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DelTang 2.4GHz receivers - pt.I
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 Posted: Mon Jul 11th, 2016 12:18 pm
   
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Philipp M
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I will first try it like this and then consider programming if I do not achieve it. But thanks for info. Regards, Philipp



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 Posted: Thu Jul 14th, 2016 03:29 pm
   
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Geoff L
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I am using Rx105s and Tx3 with toggle switches to operate 9g servos to throw turnouts. Can anyone advise a way to change (reduce) the speed of the movement of the throw bar, please?

Thanks,

Geoff

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 Posted: Thu Jul 14th, 2016 03:48 pm
   
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DavidT
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You could replace the toggle switches with pots which would allow you to control the speed manually. Or try a 'retract' servo. They are normally slower to operate plane undercarriange legs. Regards, David.

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 Posted: Thu Jul 14th, 2016 05:03 pm
   
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bobquincy
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There are "servo slow down modules" that can reduce the speed considerably.  Disclaimer, I haven't tried one yet.



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 Posted: Sat Jul 16th, 2016 09:35 pm
   
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Geoff L
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Thank you David and Bob. I did not really want to have to carry out any major work and the space for fitting further components is limited. I have seen an intermediary device advertised that would sit between the servo and its operator but at a cost, financially and spatially (if it was in stock). This seemed to have three pots to adjust end settings and speed. At a Modellers Day to-day I saw a small board from MERG with a similar function and miniature pots. Given that the end settings can be set using the Tx, I had been curious as to whether there might have been a simple fix such as fitting a fixed resistance for the required speed in an appropriate place.
As the movement is only about 1mm or so, it is hardly discernible and there are probably more important things to think about.

Geoff

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 Posted: Mon Jul 18th, 2016 04:43 pm
   
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Helmut
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A servo's speed is determined by two factors:
1. The gearing and the motor characteristics, because the motor always travels at full speed ( for the time determined by the pulse length difference of before and after )
2. The rate of pulse length changes during its travel. You may slowly adjust the pulse length of a simple servo tester to see the servo follwing this at a rate determined by the rotation of the setting pot.

Most servos come with a time of 6..10msec for a 90° rotation these days ( Mind you, they are mostly intended for airplanes and speed boats ), so a series resistance with the motor will not affect this much, and the penalty is always that there is simply not enough torque left.
In conclusion, a device that slows down a servo has to read the pulse length, compare it to one that has been stored previuosly, and then generate a pulse train with a slow rate of change from before and to after.



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 Posted: Wed Jul 20th, 2016 10:42 am
   
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Geoff L
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Thanks Bob and Fred, I am interested in how this might be developed. Currently, there is barely space in my controller for the present contents but I am looking to provide a larger housing.

Geoff

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 Posted: Wed Jul 20th, 2016 06:14 pm
   
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bobquincy
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I don't have good schematic drawing software but:
picture three resistors in series from the 3.1 V to ground: a 10K, 4.7K and 4.7K.  The voltage at the junction of the 10K and 4.7K will be about 1.55 V, the voltage at the junction of the two 4.7 K about 0.755 V.  These should equate to about full-throw and mid-throw on the servo.  Since you only need about 1 mm of movement this may be enough.

A 47K timing resistor is connected from the Xmtr input pin to the common contact of a SPDT switch.  One side of the switch connects to the 1.55 V junction, the other to the 0.755 V junction.  To complete the circuit a 20 uF (or so) capacitor is also connected from the input pin to ground.

As the switch is set to 1.55 V the cap will charge and the servo will slowly move.  After 1 RC time constant (about 1 second in this case) the cap will be about 2/3 of the way to the new voltage, after 5 RC it should be about 99% and the servo should stop.  Setting the switch to the 0.755 V junction should reverse the process.

Select a final capacitor and timing resistor value to suit how slow you want the servo to move.  The timing resistor should be at least 10x the value of 4.7 K resistors to avoid affecting the voltage divider string.

All this depends on the input impedance of the Xmtr but if it is similar to a TX2 it should be ok.  If I missed something, someone feel free to correct me.  :)



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 Posted: Wed Jul 20th, 2016 09:38 pm
   
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fallen
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Sounds good Bob.

The only change I would suggest is that the resistor value at 47k might be a bit high in relation to the input impedance of the TX module, which I freely admit I do not know, but I'd guess at about 100k.

I'd suggest 10k resistor and 100 microfarad cap as a starting point. The same time constant but lower impedance.

You are correct that this will load the resistor chain more, but only whilst the capacitor charges, the voltage end point of the transient will be the same.

In practice it will be a case of try it and adjust to what is required.

Frank

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 Posted: Sun Jul 31st, 2016 06:45 pm
   
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Philipp M
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Good morning,

while my Rx61d runs not on a battery, is there a solder point, where I can connect a capacitor to buffer the receiver without buffering the motor? That would help to keep the processor alive for short times.

Best regards,
Philipp

Last edited on Mon Aug 1st, 2016 08:09 am by Philipp M



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