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Little Foot Display Firmware

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Astroquattro:
Hi,

@Armado,
I just told you my motives why I'm not looking for a stand-alone version. That was a good idea for a time in which powerful computers filled an entire floor of on office building and personal computers where huge and heavy fawn boxes which needed power cords.
Today everybody can have a capable labtop or notebook computer for less than 150€ (www.luxnote.com for example) or run a tablet for less than 100€ (http://www.efox-shop.com/tablet-pc-notebook-c-129 for example) which provide a very usable usb port.
That in mint there is no point in having a stand-alone version anymore. Despite, if one chooses the Arduino as basis, one sure can have a stand-alone version but it's less capable. The main reason for not choosing such a version is, that my ideas involve ccd cameras. And that is a key requirement! Because you definitely NEED a computer anyway, there really is no point in doing less.
I told you that I don't want to go to market with my solution, which I need for my home town observatory, because I don't have the time nor the wish to run a company. I am a professional astronomer and my duty is to research the universe. I've been to Kit Peak, Skinakas, Carla Alto and other observatory they have a variety of tracking systems, but mainly they use SPC which stands for serial programable controls. They operate huge DC motors attached to cvt gear drives to reach nano-arcsecond resolution and being able to move up to 300 tons of steal from on horizon to the other in less than 5 minutes.
For smaller telescope like our 24" Cassegrain or the one's RC optics produces or planewave the mounts are smaller and the weight is less so one does not need heavy duty motors but DC motors with gears attached to belt drives or friction gear drives are common. I moding my on modified Vixen SPdx (images attached) to make use of a belt drive in declination. I have an eight inch fork mount from Meade operating a C8 (when it arrives by mail the next days) which will be modified in more than the same way (both axis). During my research on tracking systems I found out that worm drives came up in the 70th because belts didn't provide the same duration at that time. Older people might remember that it was useful to have a spare belt in they car or at least have accompany by a tights wearing girl because cars those days broke down with ripped belts. Today this belt are high-end products if they are taken care of. As a racing bike driver I change my chain every year to get the most out of it and thats about 12k to 15k kilometer a year.

You see, if one goes professional one climbs up the ladder in the requirements.  The third image attached are the optics at our observatory. 24" of course could be pointed by hand because the mounting is so smooth-running that if it's not fastened by the gears of the motor it is moved by the slightest air-movement in the dome.
Thomas will agree that with such an instrument you won't go for a stand-alone version. Whats good for semi-professional use is good for amateur use because you get both for a small price.

It is the same discussion why one would choose a dobson mounting. Ok if one just wants to look or do a messier marathon (which one could do just two times a year) a dobson is ok, but for all other purposes you need a tracking to be comfortable. For taking photos (whatever scientific or entertaining) you need a guided tracking, not only to even out the pendulum which comes from the conversion of a circle (angular based) to a linear movement, but to deal with the seeing. Yes, down to six inch telescopes you have to deal with shifts caused by the seeing because those scopes' resolution lies in the seeing area up to 1arcsecond. Even a five inch scope suffers by that, when seeing is high (>1,8"). If you have a normal Vixen SP/GPdx or those replica called EQ up to 8" scopes wind is effecting the mount and that has to taken into account, too. (See image four)
Ok my modded SPdx doesn't suffer by that because I change the RA-axis to be filled with a massive 6cm Axis and the declination head is completely change to make room for a 5,2 cm axis which was drilled to 4,2 when it comes out of the head's housing. The maximum reasonable weight you can put on is 70kg (separated into telescope and counter weight). Ok I don't have such an instrument but an old friend had a 12,5" planetary newton which's weight was 36kg. That was back in the 90th's.
Maybe that cleared up why I am not looking for a stand-alone system, despite, I have the LF which runs nicely if I just want to look for wellness reasons.

@lizard,
I have a working implementation of Arduino Mega 2560 plus Adafruit MotoShieldv2 operating various Steppers by now. So the start was done some weeks ago. I have two different breakout boards L6470 from SparkFun which do 1/128 microstepping by hardware. The Adafruit MotorShield does microstepping by software and I implemented a small routine to calculate the angulars for getting infinite microsteps out of it if one wishes. The Adadruit stepper library does 1/8th  and 1/16th when you down load it. I added 1/32th to show how easy it is to climb up the ladder. But 1/32th will do good for amateur telescopes.
MT-1 based drives have a 48 steps motor with an 1/120th gearhead which brings down the smalles moving angular of the motor to 0.07° a step. I bought a 0.9°steps stepper from Munich Motors on Ebay for less than 12€, which does 0.05° running with 1/32 without a reducing gear.

The next steps, I have to repeat that, are filling my implemented gui with functionality and communicating with the motor via the Arduino/MotorShield by the computer.
With pyduino, a library that talks to firmata uploaded to the Arduino one can surpass the Mega2560 and just use the i/o ports leaving the calculations to the computers (multicore) cpu(s).
At that point the guiding camera comes in. We're in the possession of a 17 year old Apogee Ap7p which takes good image till today (see the unreduced forth image of ngc7331). A friend of mine bought a Sbig ST8300M five month ago. So using the Ap7p as guiding camera one need the computer to take very short image or a subregion of it make another one, favorable with in a tenth of a second, calculate the difference throw away the first image, change the second to be first, and pass the offset to the motors, all-in-all as fast as possible. The imaging camera has an e-/adu of 0.35 which does not allow lame guiding.

There are guiding systems on the market like LVI SmartGuider I and II or the SynGuider of Skywatcher. Celestron provides similar. They are stand-alone verion but suffer from the speed and accurateness of the integrated MCU's.
The fourth image show it quite clearly, Vixen N200S on a normal SPdx with a Vixen N130 as guiding scope and counter weight can't be tracked anymore with the highest aggressiveness chosen at the LVI SmartGuiderI. We're taling here about wind up to 20km/h which is common in spring and autum around here.
Stand-alone comes to a limit here and that's use amateur stuff!

