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Aug 28, 2017, 10:37 AM
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Hi Brutus1967, do you give me information about the aircraft engine you have? Where did you put the inductance there is a magnet? Does the magnet rotate with the crankshaft? There is only one magnate or more magnets? The inductance you understand by how many Henry is it? What trouble gives you now?
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Aug 30, 2017, 11:32 PM
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Just use a hall effect sensor.......just like use in my Futaba GV-1......the sensor is just installed on the side of the crankshaft ...
Predator Helicopter with Futaba GV-1 Governor (5 min 36 sec)
Feb 09, 2018, 06:14 AM
Closed Account
Thread OP
Quote:
Originally Posted by edwin1
Subbed. I'm interested too. I didn't see any cdi tach ability in their telemetry. Not interested in designing my own. Got enough to do as it is.
Edwin
Quote:
Originally Posted by edwin1
I wonder if you can do a Y cable between the sensor and ignition module and feed that to the telemetry directly?
Edwin
Quote:
Originally Posted by larryoakley
I have been searching for an RPM sensor like this, I can't believe FrSky has no solution available in the market for gas users.
Update:

It is possible and VERY simple to take the RPM reading directly from the tach-output of the RcExl ignition:

Just connect the ground and pulse of the tach output to the sensing wires of the RPM/temp interface, with an Elco of about 100 uF in the pulse line (+ side of Elco connected to pulse of ignition, - side of Elco connected to the red sensing wire).

And presto, super stable RPM read-out, verified with the tacho in my old Futaba FC-28, over the full range less than 25 RPM difference.

Never knew it could be so simple.
I am told any value between 0,2 and 200 uF would work, but I have not tested that.
I have no idea HOW it works, I just know it does.
I did not invent it myself, and it is very possible this solution has allready been presented here by other posters.
If so, apologies, I am NOT trying to take credit here, I just hope to help people along.

Apart from actual engine RPM being just "nice to know", this thing has a few more serious applications that can be very handy.
I am personally using it for 2 things:
First, since I am flying fourstrokes, and these usually are not the loudest kids on the block, a deadstick alarm can come in handy. This is in my Taranis activated by a logical function using "RPM=0" and "ignition switch armed". As soon as both conditions are met, the Tranny starts repeating "engine off"...
Killing the ignition switch kills the annoying warning if desired.
Second, the model timer is set at "manual reset" which means, it memorizes the last value and starts counting from there next session (cumulative).
The timer is activated on the condition "ignition armed", and "RPM>250", which means, the timer runs when the engine runs, and stops counting when the engine is at standstill, regardless of deadstick or intentional kill.
This results in the timer displaying actual total engine runtime (try it, you'll be amazed how little runtime our model engines actually make).

Works for me.
Last edited by Brutus1967; Feb 09, 2018 at 01:19 PM. Reason: Stupid typo's....
Apr 22, 2018, 12:21 PM
Secretary AAG, India
hey Brutus.. love your simple solution... which Frsky RPM sensor are you using for this application?
is it this ? https://ae01.alicdn.com/kf/HTB1Uwzun...pg_640x640.jpg

Regards
Sandy
Apr 23, 2018, 10:08 AM
Registered User
Quote:
Originally Posted by Brutus1967
Not anything spectacular, just something fun:

Made a logical switch that opens the throttle a bit when RPM gets below specified idle.
It is not a real stable RPM control, but amongst others it prevents a cold engine from stalling, and it automatically opens the throttle a bit before starting, to come back to idle after a few seconds, without having to fiddle with the throttle stick...

Really practical? No idea yet... for now it is more intended as a fun way to learn working that Taranis programming...

If you watch closely, you see the throttle action, the Taranis does that all by itself...

https://www.youtube.com/watch?v=-JgukkHz35c

EDIT: above vid was with still a very simple single logical switch (RPM below treshold, throttle opens slowly, RPM above, throttle closes slowly).
This results in a control that continuously and slowly oscillates around the setpoint.
Updated it with an array of 10 switches with each a different treshold value, and 1/10th of the influence. The outputs of those ten switches are added and the result is something that more resembles a kind of PI controller: at some point one half of the switches cancles the other half out, and the system kinda sorta finds an equilibrium. It is not a PI controller, but it does a fair job imitating one.

The number in the top of the display represents the throttle servo position (and thus the control response)

https://www.youtube.com/watch?v=b3cp...ature=youtu.be

Apologies for the 90 deg tilted image... the Original file shows normal, I have no idea what happened here
this is cool and all but the engineer in me wants to do this with an LUA script that solves the PID equations and can be tuned with P, I, and D constants. of course, losing th erpm signal would cause a problem so i'd also include error checking on the rpm telemetry.
Apr 27, 2018, 11:25 AM
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Thread OP
Quote:
Originally Posted by sandyjain
hey Brutus.. love your simple solution... which Frsky RPM sensor are you using for this application?
is it this ? https://ae01.alicdn.com/kf/HTB1Uwzun...pg_640x640.jpg

Regards
Sandy
Yup... that's the one...
Apr 29, 2018, 03:01 PM
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Thread OP
Quote:
Originally Posted by raleighcopter
this is cool and all but the engineer in me wants to do this with an LUA script that solves the PID equations and can be tuned with P, I, and D constants. of course, losing th erpm signal would cause a problem so i'd also include error checking on the rpm telemetry.
really like that too, but truth is, I severely suck at anything software, so I don't have the faintest clue how to write LUA scripts.

But I have to dissapoint you, in that the data refreshment rate is not fast enough to let a PID based control function work properly. At least, the delay between RPM changes and the arrival of that information at the transmitter also made my "controller" (which basically imitated a PI controller) way too slow to work properly....
Apr 29, 2018, 06:16 PM
Registered User
Too bad. Dead time is the killer of control loops.
Apr 30, 2018, 05:21 AM
Closed Account
Thread OP
Yup....

I have no idea how long that dead time is, but if I would have to guess, at least 1/3rd to 1/2 sec, and that is way too long for a control loop with the fine corrections needed to control idle properly....

I just thought it fun that Taranis at least in theory is capable of things like that....
May 02, 2018, 07:40 AM
Registered User
just tested this setup works great with the frsky temp and rpm sensor on satio CDI
May 02, 2018, 08:18 AM
Closed Account
Thread OP
Great, huh? I was pretty amazed to that it could be so simple....

Happy to have helped!
May 03, 2018, 12:33 AM
Secretary AAG, India
Quote:
Originally Posted by yak-54
just tested this setup works great with the frsky temp and rpm sensor on satio CDI
Any pics pls ? You did it with which capacitor?
Thanks n regards
May 03, 2018, 02:39 AM
Registered User
Quote:
Originally Posted by sandyjain
Any pics pls ? You did it with which capacitor?
Thanks n regards
50v 220uf cap
Last edited by yak-54; May 28, 2018 at 01:36 AM.
May 27, 2018, 01:55 PM
Secretary AAG, India
Thanks.... but you are not using the signal wire (white) from the hall sensor of the CDI ? The capacitor seems to be in the +VDc (red) wire.
Brutus has shown that the capacitor must be in the white - signal wire.

Please clarify. I have finally got the Frsky RPM sensor today and would like to make the adapter tomo.

Regards
May 27, 2018, 07:03 PM
Registered User
Quote:
Originally Posted by sandyjain
Thanks.... but you are not using the signal wire (white) from the hall sensor of the CDI ? The capacitor seems to be in the +VDc (red) wire.
Brutus has shown that the capacitor must be in the white - signal wire.

Please clarify. I have finally got the Frsky RPM sensor today and would like to make the adapter tomo.

Regards
my CDI has tachometer output


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