13 replies to this topic

[LU1AR]

After restoring a second hand ETX-90 RA telescope (The model that only has Right Ascension tracking), I noticed that many modified the power regulator to stabilize its movement.
Also, like mine; many are spoiled by leaking batteries left behind inside.
So I decided to go for a unique Lithium element; It does not spoil by draining electrolyte and can be stored -for years- maintaining a charge.
As the Lithium element has to be charged to a very exact voltage regime and prevent its level from falling below a certain point; I opted for a 1 element charging pad that is used in robotics kits. It uses Micro USB input and gives protected output.
The battery output is between 3.2 and 4.7 Volts. So, for precise regulation I turned it up to 5 Volts using a small 5 volt upconverter source, which gives me a regulated voltage. There are lots of power supplies like this, for Arduino environment.
I make this voltage adjustable for the motor by means of a PWM regulator (By Pulse Width Modulation), which supplies the motor with a voltage of 5 Volts pulsed at 30 Khz, which are integrated into the motor to equal a voltage of 1, 9 volts; where the motor has proper Right Ascension tracking.
The interesting thing is that the motor always receives pulses of 5 volts, which is more than double its working voltage; but trimmed in such a way that it does not exceed the turns at which it must turn. However, this way of use, makes the motor have a high torque from the start, which is able to drag the telescope mechanism with greater force. This allows us to adjust the mechanisms with less play, without danger that the motor cannot move it. All of which makes the use of the telescope more precise and comfortable.
The complete system, drain less than 20 mA. and have a tracking error of les than 4 minutes a day, without any sort of precise adjustment.
I hope this will be useful for you.
Regards.
Edgardo

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[LU1AR]

More updating for the ETX-90 RA.
Another detail that I want to emphasize is that I enlarged the holes where the side legs enter that allow the telescope to be used in Polar form on a table.
The legs go in loosely as they only thread one turn onto the plastic, rather than the anchors below.
It was enough to enlarge the holes in the lower cup, so that the legs screw three turns and abut against the metal.
The difference in stiffness is very noticeable and I recommend it.
Clear skies.

Edgardo

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[sg6]

I could be utterly wrong but doesn't the ETX90 take 3 AA's so making 4.5v and then isn't there a 4.8v lithium battery?

I know I have few at 3.7v and thought there is at least one up in the 4.x voltage range. Actually thought I had one.

 

Just thinking you may not have needed to step the voltage up.

 

Maybe the higher rated one is 4.2v but half think possibly higher. Finding one could be the problem as 3.7v seems to have become the standard.

 

And I have only half looked in the rear of one ETX-90 RA once so could be wrong on 3AA's being the power source.

[LU1AR]

I could be utterly wrong but doesn't the ETX90 take 3 AA's so making 4.5v and then isn't there a 4.8v lithium battery?

I know I have few at 3.7v and thought there is at least one up in the 4.x voltage range. Actually thought I had one.

 

Just thinking you may not have needed to step the voltage up.

 

Maybe the higher rated one is 4.2v but half think possibly higher. Finding one could be the problem as 3.7v seems to have become the standard.

 

And I have only half looked in the rear of one ETX-90 RA once so could be wrong on 3AA's being the power source.

Dear Friend: This model use 4 AA cells, which were ruined inside. The motor needs 1.9 Volts, but lowering the voltage of a Lithium cell (which is simple) to 1.9 volts; drag is very poor. In addition, it is difficult for him to move on cold days and the tracking has an error of near 1 hour every 24.
By raising the voltage to 5 Volts, we can use a pulse width modulator, which gives 5 Volts pulsed in such a way that its average equals 1.9 Volts, but the torque is quadrupled.
Thus, the motor grinds very regularly (4 minutes apart every 24 hours) and has the strength to move the mechanism firmly even using heavy eyepieces or pigiback cameras.
Regards.
Edgardo

[foxshark]

I know this post is a few months old now, but I just wanted to say that I liked the solution. I have been working on some H-bridge/Arduino options for my 90M that also had battery leak. Before that, I was looking at some no-programming solutions using something like a voltage regulation, power distribution, and brushed motor speed control (ESC) combo board for a mini quadcopter. This, however, is much more intuitive. How has it been holding up for you? I hear some of those PWM motor controllers can be short lived if you get a bad unit.

