Scara based 3d printer - v2 in progress

GitHub repository

Scara 3d printer cost calculations for V1

Approximate cost calculation for V1:

• 51$ — 5 Nema17 (you need only 4, so you get 1 for spare parts)
• 32$ — Ramps 1.4+5 Dvr8825+LCD (you need 4 drv8825, so you get 1 for spare parts)
• 7$ — E3DV5 (china made) with 1m PTFE tube (0.5m for spare parts)
• 2$ — extruder gear
• 6$ — gt2 pulleys and gt2 belt
• 5$ — 6mm smooth rods (2x20cm)
• 4$ - 4 LM6UU linear bearings
• ~10$ — ball bearings+bolts+screws+other stuff
• 10$ - external power supply 8.5A 12V

Total: 127$ (with power supply, but without ABS filament — approx 200g)
NOTE: All prices from my aliexpress orders, free shipping to my country, no taxes (in my country taxes begins only from 200+$).

NOTE2: V2 seems to be in the same price level, but not cheaper.

Ways to save costs:

• ~8-10$ - get rid of of LCD module 
• ~5-7$ - Replace one Nema17(for gearbox) to small 2.5$(28BYJ-48 12V) stepper + printed high ratio spur gears.

Not a lot.

More global idea:
Replace 2x10$  Nema17 steppers to cheap DC MOTOR + Hall Sensor + L293N + gearbox. The main problem is a backlash free gearbox. I think gearbox should have approx 1:100 gear ratio.

Backlash free gearbox ideas.

1. Looks like it is possible to combine 2 stage of 1:10 belt driven gears. Belt driven gear theoretically backlash free. 1:10 belt driven gear is a 16 teeth gt2 pulley and 160 teeth pulley (~101mm diameter), or use more stages with less teeth pulleys (seems like better due to the less belts length).
2. Planetary gears - at least 2 stages required - i tried to print - seems like printed does not work well.
3. Hypocycloid Gear - looks better but seems like it does not work due to printing precision, plus vibration may affect print results.
4. Harmonic drive - not tested
5. Classic gears - seems like not backlash free, there are a few ways to decrease backlash, but i not sure.

NOTE: It is just an idea

Printrun is forked

https://github.com/pavlog/Printrun

My first ideas:

• Add mark to show center of ccordinated - DONE
• Fix or rewrite ugly 3d viewport rotation (is Repetier like viewport rotation) - DONE

Scara - idea to use big pulley without teeth