Posted on Tue, May 10, 2011
LaunchPoint Technologies has invented a magnetic spring technology (U.S. Patent 7,265,470) that enables high-speed motion of mechanical devices with minimum energy consumption. LaunchPoint has been funded to apply this technology to a filter switching mechanism, to electronic engine valves, and foresees applications in a wide range of industrial valves and other mechanisms.
Prior to this invention, high speed point-to-point motion was only accomplished with relatively high power motors. The motor converts electrical energy to kinetic energy in a moving mass and then extracts that kinetic energy to bring the mass to a stop. Such an approach requires a large motor that adds inertia to the system and consumes ~25% of the total energy in motor heating during the acceleration and deceleration. Thus, the large motors increase both cost and energy consumption.
The idea behind the magnetic spring technology is to use the energy stored in a magnetic field to move an object back and forth rather than using a motor. While conventional mechanical springs can accomplish this same task, the maximum force occurs at the end-points, introducing jerky motions that cause noise, wear, and unwanted vibrations. LaunchPoint’s magnetic spring technology, however, allows for “soft landings” at each end-point because the restoring force drops precisely at the end-points.
The spring can be fabricated in either a rotary or linear form. Figure 1 depicts a rotary version of the magnetic spring (left panel) together with a finite-element model of the magnetic fields (right panel). The outer pink magnet array is fixed and the inner array rotates. Looking closely at the magnetization of the magnet segments, one sees that there is an alternating pole pattern on both rings with 3 pole pairs per revolution. In addition to inward and outward oriented magnets, there are additional magnet orientations chosen to maximize the stiffness of the spring.
Figure 1. (left panel) Solid model of magnetic spring having 3 pole pairs on the inner and outer magnet arrays. (right panel) Finite-element model of the associated magnetic fields.
Unlike a conventional torsional spring having a linear torque versus angle characteristic, the magnetic spring has a periodic torque versus angle characteristic as show in Figure 2. When the north poles on the inner array align with the south poles of the outer array and visa versa, the magnetic spring applies zero torque and lies in a stable equilibrium. When the north poles align (and the south poles align too), the torque is zero and spring is an unstable equilibrium. This torque profile is very similar to a pendulum which has one stable and one unstable equilibrium point. Such a characteristic can be used to affect rapid motion with very little external force. Think of the pendulum in the inverted, unstable, configuration. With a very small forces provided by, say, a motor, the pendulum can be maintained in the inverted position. Likewise, with a small “nudge” the pendulum will swing to the right and then back up on the left, returning to the vertical position. In this process, potential energy is converted to kinetic energy and back again. In the magnetic spring the potential energy is created with the magnetic fields rather than the gravitational field. Further, in the magnetic spring we can effectively change the length of the pendulum and the force of gravity to achieve very high-speed motions.
Figure 2. Torque versus angle for the rotary magnetic spring of Figure 1 and a corresponding pendulum analogy for switching between unstable equilibria.
LaunchPoint received funding from Raytheon Company for a rotary version of the device to use in a fast filter-switch mechanism. Figure 3 depicts two rotating filter wheels developed in collaboration with Raytheon Company that rapidly change orientation using LaunchPoint’s magnetic spring technology. The wheels counter-rotate to cancel torque disturbances to the system supports.
Figure 3. Implementation of two magnetic springs in a filter switch mechanism designed in collaboration with Raytheon Company.
Additional funding was awarded by the National Science Foundation (Award No. IIP-0945595) to evaluate a linear version of the magnetic spring as an electronic engine valve actuator. The electronic engine valve is the ‘Holy Grail’ of engine technology. At each engine speed and operating condition, the valve timing can be optimized, enabling a 20% improvement in fuel mileage.
The first bench-top prototype of the valve mechanism is shown in Figure 4. This prototype has a stroke of 8mm and switches position in ~3 milliseconds. A follow-up SBIR Phase II grant (Award No. IIP-1058556) from the National Science Foundation will fund a speed-up to 2 milliseconds and a demonstration in a single-cylinder test engine.
Figure 4. Prototype electronic valve actuator developed with National Science Foundation funding. This linear magnetic spring has unstable equilibria spaced by 8mm and switches in ~3 milliseconds.
The implementations we have introduced above are just two of the many potential applications requiring rapid point-to-point motion. The reader is encouraged to contact us about integrating the magnetic spring technology into their own application.
Posted on Wed, Apr 13, 2011
LaunchPoint Technologies has developed an electric motor that gives better power and efficiency performance per pound than any other motor commercially available.
The military, systems integrators, electric vehicle manufacturers, and remote-control UAV hobbyists have all expressed interest in our motor design.
