Electric vehicle pioneer favours wireless test rigs.


A company that has been at the forefront of electric vehicle design and development for over 20 years has supplied a test rig based on a wireless torque sensor to a world renowned British University automotive research facility.

Tirius has been built on pioneering work on an all-electric single seat racing car and a series of record breaking vehicles. It continues to bring the latest technology to clients in the form of product design and development and the provision of its range of electric drive systems.

Head of Tirius, Dr Tim Allen, explains: “We are helping the university’s research team develop electric drive train technology typically found in ‘A-Class’ cars, for example urban runarounds and small family hatchbacks. Specifically we are currently looking at permanent magnet traction motors in a number of sizes and configurations, with a view to optimising electronic control for each motor type.”

The research involves running each motor on a test rig through its full output range and mapping its torque output at many points to build up a performance profile. The design of the controller can then be matched to the motor characteristics. This should be able to ensure that the motor runs in its optimum operating zone as much as possible, maximises motor life and regenerative braking, minimising wear, and is as energy efficient as possible.

The design of the test rig is in fact quite simple, thanks to the torque sensor, a TorqSense, as made by Sensor Technology.

“We are pleased to promote TorqSense and the guys at Sensor Technology,” says Tim. “We have been using their kit for many years and in many different roles. The bottom line is that they are easy to use, accurate and great value – partly because they can be re-used once their original project has been completed.

TorqSense is a good choice for this work because its non-contact operation allows rapid set-up during the profile building test runs. It also means extra drag forces are not added to the system, so measurements represent true values and calculations are therefore straightforward.”

TorqSense uses two piezo-electric combs which are simply glued to the drive shaft at right angles to one another. As the shaft turns it naturally twists along its length very slightly and in proportion to the torque, which deforms the combs changing their piezo-signature. This change is measured wirelessly by a radio frequency pick up and is a measure of the instantaneous torque value.

Its data is output to a very user-friendly computer screen which uses graphics to aid easy interpretations. In fact the display on the computer is similar to a car’s dashboard, so most people understand it intuitively. Further, the data is automatically logged for further analysis.

Tim again: “With our type of research work there are some potential errors that we have to look out for, including time-based zero-drift, bending moments on the shaft, bearing losses, temperature fluctuations etc. These are easily accounted for with TorqSense-based test rigs. Normally you have to account for the drag caused by the slip rings, but the wireless TorqSense does not use them, so that is one less calculation – and one less fiddly fixing task.

“A great benefit of TorqSense is the ease with which it can be mounted and dismounted, which simplifies research work where frequent reconfiguring is required.”

The University project will take two or three years to complete and the TorqSense test rig will be worked hard during this time. “At the end of the work, I have no doubt that the TorqSense will be reused in a new research program. It’s what we do in-house at Tirius.”


@sensortech #PAuto

Thames to sparkle under its own power


W.S. Gilbert in one of the librettos for the famous Gilbert & Sullivan operettas prophesies:

“…they’ll set the Thames on fire
Very soon; very soon.”

Well this story, while not an exact fullfilment, strikes us as perhaps been something Mr Gilbert might have appreciated.

...the start of the future?

A small proportion of the Thames is to be illuminated using power generated by the flow of the river itself, as Kingston University tests prototypes of a new hydroelectric turbine design.

The turbine will sit on a pontoon and will provide a floating test and measurement laboratory. On this will be an array of sensors and monitors, including a TorqSense the wireless torque sensor from Sensor Technology Ltd.

“To say that this is a harsh environment for laboratory equipment is a bit of an understatement,” says Rod Bromfield, Senior Lecturer, of the Faculty of Engineering, Kingston University. “We can only use robust kit with a proven industrial pedigree.”

The turbine under test has been developed by Hales Marine Energy near Eastbourne on the English south coast and is expected to be deployable in tidal seas as well as rivers. The design application of this turbine is to sit on a submergible tank that will sit on the sea bed and can be floated up to the surface when required. Significantly, the design is almost infinitely scalable: the unit under test is 1m diameter and produces about 1kW; 5m turbines suitable for inshore deployment would generate round 20kW; smaller units would be ideal for river use.
With access to the test site being by small boat, Rod knew that his test regime had to be both simple and comprehensive.

