I’m completely new to this and a complete no-know about electronics but I have a few questions not related to a typical UAV.
For reference and typical for 2 stage recovery.I launch rockets in The Netherlands and as a side project I want the rocket to be recovered by a steerable parachute and returned to a fixed waypoint. Preferable this waypoint would be right next to the launch pad. Basically the return-to-launch (RTL) feature of the ArduPilot.The rockets are launched twice a year on a military shooting range with restricted airspace and typically achieve heights between 1500 – 2000m. Because of wind, the rockets have either a small parachute for a rapid decent or drift for several km from the launch pad. Ideal situation would be a parachute that could steer / circle the rocket back to the place where it was launched. Two main reasons: 1) safety, 2) higher flights possible with less drift.RC is not an option because at 1km the rocket under chute is hardly visible.I have a 3 stage plan of approach:Stage 1) Proof of principle - by means of building a prototype and launch it from a RC plane. There is an organisation which does just that: www.rc-parachute.nlStage 2) Single stage recovery of a test rocket from an altitude of +/- 1km. All pyro events are triggered by means of a RDAS tiny.Stage 3) Dual stage recovery from an altitude of 2 km. First a small drogue is released for a rapid but controlled decent to 1km after which the steerable parachute will be deployed and the ArduPilot should take over. Again all pyro events will be triggered by the RDAS.A few questions arise:Stage 1-21) I think I figured this one out already but is it possible to have an independent direct power supply which does not go through the ESC?2) Can the unit be switched on/off by means of a physical toggle switch next to the unit and not through and RC receiver?3) I will not be using IN 1 & 2 on the ArduPilot. Does the unit still function? Basically all I will be using is the rudder servo to control the steering of the chute. The rest is not used.4) I have the possibility to get a GPS lock when the rocket is at the launch pad and the GPS receiver is out (for reference see photo below. Before launch, I have to put the receiver into the aluminium or carbon fibre rocket. There it will lose GPS lock and only after apogee when the parachute is out the GPS receiver is hanging free again and able to get a lock again. Is this possible? How long would it take for the GPS to get a new lock and does the ArduPilot remember the first GPS lock thus returning to the launch pad (the unit is not switched off)?Stage 35) Experience proves that when the rockets rapidly descents under the drogue chute only it rotate on its longitudinal axis even if swivels are installed in the lines. Is the GPS receiver still able to get a lock when, for example, it rotates at 1Hz on its own axis?Looking forward to your comments and I thinks this will be quite a fun project.JurriaanPS - I’m not trying to make the next DIY cruise missile (there is a distinct difference between a rocket and a missile as my rockets lack guidance).For more info www.nerorockets.org or my personal site www.verticallimits.nl
Thank you for showing interest in this project. I must note my RTL project is currently moving at a slow pace. At this moment I have a working easy star with the ardupilot for about half a year now. I would definately recommend you to take this approach to make sure your ardupilot is working / set up correctly and it is quite a learning experience. Further more I have recently purchased 2 of these parafoils: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=... - as the reviews are quite good & http://www.hobbycity.com/hobbycity/forum/forum_topics.asp?FID=75 for your information. So for the future I have to make a motorized pod / cart to get the parachute and ardupilot up in the air and do more testing with the PID values for the parachute. This is were I'm at this moment. I have yet to test the ardupilot & airfoil together. Although I have flown a friends parafoil in the past and I think it is possible to have an Ardupilot mounted on them. However I have no clue yet how to activate the Ardupilot without an RC Tx/Rx as that would be necessary in a HPR rocket. But to many project at this moment as I'm still busy with my rockets and just started an FPV easystar project the RTL has been but on the back burner. So many cool project so little time. Good luck
JvcB, any updates on building a guided recovery system for high power rockets? I've recently got into HPR and really would like to incorporate a return-to-launch guidance system into the 2nd stage main chute.
Yes, it's all interesting stuff and I think sharing knowledge is key to success. I had thought that a degree of free fall of the payload under a drogue before opening the main was a good strategy as it meant a quicker return and therefore less drift. It does pose so significant engineering problems though :)
Ed, I'd love to drop by and participate in a launch. I've read around quite a bit and i'm aware of the CU projects and your successes! Congrats on all the mainstream press the teddies got :)
I'll second the idea to get a discussion underway that wasn't hijacking JvdB's thread! I've got access to a good webserver where i can host a group blog or wiki, but I would suggest that meeting on the #highaltitude irc channel (see Ed's post above) would be a good place to start. Ed, how often do people get together on IRC? There is also an excellent source of (UK-centric) information at http://www.ukhas.org.uk/ where I have been lurking for what feels like an eternity! I'd like to participate and share with that community when I have something worth talking about.
