Custom telescope mount using harmonic drives and ESP32

Post by [deleted] » Wed, Aug 20, 2025, 4:38 PM UTC

fest wrote: post #105

topspin wrote: post #90

From the blog: "Not surprising once you understand that slewing to a target significantly increases the number of pulses per second sent to the motors, and everything became just too much to handle for our little ESP32." A hobby application of mine involves driving multiple steppers at high-ish frequencies, following sigmoid curves precisely and no tolerance for glitches, because the mass and the cost of the device(s…

When I was doing stepper control on rp2040 I looked into using PIO but the 5 bit counters and 32 instruction limit made it too awkward to use. What worked better for my needs was dedicating 2nd core for just motion control and bit-banging the step/dir signals- simple to implement and good enough for the modest needs I had (just trapezoidal velocity profile for single axis motion).

Post by topspin » Wed, Aug 20, 2025, 6:12 PM UTC

fest wrote: post #105

topspin wrote: post #90

From the blog: "Not surprising once you understand that slewing to a target significantly increases the number of pulses per second sent to the motors, and everything became just too much to handle for our little ESP32." A hobby application of mine involves driving multiple steppers at high-ish frequencies, following sigmoid curves precisely and no tolerance for glitches, because the mass and the cost of the device(s…

When I was doing stepper control on rp2040 I looked into using PIO but the 5 bit counters and 32 instruction limit made it too awkward to use. What worked better for my needs was dedicating 2nd core for just motion control and bit-banging the step/dir signals- simple to implement and good enough for the modest needs I had (just trapezoidal velocity profile for single axis motion).

    ; PIO program for high-precision stepper profiles with a two-word data format.
    ; RP2350 clock is 150 MHz
    ; Word 1: [32-bit Low-Time Delay]. A value of 0 is the sentinel to stop.
    ; Word 2: [32-bit Repetition Count] (N-1).

    .program stepper_pwm
    .define HIGH_PULSE_CYCLES 2998 ; 20us @ 150MHz. Total delay is (CONSTANT + 2) cycles. 3000 - 2 = 2998.
    .side_set 1 opt

    entry_point:
        pull block              ; Pull Word 1 (Low-Time Delay) from DMA.
        mov x, osr              ; Copy to X for sent sentinel test
        jmp !x, process_step    ; fall through to the stop_sequence when sentinel == 0

    stop_sequence:
        nop side 0              ; Force the output pin LOW.
        irq set 5               ; Signal the core that the profile has finished.

    halt_loop:
        jmp halt_loop           ; Halt state machine.

    process_step:
        mov y, x                ; Y now holds the 32-bit Low-Time Delay.
        mov isr, y              ; Save LOW delay in ISR for use in every repetition.
        pull block              ; Pull Word 2 (Repetition Count) from DMA.
        mov x, osr              ; X now holds the 32-bit Repetition Count.

    rep_loop:
        ; High pulse duration = (HIGH_PULSE_CYCLES + 2) clock cycles.
        mov y, HIGH_PULSE_CYCLES side 1

    high_loop:
        jmp y-- high_loop side 1
        ; Low pulse duration between reps = (LOW_DELAY_FROM_ISR + 3) clock cycles.
        mov y, isr side 0

    low_loop:
        jmp y-- low_loop side 0
        jmp x-- rep_loop        ; Decrement repetition counter and loop if not zero.
        jmp entry_point         ; Finished all reps for this step, get the next one.

Post by wallflower » Thu, Aug 21, 2025, 4:34 AM UTC

HorizonXP wrote: post #22

Amazing project and write up, very good timing too! I’ve been into amateur astronomy since I was 13, owning a few telescopes and spending many hours with family at star parties. This week I pulled out our big Meade 10” SCT and our small Meade 4” Newtonian to show my 7yo son the moon and Saturn from my parents Bortle 8 backyard. It was wonderful seeing his awe and surprise, and the fact that my parents were there to s…

Post by contingencies » Wed, Aug 27, 2025, 7:34 PM UTC

nullc wrote: post #99

sheepscreek wrote: post #55

Earlier quoted context omitted.

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I used OpenSCAD a long time ago because it felt very natural having spent a lot of time with POVray as a teen. But I found it to be very difficult to design parts with specific dimensions that were needed to line up with objects in the real world. In FreeCAD (/Solidworks/Onshape/solvespace/etc.) it's easy to just create a logical sketch of your part, fix the require dimensions, angles, symmetries, etc and it solves f…