“The critical measurement is torque, as this indicates the power we can derive from the system. We had to be certain that we would get continuous measurements over an extended period of time, because we need to map power production against actual river flow. Also for this technology to succeed in the emerging green power market it must be capable of continuous and predictable energy production.”

One of the engineering issues that Rod faced was the relatively slow revolution of the turbine, in this test below 50rpm. This helped define the choice of the TorqSense, but it is also a key feature of the Hales turbine – the slow speed means less stress on moving parts and therefore less servicing. It also minimises habitat disturbance, so that the ecological impact is low.

“When I contacted Sensor Technology I was very concerned about vertical mounting and harsh environment performance,” recalls Rod. “Fortunately there have been TorqSenses installed vertically, including several high up on vertical axis wind turbines, where they have to withstand gales, hurricanes and lashing rain.”

In a Torqsense transducer, surface waves are produced by passing an alternating voltage across the terminals of two interleaved comb-shaped arrays, laid onto one end of a piezoelectric substrate. A receiving array at the other end of the transducer converts the wave into an electric signal.

The frequency is dependent upon the spacing of the teeth in the array and as the direction of wave propagation is at right angles to the teeth, any change in its length alters the spacing of the teeth and hence the operating frequency. Tension in the transducer reduces the operating frequency while compression increases it.

To measure the torque in a rotating shaft, two saw sensors are bonded to a shaft at 45deg to the axis of rotation. When the shaft is subjected to torque, a signal is produced which is transmitted to a stationary pick up via a capacitive couple comprising two discs, one of which rotates with the shaft, the other being static.

The design of the Hales turbine is reassuringly simple, and therefore likely to survive underwater installation with long service intervals. It was developed by Paul Hales, a design engineer who has spent a career associated with the sea.  “It’s based on the traditional water wheel, but mounted on a vertical axis – on its side,” he explains.

“Using modern engineering and materials it is possible to take this effective early turbine and by turning the output shaft to the vertical to immerse the whole turbine into the tidal flow. To overcome the high resistance on the wheel blades that on one side are trying to move against the water flow, they are shaped and hinged to present a minimum resistance. The large blade area on the drive side produces very high amounts of torque (rotational force) at low speed, in the range of 10 -20rpm.
Coupled with modern permanent magnet generators that can start producing electricity rotations as low as 2rpm, my turbine can offer the possibility of tidal generation worldwide.”

Paul continues: “Water is nearly 800 times denser than air so it carries far more energy, making water turbines a very attractive alternative to wind energy. Notably seabed systems are not an impediment to shipping, nor do they have any visual impact and ecological issues are minimal for low speed systems.”

Paul says that he could envision an array of his turbines on every headland along the English Channel and at intervals down the Thames.

“Of course, that is just the start. The simplicity of the design, its robustness and low maintenance, relative ease of installation all add up to making it suitable for deployment in remote and less developed areas. Its low ecological footprint addresses many of the issues raised by environmentalists. Its continuous and utterly predictable power output overcomes the intermittency associated with wind, wave and solar power.

“When, over the test period, people stand on Richmond Bridge and watch a modest array of lights bobbing about on a buoy, they may not know it but they will be seeing the future!”

And so we get back to W. S. Gilbert:

“…they’ll set the Thames on fire
Very soon; very soon.”

See also Power from the Sea and Tidal turbine developement in Ireland & Canada published earlier this year

Tidal turbine development in Ireland and Canada


Novel sensors aid tidal turbine development

A few months ago we reported on an application on harnessing electrical power from the sea out in Galway Bay on the west coast of Ireland. Today we have a report from the other side of the country, Greenore, at the mouth of Carlingford Lough in Co Louth. This company is also working on using the tides but is different in that their generators are completly submerged at the sea bed.

