On-board Unit

The purpose of the OBU includes:

  • Operational modes
  • Traction and braking control
  • Driver Machine Interface (DMI) - the train drivers (remote) panel
  • Speed and direction supervision
  • Automatic Train Operation (ATO) (“Driver less” operation)
  • Train position establishment

Operational modes

The OBU has following operational modes: Staff Responsible SR, Shunt mode SH, Full Supervision FS, Automatic Train Operation ATO and Neutral N. The operational mode is selected by the train driver using the mode selector at the DMI, except that some modes requires permission from the RBC. Mode Neutral is implicit selected, if the RBC does not accept mode SR or SH. If communication to DMI is lost, mode ATO is selected after a predefined time.

Mode Description
Neutral The train is forced to stand still. In this mode the train cannot be operated.
Staff Responsible The train is running as ordered by the driver via DMI. No supervision is applied. This mode requires permission from the RBC.
Shunt Mode The train is running as ordered by the driver via DMI. Speed is limited by the OBU to a maximum speed given by the RBC. Position is supervised as well, keeping the train within a pre-defined shunting area. Shunt Mode requires permission from the RBC, to ensure the shunt area is available.
Full Supervision The train is running as ordered by the driver via DMI. Speed and direction is supervised by the OBU based on received MA. Mode FS does not require permission from the RBC as this is implicit given via the MA.
Automatic Train Operation The train is running automatically as allowed by the RBC via issued MA. This mode does not require permission from the RBC.

Driver Machine Interface

The DMI provides indications and commands as required for a driver to run the train. As the driver - for good reasons - cannot be in the train, the DMI is realised as a remote control panel with wireless connection to the OBU.

The DMI will include:

  • Commands
    • Operational mode selector (Switch, 5 position)
      • DMI off (DMI power down)
      • Staff Responsible SR
      • Shunt Mode SH
      • Full Supervision FS
      • Automatic Train Operation ATO
    • Direction selector (Switch, 3 position)
      • Forward
      • Neutral
      • Reverse
    • Traction selector (Switch, 5 position)
      • Level 4
      • Level 3
      • Level 2
      • Level 1
      • Neutral
  • Indications
    • Speed (Analog meter)
    • Movement Authority (Pilot indicator)
      • Long MA (Green)
      • Short MA / shunting allowed (Yellow)
      • No MA / no shunting (Red)
    • Status (Pilot indicator)
      • Error (Blue)
      • DMI active (White)


Operational Mode selector

This selector will set the operational mode as defined above given following conditions:

  • Mode SR and SH requires permission from the RBC. If the RBC cannot allow mode SR or SH, mode N will implicit be selected. This will stop the train.
  • If the selector is set to OFF the DMI will power down, closing the communication with the OBU. Following a period without connection to the DMI, the OBU will change to mode ATO.
  • Changing operational mode requres the train to be at stand still and the Direction Selector in position Neutral in order for the selected mode to be effective. If the train is not at stand still or the Direction Selector is not in psition Neutraal when changing mode, mode N wil be selected. In this case, the train will be forced to stop.
  • The selected mode will be effective when the Direction Selector is in position Neutral and the train is at stand still.

Direction Selector

The Direction Selector is active in mode FS, SH and SR only. In other modes, it has no functionality. However it has to be in position Neutral in order to allow change of operational mode.

Position Forward will select driving direction forward as defined by the type of train. Position Reverse will select the oposite driving direction. In these two positions, an MA request will automatic be send to the RBC, given the current mode is FS and no MA is awailable.

Traction selector

The Traction selector is active in mode FS, SH and SR and only when a driving direction has been selected. The selected position will activate the traction control to drive the train accordingly.

  • In mode FS traction control is further controlled by the Supervision System. If the remaining distance to EOA is less than a predeined “braking distance” (optional depending on speed), the maximum traction will be reduced proportionally - eventually forcing the train to stop at EOA.
  • Traction is limited in mode SH as well, keeping it below a value given by the RBC. Further traction is limited in order to keep the train within a predefined shunting area.
  • In mode SR traction is not supervised.


Mode N is indicated as follows:

  • STOP (Red)

In mode FS, the MA indicators will be active, showing the actual MA (if available). The MA will be indicated as

  • STOP (Red): Train is at EOA or no MA is available for the selected driving direction.
  • Short MA (Yellow): MA is availabel for selected direction, distance to EOA is short.
  • Long MA (Green): MA is available for selected direction, distance to EOA is long.

The actual MA indicator will flash, if the OBU has intervened driving and is “braking” the train (i.e. reducing traction).

In mode SH, the indicators will be active, showing when shunting is allowed:

  • STOP (Red): Train is close to border of shunting area and is prevented from continuing in selected direction (i.e. is forced to stop).
  • Shunting allowed (Yellow): Train may shunt in selected direction.

In mode SR, the indicator will show:

  • Staff Responsible (Red - Green): No supervision.

Errors are indicated as follow:

  • No connection to OBU (Steady blue), the DMI has no connection to the OBU
  • No traction power (Slow flashing blue), the train has no traction power.


Traction control

The purpose of the traction control sysrem is to control the model train motor based on the driver commands. By this it will emulate the behavior of real trains - that is, emulating low acceleration and braking capability and high mass.

For version 1 of the Winter Train a simple approach will be used. The driver will control traction in five levels including neutral. The actual traction order (i.e. motor power) for each of these levels will be statically assigned in the OBU.

FIXME Optional a more advanced control will be used, reflecting how steam locomotives are operated.

The driver of the Winter Train will have following possibilities to run the train,:

  • Apply driving force at two levels, Fd1 and Fd2
  • Apply braking force at two levels, Fb1 and Fb2
  • Apply no force

At any time a decelerating force Ff(v) due to overall friction is active. This force is dependent on the speed v and the assumed adhesion coefficient.

The speed of a model train is approximately proportional to the applied traction voltage (within a certain range). Given this, the required traction voltage Vt can be expressed as: tractive effort [N] * speed [m/s] / current [A] An example of a tractive effort curve for the LGB Stainz is expressed in the following diagram. The tractive effort can be roughly expressed as: Ftr=Pengine / v

to be included.

Supervision System

In mode FS the OBU will supervise the traction actual train speed and driving direction according to the current Movement Authority given by the RBC. If no MA is available traction will be disabled.

In mode SH the traction will be supervised against a maximum value provided by the RBC as part of the authorization to operate in mode SH. Further both traction and direction will be supervised, in order to prevent the train from leaving a defined shunting area.

In mode SR traction and direction is not limited; the driver have full responsibility of the train.

Mode SH and SR can only be selected if authorized by the RBC.

Automatic Train Operation

Automatic Train Operation will, based on the actual Movement Authority (MA) given by the RBC, control the traction of the train.

it/wintertrain/design/obu/start.txt · Last modified: 2020/10/02 22:30 by jabe