My Wemos D1 R32 + CNC3 + GPS


Frank Henriquez
 

Hello all, I'm mixing the OTA from my old Celestar 8 with the fork from a Powerstar 8 (which has a Byers worm gear) and driving everything with Onstep.

For this project, I've used the Wemos D1 R32 + CNC3 since I only need two motors (I may eventually add a focuser). So far, the electronics and software part of this build have been uneventful. The Wemos board has been temperamental with uploads, but it seems to have settled down. 
For reference, in case anyone starts a new build this is what I used:  Wemos D1 R32  a CNC3 clone board and TMC2209 stepper motor drivers, all from Amazon. One of the CNC3 boards had a few poor solder joints and some solder splatter, which I fixed/resoldered. The TMC2209 boards also looked hand soldered, with the header pins not quite straight. I fixed those as well.
The TMC2209 driver boards have extra pins on one end that would short out the motor voltage capacitor under the driver board - those were removed. Mine are configured for 32 microsteps/step with 400 step motors.
For the GPS module, I used a BN-220 which has on-board flash. I soldered a right angle header


Frank Henriquez
 

Sorry for the cut-off post.
The right-angle header for the GPS is on the exposed pins 32 and 33 on the Wemos board. This particular GPS module comes with convenient leads for RX , TX and power.
The additions to my config.h are pretty simple:

#define SERIAL_GPS         Serial1

#define SERIAL_GPS_RX           32 //pin available on Wemos R32 board
#define SERIAL_GPS_TX           33 //pin available on Wemos R32 board

#define SERIAL_GPS_BAUD         9600

My issues now are all mechanical. The Powerstar base has very little room for a stepper to drive the worm directly (the original stepper is a 300:1 geared motor) so I'm testing it with a NEMA 14 400 step motor which can move the RA well. There's no room for a flexible coupler between the worm and stepper, so there's quite a bit of wobble. In the picture below, I've cobbled together all the parts. The NEMA 14 motor is attached to the worm with the original, flimsy aluminum strip that held the old motor:

https://live.staticflickr.com/65535/51811400324_6b917dedfa_o.jpg

Thanks for reading so far.


George Cushing
 

Frank, Kevin Ma's did Meade fork conversion. For DEC, I used a 1:80 harmonic drive gear and a NEMA17 with 1:10 low backlash planetary gear.


Frank Henriquez
 

Hi George, while the NEMA14 stepper that I'm using works great, any minor deviation between the worm and the stepper shaft will cause a noticeable wobble. I tried shimming it and carefully adjusting the grub screw on the worm, but it just won't go away. There's also very little room in the case.

I'm going to take the case to a local machinist and have him rotate the worm assembly to make the end perpendicular to the side, then have him mill a hole for the shaft of a NEMA17 stepper (and mounting holes). I'll be able to use a flexible coupler between the stepper and worm. I can just print a case to cover the motor and electronics.

Where did you get the harmonic drive? I've thought of using a belt drive or a 3D printed dual herringbone gear. I also saw this 3D printed harmonic drive: https://www.youtube.com/watch?v=Emvo3bLT-Z4
PLA should be strong enough. If not, I can print it in a 3D engineering resin.