# building a synchrophasometer

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I'd like to build a synchophaser indicator like in the King-AirIt' a black & white disk turning left or right proportionally to disphase of the propeller.Question: which variables to use to calculate this disphase ?the prop RPM difference ? how to built it, steppermotor, or servo link to a pot which drive an electrical DC motor ?Other ideas ?Thank'sBOB

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Sounds like you need to subtract port engine's rpm from starboard engine's rpm. If you end up with a negative value, the motor will spin one way, the speed of which depends on the difference between the two rpm's. More difference equals higher speed.If you work as a percentage, from 1 to 100, then the difference will be given as a speed percentage. Here's an example:Engine 1 rpm = 60%Engine 2 rpm = 50%Difference = 10%Now using a motor speed scale from -100% max speed (anti-clockwise) to 100% max speed (clockwise), the motor will turn at 10% (clockwise) of it's max speed.If the values were reversed, ie engine 1 was 50% and engine 2 was 60%, the difference would be -10%, making the motor spin the same speed in the other direction.How you would interface this, I'm not sure, but worth looking at both methods to see which would work best.

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Very hard to do...You should have electronics knowledge, the easiest way is this (using FSBUS CCC):-you make a circuit which defines what will the disphase be (i mean take engine1 param, engine 2 param and calculate the disphase)-this is then sent to a servo controlled by FSBUS, and you have to calibrate the values of the SERVO Object in order to obtain full left and right deviation at maximum disphase (which is what? 0-100 or idle-maxthrust?)-once you have this you need a circuit which translated the servo control command into a pwm cc motor drive.Not so difficult to do (pwm and servo control ar very very similar) but i can't help.

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One thing you may have trouble with is the electrics for a simple 2-wire motor. Switching polarity will turn the motor in the opposite direction.Another problem lies with the use of a pot to govern the speed of the motor. As a typical pot has 3 terminals, the centre being input, the two outer ones will distribute the total resistance according to how the pot is turned.Full left might give 100k - 0k, centre will give 50k - 50k, and full right might give 0k - 100k for a 100k pot. This may not be accurate as one 100k pot I tested only gave 98k at each end :(Using only the centre pin and one outer will give the results you might need. The problem still lies in the motor knowing which direction to turn! Since my knowledge of electronics is only basic (my field being engineering design) I doubt I'll be able to come up with circuitry to allow the positive and negative to be reversed.

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I am so stupid!Really really stupid!With a hacked servo you're all set.I do not know if it reproduces the different speed, but surely it rotates one or the other sense.Just google for "hacked servo": it means takeing out the control pot from the servo to be sostituted with a resistor, and cutting the lock tap on the main shaft in order to let it turn more then 180

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That's the principle used by simkits gauges(altimeter or gyro)But I don't really known how it workMy idea : delink the servo-pot from the servo motor you can now link the free pot to another servo to turn it left of rightthan will drive the servomotor to turn continiously CW or CCW but I don't know if the speed is proportional on if it constant speed.Does someone have an idea about that ?BOB

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The speed should vary with voltage. Easiest way to alter this is to change the resistance. Getting the resistance to change via FSBus is not a technique I'm aware of.....

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I've just unscrew a servo delink remove the gears andThat's work fine when I turn the pot left the motor turn proportionalyit's very sensitive I'll couple it with some reduction gear to make very small movement of the pot.BOB

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There's an easier way:You just unlink the pot, fix it in the middle pos:When you set the value in FSBUS to 127 (middle) the motor stopwhen you set a lower value it start turning left with a proportional speed --> That's the way to build a tachometer.- unlink the pot- assigne the difference between props RPM with and offset of 127to the servo.That's it :-)Much easy that I was thinking ...BOB

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Yeah, but won't it turn in one direction only? The idea of the 'synchrophasometer' is that it gives you a visual indication of how much the props are out of sync. It's designed to rotate both ways.

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if you block the pot in the middle positionwhen you send a smaller value it turns leftwhen you send a 127 value it stopswhen you send a higher it turns rightthat's exactely what we need :-)Need to try to find the good range to calibrate the values. The best is to cut the pot centerpart and to glue it to avoid it move with frictionthen to determine the middle value (around 127).That's exactly the modified servo's of simkits.http://www.simkits.com/manuals/en/11%20Mod...vo%20HS-322.pdfCUBOB

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>Yeah, but won't it turn in one direction only? The idea of>the 'synchrophasometer' is that it gives you a visual>indication of how much the props are out of sync. It's>designed to rotate both ways.Yep, it does - basically the thing is that you cut off the feedback of position so the poor servo will try to turn forever towards the given position - the farther it is, the faster it turns, and whichever side of the center point it is, that's the direction to turn to.. Since the feedback is wired permanently to "middle", by setting the servo to "127" or so, the turning should stop. There were two pages I remembered from google:http://www.v1ru5.org/warships/howto/servo_hacking.htmhttp://www.seattlerobotics.org/encoder/200009/S3003C.htmlThe second one is looking more sophisticated with a trimmer to fine tune the center point etc - but the first one looks very simple and easy to try - and fsbus allows you to adjust the midpoint as well, though not with super accurate granularity - but it could just work, so it is worth trying, at least it is not hard to see, and the basic servos are not very expensive.Good luck and let us know if it works out? :-)This sounds like a great little gauge on the panel by the way, probably adds a lot to the "feel"..//Tuomas

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That's what i said :-roll

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