02. Hardware design
1. Concept design
A. Required precision
The formulas on this page are partially assisted by ChatGPT.
Prompt: Calculate the motion accuracy of a robot using a stepper motor nema 17. It works with wheels and an arm, and the calculation is based on a wheel diameter of 50mm and an arm length of 170mm.
I calculated the XY-axis wheel and Z-axis arm accuracy based on rough dimensions, a 1.8° stepper motor, 170mm arm length, and 50mm wheel diameter. Accuracy can be improved later by adjusting the gear ratio or using "microstepping".
a. Wheel Precision
| Item | Value | Formula |
|---|---|---|
| Wheel Diameter (D) | 50 mm | Input parameter |
| Step Angle (θ) | 1.8° | — |
| Wheel Circumference (C) | 157.08 mm | C = π * D |
| Wheel Movement (d_w) | 0.785 mm/step | d_w = (θ / 360) * C |
b. Arm Precision and Gear Ratio
| Item | Value | Formula |
|---|---|---|
| Arm Length (L) | 170 mm | Input parameter |
| Step Angle (θ) | 1.8° | — |
| Arm Tip Movement (d) | 5.34 mm/step | d = L * sin θ |
| Required Precision (P) | 0.5 mm/step | Input parameter |
| Required Gear Ratio (R) | Approx. 10.7:1 | R = d / P = 5.34 / 0.5 |
C. Estimated weight
I made a very rough weight estimate and it ended up being about the same weight as small 3D printers (such as Kingroon KP3S or BumbLab A1 Mini).
| Name | Weight (kg) | Quantity | Total Weight (kg) |
|---|---|---|---|
| Stepper Motor | 0.3 | 6 | 1.8 |
| Filament Spool | 1 | 1 | 1 |
| Extruder | 0.25 | 1 | 0.25 |
| Battery / power supply | 0.5 | 1 | 0.5 |
| Frame | 0.5 | 1 | 0.5 |
| Others | 0.25 | 1 | 0.25 |
| Total | 4.8 kg |
C. Required torque
Arm Torque Calculation
| Item | Value | Formula |
|---|---|---|
| Arm Weight (m) | 0.6 kg | Input parameter |
| Arm Length (L) | 0.17 m | Input parameter |
| Gravity (g) | 9.81 m/s² | — |
| Center of Mass | 0.17 m | Input parameter |
| Load Torque (T_load) | 1.001 N·m | T_load = m × g × L |
| Gear Ratio | 30:1 | — |
| Motor Torque (T_motor) | 3.335 N·cm | T_motor = T_load / Gear Ratio × 100 |
D. Motor selection
I started by looking at the motors commonly used in 3D printers, and the Kingroon KP3S I disassembled also used two types of Nema17 stepper motors for the XYZ axes and the extruder.
I tried using the stepper motor on week 04 assignment.
E. Omni wheel
a. How omni-wheel works
b. Selection
A larger wheel means more movement per revolution and is less accurate, so a smaller wheel is better, but it needs to be larger in diameter than the Nema17. hypothetically selected a diameter of 58 mm. I downloaded omni wheel STEP model from McMaster-Carr.
F. Power source
For infinite print size, it would be ideal to run it on battery power, but for now I think it's more realistic to power it with a wired connection, given the power usage of the heater. I'll have to consider the actual power usage later.
2. CAD modeling
A. Approx. dimensions
I started by designing a standard 1kg spool holder. I placed it in the center of the machine so that the weight distribution would be stable even if the amount of filament remaining changed.
For design tips and process, visit 2. Computer-aided Design.