Ok after having answered question one about if 'here' is the right place to talk about an open_hardware solution, let's move on to step two, questioning the requirements list:

- What do we need?

cheers,
Christian

Ps: The images have to be reduced in size to fit those tight and ancient requirements of the forum software, that I provide image number for at once and the others in a different post. Image ngc7331xxx is a raw fits image on a windy day in April this year. The LVI got to it's limits.

Astroquattro:
But let's open up a new thread for the requirements. Look here http://forum.lfep.de/index.php/topic,290.0.html

Attached are the missing images from above.

the_lizardking:
I started to build an encoder based PEC with Arduino 2560 based on the idea of Orlando and he is almost finished, I think we will get this code so we catched already two birds with one song.

Armando:
Hi Christian,

as stand-alone controller I meant a controller able to track with no PC aid. I was not referring to GoTo...
I agree with you about the GoTo capabilities that can be simply available by PC. Since guiding is a requirement that obliges to use a PC then we can ignore stand-alone GoTo capabilities...
When you spoke about "surpassing the Mega2560 and just use the i/o ports leaving the calculations to the computers (multicore) cpu(s)" were you referring to guiding calculations?
In a few word what we need is a controller that can track by itself. Ok?

CS
Armando

Astroquattro:

--- Quote from: Armando on Wednesday, 18.09.13 - 18:32:08 - CEST ---Hi Christian,

as stand-alone controller I meant a controller able to track with no PC aid. I was not referring to GoTo...
I agree with you about the GoTo capabilities that can be simply available by PC. Since guiding is a requirement that obliges to use a PC then we can ignore stand-alone GoTo capabilities...
When you spoke about "surpassing the Mega2560 and just use the i/o ports leaving the calculations to the computers (multicore) cpu(s)" were you referring to guiding calculations?
In a few word what we need is a controller that can track by itself. Ok?

CS
Armando

--- End quote ---

No, Goto was never an option, you're right, but stand-alone isn't an option to as I pointed it out.
You're right, stand-alone means a device that does control the motors without a high-level computer. Acutally a microprocessor aka MCU is a computer but on a lower level. There are plenty of similarities between a CPU and MCU. The manufacturing process, internal memory banks, bus-systems, but CPUs do have a different architecture and therefor different instruction sets.
Atmel produces microcontrollers like the Mega32 or the Mega128 or the Mega162 like AR used in the LF but that was years ago. Arduino started with a Mega162 and evolved their boards to a Mega2560. Those MCU do have frequencies about 40 Mhz. CPU's have core frequencies up to 4Ghz.
You see, all we're talking about here is speed, huge amounts of data to get really precise ans very fast movements here. We are talking about 1/10 to 1/100 arcseconds here. MCU are not capable of calculating so fast. Their bus systems are slow, too, so the calcualted signal takes time to get to the motors. Responses time is as important as calculation speed.

When I was talking about calculations above, I didn't only meant auto guiding but position changing in general. There is more to control a stepper motor than meets the eye.
Microstepping for example. To understand what where talking about you have to get the right picture. A stepper motor consists of at least to or more coils which are placed at right angles with each other. There is a magnet attached to the rotoraxis. Let's number the coil wires going from right to left and afterwards from bottom to top. If you give power to the first coil the electrons move from wire 1 to 2 generating a field which forces pushes off the magnet for a certain angle producing one step. Next power has to be given to the second coil and electron move from wire port 3 to 4 doing the same. Now the magnet turnt around so much that the fields have to be switched, the next sequence will start from wire end 4 to 3 turning the magnet and so on. This is called full step. Of course that is the easiest model of a stepper but in principal it's what happens inside. At half step mode, there is a specialty and both coils are getting powered.
For microstepping changing reference voltage is needed to do subturns.
To get the signals to the right coils in the right sequence a principal called h-bridge is used and it is available in a variety of chips. The most popular are the L293 and the L298.
The controlling technique is called pulse width modulation or short PWM. DC motors can be controlled with it to but normally PID is used to control the speed. PID stands for proportinal integral differential.
Steppers can only be controlled by PWM and that's what makes the controlling hardware so special. DC motors can be controlled by just a power source and a potentiometer because you do not have to subdivide the signal and send it to different coils.

Steppers are made for precision and max torque. That's why the are used in telescope mounts, drilling machines, 3D printers (preferable with glas scales).

I think at this point we can finish our small excourse into what's about electric motors. Now we have an equal understand and won't suffer from different definitions.

Back to topic.
So we do need at least a h-bridge but we can't attach it to a serial, parallel or usb port right away. Singals have to be prepared. That means they have to be converted from digital to analog, they possibly have to be amplified to be at use. Sometimes the power has to be limited to shield the motor coils from damage. Therefor we need peripheral hardware like capacitors, resistors, rectifiers, transistors... But that's not all there is. In principal we have to generate a PWM signal which basically is a timer.
Of course the basic parts can be done with a MCU as good as with a CPU but CPU can do that faster and twice at the same time. MCU can used to one operation at a time. Actual Intel CPU's can do up to four operation simultaneously. So one can calculate the off-sets in right ascension and declination at the same time and pass that signal at the same time to the motor.

So that makes stand-alone version slow and sluggish. That's not what we want. That's why we turned to more modern hardware and that forbids building a stand-alone version.

@lizard,
What do you think a PEC really is? For what do we will need PEC if we have auto guiding. As a matter of a fact, for auto guiding every camera can be used not only ccds but preferable.

cheers,
Christian

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