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Old May 24, 2011, 09:07 PM
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Mini-HowTo
How to fit the new type HK401 gyro sensor to a KK board.

I have finally looked at the new gyro sensor in the HK401B gyro.

It is located on a small PCB soldered to the bigger gyro sub-PCB, apparently serving as a drop in replacement for the old Murata sensor. The gyro sub-PCB is identical to the one used with the old sensor, with the same 6.8 kOhm output resistor, and the same pinout.



However, there is a important difference. The output resistance of the old gyro sub-PCB is about 6.8 kOhm, and the new one is measured to about 17 kOhm. The output resistance is the R (resistance) part of the RC low pass filter on the KK board.
By just using the new gyro as it is, the frequency of the low pass filter is decreased from 34 to 14 Hz. This may change the performance of the KK board. (I have not tested that yet)

Luckily this is easy to fix: On the smaller PCB with the gyro sensor itself, located on the gyro sub-PCB, there is a 10 kOhm resistor (marked with 103). It is connected in series with the 6.8 kOhm resistor (marked with 682) on the bigger PCB. Just remove the 10 kOhm resistor and jumper the pads with a thin wire or solder blob.

UPDATE: Another way is to leave the gyro as is, and replace the 0.68uF filter capacitors with 0.27uF. It will give the same cut off frequency.



Another difference is that the output signal from the new gyro is about 3 times (Peak-to-peak) larger than the old one.



This is not a problem.

The new gyro needs 3V supply. I have tried it on 5V, it worked, the current only rose from 6.3mA to 7.1mA, and since the output is ratiometric, the output signal got even larger. But since I do not have more data on the new sensor, we have to settle to 3V.

Its no-movement output of about 1.5V, coupled with the need for a larger Vref for the ADC since the output signal is bigger, means that we can also use a Vref of 3V, simplifying the conversion.

Change the R10 from 68 to 330 Ohm to get 3.1V and supply the gyros with this voltage through one 10 Ohm resistor per gyro. That is, replace the R1,R2 and R3 with a 10 Ohm resistors, leave their input pin in the air and tie them together, and solder them to the output pin of the voltage regulator.



Upon flight testing with unmodified firmware, the gain potmeters had to be reduced 50% due to the new gyros larger output signal. There where no difference in the behavior of the KK board compared to one with the old gyros. A modification of the firmwares gain potmeter scaling value can be done, but it is not necessary.
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Last edited by kapteinkuk; May 29, 2011 at 05:39 PM.
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Old May 26, 2011, 06:00 PM
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Thanks a lot ! I'm just fighting with this new gyro and now will try this sollution.
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Old May 28, 2011, 01:29 PM
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Another way is to leave the gyro as is, and replace the 0.68uF filter capacitors with 0.27uF.

It will give the same cut off frequency.
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Old May 30, 2011, 01:15 PM
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New syro sub power supply

KapteinKuk, I might be asking the obvious but could you tell if the new gyro can work on 5V without any supply modifications? Reason why I'm asking is that I got 1 old and 2 new hk401b's when I ordered them from HK so can I feed them with the same Vcc i.e 5V or do I have to supply the new one's with 3V only?
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Old May 30, 2011, 06:40 PM
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As written in the 1st post, I tried it on 5V and it worked. But who knows how long?

And since the output is ratiometric, the zero rotation voltage rises to 2.5V, making it necessary to modify Vref.

I would either buy more gyros, or do the mod in the 1st post, the old gyro also works on 3V.
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Old May 30, 2011, 11:22 PM
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Ok Thanks!
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Old Jun 04, 2011, 08:05 AM
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Need answer fast, the soldering iron is warming up...

Quote:
Originally Posted by kapteinkuk View Post
Another way is to leave the gyro as is, and replace the 0.68uF filter capacitors with 0.27uF.

It will give the same cut off frequency.
I don't have 0.68uF SMD capacitors at hand (I have hundreds of other values though)

So... rummaging through my components, how about using a 1uF capacitor and a 4.7K resistor (and bridging the resistor on the gyro board as shown)? that would give a low pass filter of 33.9. Is that close enough?
I don't know how critical that value is.
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Old Jun 06, 2011, 07:56 AM
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Should work fine!
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Old Jun 06, 2011, 09:26 AM
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Quote:
Originally Posted by kapteinkuk View Post
Should work fine!
Excellent!

I've already assembled the control board and now I'm dusting off my ISP AVR programmer to try and program it.
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Old Jul 06, 2011, 03:35 AM
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new murata gyro sensor

Hi kapteinkuk,

i am building quadrocopter and i need your advice. I am using kk green board with Kim's 2.0 firmware. The problem is that i have two old and one new murata gyros. I placed new murata gyro to YAW position without any modification. Two of the quad's motors (3 and 4) spinning two times faster than others. I have measured voltage on gyros output all they are different.
Roll - 1.29V
Pitch - 1.35V
Yaw - 2.00V

does it has to be all equal ? how can i modify PCB to make all of them same voltage ?

Thanks
Rimas
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Old Aug 29, 2011, 09:13 PM
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Hey everyone,

I just did this mod on my new KK board and found something very interesting about these new gyros - they are extremely sensitive to sunlight. Especially the yaw gyro, as it is directly exposed in its upright position

I used black foam tape on mine and it did the trick

I'm sooo glad I solved this issue, I was just about to give up on this board when I discovered this... Even ordered an HK board in the mean time (which just arrived btw!) but these new gyros are somewhat better than the old metal cased ones, as long as you keep them away from the sun

Thanks KK for this thread BTW, I really appreciate all the efforts you are putting into this

Marc
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Old Aug 29, 2011, 10:04 PM
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Marc, what issues did the direct sunlight cause?
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Old Aug 30, 2011, 01:14 AM
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Yaw control was very erratic, it would fly somewhat fine and then it started jerking in half circles for no apparent reason

Direct sunlight will cause an instant reaction - cast a shadow with your hand and it will stop instantly. I could not reproduce it inside, though. Only the sun seems powerful enough to cause this behavior

Marc
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Old Aug 30, 2011, 01:35 AM
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Quote:
Originally Posted by Markz View Post
Yaw control was very erratic, it would fly somewhat fine and then it started jerking in half circles for no apparent reason

Direct sunlight will cause an instant reaction - cast a shadow with your hand and it will stop instantly. I could not reproduce it inside, though. Only the sun seems powerful enough to cause this behavior

Marc
I think I had the same problem, I assumed it was a malfunctioning gyro so I replaced it and then it stopped spinning like a dervish.

I have a short video of the problem, is this what you are seeing on your tricopter?

Tricopter yaw glitch (0 min 26 sec)
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Old Aug 30, 2011, 03:05 AM
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Yep, that's exactly it

It's probably always stopping at the same place because of sun's direction
Your gyro is probably still good, it would be nice to see if someone can duplicate this

Thanks for the vid

Marc
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