tail + maybe 2 gyro temperature . That would be 16 integers. If I write
the firmware that is the stat I would dump.

The debug port has 4 leads:
V+, ground, data in, data out.

So my theory is that the port is plug into tiny serial data logger,
just like the heli black box I was planning to build. The serial logger
is very small to attach to the debug port and get power from it.
The serial logger fly with the MCPX recording all status, every 7.5ms.

Then the engineer should be able to take the serial log after the fly and
analyses how the FBL control works. Just like the race car team analyze
their data after each race.

Because you have the full log, you can identify problem like tail kick and
shakes and fine tune the FBL firmware.

That is how I would build it and use the debug port if I am the engineer building
it. I suspect that is what they do. I will likely using the same plan to test my
firmware as well.

[SuperX7]

Pardon my ignorance and lack of understanding on this matter but would one be able to re-program the board so you can mount the PCB at a different orientation to the frame using this procedure?

[coredump]

It is certain possible if you flash the board and write yoru own FBL firmware.
But that is not a easy task. I assume the FBL firmware is the holly grail of
the MCPX proprietary secretes. The performance of the FBL system, affect
the feel of the heli a lot.

Without reprogramming the MCPX firmware. You need to keep the gyro
chip facing the way it is designed. If you are brave enough, you might able to
cut out the gyro circuit on the mcpx board with the near by circuits.
Make it face up right. Then you just need to reconnect about 5 signal wire on
V1 and 3 signal wire on V2, plus the power and ground. That should work.

It will very likely ruin your board. But I think it can make to work as well.
I can close study the board again and see if that is possible.

[coredump]

Another idea is have a i2c bus intercept chip on V2. It intercept the i2c
bus and provide a virtual gyro chip with the channel swapped. Swapping
gyro gain direction is tricky, because you need to know the base value.

The interception will cause delays in the gyro response reaching to the
MCU, that might affect the FBL system performance. Since the gyro was
read at about 400 Hz. If you can keep the bus intercept with in 1ms, I guess
it can make to work as well.

[cp11]

I'm not sure what rotating the signal would entail, but running at something slow like 8MHz you could get 1000 instructions in 1 ms which should be enough to do whatever you need. Maybe you could play with the gyro gain as well? I'm not sure if it's taken into account in the gyro output or the MCU.

[coredump]

Yes, that is why I said it is possible. If you are talking about attiny series.
Most of them only have one i2c bus at most. So you need to do bit banging
on the second i2c bus, which will burn a lot of instructions.

If you have the virtual gyro chip, adjust gyro gain is of course possible.
I already have too much stuff on my plate. If some one want to give that
virtual gyro chip a try, I can help providing some suggestions.

[SuperX7]

Originally Posted by coredump

It is certain possible if you flash the board and write yoru own FBL firmware.
But that is not a easy task. I assume the FBL firmware is the holly grail of
the MCPX proprietary secretes. The performance of the FBL system, affect
the feel of the heli a lot.

Without reprogramming the MCPX firmware. You need to keep the gyro
chip facing the way it is designed. If you are brave enough, you might able to
cut out the gyro circuit on the mcpx board with the near by circuits.
Make it face up right. Then you just need to reconnect about 5 signal wire on
V1 and 3 signal wire on V2, plus the power and ground. That should work.

It will very likely ruin your board. But I think it can make to work as well.
I can close study the board again and see if that is possible.

Could you possibly show me exactly what component/s we are talking about? As you say it may be easier to just remove the part, rewire it to the main board instead of trying to reprogram the firmware.

[coredump]

Yes, for the moment that is the easist way. Other method require need a lot
of programming which does not exist yet.

Here is the gyro chip I am talking about, on a V2 1.3 board:


You need to connect the lower 3 data lines I am tapping on.
Then plus ground and 3v voltage. If you have a truely broken
v2 board, you can cut that gyro out and attach to a good board
instead of ruining a good board. BTW, I am still searching for
a truely broken V2 board.

See that gap between the receiver chip? Just follow that gap to
cut it out. The reverse side has the same gap matching this side.

If you want, I can try my best to custom mod one for you, given
that you understand there is risk ruining the board in the process.

