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Jul 30, 2019, 03:22 PM
out to have fun
dbishw92's Avatar
Jim any more news on the version with the gyro?
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Jul 30, 2019, 08:32 PM
Thread OP
With a turbine you likely will never see an issue. It's only gas engines (HV ignition systems) where this was observed. We can swap out any system where there is a concern/issue because of the MKS777 servos.
Aug 09, 2019, 05:50 AM
If it has wings it will fly...
ckleanth's Avatar
Jim, be interested to know why there is an issue with these servo only when a HV ignition is present. Not sure why there's a link?
Would be possible to describe the change to the x24 to remedy the issue?
Aug 09, 2019, 01:42 PM
Thread OP
The issue is that the servo requires higher drive current for the signal line. I am guessing that instead of using a MOSFET on the PWM signal input, they are using a transistor. The industry standard is to use 1K ohm series resistors for each signal line from the receiver. At 3.3v this means that the servo's signal line has up to 3.3mA of drive current. Whatever the servo is using for triggering the PWM pulse internally is marginal at that max drive current, and outside interference (like a HV ignition system) can cause the PWM signal to be corrupted.

The "fix" is to use a 100 ohm series resistor for the PWM output from the X24. This provides up to 33mA (@3.3v) of drive current. The X24 has buffer ICs for the PWM output which can provide about 100mA (@5v) for each of it's 8 outputs. That current is limited by the series resistor right now to about 5mA. Most receivers output 3.3v for the signal voltage.

The reason why we use a series resistor is two fold -first, it helps to prevent ringing which is an oscillation caused by a PWM signal. Secondly, it allows you to short the signal output to ground without taking down the entire system. 3.3mA is extremely low current, so a shorted servo won't kill the CPU or other servos on the bus. 33mA is still pretty low, and since the X24 has a buffer/booster/isolation IC between the servo bus and the CPU the higher current drive won't be a problem even if one entire set of 8 servo ports is shorted. The next production run (end of the year) will probably have 100 ohm resistors instead of 1K resistors.

MKS has already said that they are fixing this issue because it affects any system that uses the standard 1K series resistors, especially with 3.3v signals.
Last edited by JimDrew; Aug 09, 2019 at 01:49 PM.
Aug 09, 2019, 02:57 PM
If it has wings it will fly...
ckleanth's Avatar
Interesting.. this is the second time this year i have come across an issue with servo on the signal line. One servo model from a different brand was more susceptible to long low quality wires because of somewhat higher resistance and because cpu was working at 3v.
Aug 10, 2019, 10:30 AM
Jacob Helber
Re-maiden went great after replacing my cb200 with the xps24. It was nice to be able to do full throttle rifle rolls without the ailerons shutting down.

On a side note, I've been messing with an arduino the past few nights and have been able to make a mock up sensor that will send battery telemetry for both rx batteries to the radio. Just need to order a few sensors and components to see how small I can package it and then give it a whirl in the plane.

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Aug 10, 2019, 06:19 PM
Thread OP
Congrats on the re-maiden! The batteries are wired in parallel (electronically) by the X24, so unless there is a big difference in cell impedance (which happens) they really should be identical.
Aug 21, 2019, 03:59 PM
Registered User
Any work or updates on adding Jeti telemetry to monitor current consumption?
Aug 21, 2019, 07:06 PM
Jacob Helber
Quote:
Originally Posted by WR_Rider
Any work or updates on adding Jeti telemetry to monitor current consumption?
If you're asking me, no haven't had time to mess with it. I'm also planning to add engine temp since I'll lose the open ext port so still trying to find a suitable thermistor for that.

I dont think Jim plans on adding to xps24 as there aren't any current sensors on the main battery inputs. Plus after ordering and playing a little bit with one of the sensors available, I have some reservations about using them on a gas plane with the amount of vibrations. Plus it wasnt very accurate as I didnt trust the smaller current sensor nor have a way to do surface mount components/pcbs.

The hardest part (for me anyways)is done though and that was getting jetibox to talk both ways with the uC. I'd be happy to share code and what not if anybody is interested.

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Aug 23, 2019, 11:54 PM
I love aerobatics and 3D!
Quote:
Originally Posted by JimDrew
With a turbine you likely will never see an issue. It's only gas engines (HV ignition systems) where this was observed. We can swap out any system where there is a concern/issue because of the MKS777 servos.

was about to order an X24 for a EF 104" Extra used for Freestyle. I'm using a DA120 and MKS 380 servos, which seem to have very similar specs to the 777's that seem to cause issues with the X24. Should I be concerned?
Aug 24, 2019, 02:08 AM
Jacob Helber
Quote:
Originally Posted by JuanSG
was about to order an X24 for a EF 104" Extra used for Freestyle. I'm using a DA120 and MKS 380 servos, which seem to have very similar specs to the 777's that seem to cause issues with the X24. Should I be concerned?
I am running 599s with the exception of 2 777s on the rudder and a da120. No issue.

The 599s are essentially 380s with a standard 25T spline.

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Aug 26, 2019, 04:11 PM
Thread OP
Quote:
Originally Posted by WR_Rider
Any work or updates on adding Jeti telemetry to monitor current consumption?

The X24 can not output current consumption. The only time current is actually measured is when connecting a power source to the MATCH power input and doing the servo matching. This is not possible with power provided by the main power inputs.
Aug 26, 2019, 04:13 PM
Thread OP
Quote:
Originally Posted by JuanSG
was about to order an X24 for a EF 104" Extra used for Freestyle. I'm using a DA120 and MKS 380 servos, which seem to have very similar specs to the 777's that seem to cause issues with the X24. Should I be concerned?

There is no "concern". You just need to specify that the X24 will be using MKS777A+ servos when ordering. No other MKS servos have been reported to have an issue, and this issue was only with HV ignition systems (like GP123 7.0v).
Aug 26, 2019, 11:18 PM
Registered User
Quote:
Originally Posted by JimDrew
There is no "concern". You just need to specify that the X24 will be using MKS777A+ servos when ordering. No other MKS servos have been reported to have an issue, and this issue was only with HV ignition systems (like GP123 7.0v).
Iím guessing itís a good thing I read this. I recently pulled my XPís from a plane using 777 to put into a plane with 777+ís.

Is this something I can send in for an update? What are you doing to them?

Thanks
Aug 26, 2019, 11:53 PM
Thread OP
If you are using a 777+ servos with a HV ignition system such as GP123 (not a DA, DLE, RCGF, etc.) then we can change the output port resistors.


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