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Author Topic: Dome Motorisation  (Read 4724 times)

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Offline chris.bailey

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Re: Dome Motorisation
« Reply #15 on: 20:58:03, 11 March, 2017 »
ps

The motor controller I used is one of these MD03 H-Bridge units http://www.robotshop.com/uk/devantech-md03-50v-20a-h-bridge-driver.html but I'm sure I wouldn't have paid anything like that for it. It is fairly easy to interface to and my full Arduino code is as follows (I have a display on my dome controller so a lot of the code is to do with that and reading the dome actual azimuth)


//------------------------------------------------------------------------------------------------------------
//Rosemount Dome Controller version 1.14                                                  Chris Bailey - 2014
//------------------------------------------------------------------------------------------------------------
#include <Wire.h>            // use I2C library
#include <SoftwareSerial.h>                     // Software Serial library needed for display
SoftwareSerial mySerial(3,2);                   // Display Data Pins 2 and 3

#define CMPSADDRESS 0x60         // address of tilt compensated compass

#define MD03ADDRESS 0x58                       // Address of MD03 Motor Controller
#define MD03CMDBYTE 0x00                       // MD03 Command byte
#define MD03SPEEDBYTE 0x02                       // Byte to write to speed register

int domedeltatol = 2;              // dome azimuth delta tolerance
int tempdometgt=0;                              // if 0 from getdometgt then not updated from SkyX
int dometgt = 0;            // dome target azimuth
int domeact = 0;            // dome actual azimuth
int domedelta;               // dome azimuth delta from target
int motordir;               // flag to indicate direction of travel  1=CW, 0=CCW
byte motorspeed;            // motor speed
byte maxmotorspeed = 255;         // maximum motor speed
char tempstring[4];                             // string for printing to display
//------------------------------------------------------------------------------------------------------------
void setup() {
  Serial.begin(9600);
  Wire.begin();
  mySerial.begin(9600);                         // set up serial port for 9600 baud
  delay(500);                                   // wait for display to boot up
  mySerial.write(254);                          // move cursor to beginning of first line
  mySerial.write(128);
  mySerial.write("                   ");        // clear display
  mySerial.write("                   ");
  mySerial.write("                   ");
  mySerial.write("                   ");
}
//-----------------------------------------------------------------------------------------------------------
void loop() {
  tempdometgt=getdometgt();            // Get target dome azimuth from SkyX
  if (tempdometgt!=0){                           // If 0 then not updated from SKy X so ignore
    dometgt=tempdometgt;
  } 
  mySerial.write(254);                           // move cursor to beginning of first line
  mySerial.write(128);                           // 128 + 0-19
  mySerial.write("Dome Target = ");
  dtostrf(dometgt,4,0,tempstring);
  mySerial.write(tempstring);
  domeact=getdomeact();
  mySerial.write(254);                           // move cursor to beginning of second line
  mySerial.write(192);                           //128 + 64-83
  mySerial.write("Dome Actual = ");       //Get actual dome azimuth from CMPS10
  dtostrf(domeact,4,0,tempstring);
  mySerial.write(tempstring);
  domedelta=dometgt-domeact;           // delta of act from tgt
  mySerial.write(254);                            // move cursor to beginning of third line
  mySerial.write(148);                            //128 + 20-39
  mySerial.write(" Dome Delta = ");
  dtostrf(domedelta,4,0,tempstring);
  mySerial.write(tempstring);
  motordir = domecworccw (domedelta);        // 0 = Counter Clockwise, 1= Clockwise
  if(motordir==0){                                // swap values over for reversed motor
    motordir=1;
  }
  else{
    motordir=0;
  }
  mySerial.write(254);                            // move cursor to beginning of fourth line
  mySerial.write(212);                            // 128 + 84-103
  if(motordir==0){
    mySerial.write("  Motor Dir = CW  ");
  }
  else{
    mySerial.write("  Motor Dir = CCW ");
  }
  if (abs(domedelta) > domedeltatol){      // domedelta outside of tolerance
    if(abs(domedelta) >5) {         // if domedelta>5 full steam ahead
      motorspeed =maxmotorspeed;
      MD03sendData(MD03SPEEDBYTE, motorspeed);   // Sets speed to motorspeed
      MD03sendData(MD03CMDBYTE, motordir+1);    // 1 runs the motor forward and 2 runs backward
    }
    else {
      motorspeed =maxmotorspeed/2;           // half speed short dome slews
      MD03sendData(MD03SPEEDBYTE, motorspeed);   // Sets speed to motorspeed
      MD03sendData(MD03CMDBYTE, motordir+1);    // 1 runs the motor forward and 2 runs backward
    }

