Simple Servo-Based Panorama Platform 

Concept

• Automated Pan/Tilt movement

• Use of RC-Servos

• The Camera-trigger is operated via a lever arm by an RC-servo

• Servos are controlled by Pololu Micro Serial Controller

• Control by C-Control microcontroller, LCD display and keypad

• Various programs account for variation of panorama size, zoom-factor, focusing mode, exposure length etc.

• Pan-axis: >360° with a sail winch servo, 5x reduction (using Lego-gears) to achieve positioning precision sufficient for Gigapixel panoramas with 18x zoom

• Tilt-axis: -45° to > 90° with a high torque RC servo (ca. 68 Ncm at 6V)

I did some major improvements on the design  - see Updates section

Design considerations

• Prevent „servo jitter“ (turn-off servos after movement to avoid jitter during focusing/exposure – that is a very nice feature  implemented with the Pololu controller). The holding torque of the servo needs to be sufficient to hold the tilt-position

• Minimize torque on the tilt-axis (tilt-axis through the cameras center of gravity)

Technical Design

Watch the platform in action   (7 MB QuickTime movie)

Features

• Up to 20 images/minute (with manual focus/AF-lock)

• Use of standard components (RC-Servos, Lego-gears)

• Gigapixel panoramas (up to 18x zoom)

• Spherical panoramas

• Size scalable – thus suitable for larger cameras (my config works well with the Lumix DMC-FZ28 weighing approx. 418 g)

Servo Specs.

Pan axis:

PRO LINE SEGELWINDE SW1200 JR

Torque: 115 Ncm (6V)

The sail-winch servo  makes roughly 7 turns

Tilt axis:

PREMIUM HIGH TORQUE SERVO MC 5018 HB

68 Ncm at 6V

Camera trigger:

Modelcraft ES 05

12 Ncm at 6V

Servos are only switched-on to move an axis. To prevent servo-jitter they are switched-off after the movement. Thus, the holding torque - in particular that of the tilt axis -  needs to be large enough counter the torque the camera puts on that axis. At 18x zoom, an unbalanced torque can cause problems - the tilt position may not be stable enough.  The remedy is to balance the tilt-axis  by a small counterweight (not shown in the pictures here). A magnet (used as a weight) on a small (ca 3x8 cm) steel-plate does a great job in  improving the positioning accuracy.

Yet To Do

• Size reduction of the electronics (C-Control Mega128 stand-alone-board)

• Use of only one battery pack (instead of three)

• Design is currently not ergonomic (e.g. Keypad and LCD-Display)

• Reduction of  the backlash of the Pan-axis – precision is close to its limit at 18x zoom, though usually this is not a problem - Problem solved: see below

Design Update (08.02.2010)

Stepper Driver and Power-Supply

I have replaced  the Pan-Axis-Servo by a stepper motor. Positioning with  the sail winch servo was not 100% relieable at  large zoom, with the stepper it is. A further advantage of the stepper is that the pan position can be adjusted by hand if necessary (for example to repeat a column of images).

The stepper motor is controlled with an Allegro A4983 microstepping bipolar stepper motor driver (very easy to use with the Pololu A4983 Stepper Motor Driver Carrier).

Due to microstepping sufficient positioning accuracy can be achieved without additional gears, thus there is no backlash problem as in the previous design.

The stepper is inside the white box. An O-Ring (around the square aluminium block that sits ontop of the white box) generates a friction torque. This is necessary to  quickly stop the pan-axis when the end-position is reached and to prevent vibrations.

Stepper Specs:

Bipolar stepper motor: Trinamic Qmot 1.8°, 1A, 0.27 Nm 

• Microstepping with 1/16 steps (Stepping rate ca. 500 Hz) 

• To dampen oscillations of the pan-axis   I use an O-Ring seal to generate friction between the rotor an the housing.

As a power supply I use two NiMH power-packs (with 7.2V, 3300 mAH each) in series. To generate the 5 V for the RC-Servos  a buck-converter will be used (very small losses).

New Tilt-Axis Servo

When the tilt axis failed (broken gears) I replaced the servo by a more durable servo with metal gears. However, I realized that the holding torque was not suffient if the servo is switched off in order to prevent servo jitter.

I found that a very reliable solution is using a digital robot servo like the Graupner RBS581 RB1000BB. This servo is very precise and doesn't jitter, so that it is not necessary anymore to switch off the tilt servo for an exposure.

I've also changed the attachment of the tilt servo: The servo is now mounted with cable ties (two black Lego-bars ensure proper positioning). This enables easy coupling and decoupling of the servo with the tilt-axis-shaft. The new feature enables safe transport of the platform (without the danger of breaking the servo gears).

Camera settings (Lumix FZ28) for panorama images

• Manual-Mode:Manual Focus, fixed ISO, fixed white balance, exposure and f/# at specified values

• Program-Modes: use AF/AE-Lock, fixed ISO and white balance

• Autofocus: use AE-Lock, use fast autofocus mode, focusing may require a significant amount of time (to be considered in the platforms timing parameters) and may not work if an image shows the sky only

C-Source Code for the Panoramic Head Controller

The source files for the C-Control Pro based Panorama Head controller can be downloaded here.

The source files for the new platform design with stepper-motor can be downloaded here