[LU1AR]

Almost all ETX-90s; They have broken the support of that little "fart finder", which they bring from the factory. It is because the bracket touches against the left jamb, when the tube reaches the end of the path. Once it broke and fixed; it breaks again easier.
While deciding how to reposition the finder, it occurred to me to use a green laser as a designator, which works wonders.
Before facing an adjustment system, I found a green laser sight, which brings X and Y adjustments. It uses a rail support, which forced me to make an adapter where the finder used to go.
The sight is black anodized, waterproof and suitable for bad weather. It is adjusted in both axes, with a small Allen key (Provided). Looking at laser forums (Here), I see that it is the only one that does not crouch in low temperatures. Conventional lasers wrinkle when it's cold, but when they work they are a little more powerful.
The battery provided is Lithium, but NOT RECHARGEABLE. But it can be replaced by a rechargeable one, of the same format.
Tonight, I take advantage of the cloudy sky of My Dear Buenos Aires, to point the beam at the clouds and center it on the field of a short eyepiece. My ETX-90 is getting powerful.
PS: The 35mm film tube. It is the cap that covers the eyepiece holder; so that no dirt gets into the mirror. There is a small hole at the bottom and a bag of Silica Gel is kept inside, which removes the moisture from the tube. I had a lot of work; to get the fungus out of that OTA, which is of impressive quality.
Regards.
Edgardo

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[LU1AR]

I know this post is a few months old now, but I just wanted to say that I liked the solution. I have been working on some H-bridge/Arduino options for my 90M that also had battery leak. Before that, I was looking at some no-programming solutions using something like a voltage regulation, power distribution, and brushed motor speed control (ESC) combo board for a mini quadcopter. This, however, is much more intuitive. How has it been holding up for you? I hear some of those PWM motor controllers can be short lived if you get a bad unit.

Since I installed the PWM control I have enjoyed my ETX90 telescope much more.
The PWM unit is sold for robotics and is used to regulate DC motors -with brushes- and lights. Parts cost less than $ 5 including the miny USB charge regulator and the DC/DC upconverter.
In the photos you can see two 18650 Lithium elements, because they are dummy copies of 600 mA each. I connected a pair in parallel.
Thanks for your comment.
Edgardo
 

[MikeBY]

Since I installed the PWM control I have enjoyed my ETX90 telescope much more.
The PWM unit is sold for robotics and is used to regulate DC motors -with brushes- and lights. Parts cost less than $ 5 including the miny USB charge regulator and the DC/DC upconverter.
In the photos you can see two 18650 Lithium elements, because they are dummy copies of 600 mA each. I connected a pair in parallel.
Thanks for your comment.
Edgardo
 

I  like your solution to improve motor performance. How did you adjust the PWM motor controller to provide the correct duty cycle? Did you simply measure DC voltage or some other method?  Do you have a source for this part?  Have you had any heat problem with the motor?
18650 Li-Ion cells are available with much higher capacities. A single 2500 mAh cell, much less a pair as you've configured your holder to carry would provide gobs of power. 

[LU1AR]

I  like your solution to improve motor performance. How did you adjust the PWM motor controller to provide the correct duty cycle? Did you simply measure DC voltage or some other method?  Do you have a source for this part?  Have you had any heat problem with the motor?
18650 Li-Ion cells are available with much higher capacities. A single 2500 mAh cell, much less a pair as you've configured your holder to carry would provide gobs of power. 

I used two (Fake) elements - in parallel - because I had them on hand. With the consumption of the ETX-90 they are enough to use it for 30 hours. There is no problem in using a single cell of good quality (AND capacity).
Regarding the adjustment, I used the VOM and adjusted the PWM to obtain a voltage in the motor of 1.9 Volts. as provided by the linear regulator.
The potentiometer on the PWM module allows for a very wide excursion, so I added a resistor in parallel to reduce its travel and be able to use a half turn, to get the expanded setting. It is not necessary for the visual use that I give it; but as soon as I calibrated it, it was left with an error of 4 minutes in 24 hours. So I didn't touch it.
I found the value of resistance experimentally. I don't remember it, but it is something very basic.
Regards.
Edgardo
 

[greghoro]

Edgardo,

 

I like this approach. I'm somewhat confused by your block diagram in first posting, specifically, the elimination of the existing circuit board.