Non-contact torque sensors from Sensor Technology are playing a key role in the development of commercial-scale in-stream tidal turbines produced by OpenHydro. The company is using these novel sensors, which are based on surface acoustic wave (SAW) technology, to accurately measure rotational speed and frictional forces in a simulator for the turbine bearings, thereby allowing it to optimise the performance and reliability of its innovative products.

OpenHydro is a technology company that designs and manufactures marine turbines to generate renewable energy from tidal streams. The company’s vision is to deploy farms of tidal turbines under the world’s oceans, where they will dependably generate electricity with no cost to the environment. This method of producing electricity has many benefits.

Because the turbines are submerged, they are invisible and they produce no noise. And because they are submerged at a considerable depth, they present no hazard to shipping. An advantage that is possibly the most important, however, is that the tides are completely predictable, which means that the energy output of the turbines is equally predictable. There are no large seasonal variations and no dependence on the vagaries of the weather, as there are with many other renewable energy sources.

Reliably and efficiently harvesting energy from the tides, however, requires the use of novel technology and, in the case of OpenHydro, this takes the form of open-centre turbines that can be deployed directly on the seabed. Clearly, installation in such an inaccessible location makes reliability a prime consideration in the design and construction of the turbines. For this reason, OpenHydro carefully and comprehensively evaluates the performance of all of the components used in its turbines.

For the bearings, this evaluation involves the use of a simulator that allows the company’s engineers to determine how frictional forces in the bearings vary with different loads and rotational speeds. Central to the operation of this simulator is the measurement of torque in a shaft from the motor that drives the bearing under test. With conventional sensors, it is hard to carry out this type of torque measurement accurately and reliably, but OpenHydro found that Sensor Technology’s TorqSense RWT320 series sensor provided an ideal solution.

Like all TorqSense sensors, the RWT320 units depend for their operation on surface acoustic wave (SAW) transducers. These transducers comprise two thin metal electrodes, in the form of interlocking “fingers”, on a piezoelectric substrate such as quartz.

When an RF signal of the correct frequency is applied to the transducer, surface acoustic waves are set up, and the transducer behaves as a resonant circuit. If the substrate is deformed, however, the resonant frequency changes. When the transducer is attached to a drive shaft, the deformation of the substrate and hence the change in resonant frequency will be related to the torque applied to the shaft. In other words, the transducer operates as a frequency-dependent strain gauge.
Since the transducers operate at radio frequencies, it is easy to couple signals to them wirelessly. Hence TorqSense sensors can be used on rotating shafts, and can provide data continuously without the need for the inherently unreliable and inconvenient brushes and slip rings often found in traditional torque measurement systems.

“We chose the RWT320 because of its convenient wireless operation, and because it was easy for us to fix in line with an existing shaft in our experimental set up,” said Kevin Harnett, Mechanical Engineer at OpenHydro.  “In addition, this model of sensor has integral electronics and a serial output, which means that we can link it directly to a laptop computer in our test laboratory. This is a very straightforward and convenient arrangement.”

OpenHydro uses the RWT320 sensor in conjunction with Sensor Technology’s TorqView software. This offers a choice of dial, digital bar and chart graph format display for torque, RPM, temperature and power. It also provides facilities for realtime plotting and for data recording, and can output stored results as files that are compatible with Matlab and Excel.

“We have found both the sensor and the software very easy to work with,” said Kevin Harnett, “and the sensor has proved itself to be well able to withstand the tough operating conditions in our laboratory. We’ve also received excellent technical support from Sensor Technology, which was very helpful as we have never previously worked with sensors of this type. Overall, we’re very happy with product and the service we’ve received, and the sensor is providing invaluable data for our development work.”

Proof that this development work is yielding dividends was amply provided late in 2009, when OpenHydro deployed the first commercial-scale in-stream tidal turbine in the Bay of Fundy, Canada, on behalf of its customer, Nova Scotia Power.

This 1 MW unit was arrived on site on 11 November and was operational, rotating with the tides, collecting data and producing energy by 17 November.