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[ijdarroch]

Oh great and wise Oracle of AstroEq
I am trying to computerize a GEM that I was given along with a 14" Mak telescope. There are some unusual parameters: 1. The telescope weighs 240 Lbs. 2. The mount is huge.
I am using an Arduino Mega 2560 , TB600 drivers and .9 Deg Nema 23x82 motors. Everything is talking to each other and seems to work well in the tracking mode. ( although I have not actually tracked a star at this point)
The issue I have is the Goto speed. At the highest speed in Goto mode it slews  so slowly that it would take all night to get from park to a star I might wish to track.
Here are the settings for the Arduino:
ST4 Rate:0.9, Advanced HC: Disabled, GP101Driver Type; Open Drain ( I have tried both settings here), Motor driver IC type: DRV8834, uStep Gear Change: Disabled, Motor Microsteps: 32uStep. ( I have used all of the settings in this drop down menu and the 32uStep setting working the best)
RA Drive: Worm Rat: 18:1, Motor Drive Ratio: 4.14:1, Goto Rate (x sidereal): 468
Dec Drive: Worm Ratio: 19.48:1, Motor Drive Ratio: 4:1, Goto rae (x Sidereal): 551
I need the motors to get to a much higher rpm in the Goto setting but if I try to go higher in the Goto rate the motors lose their minds and vibrate.
Any ideas on how to get the motors up to 1000 RPM from about 50 RPM?
Please bear in mind that while I am a huge fan of Arduino I have never written any code and haven't a clue how to do it.
Thanks in advance.
Regards
Ian

[ecc2000]

Hello,

With a TB6600 how did you connect the microswitch controls MS1 MS2 MS3?, Because if you have not connected these Astroeq controls do not manage them in principle!

Astroeq manages microsteps orders through MS1 MS2 MS3 for goto!

I'm also interested in knowing how you connected the Arduino Mega to the TB6600? would you have a diagram to present?

Thank you

Pierre

[ijdarroch]

Hello Pierre
I am not sure that I understand your question re MS1, MS2 and MS3. I am using EQMod to access the Goto commands.
I have attached a wiring diagram for the TB6600.  and a sreen shot of the EQMod.
Regards
Ian

[ijdarroch]

Ooopps the wiring diagram didn't get sent in the last post.
Sorry about that
Ian

[ecc2000]

Hello,

Let me explain !

On cards with the TB6600 there are microswicht to select the microstep mode, whole steps, half steps, quarter steps .... and this up to 32 microsteps!

With the 8825 or 4988 drivers, the three ms1 ms2 ms3 inputs are available and are controlled by Astroeq!

For sidereal speed this does not pose any problems, you just have to configure the number of microsteps on the TB6600 with the microswicht and configure Astroeq for the right speed!

For goto, it's Astroeq which changes the state of the ms1 ms2 ms3 inputs on the 8825 or 4988 drivers, but it can't do it on the TB6600!

I already asked the question on another discussion post but remained unanswered .. !!

It would be necessary to remove the microswicht on the TB6600 to be able to control them with Astreq by pulling connection wires, but the problem is that the high or low control states do not correspond with the 8825, even when mounting three state inverters logic in the outputs it would not work, the solution is therefore in changing the lines of code in the Astroeq program and that I do not know how to do, which is a shame, because we could have a very very efficient system without having to go through 8825 which in the end only apply to 3D printers.

We could also use TB6560!

I also found Sanken integrated circuits very efficient up to 3A and very easy to wire!

To have a very complete system, a small utility to configure the ms1 ms2 ms3 commands would be a total success!

Here we are trapped in the 8825!, Personally I think it would be time to change it given the number of people who had problems!

Good day Sincerely,

Pierre

[TCWORLD]

Hi Ian,

There is no issue regarding the microstep select pins. With the "Gear Change" mode set to "Disabled" as you have it, the AstroEQ will simply assume a fixed microstep ratio - in this case 1/32.

If the motors are stalling and vibrating, it basically means they cannot sustain enough torque to rotate at the desired RPM. This is usually caused by one of three things:

• Motors with too little torque capabilities (stepper motor torque decreases from "Holding Torque" at 0RPM, to no torque at some max RPM)
• Drivers which are not providing enough power (e.g. current limit too low, or voltage too low). If you are using external drivers, you could use a 12V supply for the AstroEQ and a higher volage supply like 24V or 36V for the drivers.
• Too much load on the stepper motors due to the mount not being balanced or the work gear being overly tight.

Given that the scope is 240lbs, you'll need a heck of a lot of torque to move the scope at high speeds. If you are only using 12V for the stepper drivers, you can likely get much more speed by upping the driver supply. Stepper motors are inherently inductive which causes a drop in torque at high speeds due to voltage drop across inductor. By increasing the voltage you can reduce this loss of torque.

The TB6600's appear to be rated for up to 42V, so if you were to supply the Arduino with just the USB port (don't connect VIN), and then supply the drivers with say 36V you will liakely get much better performance.


Kind Regards,
Tom


@Pierre AstroEQ is open source. If you want to try different changes, you are welcome too. As I've said previously I am currently nearing the end of my PhD studies so have little to no time to develop AstroEQ further - it was started and remains a hobby, over which work and studies take priority.

[ecc2000]

Tom,

Super I was not aware!

If I understand correctly, when we put on desable we still have accelerations in goto? and we can adjust in the utility simply with goto speed?

So if you put TB6600 or TB6560 in 8 microsteps, you just have to configure the utility in 8 microsteps?

Can we play on ratios with all this?

Well I can not do tests at this level because I have disconnected everything and, I will try to program a 162 by the arduino Uno!

A +
Pierre

[TCWORLD]

@Pierre, correct. With gear change disabled, everything still works (accel/decel), just with a fixed microstep level. As long as the value selected in the config utility matches the actual parameters of the driver, it will track at the correct speed. Goto speed will however be limited to at most the calculated "IVal" parameter (vs. 8 x IVal if gear changing is enabled).

[ecc2000]

OK thanks a lot ! great news !

So in this case it is the clock speed in the microprocessor that changes if I understand correctly?

In the configuration the selection rather the setting of the goto value also works in the case of a TB6600 set to 8 microstep see 4?

Thanks again,

Pierre

[ecc2000]

Hello,

To convert the output signals of the Atmega162, I think that a Pic 18F microcontroller ... might be enough?

Because adding an Arduino seems to me not that good for reliability over time!

Good night,

Pierre

[paul_astrix]

If it is open source, rewrite the code to ramp up the *acceleration* slowly.

It's likely the motors are stalling on the high rotational inertia. A slow siredal start, gradually speeding up over 10 to 20 seconds may help.

The code might already do that, but was tuned to a lighter scope with a step gear change I think.

CNCs have programmable ramp up times and max speed to avoid losing sync.

Steppers with encoders and controllers are becoming cheap. Theoretically they won't loose sync at any speed.

But as Tom said, try 36V or even 48V first.

Thinking ahead, potentiometers for acceleration and top speed on 2 Arduino analog pins could be useful to tune in real time.

Paul