DroneCAN Internal Combustion Engine node

This board is dedicated to controlling an internal combustion engine such as DLE-20 (opens new window) or DLE-35 (opens new window) using Electronic Ignition Module.

Based on input command RawCommand (opens new window) it activates ignition, starts a starter to run the engine and turn the starter off when the internal combustion engine is working. It measures several engine parameters such as engine rotation speed and sends it to UAVCAN network as uavcan.equipment.ice.reciprocating.Status (opens new window) message. It also might be equipped with fuel tank sensor based on differential pressure sensor, so the node will send uavcan.equipment.ice.FuelTankStatus (opens new window) message.

1. DroneCAN interface

This node interacts with the following messages:

№	type	message
1	subscriber	uavcan.equipment.esc.RawCommand (opens new window)
2	publisher	uavcan.equipment.ice.reciprocating.Status (opens new window)
3	publisher	uavcan.equipment.ice.FuelTankStatus (opens new window)

Besides required and highly recommended functions such as NodeStatus and GetNodeInfo this node also supports the following application-level functions:

№	type	message
1	RPC-service	uavcan.protocol.param (opens new window)
2	RPC-service	uavcan.protocol.RestartNode (opens new window)
3	RPC-service	uavcan.protocol.GetTransportStats (opens new window)

2. Hardware specification

(in work)

3. Wire

This board has 4 connectors which may deliver a power to this device. They are described in the table below.

№	Connector	Description
1	Power socket (XT30)	This board consumes more power than a typical UAVCAN node, so it is powered using an additional socket.
2	UCANPHY Micro (JST-GH 4)	Devices that deliver power to the bus are required to provide 4.9–5.5 V on the bus power line, 5.0 V nominal. Devices that are powered from the bus should expect 4.0–5.5 V on the bus power line. The current shall not exceed 1 A per connector.
3	6-pin Molex (502585-0670 (opens new window), 502578-0600 (opens new window))	Contacts support up to 100 V, 2 A per contact. But the board may work only with 2S-6S.
4	SWD	STM32 firmware updating using programmer-sniffer.

It also has following board-specific connectors:

№	Connector	Description
5	Fuel tank sensor based on MS4525DO	i2c
6	Starter	GPIO output pin
7	Spark ignition	GPIO output pin
8	Gas throttle	PWM with frequency 50 Hz and duration from 900 to 2000
9	Air throttle	PWM with frequency 50 Hz and duration from 900 to 2000
10	RPM sensor	Input capture
11	Temperature sensor	One-wire

4. Main function description

On the input the node has RawCommand (opens new window) message.

The node controls 3 devices: Starter, Spark Ignition and Gas Throttle. The control of these devices is performed in their own task, it means their logic are independent from each other.

Internally, the node has a safety mechanism called kill-switch. If the setpoint is not appear for 2 seconds, it will automatically change the state of each devices to default.

4.1. Gas throttle

Gas throttle is responsible for thrust created by an engine. The output PWM is linearly controlled by RawCommand. The lower and higher borders of duration are defined in corresponding parameters. Check corresponded parameters in the section 6.5. Gas throttle.

4.2. Air throttle

The main function of the air throttle is to supply and regulate the air flow necessary for the formation of the air-fuel mixture.

Typically, we want a bit less air during the starting the internal combustion engine. It is more fuel costly, but the motor may start easilier. Let's call it the initial throttle position.

When the motor is already working, we want to maintain a constant optimal fuel to air ratio. In simplest case it might be just another throttle value called goal.

The idea of the suggested air throttle algorithm is to linearly open the air throttle from the initial to the goal state for a specific period of time and keep it until the new starter iteration starts.

Although the default goal state is specified in parameters, an operator may specify the actual goal value in real time during preflight checks using ArrayCommand message with the index specified in parameters.

4.3. Spark Ignition

Spark Ignition allows to enable or disable engine. It is controlled by a simple GPIO output pin that has 2 states. If the value of RawCommand of the corresponding channel is higher than some offset, it will be enabled. Otherwise it will be disabled. Check corresponded parameters in the section 6.2. Spark ignition.

4.4. Starter

Starter allows to automatically run an engine. It is implemented as GPIO output pin, so it has 2 states. If the input channel value is greater than the offset, it will perform an attempt to run an engine with a duration up to a certain time. If an attempt is unsuccessful, it will turn off for a certain time (to signalize that it's unsuccessful), and then try again. If the median speed for last second is greater than some certain value it will stop attempts. Durations and offsets can be set up in parameters. Check corresponded parameters in the section 6.3. Starter

4.5. RPM measurement

This sensor is based on hall-sensor. It counts the number of impulses for the last short period of time, filtrate the data, fills the uavcan.equipment.ice.reciprocating.Status (opens new window) message and sends it.

4.6. TTL

For the safety reasons, if there is no RawCommand for last cmd_ttl_ms milliseconds, the node will set all controlled values to the default states. It means, that that Starter will be turned off, Spark Ignition will be disabled and Gas Throttle will be in the default position according to the specified in parameters value.

5. Auxiliary functions description

5.1. Circuit status

This node as well as any other our nodes measure 5V and Vin voltages and send them in 2 uavcan.equipment.power.CircuitStatus (opens new window) messages.

These voltages might be visualized using our custom custom uavcan_gui_tool (opens new window).

