Low Cost Linear Synchronous Motors
Designed & built by
William Bowley &
Lawson Gallup
OpenLSM is an experimental project with the objective of designing low-cost permanent magnet linear motors for Cartesian motion systems such as pick-and-place machines or CNC machines. The project will fulfill this goal by using readily available materials and tooling, combined with reduced-order and finite element models.
Important
- Design low-cost permanent magnet linear motors for Cartesian motion systems.
- Develop computational models that are validated against experimental measurements.
- Demonstrate continuous thermal steady-state operation under defined operating conditions.
More specific targets (force density, efficiency, cost, etc.) to be defined as the domain becomes clearer.
The methodology for openLSM is to design a reduced-order or finite element model to compute the expected results for a specific motor topology. The resulting model is used to tune design parameters either manually or via algorithmic optimization. The parameters are then used to produce a CAD model, which is fabricated and experimentally tested. Discrepancies between predicted and observed performance are used to update the model for subsequent iterations.
Conceptual Design ↔ Reduced-order / FEA Model
↓
Design Parameters ↔ Detailed Design (CAD)
↓
Fabrication & Testing
↓
Post-Analysis & Model Validation
↺
An ironless planar linear motor with a polylactic acid (PLA) armature featuring 6 slots, hand wound using 0.2 mm diameter enameled copper wire and 5 mm wide Kapton tape, with 2 slots in-series per phase (WYE). The stator, similar to the armature, was printed in PLA and had 4 pole pairs per armature length and 10 pole pairs total. The motor produced measurable force, though the magnitude was not quantified before the PLA coil forms deformed due to thermal stress.
Figure 2: Prototype Alpha. Side view on test stand
The main conclusion from Prototype Alpha is that planar linear motors likely require laminated silicon steel armatures to produce force efficiently. In response, Prototype Beta shifts to an ironless tubular topology with the goal of quantifying force output and thermal performance.
(Conceptual). Revision 2 of the ironless tubular linear motor design. Not yet validated for fabrication.
An ironless tubular linear motor with a carbon fibre nylon (PA6-CF) armature featuring 12 slots, mechanically wound using 0.4 mm diameter enameled copper wire, with 4 slots in-series per phase (WYE). The stator, unlike the armature, is made of layered carbon fibre epoxy to form a tube with an internal radius of 5 mm and outer radius of 6 mm. The poles are 20 mm in length and 5 mm in radius such that they can be inserted into the stator tube in this pole arrangement (N-S|S-N), using generic superglue to secure the end poles.
Figure 3: Prototype Beta REV 2. Cross-sectional view of the tubular linear motor showing the stator & armature.
The radial heat-sink is made of aluminum as mentioned above with radial fins pitched at 1.50 mm, axial thickness of 0.50 mm, and radial thickness of 7.30 mm. The thermal interface material is still to be determined. This is expected to improve thermal steady-state conditions, though both this assumption and the analytical eddy-current model remain to be validated experimentally.
Important
See the motor design notes for the full electromagnetic and thermal rationale of Revision 2.
The integrated sensor boards are a platform for measuring the motor's position, acceleration, and thermal profile T(z, t). The system consists of two boards: an encoder board with an estimated accuracy of 10–20 µm, and a sensor board featuring a thermistor array, 3-axis SPI accelerometer, encoder interface, and RS-485/RS-422 output, all controlled via an STM32.
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| Top layer — Bare PCB Armature Data Board | Top layer — Bare PCB Encoder Board |
Note
See 03_boards for the supporting PCB designs that enable motor development.
All internal documentation can be found within this repo's issues.