 

The photograph shows the original circuit board and I assume you are still using elements of it for On/Off control and N/S hemisphere selection.  If so, where does it fit into the block diagram and where are the connection points, both in and out?

 

Note, as Foxshark indicated, my RA also takes just 3 AA batteries

 

 

Regards,

 

Greg

[LU1AR]

Edgardo,

 

I like this approach. I'm somewhat confused by your block diagram in first posting, specifically, the elimination of the existing circuit board.

 

The photograph shows the original circuit board and I assume you are still using elements of it for On/Off control and N/S hemisphere selection.  If so, where does it fit into the block diagram and where are the connection points, both in and out?

 

Note, as Foxshark indicated, my RA also takes just 3 AA batteries

 

 

Regards,

 

Greg

The OnOff key remains for that function. The hemisphery change key; only reverses both motor cables. I did not include it in the diagram, because it is made in the PC that I used to support my circuits.
The modifications are not detailed, since they vary with the components that are available in each place. My country is governed by a Latin American left party that makes everything more difficult.
You North Americans, are lucky to have everything close at hand.
Regards.
Edgardo

Edited by LU1AR, 25 May 2021 - 03:00 PM.

[LU1AR]

SMALL IMPROVEMENT FOR ETX TELESCOPES

We "oldtimers" are reluctant to use Autostar, because we are comfortable with the setting circles, that we learned to master half a century ago.
But sometimes, it is difficult for Us to find the faithful of the graduated circles, because it is only a triangular imprint on the plastic. In fact, it is easier to locate it by touching it than by seeing it.
Recently I found a white paint marker and immediately; thought that it would be good to replace the little pieces of paper that I had stuck on my telescope, to see where to insert the tripod screws. The triangles were painted right away.
With very little expense, I have greatly improved the comfort of using my beloved ETX.
Edgardo

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[PEU]

Hola Edgardo, not sure if I can post in spanish, so just in case, English it is. I also live in Buenos Aires and have an old ETX90 like yours, after many years of being stored in a very well protected wooden case (http://www.weasner.c...made-case1.html) I opened it and found two problems, depleted batteries almost damaged the control board and the arms had their attachment legs broken. Googling found this excelent thread of yours and I have a couple of questions:

 

1) regarding your circuit board mod, can you shed some light about how it works, does the control board pulses the motor, or its just a power suply and the motor turns continuously when powered? If this second option is the case, I understand you adjusted the PWN until a full turn is a day, is this correct?

 

2) If my assumption in 1) is correct this means you only used the old board for its switch and to confortably locate the 18650 battery holder right? If not, please tell me how to calibrate it.

 

For the broken legs I plan to 3D print some solution, it doesn't seem to be a big issue.

 

Thanks!

 

Pablo

 

 

 

[LU1AR]

Hola Edgardo, not sure if I can post in spanish, so just in case, English it is. I also live in Buenos Aires and have an old ETX90 like yours, after many years of being stored in a very well protected wooden case (http://www.weasner.c...made-case1.html) I opened it and found two problems, depleted batteries almost damaged the control board and the arms had their attachment legs broken. Googling found this excelent thread of yours and I have a couple of questions:

 

1) regarding your circuit board mod, can you shed some light about how it works, does the control board pulses the motor, or its just a power suply and the motor turns continuously when powered? If this second option is the case, I understand you adjusted the PWN until a full turn is a day, is this correct?

 

2) If my assumption in 1) is correct this means you only used the old board for its switch and to confortably locate the 18650 battery holder right? If not, please tell me how to calibrate it.

 

For the broken legs I plan to 3D print some solution, it doesn't seem to be a big issue.

 

Thanks!

 

Pablo

 

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Hola Pablo. Puedes contactarme a edgardomaffia@gmail.com y con gusto te ayudaré a poner en condiciones tu telescopio.
Disculpa la demora en responder, pero estuve con Dengue y no ingresé al foro.
Saludos.