Multiwii Write RC

Writes raw RC values to the auto-pilot.

Library

Description

The Multiwii Write RC block uses the Multiwii protocol on the input stream to send a command to the aircraft to write raw RC values to the auto-pilot. The Multiwii Write RC block sends a MSP_SET_RAW_RC message to the auto-pilot.

This block is designed to be used with blocking I/O. It is typically used with a stream connected to a serial port. To open the stream a Multiwii Connect block should be used.

The input of the block is a vector of RC values. The units depend on the Input units parameter. The order of the RC channels in the vector depends on the auto-pilot but the first eight channels are typically roll, pitch, throttle, yaw, auxiliary 1, auxiliary 2, auxiliary 3 and auxiliary 4, in that order.

In order for the RC channels to be recognized by the auto-pilot, the auto-pilot receiver must be set to MSP RX input (control via MSP port). Also, the auxiliary 1 channel is typically used for arming a quadrotor. For example, start with low throttle (third RC channel) and then switch the auxiliary 1 channel from a low value to a high value (e.g. 1000 to 2000) to arm. At that point, the throttle can be increased.

A copy of the stream is also output so that the Multiwii blocks may be chained together.

If an error occurs, then the block returns a negative error code at its err output. The Compare to Error block may be used to check for specific error codes. If the stream is not valid because it is not yet connected, the err output will be zero since this condition is expected and the validity of the stream may be checked using the con output of the Multiwii Connect block.

Limitations

Minimum execution frequency

The Multiwii Write RC block must be called at least once a second or the auto-pilot will revert to default RC values, which are typically low throttle.

Helpful Hints

Other uses of this block

Although it is intended for use in the main diagram with the other Multiwii blocks, the Multiwii Write RC block may be used with the Advanced stream blocks, even in an asynchronous thread.

Input Ports

stm

A reference to the stream created by the Multiwii Connect block. If a connection has not yet been established, then the err output of the Multiwii Write RC block will be zero.

rc

This input depends on the Input units parameter. Each element of the input vector corresponds to a separate RC channel. However the data type and range changes depending on the input units. Refer to the Input units parameter for details.

The input vector may be fixed or variable-sized.

Output Ports

stm

A reference to the stream. This output is merely a copy of the stm input. Providing this output makes it much easier to establish the execution order of Multiwii blocks in the diagram because Simulink generally executes daisy-chained blocks in sequence.

err

An int32 value indicating whether the message was sent successfully. This value will be positive if message was sent successfully. It will be zero if no message was sent. If an error occurs then this value is a negative error code. See Error Codes for the different error codes and their values. Use the Compare to Error block rather than the error code itself to check for specific error codes. To check for errors in general use the Compare to Zero block to check whether the err output is less than zero.

Parameters and Dialog Box

Input units

This parameter determines the data type and units of the rc input. The table below shows the input for each of the different units:

Targets

See Also

• Multiwii Connect block
• Multiwii Communications

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