  }
  else {                                // if dome delta within domedeltatol stop motor         
    motordir=0;
    MD03sendData (MD03CMDBYTE, motordir);     
  }
  delay (1000);                                   // Do 1 per second updates.CMPS10 minimum delay 640ms       
}
//------------------------------------------------------------------------------------------------
int getdometgt () {
  // Read Dome Target Azimuth from Bluetooth Serial Port sent from VB controller
  int value=0;
  boolean done =false;
  while (!done){
    if (Serial.available()){
      char ch = Serial.read();
      delay(100);
      if( isDigit(ch)){
        value = (value * 10) + (ch - '0');
      }
      else{
        done = true;
      }
    }
    else {
      break;
    }
  }
  return value;
}
//-----------------------------------------------------------------------------------------------------------
int getdomeact() {
  // read Dome Actual Azimuth from tilt compensated compass.
  byte byteHigh, byteLow, fine;             // high and low bits of bearing
  int bearing;                                       // full bearing read from CMPS
  float bearingcal=0;                // bearing calibration value from interpolation
  // CMPS10 bearing calibration NESW array values. CW correction = +ve
  float cal[]={0,-10,-12,-14,-8,+8,+12,+8};                                 
  char pitch, roll;                // pitch and roll not used but need to be read
  Wire.beginTransmission(CMPSADDRESS);                // begin communication with CMPS
  Wire.write(2);                 // initiate read
  Wire.endTransmission();
  Wire.requestFrom(CMPSADDRESS, 4);           // request 4 bytes from CMPS
  while(Wire.available() < 4);                   // Wait for the bytes to arrive
  byteHigh = Wire.read();              // Store values
  byteLow = Wire.read();
  pitch = Wire.read();
  roll = Wire.read();
  bearing = ((byteHigh<<8) + byteLow) / 10;        // Calculate full bearing

  if (bearing>=0 && bearing<=45){                    // calibrate bearings in quadrants based on interpolation
    bearingcal=cal[0]+(((cal[1]-cal[0])/45)*bearing);
  }
  if (bearing>45 && bearing<=90){
    bearingcal=cal[1]+(((cal[2]-cal[1])/45)*(bearing-45));
  }
  if (bearing>90 && bearing<=135){
    bearingcal=cal[2]+(((cal[3]-cal[2])/45)*(bearing-90));
  }
  if (bearing>135 && bearing<=180){
    bearingcal=cal[3]+(((cal[4]-cal[3])/45)*(bearing-135));
  }
  if (bearing>180 && bearing<=225){
    bearingcal=cal[4]+(((cal[5]-cal[4])/45)*(bearing-180));
  }
  if (bearing>225 && bearing<=270){
    bearingcal=cal[5]+(((cal[6]-cal[5])/45)*(bearing-225));
  }
  if (bearing>270 && bearing<=315){
    bearingcal=cal[6]+(((cal[7]-cal[6])/45)*(bearing-270));
  }
  if (bearing>315 && bearing<=359){
    bearingcal=cal[7]+(((cal[0]-cal[7])/45)*(bearing-315));
  }
  bearing=bearing+bearingcal;
  if (bearing>360){                                  // check for > 360 bearing value after calibration
    bearing=bearing-360;
  }
  return  bearing;
}
//---------------------------------------------------------------------------------------------------
int domecworccw(int delta) {                       
  // Logic for shortest rotation based on domedelta
  int dir = (delta>0) ^ (abs(delta)>180);           // 1 for clockwise or 0 for anticlockwise
  return dir;
}
//---------------------------------------------------------------------------------------------------
void MD03sendData(byte reg, byte val){               
  //function for sending data to MD03
  Wire.beginTransmission(MD03ADDRESS);
  Wire.write(reg);
  Wire.write(val);
  Wire.endTransmission();
}
//-----------------------------------------------------------------------------------------------------
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Offline petevasey

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Re: Dome Motorisation
« Reply #16 on: 22:40:36, 11 March, 2017 »
Hi, Chris,

Strewth!  Are you by any chance a computer programmer by profession?  A very nicely annotated program, but means very little to me at the moment.  All I'll be trying to do is run the motor at two or three speeds (fast, slow and sidereal) in different directions - no complications with links to computers etc.  I might try for a home position using some form of detector, but that's about the limit.  For now.

An interesting learning curve ahead  :scare:

Cheers,

Peter.
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #17 on: 08:39:45, 12 March, 2017 »
Strewth!  Are you by any chance a computer programmer by profession? 

