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HomeAircraftHelicopterHelicopter Main Discussion › Servo help
08-31-2015 08:42 PM  3 years agoPost 1
sst09

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north conway nh usa

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Can some one help me i need to wire 2 micro limit switch into a servo don't know how to wire into the servo

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08-31-2015 11:21 PM  3 years agoPost 2
Blax1

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Sydney Australia

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Not sure what your up to?

But you can "limit" the servo arm travel by using the travel menu in most Tx's

Servo wiring is Positive, Negative and the signal wire (Mostly the centre lead) check your servo spec sheet for actual details

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08-31-2015 11:27 PM  3 years agoPost 3
sst09

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yes you can using a 360 servo with 2 limtit switch and 2 diodes the servo will use a worm gear as a stepping motor does and when it reaches the switch it hits it and shuts off the servo. then when you with it to go down and it its the bottom switch it shuts off.

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08-31-2015 11:44 PM  3 years agoPost 4
sst09

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servo help
here is the schematic i just don't under stand the servo part

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09-01-2015 12:26 AM  3 years agoPost 5
EEngineer

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TX

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Not sure what your up to?
I went to the RCG thread mentioned at the bottom of the schematic.

As best I can tell, this is for FPV drone racing.

They've managed to create their own quad. A lot of custom parts have been made using a 3D printing system.

And it looks as if the servos will control the angle of the 4 motors. Perhaps that makes it more agile in the "turns".

sst09 can fill us in.

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09-01-2015 12:32 AM  3 years agoPost 6
sst09

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north conway nh usa

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the servo is a 360 rotation. it has a worm gear on it. and theres a plate on the warm gear so when it hits the switch up it will shut servo off. then when go down it will hit switch and turn servo off.

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09-01-2015 12:39 AM  3 years agoPost 7
EEngineer

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TX

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Contact switches?

On the schematic, which switch is which?

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09-01-2015 12:43 AM  3 years agoPost 8
sst09

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micro limit switches. ill post a few pics of sometimes. its a drone and used to retract legs up and down

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09-01-2015 12:45 AM  3 years agoPost 9
sst09

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switch
on the right side inside you can see the micro switch at bottom so when the black pcs on worm gear hits it it stops the 360 servo same going up

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09-01-2015 12:46 AM  3 years agoPost 10
sst09

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north conway nh usa

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bottom right pics you can see them good with the black stopper on worm gear

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09-01-2015 12:47 AM  3 years agoPost 11
EEngineer

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TX

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On the schematic, which is the up-limit switch? S1 or S2?

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09-01-2015 12:48 AM  3 years agoPost 12
sst09

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theres 2 micro limit switch with 2 diodes in line then going to the servo

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09-01-2015 12:50 AM  3 years agoPost 13
EEngineer

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TX

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Which is the up-limit switch?

S1 or S2, as depicted in the schematic diagram?

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09-01-2015 12:52 AM  3 years agoPost 14
EEngineer

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TX

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Gotcha...you reached your post limit.

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09-01-2015 12:54 AM  3 years agoPost 15
EEngineer

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TX

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I'll take a crack at the circuit theory.

The servo PCB is supplying voltage to turn the servo, and has circuitry to reverse the motor voltage polarity to change servo rotation. The polarity of the voltage determines which direction the motor spins. Reverse the polarity and the servo spins in the other direction.

This circuit(w/optional fuse) is inserted between the two wires from the servo PCB to the servo motor(which is NOT a brushless servo, as brushless servo motor would have 3 wires and not 2 wires). So, this circuit is for a brushed and/or "coreless" servo motors.

When the servo is spinning the worm gear(in either direction/either voltage polarity), both switch contacts are normally closed(allowing current flow in either direction) unless one of the limit switches are "switched".

When the voltage polarity is in "one way", D2 is forward biased(allows current flow) and D1 is reversed biased(blocks current flow). When the voltage polarity is reversed, D1 and D2 work in the opposite way.

(revised to read better)....

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09-01-2015 01:22 AM  3 years agoPost 16
EEngineer

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TX

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In both cases, S1 and S2 allow the flow of current in either direction since their contacts are "normally closed".

When the S1 limit switch is activated(goes open, blocking current), D1 is reversed biased(blocks current flow)....and the motor stops and cannot move any more in that direction(voltage polarity).....but D1 can pass current if the polarity is switched.

When the S2 limit switch is activated(goes open), D2 is reversed biased(blocks current)...and the motor stops and cannot move anymore in the other direction(opposite voltage polarity)....but D2 can flow current if the polarity is switched.

D1 and D2 act to steer current "around" the switch in the "open" position(open when switched open), when you want make the motor spin in the other direction.

And visa versa.

(also revised)

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09-01-2015 01:46 AM  3 years agoPost 17
EEngineer

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TX

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As far as the "cut" as depicted in the schematic, you will have to use your DVM and the schematic as a reference to find out where to make the "cut".

Trace things back starting at the motor wires, working towards the servo PCB.

Take your time and double check before making the "cut".

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09-01-2015 04:57 AM  3 years agoPost 18
EEngineer

rrProfessor

TX

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It's a "clever" electromechanical circuit that controls the actions of a "brushed" PWM servo motor.

Don't need to worry about how fast or far the servo travels in between the mechanically adjusted "limit" switches....if it hits the limit, it can only move the other way.

Nothing get "jammed up", unless the mechanics of the switch assy. fail.

sst9, I can envision the limit switches mounting "arrangement" such that you can move it either way before "locking it down" with bolts.

Would make "limit" adjustment "fine tuning" easier on "the bench".

FWIW

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09-01-2015 05:15 AM  3 years agoPost 19
EEngineer

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TX

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Your project is cool.

Tilt rotor quads....amazing...^5's.

With regards to S1/S2 and D1/D2, things to consider...

S1/S2 are mechanical and have a "limit" on how many times they switch from the normally closed position.

Now D1/D2 are 3A diodes and can "handle" 3W of power, with a .5V voltage drop when conducting 3A of current.

Diodes first....using this method....how much current will your tilt rotor mechanisms require from the servo motor(that's where the current draw is)?

Higher torque = higher current.

There are other diodes, in the same size package, that will allow for more current draw.

With regards to the mechanical "limit" switches...

Consider that switches have a "contact resistance" spec....in addition to a "life cycle" spec(how many times can it be switched before it fails).

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09-01-2015 05:20 AM  3 years agoPost 20
EEngineer

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TX

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You want a limit switch that has the least "contact resistance" at 3A....or 5A(with diode upgrade)......

While at the same time having the greatest "life cycle...that's been tested at the factory with certification docs....).

Seems like these limit switches are "mission critical" and cannot fail.

Spend the extra $ to get high quality limit switches....it won't bust your budget.

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HomeAircraftHelicopterHelicopter Main Discussion › Servo help
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