Levelation Lite
The Electric Scissor Jack
An electric scissor jack can be used in place of a corner steady. The quality of the motor and gearbox on the jack are more than adequate for the very light duty of rotating the trailer's chassis about the suspension until a level deck is achieved.
The jack requires some minor modifications to increase its suitability to this purpose:
- The crown must be removed to lower its profile,
- In place of the crown a footplate must be added to increase the ground-contact area,
- A skid should be added to protect the motor from accidental contact with the road,
- The limit switches and associated wiring as well as the control panel are discarded,
- A suitable quick-release mount is needed to attach the inverted jack to the trailer chassis.
Scissor Jack Quick-release Mounting
In order to make the electric scissor jack available for other purposes, such as jacking up a car, it can be mounted in a quick-release bracket, which requires only one 17mm AF nut to be loosened to release the jack. When provided with an extension power cable the jack can hen be used for other purposes.
End-of-Travel Detection
The controller does not require limit switches - end-of-travel is detected by the sharp rise in motor current that occurs when the motor is slowed at reaching the limit of its travel. (This can also happen when the motor encounters some other insurmountable obstacle). When the motor current reaches or exceeds 8A while extending the leg the control unit assumes that end-of-travel has been reached or an insurmountable obstacle has been encountered. For retracting the leg the current limit is reduced to 5A since there will normally be less load on the motor during this operation.
Once end-of-travel is detected further movement in that direction is blocked by the control logic. The block is removed when travel in the opposite direction is initiated.
The Mobile Phone App
The CaravanPilot app for Android phones has a control screen with 8 buttons and a spirit levels on each of an X-Y axis to facilitate the levelling process. While any button is pressed all other buttons are disabled. The magnitude of motor current is shown on the screen. If the the phone moves out of Bluetooth range of the control unit all motors will be immediately deactivated.
The Levelling Sequence
Although the jacks each have a 2-ton lifting capacity they are never intended to lift any trailer wheel clear of the ground. Doing so would dangerously destabilise the trailer. The purpose of the jacks in this application is to rotate the trailer chassis about the axle until the deck is horizontal in both the longitudinal and lateral axis.
At the start of the sequence the longitudinal axis must be horizontal or nose down. If this cannot be achieved by lowering or removing the jockey wheel then the site should be considered unsuitable.
As a first step the nose should be raised by alternately extending the front jacks until the longitudinal axis is horizontal. Both jack should share the load equally.
Then both rear jacks should be extended alternately until they too both touch the ground with light but equal pressure.
Now the jacks on the lowest side of the trailer should be extended alternately until the lateral axis is also horizontal. The road wheel on the lowest side must not be allowed to lose contact with the ground.
Calibrating the Levelling Crosshairs
Many mobile phones have camera lenses that stand proud of the rear surface of the device and prevent its lying flat on its back. To eliminate these, or other instrument errors that may exist in the mobile phone or its jacket, you can calibrate the crosshairs to zero by placing the phone on a flat and level surface, and then double tapping the Caravan Pilot title. The phone will buzz and the red dots will centre. This calibration will apply until the app is terminated.