Ed, I also had a look at your summer job :) Thats awesome stuff. I still think that the MER (Spirit and Opportunity) EDLs were some of the most exciting 8 mins I've ever seen. Certainly an inspiration for my project.
Funny enough, I am also working on a project very similar to this for HAB's.
Guys, one thing to keep in mind is that at altitude, the air density is not enough to inflate most parachutes, much less a ram-air parachute.
I have been given data from the adviser for a balloon group in GA that shows 3-axis acceleration values and rotational rates as the flight progresses. You can clearly see where the balloon is disconnected. The parachute on this design was attached directly under the balloon so it 'deploys' as soon as the balloon disconnects the chute is out in the (clean) airstream. The data shows the payload comes down with almost no speed reduction and rotates very very fast and in a very unpredictable way. It is also interesting to see at how low of an actual altitude the chute becomes effective.
If you intend to use some form of parafoil, you will have to have something that deploys when the balloon is released to stabilize your platform and then deploy the parafoil at a certain altitude.
Doing this will also help mitigate any unwanted drift on the way down, but you will still have to deal with drift on the way up. This can be partially combated by adding more helium to your balloon to increase the accent rate, just beware you don't inflate it too much, else you risk a burst at too low of an altitude.
My current plan for high altitude deployment is a ballute of some kind. Depending on how the ballute is implemented, it will either function on its own, or in conjunction with a drogue chute that will act as the drag needed to deploy the ram-air.
Also, keep in mind that while a ram-air is basically a wing, you have limited control. Steering can be added on the left/right TE of the chute, but AoA must be set by how the lines are attached and connected. This can be troublesome as turning into the wind can create problems since you don't have a human body to adjust and 'braking' a canopy can be challenging.
Ya know.. with so many of us working on this idea.. maybe we need to start our own area somewhere...
I have given this some thought also over some years, but I tend to end up having the best solution being a steerable rocket on return. If you give it some more control surfaces and put servos on them, and then have an altitude trigger on a normal chute you should be able to get it down fairly accurately. So once the rocket reaches apogee it should activate guidance, and then aim for a circling glidepath above the launch pad, and once it is low enough it should patternfly to loose as much speed as possible, and then at a lower altitude deploy normal slow descent chute after a drouge to get it in the right position.
I do not know if this would be legal tho, but I think it would also have a shorter return to base time than a chute deployed high up instead of gliding down "heavy".
Incidentally I am also in the Netherlands :-).
I notice you're from London. If you want to come to one of our near-space launches here in Cambridge, you'd be most welcome. There are some people other than us working on near-space recovery systems too. Can I recommend the #highaltitude irc channel on irc.freenode.net? Most of the UK's near-space balloon launchers can be found there.
I do near space stuff myself (cuspaceflight.co.uk). I mainly do electronic and control, but also specialise in recovery after a pretty educational summer job (vorticity-systems.com).
So, your projects are pretty close to my heart! You'll notice the 'meteor' project on our team page - it's precisely what you're describing. It's been on the back burner a bit as all the effort is going into Martlet and Aurora at the moment.
Control - it's harder than fixed wing because the parafoil (or whatever) is not rigidly coupled to the inertial measurement system that the flight computer uses. It's flexible, it vibrates, it twists. The suspension system has lots of oscillatory modes.
This means you have lots of added crud to filter out. Starter for 10: commanding a bank angle rather than a turn rate is a good thing to do. One is a function of the other, but a bank angle is subject to less noise than a turn rate.
Other problems. The 'added mass' effect of parafoils. Fairly complicated aerodynamics, but essentially a parafoil accelerates both itself and the air around it when deployed. If there is no air around it (in near space) you end up with a moment that causes the parafoil to drop forward relative to the payload, and eventually it will wrap itself around the payload and you have a problem. Simulations for parafoils on Mars, with its thin atmosphere, found the same result. It's a no-go. You'll have to get some decent dynamic and static pressures going before you deploy a parafoil.
Batteries are fine. Put everything in a polystyrene box - it can easily be kept around freezing. If the batteries have to dump some juice into actuators, they'll quickly warm up too.
