Using Low-cost Stepper Motors for Dobby Mechanism

This project explores the utilization of low-cost stepper motors to create a dobby mechanism for a loom. It details the stepper motor requirements, including weight to lift and lever arm dimensions. The project also considers motor options, pricing, and control electronics, aiming for an efficient and cost-effective solution. The provided images offer insights into the total weight of the shafts, assembly configurations, and power connections. With a focus on NEMA 17 stepper motors and driver options, this endeavor showcases a budget-friendly approach to implementing a dobby mechanism.

• Stepper Motors
• Dobby Mechanism
• Loom Project
• Low-cost Solution
• Control Electronics

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Uploaded on Feb 19, 2025 | 0 Views

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1. Using Low-cost Stepper Motors To Create a Dobby Mechanism

2. Stepper motor requirements Loom : Weight to lift- Weight of 8 shafts: 2.6 Kg (raw weight) ~5 Kg (with warp tension) Per Shaft @ 8 shafts ~0.6 Kg per shaft Lever arm to lift weight- 5 mm shaft on motor (5/16 ) 1 mm cord diameter ~8 mm shaft diameter (with tape) Lever arm ~ 5 mm = 0.5 cm Approximate torque requirement: Torque = 0.6 Kg * 0.5 cm = 0.3 Kg-cm (lifting power) Motors: characterized by Holding Torque , not dynamic lifting power Maximum rotational speed not specified Nominal motor de-rating factor: x10 = ~3 Kg-cm (30Ncm) Price consideration: Nominal $100 for project, $50 for 10 motors, ~ $5 - $8 per motor Search for Stepper motors: NEMA 17 (NEMA 23?) footprint Over 3 Kg-cm torque 6 wire (to simplify control electronics) Less than .5 Amp per phase @ 12VDC Vertical view Motor 1.75 square 4 x 26.75 base 0.42 spacing between shafts (8 shafts / 3 ) Shaft 6 Wire Motors (12V to ground switching): ULN2003A Darlington drivers (7 channel ) .5A/channel $0.51 per part 8 motors * 4 channels per = 32 driver channels 32/7 = 5 ULN2003A packages ($3.57) 4 Wire Motors (full voltage reversal): L293d 4 channel drivers.6 A/channel $3.91 per part Type 42BYGH404 (NEMA 17 footprint) 1.65 x 1.65 x 1.57 (42.4x42.3x72 cm) 3.4 kg-cm (47.2 oz-in) .4A per phase ~ $6 per (Summer of 2018) https://www.circuitspecialists.com/nema_17_stepper_motor_42bygh404.html?otaid=gpl&gclid=Cj0KCQjwjrvpBRC0ARIsAFrFuV8v7XcrsvspC- rLUqVF1CWTetYBij41v3zOubxWgQV1JUICdI5XC2QaAiWJEALw_wcB Blk & Wht to +12 Red/grn yel/blu to drivers (Coil centers actually white & Yellow) Position sensors/sensor mux (?) 8 motors * 4 channels per = 32 driver channels 32/4 = 8 L293d packages ($31.28)

3. Total weight 8 shafts (Scale resting on lower rails of castle) Lever arm to raise shafts: 5mm shaft + 12 tape to increase shaft diameter Total width of 8 shafts ~3 0.42 spacing between shafts Blue tape on rods increases diameter, utilizing reserve torque in motors to reduce number of rotations (and time) required to lift shafts collars on 5/16 rod hold connecting thread to rod, easy to adjust for length & position Assembled Left Side Shaft motors 2,4,6,8 Assembled Right Side With power & USB connections Shaft Motors 1,3,5,7 Interior Right Side (Ends of Shaft Rods 1,3,5,7 In holes in right side) Black threads connect Weaving shafts to rod, Loop fits over screw head for ease of removal

4. Right 12V USB Footswitch

5. Left