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[Sumukh P]

Hii.. I have Bresser Galaxia 114/900 EQ2 telescope. I want to know if this mount is supported by AstroEQ. I want to make DIY AstroEQ.

[TCWORLD]

Hi,

Theoretically it is possible. If you can find a way to attach bipolar stepper motors to the mount and work out the gear ratios.

However given that the EQ2 is a very small mount for the size of telescope on it, I can't say for sure how good the performance will be. For simple go-to and tracking it may well be fine if you don't try to slew too fast.

[Sumukh P]

Ok. Bresser has provided an arrangement to attach motor drive from GoTo. But since GoTo is costlier I think it is better to make one with stepper motors. I am not from engineering background. Can you tell me how to find gear ratios??

[Sumukh P]

Hii again, I have designed my own PCB for using Arduino Mega2560 and DRV8825 stepper driver ICs, for German EQ2, which I have. I have burned the AstroEQ firmware in MEGA.

I opened the mount to calculate worm gear ratio in both RA and Dec axes.
(Please correct me if I am wrong in following calculations)
I have a stainless steel gear on worm shaft, with 140 teeth. (Mount allows to have tracking motors). So I purchased an MK8 Extruder Drive Gear 26Teeth, which has exactly same tooth size as that of SS gear. So the motor gear ratio becomes 140/26= 5.3846153846. Which I am giving Input in AstroEQ configuration utility. My RA worm gear has 138 teeth, so Worm ratio, I am giving as 138. It is giving Axis step/rev as 4755693. Worm steps as 34462. Sidereal bVal as 16558. Ival as 300.

Q.)  What is the unit of bVal?

Again my Dec has 87 teeth for worm gear arrangement. If I want to use motor directly then Motor gear ratio is 1:1, but If I put 86 as worm gear ratio, It is giving an error.

I want to know how the parameters are calculated in AstroEQ configuration utility.

I calculated on my own the RA tracking speed and other things, I am getting different numbers.

I will share that Excel sheet here. Can anyone have  a look at this and tell me.

[TCWORLD]

Hi,

The calculations are as follows:

• aVal = steps per axis revolution = "motor gear ratio" x "worm ratio" x (360/"step angle") x "microstep mode"
• sVal = steps per worm screw revolution = "aVal" / "worm ratio"
• IVal = interrupts per step = found by trial and error by minimising sidereal rate speed error
• bVal = interrupts per second = "IVal" / (86164.0905 / "aVal")

The "bVal" is essentially the base timing value for the system. A timer is configured to run at "bVal" interrupts per second, then the motor will be stepped after a certain number of interrupts. The number of interrupts sets the speed of the mount. To run at the sidereal rate the mount would make a step every "IVal" interrupts. To go at twice the sidereal rate it would step every "IVal"/2 interrupts, and so on. This is why when "IVal" gets too low there are fewer possible high speed values because of integer rounding of the reciprocal.

The AstroEQ config utility needs to be able to calculate an "IVal" of <1200 (I forget the exact reason now as it was a long time ago that I worked it out, I think it was due to higher values confusing EQMOD but I could be wrong). Additionally the interrupt rate in the system is limited by both clock frequency, but also the number of clock cycles it takes the processor to perform each step of the motor (make the step, update encoder positions, update the IVal counter, accel/decel routines, bVal dithering for higher speed accuracy, etc.) which if both motors are running flat out is about 480 clock cycles. This gives a second upper limit on "IVal" of (86164.0905 x 8000000.0)/("aVal" x 480).

Looking at your DEC axis values basically your gear ratios are not high enough and so the calculations violate the upper limit of "IVal". The only solution to this is to either increase the gear ratios, or get motors with a lower step angle. However if you find yourself pushing the upper limit of IVal it is usually going to result in a very low resolution of the mount (you'll be ending up with more than 1 arc second per microstep of the motor).