More a professional Googler ;) I have to annotate code heavily so I have a chance of working out what I have done a couple of weeks later. Its run happily for the last three years so was well worth the effort/

As I said, a lot of that code relates to the display I added (which displays actual and target dome azimuths and the move direction), reading the actual azimuth from the electronic compass and reading in the target azimuth from Bluetooth. The bits to do with sending data to the motor controller is just a few lines but that did take a lot of trial and error as the data sheets for these things are often written for people who know what they are doing! Coding moves for stepper motors is a LOT easier as there are various libraries that do the heavy lifting.

I do all the prototyping on a full size Arduino but tend to use Arduino Nano's when everything is finalised. The clones can be had for about £12.

I think you are right trying to just get it to step round as a starting point. Its a very easy job to read from a potentiometer on an Arduino to set the speed, add in a switch for forward and reverse and you are done. A magnetic reed sensor and one of those little Neodymium magnets makes a good home sensor. I have that part coded from an early attempt somewhere if you get stuck.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
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Offline petevasey

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Re: Dome Motorisation
« Reply #18 on: 09:38:29, 12 March, 2017 »
Hi. Chris,

'Just to get it to step round'.  That's the part I'm really bothered about.  If the full speed of the motor is 60 RPM, with a 6" drive wheel I reckon for somewhere near sidereal I need to run it for only 1/5th second every 20 minutes.  Of course there will be electrical and mechanical inertia to be overcome, so probably the pulse can be longer and/or at a higher frequency, otherwise the mark-space ratio is huge (1:6000).  Any idea what yours is set at for sidereal?  Did you find the setting by trial and error?

Cheers,

Peter.
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #19 on: 11:06:26, 12 March, 2017 »
Peter

Thats where a Pulse Width Modulation motor controller comes in and the major advantage over using relays. That allows you to run the motor much slower than its rated maximum speed, 5RPM should be easily achievable, maybe even lower. There are limits as to how slow you can go but they are very versatile. Its important though to have a motor controller that easily handles the start current of the motor.

The dome will never rotate at sidereal so you do need a way of adjusting speed of rotation and depending where in the sky you are pointing the required dome speed will change over time. Mine was initially like that and I had a small potentiometer to adjust speed and a couple of buttons to nudge forwards and backwards. I reckon I used to get 4 hours or so before it would need a manual nudge so better than nothing. Up near the zenith things get a little more complex.

All the equations needed are here http://www.dppobservatory.net/DomeAutomation/dome_synchronisation.pdf but have some Paracetamol handy. I did code these myself but then found the Ascom POTH or SkyX Dome Controller do it all for you. SkyX is very scriptable so I run a dummy dome controller in SkyX and then break out the dome target azimuth with a Visual Basic script and fire that to the Arduino over Bluetooth. The Arduino code above then does the rest. You can do similar with Ascom/Maxim but I have always found Windows COM to be a tricky beggar to work with.

You could use a spreadsheet to map those equations to required rotation speeds to get some idea of the range required. A handful of forward speeds should then cover you for several hours for most parts of the sky. A potentiometer with detents would be the ideal thing but I can't find any suppliers of them in the UK or on eBay. A normal potentiometer with a marked scale would do the same thing. I would use this to set the delay between nudge pulses rather than the motor speed though you would need to code it so that the main loop looks for a change each time around (Arduino's are not multithreaded), there are Arduino timer libraries that do such things such as http://www.forward.com.au/pfod/ArduinoProgramming/TimingDelaysInArduino.html. Thats the beauty of programming the Arduino, you can normally find code snippets that do what you want somewhere on the web.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline petevasey

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Re: Dome Motorisation
« Reply #20 on: 09:22:13, 13 March, 2017 »
Hi, Chris,

I came across this page:

https://darklondonskies.com/2014/08/17/getting-the-dome-to-rotate/

Looks interesting and appeared to work for them.  Eventually!  You can see I'm quizzing the guy about his installation.  Maybe I will need two motors diametrically opposite to balance the pressures on the dome, but I can probably use smaller diameter pulleys (waiting for the motor to arrive, it's on its way) which will help with torque and speed.   Smaller pulleys are flanged, but I would use a pulley wider than the belt to allow for vertical misalignment, and if necessary turn down the flanges a bit.  Probably a fair saving in cost over the Explora-dome acorn drive - a full diameter belt will cost around £100, but I can experiment with a much shorter length.  I'll go for 8 mm pitch to get a decent tooth depth.  A big advantage is the much reduced diameter of the drive wheel, perhaps 3 or 4" will suffice against the 6" of the acorn wheel, and although I emailed Explora-dome a couple of days ago, I'm still waiting for a price delivered.