In this blog post Mike Ricci, VP of Engineering, answers some of the most frequently asked questions (FAQs) about the LaunchPoint Dual Halbach Axial Flux motor.
1. Can I buy the LaunchPoint motor?
The short answer is “not at this time.” We have built several prototypes and tested them to a level where we have high confidence in the basic design, but we have not yet performed HALT testing (Highly Accelerated Lifetime Testing) or tooled up to produce the motors in volume.
2. Can I hire LaunchPoint to develop a Halbach array motor for my application and what would it cost?
Definitely! Depending on your performance requirements and how far you want us to take the design, we can simply deliver a lab quality experimental prototype or take the design all the way through pre-production and high volume manufacturing ramp-up, with costs ranging from tens of thousands of dollars to millions of dollars.
3. Is the LaunchPoint Halbach array motor the “best” motor out there?
To the best of our knowledge the LaunchPoint motor can generate a higher shaft output power (per pound of motor) than any motor out there (at a given high level of efficiency and at a given relatively high speed). We welcome comments and suggestions on other motors that might rival ours.
4. Why does the LaunchPoint motor achieve better performance at relatively high speeds?
Because the motor is cooled with air drawn in by the spinning rotor, airflow is limited at stall and low speeds. As a result, the motor’s continuous stall torque is lower than the high speed running torque. If the motor is provided with an external fan, the stall torque could be greatly improved, but the power density would be decreased because of the additional weight in the system. We have ongoing R&D efforts that will greatly improve the stall torque of the motor, but specific performance predictions are not yet available for that design.
5. How does the LaunchPoint motor design impact the efficiency level?
Because the LaunchPoint motor is so power dense, it has little thermal mass and thus cannot be run at a low efficiency. You might be able to get a higher power density in a different motor design by using a liquid cooled motor that is very inefficient (<90%), but relies on the water to remove the waste heat. However, in the >90% efficient design range, you won’t find a more power-dense motor than the LaunchPoint Dual Halbach Axial Flux motor.
6. Can the LaunchPoint motor be used as a permanent magnet generator?
Definitely! Our electrical machine is the most power dense available. Whether you use it as a motor or as a generator or both, it will happily and efficiently convert electrical power into mechanical power and vice versa.
7. Can you design the LaunchPoint motor for a different size, power level, or speed?
Absolutely; we have looked at designs from 100 W to 2,000 HP and from 400 rpm to 20,000 rpm.
8. How fast can the LaunchPoint motor spin?
As presently designed, our 6 inch motor can easily spin at 12,000 rpm. With some modifications the design should be good to 20,000 rpm. Our motor has no lossy iron and can therefore run efficiently at high speeds and frequencies unlike conventional iron core motors. Because the maximum speed of a motor is roughly inversely proportional to motor diameter, larger motors would have slower speeds.
9. Should I use direct drive with the LaunchPoint motor or connect it to a gearbox?
That depends on your application. If you want the lightest weight possible and don’t need a total conversion efficiency (electrical to output shaft) of >94%, the gearbox is the way to go. Spinning the motor fast to increase power output and then reducing the speed down will always be lighter than a direct drive solution (assuming an aircraft-grade gearbox). On the other hand, direct drive may be more appropriate if you cannot tolerate the maintenance that a gearbox requires or you desire a total conversion efficiency >95% and cannot tolerate the 2% loss in efficiency caused by the gearbox.
10. What will the motor cost when it goes into production?
The costs of the materials in the LaunchPoint motor are comparable to the costs of a conventional motor with an equivalent rating. The LaunchPoint motor will probably use more rare earth magnet material than an equivalent conventional design, but it doesn’t have any iron laminations that require processing and stacking. For the prototypes that we will be building in the near term, the tooling and manual manufacturing processes will require highly skilled labor costing more than 50X the materials costs. Once we have tooled up and are doing low volume production using refined manual tooling and technician-level labor we expect our cost for the motors to be roughly 5X the materials costs. In high rate production, with automated manufacturing processes and volume pricing for materials/components from suppliers, we expect the cost of the LaunchPoint Motor to be competitive with other high-end brushless PM motors with similar ratings.
11. How can I find out more about the LaunchPoint Dual Halbach Axial Flux Motor?
You can find more information on our website under electric motor design and UAV electric propulsion.
Feel free to continue the discussion with us in the comments section below and we will answer your questions as soon as we can.
Posted on Wed, Mar 16, 2011
With the launch of our new corporate website, we have added blogging capability as well as RSS feeds, email updates, Twitter and YouTube subscriptions to keep you informed and up-to-date about what is happening at LaunchPoint Technologies, Inc. We hope to open the door a bit to the world of innovation and technology business development and look forward to talking technology with you in the near future!