Servo Brick

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Features

• Drives up to 7 RC Servos with max. 3A
• Drives brushless motors (requires external ESC)
• Supports TurboPWM
• Software adjustable servo voltage, period and pulse width
• Position, velocity and acceleration controllable
• One USB port and two Bricklet ports

Description

The Servo Brick is equipped with a 32-bit ARM microcontroller and is able to control up to 7 RC servos with a maximum current of 3A. The output voltage is adjustable up to 9V, the drawn current of each servo can be measured independently. Additionally output PWM is configurable for each servo independently.

Brushless motors can be driven by usage of external Electronic Speed Controllers (ESC). The maximum motor current depends only on the ESC such that motors with 150A and more are possible to control.

It is compatible to other Tinkerforge Bricks and can be used within a stack. Two Bricklet ports can be used to extend the features of this device.

The servos can be powered by an external power supply connected directly to the Brick or by the stack internal power supply. If an external power supply is connected the Brick switches automatically to this power supply.

Controlling the device is possible in several ways. You can control it via a PC connection. This connection can be established directly with a USB cable or by other cable based (RS485, Ethernet) or wireless (WIFI) connections via an additional Master Brick with corresponding Master Extension (High Level Concept).

Since the firmware is open source it is possible to program the device directly (On Device Programming). Currently we are not offering an On Device API.

Technical Specifications

Property	Value
Microcontroller	ATSAM3S2B (128kB Flash, 32kB RAM)
Current Consumption	60mA
Maximum Motor Current (Sum)	3A
Minimum/Maximum Input Voltage	5V/25V
Output Voltage	Software adjustable 2V - 9V
Output Period*	1µs - 65535µs
Pulse Width*	1µs - 65535µs
Velocity*	0 - 65535 °/100s
Acceleration*	1 - 65535 °/100s²
Bricklet Ports	2
Dimensions (W x D x H)	40 x 40 x 16mm (1.57 x 1.57 x 0.63”)
Weight	18g

* configurable per servo

Resources

• MCP3008 datasheet (Download)
• Schematic (Download)
• Outline and drilling plan (Download)
• Source code and design files (Download)

Connectivity

The following picture depicts the different connection possibilities of the Servo Brick.

Test your Servo Brick

To test the Servo Brick you need to have the Brick Daemon and the Brick Viewer installed (for installation guides click here and here) and the Brick Viewer has to be connected to the Brick Daemon.

Connect a RC servo to a port of the Brick and a suitable power supply. Your setup should look as shown below.

Now connect the Brick to the PC over USB, you should see a new tab named “Servo Brick” in the Brick Viewer after a moment. Select this tab.

In the left part of the tab you can select the servo to control. You can enable and disable it, configure the PWM pulse width and define the degree range. Additionally you can see the current consumption of the servo. Below there are four sliders to control the position, velocity and acceleration of the servo. The fourth slider can be used to change the period of the PWM (see Configure Servo PWM for more information).

On the right side you can see the external and stack voltage. Below are graphical representations for the state of each servo. Beneath you can configure the minimum input voltage, which allows for undervoltage signals if the voltage is too low. Also you can configure the output voltage.

..warning::

A too high output voltage might damage your servo!

At the bottom right there is a “Start Test” button, which starts a test sequence that performs random movements for each servo.

After this test you can go on with writing your own application. See the Programming Interface section for the API of the Servo Brick and examples in different programming languages.

Configure Servo PWM

Typically you control a RC servo by a PWM signal with a period of 20ms and an on-time of 1ms to 2ms depending on the position you want to achieve. However, some servos do not work properly with these standard settings. Therefore we provide a fully configurable PWM.

The default value for the period is 19.5ms. This period worked on all servos we could get our fingers on (20ms did not work with some of the cheaper Chinese servos). If the datasheet of your servo does specify a preferred period, use it. But it is likely that you don’t have to change this value.

More interesting is the minimum and maximum pulse width. The default pulse width is 1ms to 2ms. Most servos can however rotate further when minimum/maximum pulse width is decreased/increased. If your servo comes with a datasheet we recommend to use the values described in there. If you don’t have a datasheet you can try to incrementally extend the pulse width until the servo starts to rattle. Use the biggest pulse width that does not produce rattling.

Warning

A wrong PWM configuration for an extended period of time can damage your servo.

Power Supply

The Servo Brick is equipped with an internal power supply. It offers the possibility to adjust the output voltages for the connected servos. The internal power supply can be powered through the black on-board power-connector or through a Power Supply in a stack. The Servo Brick switches automatically to the on-board power-connector when there is a voltage measured. Since we use a step-down controller for the internal power supply please consider that the input voltage of the Brick has to be 1V higher than the configured output voltage to assure stable operation.

Warning

A too high output voltage can damage your servo.

Usage of ESCs to drive brushless motors

With this Brick you can control up to 7 brushless motors by using external Electronic Speed Controllers (ESC). Simply connect the brushless motor to the ESC and the ESC to the Servo Brick. With this construction the maximum brushless motor current only depends on your selected ESC.

Warning

Many ESCs have a build-in Battery Eliminator Circuits (BEC) which can be used to power RC receivers. If you use a ESC with BEC you have to disable it! Otherwise your ESC or the Brick can be destroyed. To disable BEC you have to remove the red wire from the connector you plug in the Servo Brick (external video tutorial).

Warning

If you use the same power supply for your ESC and the Servo Brick, additionally you have to remove the black (GND) wire too. If you don’t remove it, the motor current can flow through the Servo Brick and can destroy the current measurement circuit.

Error LED

The red LED is enabled so long as the input voltage is below the user configurable minimum voltage.

Programming Interfaces

High Level Programming Interface

See High Level Programming Interface for a detailed description.

Language	API	Examples	Installation
Modbus	API
TCP/IP	API
C/C++	API	Examples	Installation
C#	API	Examples	Installation
Delphi	API	Examples	Installation
Java	API	Examples	Installation
PHP	API	Examples	Installation
Python	API	Examples	Installation
Ruby	API	Examples	Installation
VB.NET	API	Examples	Installation

On Device Programming Interface

Note

Coming soon!

An API and documentation for direct on device programming (comparable to Arduino) is planned. You can however already use our firmware as a starting point for your own modifications (C knowledge required).

FAQ

My servos are shaking, help!

The reason for this is typically a voltage drop, caused by repeated high current peaks produced by the connected servos. First you should check the input voltage, it should be at least 1V higher then the configured output voltage.

Typically this problem occurs when the power supply can’t handle the high current peaks. To test if your power supply is the problem, you can try batteries. Batteries normally don’t have problems with current peaks.

If you are using batteries and the problem is still occurring, check the voltage of the batteries when the servos are in use. If your batteries are too weak, the voltage is dropping (in this case use full batteries).

If your servos only start shaking when you reach the maximum/minimum angle, you have configured a too high/low pulse width. In this case you have to reduce the pulse width, otherwise your servos might get damaged over time.