[SuperX7]

Are you suggesting that you can bypass the original chip by cutting one out of an old board, then wiring it to another board thats mounted at a different angle? What would happen to the chip on the "working" board, is it disabled somehow?

I've got a board that has a burned FET, I think thats what it is - saw a puff of smoke whilst I was messing with a soldering iron and the rear servo doesn't work now so I cant use it to fly, and as I'm useless with a soldering iron, it's sitting in my box. I can send you this board for you to try? If you can get this working I'll friggin' buy a new board for ya It's my holy grail for my dream scale project.

[coredump]

SuperX7,

Yes, I think I can cut out the original gyro chip with the circuit board.
There is two priority here,
A: cut out the original gyro chip with the PCB around it without damage
the gyro circuit.
B: try to not damage the origianl board that with the gyro cut out.

A has more priority than B. If we can do both A and B, you don't need the
extra board. Just connect the gyro to the original board facing a different
direction.

If we can't do B, then we attach the cut out gyro to a second 3 in 1. Of course,
the gyro in the second 3 in 1 will have to be disconnected, and route the bus signal
to the extral gyro cut out.

Sure you can send me that board with burned out FET to try. You just need to make
sure it is a V2 board. V1 board has two gyro chip so the signal routing is more messy.
Hopefully I can fix your board, cut out and relocate the gyro chip to make it face a
different direction.

Also, can you tell me how you are going to mount your 3 in 1 in relation to the
servos? That will determine how I mount the cut out gyro chip to the 3 in 1.

BTW, my buddy is a fan of your scale project. He is pledging me to help you out :-)

[SuperX7]

Hi coredump,

Are you able to fix the burnt FET chip? I only ask as if you are successful in this crazy mod it would be a shame not to be able to use the board to fly due to non-working rear servo? I suppose we'll never know until we try it.

My board is definitely a V2, PM me your postal address and I'll mail it to you straight away.

See the image for the orientation of the board. So you can understand the image, the whole frame will be fitted backwards (tail facing the other way) - I've already done this with my current scale project and it works fine (as long as I reverse the aileron and elevator controls on my TX). This has to be done as otherwise the frame and mechanics will not fit into the fuselage.

The original PCB is in RED, the new orientation is in BLUE (turned 90 degrees counter clockwise) - obviously the gyro chip will be mounted where the red is shown (original) - it's either this or I shave off at least 5mm of PCB (2.5mm on each side) which I'm not sure is even possible...

Heh which scale project are you referring to? I have started 3, but am trying to finish the my UH-1N where I don't have to do this crazy modding (you can see this here ). If we can get this working, I'll have my cobra up and running!

[coredump]

I have SMC rework station, the one that blow hot air. Replacing 3 pin FET is easy for me. I have done much harder one. E.g. Replacing the MCU on the ESC.

As long as the MCU is outputting the correct signal. I am confident I can repair the board.

If you havent done so, can you try mounting the board 90 degree with the servo plug in? You might need some extention on the servo cable. I have long cables I can replace for you servo.

I have not fully understand how you can mount the board backwards without affecting the Z axle stabilization. I think Z axle gyro should give inverted rotation
reading. I have to try it myself.

Btw, the cut out gyro should be very close to board due to the i2c bus. I will need to test if it can mount that far.

Will PM you the address.


> Date: Tue, 26 Jun 2012 17:05:24 -0700
> Subject: Re: Progress update
> From: helislayer02@gmail.com
> To: redmons@hotmail.com
>
> On Wed, Jun 20, 2012 at 1:36 AM, Sir-C . <redmons@hotmail.com> wrote:
> > OK you know best we can use the other small one I have to swap it. Let me
> > know when you have time..
> >
> > Thx.
> > PS: Lets Fly again soon..!
>
> Hi, I saw one new in package V1 on Helifreak and I am buying it
> for it. Asking $55. The HP05 is already arrived. That is the motor
> bigger than my M5 (same one as Perry's).
>
> Chrismeasure. I have to try it myself.





Sent from my iPhone using Tapatalk

[SuperX7]

Originally Posted by coredump

If you havent done so, can you try mounting the board 90 degree with the servo plug in? You might need some extention on the servo cable. I have long cables I can replace for you servo.

Not sure I understand what you mean here? Can you do a mock diagram or explain as I'm still new to this.