The first message has circuit_id=NODE_ID*10 + 0 and following 3 significant fields:

1. voltage - is the 5V voltage
2. current - is the max current for the last 0.5 seconds (supported only by 5A node)
3. error_flags - might have ERROR_FLAG_OVERVOLTAGE or ERROR_FLAG_UNDERVOLTAGE or non of them

The second message has circuit_id=NODE_ID*10 + 1 and following 3 significant fields:

1. voltage - is the Vin voltage
2. current - is the average current for the last 0.5 seconds (supported only by 5A node)
3. error_flags - ERROR_FLAG_UNDERVOLTAGE or non of them. There is no ERROR_FLAG_OVERVOLTAGE flag because the expected max Vin voltage is unknown.

5.2. Node info

Every firmware store following info that might be received as a response on NodeInfo request. It stores:

• software version,
• an unique identifier.

5.3. Log messages

(will appear in further versions of software)

5.4. Watchdog

The node constantly performs updating watchdog values. If update is not happen for at least 0.5 seconds, it cause a hardware reset of microcontroller. This feature allows a node to leave a hang state if it is happen.

5.5. Stats recorder

The node automatically stores few parameters into the flash memory. Since writing to the flash is time consuming operation that may affect of performance, the saving request is called only after a short amount of time after disarm.

• flight_time_sec parameter keeps overall time during ARM,
• ice_time_sec parameter keeps overall time when internal combustion engine is enabled.

You might be interesting in checking the last parameter to be sure that the lift engine operation time has not expired.

6. Parameters

Below you can see a picture from gui_tool with a whole list of parameters.

All paramters are divided into several groups. Their description is provided in the tables below.

6.1. Common parameters

Following parameters are common for any nodes.

№	Parameter name	Reboot required	Description
0	ID	true	Node ID
20	err	false	If something unexpected goes wrong, the node writes code of occurred error into this value, save it and reboot. The node will continue to function, but it will keep ERROR status until this value is manually cleared. Normally, this value should be always zero. If it is not, you may contact us.
21	name	true	Unused. Reserved. In future the node name will might be configured using this parameter.

6.2. Spark ignition

№	Parameter name	Reboot required	Description
1	spark_ignition_offset	false	If raw command more than that value, spark ignition will be turned on, otherwise turned off
2	spark_ignition_ch	false	Index of RawCommand channel; -1 means disable this feature

6.3. Starter

№	Parameter name	Reboot required	Description
3	starter_offset	false	If RawCommand more than that value, spark ignition will be turned on, otherwise turned off
4	starter_ch	false	Index of RawCommand channel; -1 means disable this feature
5	starter_rpm_treshold	false	Starter might be turned on only if rpm less then that value
6	starter_try_duration	false	Period in milliseconds during which the starter will try to run the engine
7	starter_delay_before_next_try	false	Period in milliseconds during which the starter will wait between attempts

6.4. ESC status

№	Parameter name	Reboot required	Description
8	esc_pub_period	false	Period between EscStatus publication. It has info about starter voltage and current
9	esc_index	false	Index of corresponded EscStatus message; -1 means disable publication

6.5. Gas throttle

№	Parameter name	Reboot required	Description
10	gas_throttle_ch	false	Index of RawCommand channel; -1 means disable this feature
11	gas_throttle_min	false	PWM duration corresponded to RawCommand=0
12	gas_throttle_max	false	PWM duration corresponded to RawCommand=8191
13	gas_throttle_default	false	PWM duration corresponded to RawCommand < 0 or when there is no RawCommand for last half second

6.6. Circuit status

№	Parameter name	Reboot required	Description
14	enable_5v_check	false	Set ERROR status if 5V voltage is out of range 4.5 - 5.5 V
15	enable_vin_check	false	Set ERROR status if Vin voltage is less than 4.5 V

6.7. Motor speed measurement filter

It is expected that motor generates a single PWM impulse each rotation.

The algorithm increments a specific variable each time when an impulse occurred.

With frequency specified in rpm_measurement_frequency parameter it calculate a difference between previous and current number of impulses and multiply it by 60 to get the raw value of RPM. The frequency should be at least twice less than idle rotations per second of the motor. For an example, for a motor with IDLE speed 1200 RPM, the parameter might be set to 10 or lower.

Optionally, you can specify rpm_moving_avg_filter_size other than 1 to enable moving average filter. This is the easiest, fastest and less memory consumption filter algorithm to make RPM readings smoother. The default value has no effect on readings.

7. Led indication

This board has an internal led that may allow you to understand possible problems. It blinks from 1 to 10 times within 4 seconds. By counting the number of blinks you can define the code of current status.

Number of blinks	Uavcan health	Description
1	OK	Everything is ok.
2	OK	There is no RawCommand at least for the last 0.5 seconds (it's not a problem for this board, just in case).
3	WARNING	This node can't see any other nodes in UAVCAN network, check your cables, or there is no incoming data from the sensor.
4	ERROR	There is a problem with circuit voltage, look at circuit status message to get details. It may happen when you power it from SWD, otherwise, be careful with the power supply. This check might be turned off using params.
5	CRITICAL	There is a problem with the periphery initialization level. Probably you load the wrong firmware.

8. Debugging on a table

(in progress)

9. PX4 integration

This node has been successfully tested on VTOL. Here is an example of RPM and RawCommand values collected from one of the flight logs.