Due to the little mess in the licenses, we decided to clarify the terms and conditions of using RAMA a little bit. The software here is now published under the terms and conditions of the GNU GPL 2 license (as it was before). This website itself, its parts and documents published here may now be used under the terms and conditions of the Creative Commons BY-NC-SA 3.0 license, meaning that you can copy, share and modify parts of this website or the website as a whole for non-commercial purposes, as long as you provide a link to our website and publish your work under the same or compatible license. This part is now somewhat more benevolent than it used to be.
We encourage especially people involved in education, open-source projects and non-profit organizations to freely use, copy or modify all texts and figures published in this website for non-commercial purposes, as long as you give us some credit (i.e. mention this website as the source) and allow use of your work under the same or compatible license.
Software in the Downloads section was updated to the latest revisions. The MCC software now includes the Kalman filter and all control layers. However, the documentation in the Control System Software section was not updated yet, so there are some discrepancies. The Control System Software section will be updated as soon as possible .
Since this web was not updated for almost eight months, it is highest time to perform another overhaul and upgrade the information contained here to correspond to the latest development of our project.
RAMA is now capable of autonomous flights, although takeoffs and landings still have to be done manually. In flight, however, it is currently capable of completely autonomous stationkeeping and very simple trajectory tracking. See the short movie below:
The update work on this web is almost finished. Source codes of the software are now available in the Downloads section (registration required). The flight data should be updated soon (will do my best ).
Happy new year to everybody !
This web will undergo a major overhaul in the following days. Information here may be rather inconsistent until it’s finished .
Inspection of dismantled RAMA system revealed today that a faulty connector was responsible for the GPS malfunction we experienced during the flight test yesterday. As this is not the first problem we have had with this type of connector (PFH02-xx), it was decided that all connectors of this type would be gradually replaced in the whole system (the substitute being the PS 25/xx connectors, which proved to be much more rugged). Also the problem regarding the servo positions recording was investigated and a minor software flaw was quickly found and corrected.
The cause of excessive airframe vibrations is not yet known; thorough inspection of the Freya mechanics did not reveal any obvious problems. Most likely candidates are the exhaust system, the Electronic Container (EC) fixture and canopy resonance, but it might be anything completely different. The blades, either main or auxiliary, are definitely not to be blamed, as it was verified that their weight and cg positions are perfectly equal. Also the flybar and paddles seems to be out of suspicion. The main and tail shafts, as well as spindle, are brand new and therefore cannot be bent, and also the bearings were replaced as a precaution after the crash and therefore should be OK. The tail rotor drive system is working fine, with no play nor stammering, and the belt tension seems to be correct. This issue is therefore going to be investigated during the next flight test, which is preliminary scheduled for the next week.
The muffler fixture was reworked and some slight alterations were made to the canopy in order to get rid of the vibrations. However, it remains to be seen whether it works out…
Today, we have performed our first flight test since the November crash. The weather was favorable, with only weak wind blows and temperatures rising up to 8°C. With little optimism, we may say that the test was partial success . Five flights were performed overall. On the positive note, we did not encounter any safety-critical problems of any kind and did not experience any “moments” . On the other hand, some glitches were still encountered – the GPS was malfunctioning (seems to be a hardware – related problem), some servo positions were not recorded properly (apparently a minor software bug), and on top of that the airframe produced relatively high vibrations (a mechanical issue of some kind), deteriorating the measured data. This is definitely something we must look at thoroughly. Recorded data will be posted in the Experiments & Data section soon. The next flight test would take place as soon as those bugs are fixed and will be announced in this section.
The RAMA-Freya duo had successfully passed the Flight Readiness Test (FRT) last week, and therefore had been declared airworthy again. With respect to the weather forecast, the next flight test is scheduled for Wednesday February the 14th, around lunch-time. Planned program of the test consists of basic system testing, helicopter setup work and identification experiments to re-fit the mathematical model. No controllers will be tested and all flights will be carried out by a human pilot.
Right at the beginning, I would like to apologize that this web site had not been updated for a relatively long time. We have had some urgent work at the beginning of the year, such as preparing conference papers etc., and so the real work had to wait.
In the meantime, a brand new SCU (Servo Control Unit) had been manufactured and tested, and new RAMA system, now fully operational, was mated again to the Freya helicopter. Hence the RAMA-Freya couple is now in the airworthy condition again. Currently, the Flight Readiness Testing Procedure (FRTP) is being executed. We are waiting for favorable weather to enable us resume flight-testing. For the next flight test, no major goals were set. Its purpose would be only to check and setup the helicopter after the crash, to test new hardware in anger and, should everything run smoothly, to carry out identification experiments in order to obtain data needed to re-indentify the vehicle mathematical model. It is hard to tell when exactly this flight test would take place, but it will be announced soon.
