Did you ever stumble about the lack of position feedback from your servo motors? Yes? We did, too. So we decided to create the sensorimotor board which transforms your simple servo drive or DC motor into a smart device providing rich sensory feedback, such as

• absolute position
• supply voltage
• motor current and
• temperature.

The Sensorimotor basically replaces the electronics in a common servo motor and is equipped with a microcontroller, an H-Bridge (12V, 6A max.) and a communication transceiver (RS485). You pick some cheap servo motors and solder each of them to a sensorimotor board (see pin-description). Connect your motors in a Daisy-Chain, i.e. like a light string. At the end of the bus connect the host. Now you can control your string of servo motors via a single host controller such as Raspberry Pi, Linux-PC or Arduino.

Now you can use inexpensive servos for advanced robotic control projects were the feedback of position or motor current is essential, like an robotic arm or legged robot. You can also control other kinds of drives such as solenoids, e.g. for music robots (see pictures).

Advantages over common servos

• easy daisy-chain cabling with a robust bus system (RS485) for reliable communication even over large distances
• a lot of feedback such as position, speed, voltage, temperature, and current
• different control modes: position, impulse and CSL control.
• adjustable PID position control parameters

Difference to other smart servos

• fully hackable through open-source electronics + firmware
• simple protocol
• easy integration with Raspberry Pi (0) (python) or Arduino (C++)
• allows you to customize your own unique servomotor for your project

What's included?

The Sensorimotor-Boards come with all SMD parts soldered. The through-hole components are included but soldering them is left to you since you might want to decide for changing the capacitors position or using a different type of connector in your specific setup.

What do I need to do?

To gain full control over your motors it is essential that you learn how to hack them from the beginning. So in contrast to common commercial (smart) servos, some setup is to be done (also in order to reduce price).

• soldering of the through-hole parts
• soldering the boards to the motors (you might need to remove the old electronics beforehand, depends on setup)
• Sensorimotor-Firmware needs to be programmed, you can use your favorite Atmel flasher for this.
• Setting up an RS485 interface (depending on your host controller, see documentation)

What accessories do I need?

The communication bus is of type RS485, so depending on the host controller platform you want to use you need a transceiver interface. For Arduino or other microcontrollers, you just need a small breakout board with e.g. MAX485 chips or similar. For PC or other Linux machines with USB ports like the Raspberry Pi you can use RS485-to-USB converters such as the DIGITUS DA-70157 or the FTDI USB-RS485-PCB. Tell us about your specific setup and we help to select a proper interface for you.

Please give us feedback. This is a community-based project of robotics enthusiasts. The documentation is not perfect yet, so let us know what are the hard parts. Feel encouraged to contribute. We are open to your ideas. Tell us about your project and let us discuss how to make it possible. Please, also have a look at the example projects provided to get an idea of how it might help in your personal project.

Videos

Sensorimotor Assembly (full)

These videos demonstrate step-by-step how to integrate the sensorimotor into a common servo motor:

• 01 removing old controller
• 02 removing old controller, desolder details
• 03 soldering through-hole parts
• 04 prepare cover
• 05 installing sensorimotor board
• 06 test and setting fuses
• 08 setting individual motor IDs
• 09 checking all motors' IDs

Specification

• voltage 6-12V DC
• current max. 6 A
• microcontroller ATMEGA 328p
• RS485 bus
• works with any DC motor (not BLDC) < 6A of stall current