I absolutely take on board your comments about varying speed.  Indeed I have found that for some high targets the dome slit is in line with the movement of the telescope and I haven't had to move the dome for a couple of hours.  But if I can get three or four hours unattended that would be great - better than having to dive out every half hour when I'm using the 10" scope.  Then I suppose the next step is put an encoder on top of a drive wheel and learn how to program an Arduino.  I already use MaximDL, so can link it to the telescope to get the coordinates and talk to ASCOM POTH.  Paracetamol, here I come  ;)

Cheers,

Peter.
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #21 on: 09:56:16, 13 March, 2017 »
Peter

It was that page that led me to try a length of timing belt a couple of years back. I think I found a couple of metres cheap on eBay so used that as a trial. I found that you need a LOT of pressure on the belt to avoid it skipping so ideally a rubber wheel on the other side of the dome flange to keep them together. My dome rotates pretty easily so if yours does need a good shove to get it moving, I doubt it will work well.

I would go and get a sheet of 6mm ply and see how easy it would be to make an Acorn track yourself. 2 " wide strips would give you room either side for the fixings to the dome lip. Once you have a couple of lengths glued together as a sandwich it should then hold the arc of the dome. It is a far more positive engagement and with some tolerance for the inevitable out of roundness on the dome.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline petevasey

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Re: Dome Motorisation
« Reply #22 on: 20:45:18, 13 March, 2017 »
Hi, Chris,

' a rubber wheel on the other side of the dome flange to keep them together'.  Of course your dome is designed for drive wheels either side of a thin flange,  but the dome rim on mine is thick wood, so won't flex.   The whole dome might move across slightly although it will be fighting all the sprung wheels on the opposite side.   No access to fit a rear pressure wheel - I'd have to lift the dome up several inches, but it may come to that.  However there are already a number of fixed (nylon) wheels behind the rim although apparently not making contact - maybe there to prevent the dome moving too far off centre, so worth a try positioning the drive wheel opposite one of them.

The London people have a second motor on the opposite side to help balance the pressures, and of course halve the effort required by a single motor, but they are using a fairly large drive wheel - I hope to use a smaller one.  When my motor arrives, I might as well give the toothed belt method a go.  Some work to make a strong bracket, but I've got enough bits and pieces for that.  If it looks as though a single motor works without jumping, then I'll maybe go further down that path and get a second motor to balance it.  Otherwise it'll be the acorn drive and hope there will be enough torque with one motor. Explora-dome have replied, but only to state they can supply the lengths of track I require.  No price as yet!

If the 30 A robotshop PWM drive unit you suggested will slow the motor(s) down to around 5 RPM, and I can use a 4" drive wheel, then I'll be in business - 4 1/2 minutes for a full revolution of the dome, (or of course increase the speed manually if required) and slow enough that a nudge of around 3 seconds every 15 minutes will give me a few hours without manual intervention.  I could hopefully use that little timer module to switch the drive unit on and off, with a manual override switch when I need to reposition.  And of course a reversing switch.  A little control box on a flying lead will do the job.

Cheers,

Peter
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #23 on: 07:43:57, 14 March, 2017 »
Peter

I tested the motor on my dome yesterday. At full speed its around 15rpm and I can happily slow it to 2rpm. Much below that and it just hums without moving.

I'm not convinced on the two motors idea. The speed of the two would have to be exactly the same and any speed changes would have not be precisely co-ordinated or you will either get slipping or worse still ripping the teeth off the belt. Matching motor speed that precisely is not easy feat.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline ngwillym

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Re: Dome Motorisation
« Reply #24 on: 08:32:18, 14 March, 2017 »
Peter

 Have you looked into options for motorising your dome. Mine is one of the older Pulsar domes (with he big draft gap!) and I have a windscreen wiper motor with a rubber wheel. Easy way is to just nudge it round slowly and hope. Slightly more complex is to use a tilt compensated compass to read the dome azimuth and then use an Arduino to compare that to where it should be (Ascom POTH or in my case SkyX) and nudge the motor to suit. There are a lot of off the shelf solutions but they are eye waveringly expensive for what they do. I reckon mine cost me no more that £50 all in and nearly half of that was the motor controller. Motorising it really changed the game for me.