Because we would like to have an idea how many potential users are interested in RAMA, and also to monitor the number of downloads, we decided to require very simple user registration to enable our visitors to enter the Downloads section. As we do not want to bother anybody by requiring too much information, only one registration item is mandatory – valid e-mail address. All other items are optional and do not have to be filled in order to register. We hope that this type of form would not discourage anybody from registering. Please let us know if you encounter any problem with your registration, or if you find it too annoying .
This week, new EC (Electronic Container) was built, and the RAMA system was mated together. Some precautionary measures were implemented to better protect the hardware in case of an accident, and the EC internal structure was slightly altered to improve weight distribution. Those changes were accommodated into the 3.2 HW version.
The newly implemented electronic protection consists of couple of measures. Firstly, the MCC (Main Control Computer) was moved to a lower layer to improve its protection, as it is by far the most precious and expensive part of the system (excluding the IMU – Inertial Measurement Unit – but the IMU is compact and robust, and already well protected). In the previous version, the SCU (Servo Control Unit) was accommodated in the lowermost layer, and sustained only minor damage during the last accident. To better protect the PCB from disruption (as happened in the last crash), it is now underplayed by an EPP (Extruded Poly-Propylene) support layer (see the photo below). Also, the processor module is now supported by in a similar manner. The EPP is elastic but stable, and would support the PCB along its whole area (on the contrary to the spacer sleeves, which hold the PCB only by its edges). To obtain more room for the EPP layer, and to better dissipate vibrations, the PCBs are now supported by rubber silent-blocks (see the picture). Upwards, the MCC is protected by a thick foam layer, which is flexible and serves to dissipate the energy of the impact.
Unfortunately, during the Flight Readiness Test (FRT), which is always carried out before flight tests, the SCU (Servo Control Unit) was malfunctioning. The SCU was reused from the crashed hardware, as it sustained only minor damage during the accident, and could be fixed easily. At first it seemed to work properly, but it failed later, probably due to some hidden damage that could have been caused by the impact. For safety reasons, it was decided not to fix this unit anymore, but rather to build a brand new one. Obviously, the return-to-flight mission , which was scheduled for the next week, has to be postponed, as the manufacturing, burn-in and rigid testing of new unit requires some time. Due to the Christmas holidays, this work would start at the beginning of January. Therefore, should everything go according plan, the flight test could be performed sometime in the second half of that month, if weather cooperates.
Today, our Hirobo Freya helicopter was finally brought back to airworthy condition. New electronic container shall be manufactured during the next week. The return-to-flight flight tests are scheduled to take place in the second half of the December, if weather allows.
New parts have arrived today. We have received brand new blades from our sponsor KOK Composite, and also new Li-Poly battery pack for on-board electronic. The old one was scrapped, although it seemed to bee OK, for safety reasons (it was bent in the accident). The NiCD pack, which was damaged by the impact, is now fixed.
After the horrendous crash from the 8th November, the RAMA system, like a Phoenix, arose from its ashes and is up-and-running again! Now we shall cure the helicopter as soon as spare pars arrive.
Lessons learned. One of the main reasons of the crash was that the pilot did not manage to switch the autopilot off in time, due to ergonomic problems (the appropriate switch on the transmitter was not so easily reached; one had to put a hand off the control sticks in order to reach the switch). Hence the crucial switch was moved to the top of the left control stick, to improve the ergonomics. To prevent accidental switchover, the switch had to be unblocked prior to operation. When blocked, the system remains in manual control mode in all cases.
Requiem aeternam dona ei, Domine:
et lux perpetua luceat ei.
Te decet hymnus, Deus, in Sion,
et tibi reddetur votum in Jerusalem:
Exaudi orationem meam,
ad te omnis caro veniet.
Unfortunately, sometimes thinks might go wrong... Today, during the 3rd flight of the day, the pitch rate stabilizer had shown particularly poor performance, sending the helicopter down to the ground. The pilot (OK, it was me ) did not have enough time to react (I know it’s no excuse. OK, it was my fault. Yes it was. Any more questions? Grrrr…. ) and did not manage to take over the controls in time. Cause of the controller misbehavior is not yet known. The flight data were recorded up to the moment of impact and are to be investigated. The 3.1 hardware revision worked as expected, solving the electromagnetic interference problems. The roll rate stabilizer that was tested in the course of the second flight had shown promising performance.
The maiden flight tests of the improved hardware revision (3.1) are scheduled for tomorrow. Also, new controllers are to be taken thru their paces.
Today, we had the privilege to welcome a very special guest. Professor Horst Störmer, the 1998 Nobel Price winner for physics, came to see the RAMA in flesh, in the course of his visit to our university. He praised our work and we had a nice chat.