Originally Posted by coredump

I have not fully understand how you can mount the board backwards without affecting the Z axle stabilization. I think Z axle gyro should give inverted rotation
reading. I have to try it myself.

I'm not sure how it works either... as the tail is mounted the other way, I didn't have to do any mods apart from reversing the aileron and elevator command in my transmitter. That seemed to do the trick!

Originally Posted by coredump

Btw, the cut out gyro should be very close to board due to the i2c bus. I will need to test if it can mount that far.

The new board won't be too far away from the gyro. My diagram shows that its a little far, but I only drew this to show you the original position of the board. The new board can be almost touching the frame, but just at a 90 degree angle.

I almost forgot.... the wires from the servos (all 3) need to be long to reach the new board position.... I wonder if this will affect anything?

[coredump]

Originally Posted by SuperX7

Not sure I understand what you mean here? Can you do a mock diagram or explain as I'm still new to this.

I mean, have you install the 3 in 1 in the blue position as draw. Just to make sure
the servo cable is long enough to reach to the servo plug. Because you turn it 90
degree, I am worry some of the servo cable is not long enough for you.

I'm not sure how it works either... as the tail is mounted the other way, I didn't have to do any mods apart from reversing the aileron and elevator command in my transmitter. That seemed to do the trick!

I can give it a try myself.

The new board won't be too far away from the gyro. My diagram shows that its a little far, but I only drew this to show you the original position of the board. The new board can be almost touching the frame, but just at a 90 degree angle.

I almost forgot.... the wires from the servos (all 3) need to be long to reach the new board position.... I wonder if this will affect anything?

Yes, that is what I ask in the first question. Basically, do you need my help to extend
the servo cable or not. Because I do have longer servo cables. The extend the servo
cable would not affect the performance. But extending the gyro signal cable might
because the I2c bus use by the gyro is not design for long range signal passing.
I have to try it out.

[SuperX7]

Right sorry for the confusion. Basically yes, I do! I can't solder to save my life... I don't think I ever got the hang of it, not yet anyway.

Let's see how it goes with the gyro modding, if that works maybe I can send the servo bits to you? I suppose it doesn't really matter where the board is mounted as long as the cables can be connected to test the "new" gyro position when not physically mounted on the board.

[coredump]

Sure, let's try the cut out gyro first.

[toys2cars2toys]

Coredump, I'm stunned by your ability, I consider myself to be an advanced elec tech, but this stuff is mind blowing -

SuperX7
You opened my eyes to something with your scale project with the board mounted around the back
Effectively the heli "thinks" it's flying backwards, swapping the tx channels allows you to fly it "forwards"

Note the key thing is that the board has been rotated around the main shaft, as if the heli has done a 180' piro, hence the FBL code still works

Now on to your side mounted board, how about this
Imagine having the board on the side, in the same orientation as if the heli did a 90' piro, now you would have to fly it "sideways", you could achieve this with mixing on the TX to swap the Ail and Elv channels over
If this works, you'd then just have to move the board backwards, just keeping the same orientation
But this would mean the frame or at least the servos would need to be at the 90' position, which may give you problems fitting it in the fuse

[SuperX7]

Hi toys2cars2toys,

I have considered this but I still have the same problem. My dream scale project is the AH-1W which is shelved until I sort this problem out. As you probably know the fuselage on these beautiful helicopters are very narrow. I had to chop away a lot of the fuselage and mod a lot of the parts just to fit the frame (only just!) Turning the frame 90 would actually work, but as you rightly mention in your post it's actually wider, which means it won't fit

[Starcruiser]

could rotate the servo's electrically and then use the Tx mix or something to swap the AILE and ELEV functions.

[coredump]

Can't just rotate the servo electrically.

There is two part of the servo command.
The first part is from the FBL system. The second part is from the TX command.
The actual out put of the servo command is the mix of this both.
If you make TX stay center no change, and rotate the mcpx boad. The FBL
system will give negative feedback command to servo, counter the shaking
rotation. That is independent of the TX command add on top of it.
That is what FBL do.

When you change the gyro facing. The FBL feed back direction will be wrong.
That can't fix at the servo electrically level because you can't distinguish which
part of the movement is coming from the TX and which is coming from the FBL
system.

It has been combine into one output value into the servo.