Chris

Chris,

I've also go t an original Pulsar dome and was told that there was no way to automate it. Looking at it the wheels are attached to the top part and rest on a lip on the bottom part. I can't see a way to get a wheel into contact with the dome itself and even then, there are protrusions where the dome sections join together that would prevent a wheel from moving it. So I'd be interested in some pics of how you managed it with yours.
Thanks in advance
Neil
Neil G
50.8920° N, 1.4530° W
Scopes: Celestron C11 Fastar, Opticstar 127mm Apo, Celestron SLT 102, Celestron Travelscope 70
Mounts: Skywatcher EQ8, Skywatcher EQ5+Synscan, Celestron SLT 102
Cameras: QHY5L-IIM, DFK21AU, AVS DSO-1, Watec 120n, Sony A100/A580
Eyepieces: Quark Chromosphere, Parks Gold, Lumicon GEG

Offline petevasey

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Re: Dome Motorisation
« Reply #25 on: 09:02:22, 14 March, 2017 »
Hi, Chris,

Peter

I tested the motor on my dome yesterday. At full speed its around 15rpm and I can happily slow it to 2rpm. Much below that and it just hums without moving.

I'm not convinced on the two motors idea. The speed of the two would have to be exactly the same and any speed changes would have not be precisely co-ordinated or you will either get slipping or worse still ripping the teeth off the belt. Matching motor speed that precisely is not easy feat.

Chris


Good to know about your speed range although I'm surprised the maximum is only 15 rpm.  Maybe the load slows it down.  It will be interesting to check the no load speed of mine when it arrives.  Regarding variations between the two motors, yes, if running free there would be some difference in speed even if identical motors.  But they are not steppers, and I'm sure the torque arising from any slight difference would be far less than that required to drive the dome.  I would of course connect the motors to the same drive unit.  With the load being shared between the two there would only be a small increase in total current.  But I'll need to check the startup surge.  It seems to work ok for the London guys - if you look at the clip where their system is being controlled via an Arduino you will see that they have two motors running successfully.

https://darklondonskies.com/2014/09/

But hopefully one motor will do the job.

Neil, have you seen this: http://www.pulsarobservatories.com/downloads/ASSEMBLY%20%20USER%20GUIDE.pdf

Look at the motor installation section - it may help, but of course that depends on your individual dome which may be different to the model shown.

Cheers,

Peter.



Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #26 on: 09:08:52, 14 March, 2017 »
Neil

I assume then that you have the Pulsar motor thats attached to the rotating part with the nudge control? If so, that is exactly how mine started life!

If so I used that motor and changed over the control unit to a PWM motor controller, a tilt compensated compass and an Arduino. As noted above, the Arduino receives dome target azimuth information from the PC over Bluetooth and then fires the motor until the reading from the compass is within a couple of degrees of that target, with some coded logic as to the shortest distance of travel. The only downside is that the battery for the motor has to trundle round with the dome but I manage to get 10 hours out of it and have a couple of spares so on a long night swap them over before retiring.

I'll try and get some piccies but its not easy as most of it is hidden away.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline chris.bailey

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Re: Dome Motorisation
« Reply #27 on: 09:12:37, 14 March, 2017 »

Neil, have you seen this: http://www.pulsarobservatories.com/downloads/ASSEMBLY%20%20USER%20GUIDE.pdf



Pulsar changed the design of the dome edge soon after I got mine (grrrr) and added that lip to the rotating part of the dome to allow motors to be attached to the fixed part. It also makes the whole thing a little less drafty!
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline chris.bailey

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Re: Dome Motorisation
« Reply #28 on: 12:05:22, 14 March, 2017 »
Peter

this timing belt is a little heavier than the norm so might be a decent option http://www.beltingonline.com/htd8-open-length-pu-timing-belts-9994

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline petevasey

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Re: Dome Motorisation
« Reply #29 on: 13:09:20, 14 March, 2017 »
Hi, Chris,

HTD 8 mm pitch is what I was going to go for anyway, but in rubber - not only is the Polyurethane horrendously expensive, it probably won't glue very well.  Wheel and belt probably from here: http://www.bearingshopuk.co.uk/belts/timing-belts/?timing_pitch=25924  7.2 metres of 30mm wide belt will cost about £130, a wheel 76mm dia, 50mm wide around £20.  I'd just buy a couple of feet of belt for trials.

But I've come across an original photo from the dome installation.  2 Megapixel camera chip, so this is full size.  But it nicely shows how the dome is mounted.  As you see, the wooden rim is very substantial.  The grain runs crosswise, but there is a plywood facing strip with lengthwise grain.  So you can see why I might consider just buying an acorn wheel (or even making my own) and drilling matching holes in the rim.  It would take a long time for the rim to wear significantly.  I'd just do a short length at first, so no real harm done if it doesn't work.  I've got some 80 mm aluminium stock bar, and might be able to make my own acorn wheel using socket cap bolts with the end rounded off as per the attached.  But maybe the angle of attack and required spacing will be too large at that diameter.  Just a thought.  But no further action until I have the motor!

Cheers,

Peter.
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

 

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