Robotica Exotica

Pistonless Pump offers Performance

Flowmetrics has a design for a pistonless pump that they claim is as good as a gas-genertating turbopump for a first stage liquid fueled rocket. Included is this handy animation that shows how this whole thing works. It appears to be very robust, and very high performance.

We are have designed, built and tested a simple, lightweight pump(dual pistonless pump) for use in liquid propelled rockets where a reliable pump with minimal moving parts is needed. This pump has the potential to reduce the cost and increase the reliability of rocket fuel pumps by a factor of 20 to 100. The pump has been tested with a rocket engine and the pump worked perfectly.

How it works:

Rocket engines require a tremendous amount of fuel at high pressure. Often the pump costs more than the thrust chamber. One way to supply fuel is to use the expensive turbopump mentioned above, another way is to pressurize the entire fuel tank. Pressurizing a large tank requires a heavy, expensive tank. However, suppose instead of pressurizing the entire tank, the main tank is drained into a small pump chamber, which is then pressurized. To achieve steady flow, the pump system consists of two pump chambers such that each one supplies fuel for ½ of each cycle. The pump is powered by pressurized gas which acts directly on the fluid. For each half of the pump system, a chamber is first filled from the main tank under low pressure and at a high flow rate, then the chamber is pressurized, and then the fluid is delivered to the engine at a moderate flow rate under high pressure. The chamber is then vented and the cycle repeats. The system is designed so that the inlet flow rate is higher than the outlet flow rate. This allows time for one chamber to be vented, refilled and pressurized while the other is being emptied. (See Figure 1 below) A bread board pump has been tested and it works great. A high pressure version has been designed and built and is pumping at 20+ gpm and 550+ psi.

Nozzle Applet

This is a well written site describing the function of a convergent/divergent rocket nozzle, along with some design code. It is well done, and I thing does a great job of explaining some of the phenomenon associated with nozzle design. While you can understand this without a whole lot of thermodynamics, it would certainly help.

The purpose of this applet is to simulate the operation of a converging-diverging nozzle, perhaps the most important and basic piece of engineering hardware associated with propulsion and the high speed flow of gases. This device was invented by Carl de Laval toward the end of the l9th century and is thus often referred to as the 'de Laval' nozzle. This applet is intended to help students of compressible aerodynamics visualize the flow through this type of nozzle at a range of conditions.

GPS in Unusual Places

This is just plain wild. Coke has a promotion for their summer marketing blitz that includes a number of GPS-enabled coke cans hidden in the normal distribution. When you find one, you press a button to activate the can, this turns on a GPS reciever and a cellphone transponder that will direct the coke people to you to deliver your prize.

As part of the soft drink firm's Unexpected Summer ad campaign, specially designed Coke cans feature a Global Positioning System (GPS) satellite transponder and cell phone.

Winners who find one of these cans press a button to activate it, volunteer to participate and then have the grand prize delivered to them wherever they are.

The high-tech cans feature specially designed graphics and a recessed panel with buttons that, when pressed, activate the GPS technology and cellular phone. The inside of each winning can is configured with a Subscriber Identity Module (SIM) card that enables the can to serve as a cell phone that works in conjunction with the GPS transponder.

Not the usual place to find GPS, but very cool none-the-less.

Armadillo Hovers

The Armadillo Aerospace crew has been busy at work on their X-prize prototype, and are having some good success to date. They are now working on getting the single engine rocket to hover in place using control vanes in the exhaust flow. This is really neat, and coming up along the way the DC-X did its flight control, this seems a whole lot simpler.

To make up for the relatively low 10hz update rate of the GPS (I wish I had gone ahead and ordered the 20hz option) and to provide some more graceful failure modes, I combined the inertial position and velocity sensing with the GPS updates, so it gets reset every time a valid GPS packet comes in, but will coast with pure inertial data if the GPS is failing, and provide useful data between GPS updates. This isn’t as good as a truly integrated GPS / IMU system that can use the IMU data to smooth the selection and balancing of different satellite signals before generating a GPS output, but it does several positive things for us. The upwards position / velocity is easy to use the IMU for, because it can auto-orient from the gravity vector while on the ground, but to get north / east data, we now have to orient the vehicle correctly before launching. I have a magnetometer that we could use for an automatic roll orientation, but I haven’t plugged it in for a couple years.

I also updated the GPS baud rate, which doesn’t give me any more samples per second, but decreases the latency in getting the updates it does produce.

