Aerial photography and surveying can be beneficial for many businesses and industries. For example, mining companies doing aerial-surveying of mine sites, oil & gas companies conducting aerial-inspections of their offshore platforms, electricity companies inspecting high-voltage transmission lines or a real estate agent taking high-resolution aerial images of properties for marketing.
A common problem faced in these often harsh operating environments is keeping the camera or the surveying equipment steady against the wind, turbulence and the vibration from the aircraft it is mounted to. This is where a high-precision stabilisation camera gimbal comes into action. These gimbals provide users with a firm and levelled platform that allows them to capture high-quality images and data, without being affected by destabilising elements.
The need for a DC servo motor
Photo Higher was looking for a small brushless DC servo motor and gearhead combination for a high-end camera gimbal that they were designing. Located in Wellington, New Zealand, the company specialises in the design, development and manufacturing of precision camera gimbal systems for Vertical Takeoff and Landing (VTOL) for Rotary Wing Unmanned Aircraft Systems. The Photo Higher gimbals are designed to be lightweight, smooth and very stable. Their gimbals are all 100 per cent designed and manufactured in New Zealand. With the innovative design and carbon fibre manufacturing capabilities, Photo Higher is considered to be one of the industry leaders in the commercial precision camera gimbal industry.
The initial requirement was to have a DC servo motor combination with zero backlash, 40 rpm and 2 Nm output torque. The total weight of the motor combination needed to be less than 100 grams and the overall length needed to be less than 50mm. This required speed and torque was achievable, however, the weight and length were proving to be an issue. To achieve 2 Nm at 40 rpm continuous with low backlash, the combined weight of the motor and gearhead was around 370 grams, which far exceeds the weight requirement by the customer. The maxon engineers worked through all available options with standard backlash figures, having the intention of using a standard brushless DC servo combination first, and then to work on customising a DC servo gearhead to achieve the low backlash specification afterwards. The company was able to come very close to the weight, speed and torque target, but the overall length for the proposed brushless DC servo combinations was too long for the client.
The right DC servo motor
Why a brushless DC servo motor with such high power density? With most Unmanned Aerial Vehicles (UAV) applications, the power consumption is important. With higher power density and higher efficiency, brushless DC servo motors will consume less power compared to other motors, allowing the UAV to stay airborne longer.
A right angle drive option was then considered, but it was too heavy for the application. Finally, a flat brushless DC servo motor with a harmonic gearhead was settled on. This harmonic flat brushless DC servo combination delivers the required speed and torque in a flat compact form; most importantly, this combination has an output with zero backlash, which makes it ideal for a gimbal application.
After the brushless DC servo motor selection for the large Photo Higher gimbal was completed, maxon started work on three smaller gimbal designs. The smaller gimbals were more price-sensitive, therefore, the harmonic brushless DC servo combination could not be considered. The engineers then proposed several different small flat DC servos with low back lash gearheads, but either the price or performance made them unsuitable. After some discussion and with some smart carbon fibre structure designs by Photo Higher, maxon was able to use a flat DC servo motor to direct drive the gimbal.
Energy efficiency for extended survey flights
Power consumption is an important consideration for UAV applications. With higher power density and higher efficiency, maxon brushless DC servo motors offer lower energy consumption than other motors, allowing the UAV to remain airborne for longer periods of time. After numerous trials with a variety of drive units, including the use of an angular gearhead that turned out to be too heavy, an ideal solution was found – the maxon EC 32 flat, a brushless DC servo motor that drives the gimbals directly. This customised drive is flat and compact while still fulfilling the speed and torque requirements. Most importantly, the output has zero backlash, making these drives a perfect solution for camera gimbals. With the new design, the end-user can always adjust the gimbal and balance the centre mass of the entire system, irrespective of the camera brand or model. With a balanced centre of mass, fast acceleration and quick response can be achieved with minimum effort from the DC servo motors.
Customised servo controller
In addition to the brushless DC servo motors for the various camera gimbals, Photo Higher uses a custom maxon servo controller for the DC motors. The customisations included the PCB shape, control parameters, gain and connectors – all tailored to the special requirements of the application. The camera gimbals of the AV and Halo series by Photo Higher were designed for demanding applications. This allows the system to be used for film shoots. Combined with an unmanned aircraft, the system provides users with an easy way to collect and capture high definition aerial imagery and geospatial data. In addition to UAVs, the gimbals can also be mounted on various types of platforms, such as, helicopters, airships, cranes and boats.
The maxon brushless DC servo motor has helped Photo Higher attain the specifications for its high-end camera gimbal, which requires not as much power as other motors. Additionally, it has lived up to speed and torque requirements, with zero backlash.
Courtesy: maxon precision motor India