An Electronic Lead Screw controller using a Teensy 4.1

[WobblyHand]

What kind of encoder will you be using? I think the encoder clough uses is a quadrature 1024ppr which is 4x1024 = 4096 ppr. I've been looking into taking on this project as well without the TI controller. I thought about using an arduino with an LS7366R board to read the encoder's pulses since the arduino cannot handle the high frequencies of the encoder. I think the LS7366R might be worth considering and you could use a Teensy 3.x instead of the 4.

Omron E6B2-CWZ6C, same as Clough42. You might reconsider Teensy 3.x, since none are being manufactured due to chip shortages. I don't have an issue with the Teensy 4.1. For the most part my SW is done, and running, save for stuff that will come up during integration.

 

[AlanB]

I did some gear design in InkScape. Seems like there was a plugin for it. Then imported it into OpenSCAD, but FreeCAD should also be able to.

Teensy 4.0 should have enough pins as well, and may be more available. Pico is also very available.

 

[WobblyHand]

I did some gear design in InkScape. Seems like there was a plugin for it. Then imported it into OpenSCAD, but FreeCAD should also be able to.

Teensy 4.0 should have enough pins as well, and may be more available. Pico is also very available.

I figured out spur and timing gears in FreeCAD, it's a PIA, but doable. You have to use the Gear workbench. If you fall for the menu item called Involute Gear under PartDesign, you have my sympathies. That just doesn't work correctly. Fell into that rabbit hole for a while.

As for my processor, that train left long ago, May 3rd to be exact. No reason to port to a less capable processor, in my totally unbiased opinion. Everyone else can implement what they like...

 

[WobblyHand]

Ordered the pulleys! Hope they are as they described... Delivery date: sometime in mid-late August.

Went with 2 3M48T 16mm wide pulleys, one with 14mm bore and the other with a 10mm bore and a step. For the encoder installation, I got a 2M60T 7mm (6) wide pulley with a 14mm bore that mounts over the M1.5 60T gear, and a 2M40T 7mm wide pulley with 6mm bore for the encoder. Both of the 2M pulleys are without step. Now I have to figure out the belts. I suppose from the drawing I could figure out the belt length. Phew, getting a mental workout. I find this stuff difficult.

So the distance between the 3M48T pulleys is 121.12mm. The approx inner diameter of the pulley is 45.08mm. So roughly the belt should be
2 x 121.2 + pi x 45.08 = 383.86, or 384 or 385, give or take. For the 2M pulleys, for the encoder, I have more degrees of freedom, because the shaft location distance isn't tightly controlled...

 

[RJSakowski]

Ordered the pulleys! Hope they are as they described... Delivery date: sometime in mid-late August.

Went with 2 3M48T 16mm wide pulleys, one with 14mm bore and the other with a 10mm bore and a step. For the encoder installation, I got a 2M60T 7mm (6) wide pulley with a 14mm bore that mounts over the M1.5 60T gear, and a 2M40T 7mm wide pulley with 6mm bore for the encoder. Both of the 2M pulleys are without step. Now I have to figure out the belts. I suppose from the drawing I could figure out the belt length. Phew, getting a mental workout. I find this stuff difficult.

So the distance between the 3M48T pulleys is 121.12mm. The approx inner diameter of the pulley is 45.08mm. So roughly the belt should be
2 x 121.2 + pi x 45.08 = 383.86, or 384 or 385, give or take. For the 2M pulleys, for the encoder, I have more degrees of freedom, because the shaft location distance isn't tightly controlled...

The belt length for the stepper on my build was straightforward. I actually ordered two different lengths for the encoder belt because the final location was uncertain and I wasn't willing to find the belt length I ordered wouldn't work and have to wait another month for another belt. The additional cost was only a few $ so I figured it was cheap insurance.

 

[WobblyHand]

Figured out the belts. Ordered them. Now need to design the encoder mount. Just have to watch out for the belt fouling the mount, which shouldn't be too bad. Don't know how to draw the timing belts at the moment, but somehow they should fit. As a result of today's effort, I have two new designs to make. The motor mount plate, and the encoder mount. Have an idea on the motor mount, so I think I will work on the encoder mount next.

Here is the first crack at the encoder plate.

And a view of the gears and timing pulleys.

 

[RJSakowski]

Figured out the belts. Ordered them. Now need to design the encoder mount. Just have to watch out for the belt fouling the mount, which shouldn't be too bad. Don't know how to draw the timing belts at the moment, but somehow they should fit. As a result of today's effort, I have two new designs to make. The motor mount plate, and the encoder mount. Have an idea on the motor mount, so I think I will work on the encoder mount next.
View attachment 415498
Here is the first crack at the encoder plate.
View attachment 415519
And a view of the gears and timing pulleys.
View attachment 415521

I used a piece of aluminum angle with two end plates, one for the encoder mount and the other providing the mount to the lathe frame.

 

[WobblyHand]

Found a piece of 2x2 aluminum angle, but it is only 3mm thick. Think I will use some 1/4" for the encoder plate and I will mill out some thicker L brackets as feet. The design is straight forward.

Along the way, I learned something new about CAD and what not to do. Have to patch up one of my models to have it's datum in the center, so I can have it correctly locate to the shaft axis and be able to scale it about that point. I didn't do that for the encoder plate. Instead, the datum was the corner, oh well, hope I remember that for next time. I have the dimensions driven by a spreadsheet and tried to make it parametric. It wasn't quite. So my drawing is partially broken. Hope to fix it this afternoon.

 

[WobblyHand]

Slowly getting there. I will slot some holes on the bottom bracket to allow belt adjustment.

 

[WobblyHand]

Hogged out the brackets from a piece of 1" 6061. Made the encoder mounting plate, except for the corner holes. I drilled the 120 degree hole pattern at 4mm but used a 0.159 drill. This seems like a mistake. The hole size seems too big for an M3 screw. The issue is the head diameter of an M3 is 5.5mm, but the hole I made is 4.04mm, (#21) so the contact is only a ring of 0.73mm (0.029"). It really should be redone with a #30 drill which is 0.1285 or 3.26mm. I will try to save it with a washer, but the washer needs to be fairly wide, about 8mm. Guess I goofed that up. Two out of the three holes are well lined up. Don't know why one is slightly off. Used the PCD function on the DRO. The picture looks a lot worse than it is, but it gives me pause about making a new piece with smaller holes - the smaller the holes, the margin of error decreases.

Have to come up with a way to clamp the assembly for drilling. Thinking this will involve some sort of fixture. Either clamp or mount a screw to hold down the feet of the bracket and maybe a straddle clamp across holding the encoder plate to the bracket.

Still struggling with this. Haven't come up with the right combination of clamps to pull this off. So far all of my ideas require far too many setups, and a high probability the outcome isn't square. Will have to ponder some more. This setup stuff is difficult for me, due to my limited experience.