The auto-hover was somewhat smoother than before, but nor dramatically so. The overshoots are proportional to the control authority times the sum of the sensing latency and the actuating latency with the current control algorithm, so I may just intentionally slow down the valve movement. I may convert it over to a gain based control system like the attitude control, but it is trickier because the vehicle is constantly changing weight and tank pressure as propellant is depleted, so there isn’t a reasonably point on the throttle that a default actuation position could be based on. I don’t want to waste much time on it, because hovering isn’t actually an important part of what the vehicle is supposed to do.

The three videos up are pretty neat to watch.

http://media.armadilloaerospace.com/2004_05_09/autoHover.mpg

http://media.armadilloaerospace.com/2004_05_09/wrongWay.mpg

http://media.armadilloaerospace.com/2004_05_09/autoHold.mpg

The Doctor is in the Robot

This article is more about telepresence than about robotics, but it is interesting none-the-less. Patients surveyed found that they preferred to see their own doctors on-screen on-robot, rather than someone they were unfamiliar with. It is an unusual study, but I think we are going to see more of this in the future.

The 200-pound (90-kilogram) robots stand about 5 feet (1.5 meters) tall. They have flat video screens for heads, and video cameras serve as their eyes and ears.

Using a joystick, a doctor can operate the rounding robot to check on patients from another building or another country, via the Internet and wireless links.

The doctor's face appears on the robot's screen, and he or she interacts with the patient through the real-time video hookup.

The aim of the technology isn't to replace human doctors, but to make it more convenient for doctors to check in with their patients, and for patients to get quick access to personal physicians who aren't at the hospital.

Microprocessors in Unusual Places

The New York Times has an article on the development of a microprocessor controlled shoe, which senses at around 20 KHz., and responds by adjusting the physical shoe parameters at around 10 KHz. How often you will have to change the battery in your shoe is not detailed. I keep telling people that embedded control systems are winding up in places that no one has anticipated. Very interesting development, and not too expensive either.

"What we have, basically, is the first footwear product that can change its characteristics in real time," said Mr. DiBenedetto, who led the group that created the shoe, of its ability to adapt its cushioning as the wearer runs.

The shoes will have push-button controls, light-emitting diodes to display settings and an instruction manual on a CD-ROM that will advise wearers on, among other things, how to change the battery after every 100 hours of use.

Of all items of clothing, said Rob Enderle, a principal analyst for the Enderle Group in San Jose, Calif., the shoe is a logical one to be a focus of wearable technology. Unlike articles of clothing that must be washed or cleaned, shoes present a more stable place to add useful electronics, he said.

High-performance shoes, particularly those intended for athletic use, he said, have been augmented with an array of biomechanical enhancements, most of them involving compressed gases, shock absorbers and springs. But until now, he said, "I don't recall electronics being applied in shoes other than for lights."

Armadillo Aerospace Close to Hovering

John Cormak and the team over at Armadillo Aerospace have been experimenting with control systems to get their x-prize rocket to hover. I think that this is a very interesting development, and I love the fact that they publish everything they do, good and bad. This movie is pretty neat.

The second hop lifted off and hung at an angle, picking up horizontal velocity, so I cut it off quickly. I probably could have steered it back, but it was easier to just kill it. On reviewing the video and telemetry, we found that for the time that it was in the air, it was flying perfectly steady.

This is the behavior we would expect from either an offset center of gravity or vanes that weren’t calibrated straight up. We knew the mounting of the electronics had biased the weight forward, so we clamped ten pounds of weight on the back side for the next test flight. This time it flew basically straight up, still with the extreme smoothness, but we lost GPS lock almost immediately after liftoff.

We went through several tests trying to figure out what was going on. I could fly it on manual throttle just fine, but the Ashtech G12-HDMA was losing lock within a quarter second or so of liftoff. Communication with the GPS continued without a hitch, but the values would come in all the same for a ten second or so stretch. We tried mounting the amplified GPS antenna on some soft foam and even completely enclosing it in foam for acoustic protection, with no change. Russ had an idea that sounded really logical – that it wasn’t liftoff that caused the problem, but instead it was the condition of high chamber pressure on throttle up that caused the spark plug to misfire, generating RF noise. I changed the code so I only had the spark going during warmup and not during liftoff, but it didn’t change anything. I have a new GPS antenna arriving soon that we will test with on Tuesday.

We decided to go ahead and do a long run with me manually controlling the throttle and steering. I had it throttled up for 19 seconds, but I wasn’t perfectly centered under the lift when I started descending, so the last couple seconds pulled taut on the tether. Still, it was at least a 16 second perfectly controlled flight. If it hadn’t been on a tether, this test would have required a federal launch license complete with environmental assessment, which rather clearly shows how silly the burn time limit is. It looks like AST is going to grant us a burn time waiver, but only for tests at SWRS (southwest regional spaceport), which is a two-day trip away.

Posted by elkaim at 2:50 PM