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Modified continuous-rotation servos are used extensively by roboticists due to their small form-factor, enclosed motor-gearbox, ease of mounting and high-availability. Some users keep the original drive electronics and the potentiometer feedback element but this approach allows for limited position control and velocity control / profiling. Others tend to remove them and use external control/drive boards and custom-made encoders. Ideally one would prefer to have the feedback element and the new drive electronics enclosed inside the servo. Unfortunately hacks involving optical devices and code-wheels have very limited resolution and require a lot of precise work.
Magnetic encoders use spinning current Hall technology to measure magnetic flux distribution across the surface of the chip. They typically come in high resolutions and require very few external components. The operational setup requires a small disk magnet with circumferential field distribution to be attached on the rotating element whose angular deflection is to be measured, and in close proximity to the sensor IC.
This hack utilises Austrian Microsystems’ sensor IC as feedback element for a modified servo. The servo to be hacked is the popular Hitec HS485 HB.
Materials list:
- Standard-size or ¼ scale hobby servo.
- AS5040 IC
- Circular Magnet with circumferential field distribution, 2.5mm high, 6mm in diameter.
- IC breakout board (download schematics from here: http://01mech.com/magenc)
- Styrene plate 2mm thick.
- Small piece of wood 10mm thick.
- Multi-strand cables.
- Heat-shrink
Tools list:
- Flat file
- Sanding paper or abrasive disk.
- 5min epoxy.
- Hand-drill or press-drill.
- Drill bits: 3.5mm and 5mm in diameter
- Heat-gun
Magnetic encoders use spinning current Hall technology to measure magnetic flux distribution across the surface of the chip. They typically come in high resolutions and require very few external components. The operational setup requires a small disk magnet with circumferential field distribution to be attached on the rotating element whose angular deflection is to be measured, and in close proximity to the sensor IC.
This hack utilises Austrian Microsystems’ sensor IC as feedback element for a modified servo. The servo to be hacked is the popular Hitec HS485 HB.
Materials list:
- Standard-size or ¼ scale hobby servo.
- AS5040 IC
- Circular Magnet with circumferential field distribution, 2.5mm high, 6mm in diameter.
- IC breakout board (download schematics from here: http://01mech.com/magenc)
- Styrene plate 2mm thick.
- Small piece of wood 10mm thick.
- Multi-strand cables.
- Heat-shrink
Tools list:
- Flat file
- Sanding paper or abrasive disk.
- 5min epoxy.
- Hand-drill or press-drill.
- Drill bits: 3.5mm and 5mm in diameter
- Heat-gun
Remove these ads by
Signing UpStep 1Gutting the servo
Procedure:
- Start by removing the control / power electronics from the servo.
- Remove the feedback potentiometer.
- If continuous rotation is required remove the mechanical stop from the servo’s output gear.
- Disassemble the potentiometer keeping the rotation shaft. This is going to be used as a support shaft for the encoder’s disk magnet. The magnet is going to be glued onto it.
- Start by removing the control / power electronics from the servo.
- Remove the feedback potentiometer.
- If continuous rotation is required remove the mechanical stop from the servo’s output gear.
- Disassemble the potentiometer keeping the rotation shaft. This is going to be used as a support shaft for the encoder’s disk magnet. The magnet is going to be glued onto it.
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This is not your typical disk magnet (which has axial field distribution), right? Where do you find them?
http://www.01mech.com/MagEnc
Alternatively you could get them directly from Austrian Microsystems.
http://www.austriamicrosystems.com/