MERG Kit 681 - Point Motor Servo Mount

The MERG Point Motor Mount kit (Kit 681) contains enough parts to make up 6 mounts. They are designed to use the 9g size model aircraft servos. In addition Kit 682 provides parts to convert them from vertile action to horizontal action, and Kit 683 contains 12 micro switches and screws nuts etc to mount on the brackets.

Price Kit 681 £6.36 for 6 (£1.06 each), Kit 682 £1.86 for 6 (31p each), Kit 683 £7.20 for 12 (60p per micro switch)

9g servos - I got mine from Amazon for £15 for 10.

I am using mine in verticle mode, with 2 micro switches, so total cost per point motor is approx £3.76.



The brackets are 3D prints comprising 3 main parts

The pivot piece (middle) fits through the top square hole - "some filing may be required", yep i'd agree with that.
Once fettled into shape, the servo is inserted - the mounting screws supplied with the servo are used to secure it to the bracket. I found I had to trim the top servo mount to keep the pivot bar level.

Next the pivot arm and wire.
I had to shorten the servo arm to allow the pivot arm to fit over it.
The piece of piano wire is bent through 90 degrees 4mm from the end, then treaded through the top of the arm.


Jobs a good un.

The bracket can hold up to 4 micro switches - still to fit mine.

Paul

 

Hi Pete

There are several ways to operate the servos,

MERG do the Servo4 kit - http://p1mrc.com/p1mrc/view_topic.php?id=162&forum_id=12 £6.30 to operate 4 servos, these units are controlled by an input, could be from a switch, or output from a relay, DCC accy decoder, arduino etc etc. Needs setting up via a PC serial port or the ServoSet2 dedicated standalone setup device (only 1 required) £20.00

Also available from MERG is PMP18 EzyPoints v3 £1.86 controls pots on the board to set, start point, end point and speed.

Heathcote-electronics also sell a servo controller unit
Megapoints also produce a 12 servo controller unit.

If you are willing to get your hands dirty, then the arduino and raspberry pi route opens up a vast array of options.

A standard arduino Uno or Nano (or compatable / clone) can control approx 8 servos via the analog output pins, however, this can be increase by adding I2C servo expansion boards

http://www.modmypi.com/raspberry-pi/breakout-boards/adafruit/adafruit-pwmservo-driver-16-channel-12-bit-pca9685/?search=servo

You can also add multiple boards controlled from the 1 arduino, the arduino digital input pins can have switches attached to it for control.
I would point out that as the servos are controlled via dc voltage signals, I would want to keep the wire lengths fairly short, and the cost of a Nano clone is cheaper than the adafruit servo driver board. The last lot I bought from China cost £17 for 10. I also knocked up a circuit to feed DCC signals into the arduino which then lets you use the arduino as a DCC accy decoder.

Paul

 

Hi Pete

A couple of years ago I would have said the same, the MERG kits are a great way of learning, as they give simple but comprehensive build instructions, but also if your interested, a description on how the circuit works, and also fault finding / troubleshooting tips.

If you can solder wire to rail, you can build one of these kits.

Paul

 

Have a look at the Merg Servo 4 unit, or if you really feel like going down the Dark side route make arduino controllers.
Viccy Road uses two Servo 4 units with an arduino as the DCC accy controller sending the signals to the servo4 units.

I wouldn't worry about the wiring of the limit switches, its only 3 wires and the servo mount will let you attach upto 4 micro switches, giving you options for feedback and interlocking. Of course to be correct you should use two limit switches one for each end of the throw of the point blades - and that's only two micro switches and 4 wires

Paul