Heh, funny you guys should mention near space stuff - that's what got me interesed in drones - I was trying to think of a better way to recover your weather balloon payload, then thought "why not just make the payload fly itself back to the launch side? Wonder if anyone has made self-piloting systems" then on to Paparazzi, then to DIYDrones and ArduPilot. One thing I am wondering about is how will the batteries work at that altitude? I assume if they are wrapped up enough and not exposed for long enough you should be OK, but if you're talking about an hour long "flight" and you loose your charge b/c the battery gets too cold, your gliding return module could now fly hundreds of miles off target if you are really unlucky!
I will use a ramp air parachute or parafoil. The idea of a kite crossed my mind and it will be a fast and cheap solution during prototyping.
Maybe one of you guys can explain to me why a parafoil is that much different to control than a RC plane with a rudder only autopilot? The parachute will have forward motion (not as fast as a RC plane but that is good with the 1Hz GPS refresh rate. It will only loose altitude but that is the whole idea and I do not want to maintain altitude as with and RC plane. I only want to use left and right motion which a rudder only autopilot just does on a RC plane.
Jim - your goal is the same as mine, looking forward sharing info together
I'm attempting the same thing but for high-altitude balloon payload recovery rather than rockets. I'm also planning on using a large single line delta kite as my test platform to drop the payload from rather than an R/C plane. Right now i'm working on some of the servo and radio software using processing and the arduino. Arduipilot will be a natural progression for me when i go autonomous. i'm trying to document my progress over at http://jimblackhurst.com/wiki. I'm looking forward to seeing your progress!
Comments
Yes, it's all interesting stuff and I think sharing knowledge is key to success. I had thought that a degree of free fall of the payload under a drogue before opening the main was a good strategy as it meant a quicker return and therefore less drift. It does pose so significant engineering problems though :)
Ed, I'd love to drop by and participate in a launch. I've read around quite a bit and i'm aware of the CU projects and your successes! Congrats on all the mainstream press the teddies got :)
I'll second the idea to get a discussion underway that wasn't hijacking JvdB's thread! I've got access to a good webserver where i can host a group blog or wiki, but I would suggest that meeting on the #highaltitude irc channel (see Ed's post above) would be a good place to start. Ed, how often do people get together on IRC? There is also an excellent source of (UK-centric) information at http://www.ukhas.org.uk/ where I have been lurking for what feels like an eternity! I'd like to participate and share with that community when I have something worth talking about.
Ed, I also had a look at your summer job :) Thats awesome stuff. I still think that the MER (Spirit and Opportunity) EDLs were some of the most exciting 8 mins I've ever seen. Certainly an inspiration for my project.
Jim
Guys, one thing to keep in mind is that at altitude, the air density is not enough to inflate most parachutes, much less a ram-air parachute.
I have been given data from the adviser for a balloon group in GA that shows 3-axis acceleration values and rotational rates as the flight progresses. You can clearly see where the balloon is disconnected. The parachute on this design was attached directly under the balloon so it 'deploys' as soon as the balloon disconnects the chute is out in the (clean) airstream. The data shows the payload comes down with almost no speed reduction and rotates very very fast and in a very unpredictable way. It is also interesting to see at how low of an actual altitude the chute becomes effective.
If you intend to use some form of parafoil, you will have to have something that deploys when the balloon is released to stabilize your platform and then deploy the parafoil at a certain altitude.
Doing this will also help mitigate any unwanted drift on the way down, but you will still have to deal with drift on the way up. This can be partially combated by adding more helium to your balloon to increase the accent rate, just beware you don't inflate it too much, else you risk a burst at too low of an altitude.
My current plan for high altitude deployment is a ballute of some kind. Depending on how the ballute is implemented, it will either function on its own, or in conjunction with a drogue chute that will act as the drag needed to deploy the ram-air.
Also, keep in mind that while a ram-air is basically a wing, you have limited control. Steering can be added on the left/right TE of the chute, but AoA must be set by how the lines are attached and connected. This can be troublesome as turning into the wind can create problems since you don't have a human body to adjust and 'braking' a canopy can be challenging.
Ya know.. with so many of us working on this idea.. maybe we need to start our own area somewhere...
I do not know if this would be legal tho, but I think it would also have a shorter return to base time than a chute deployed high up instead of gliding down "heavy".
Incidentally I am also in the Netherlands :-).
I notice you're from London. If you want to come to one of our near-space launches here in Cambridge, you'd be most welcome. There are some people other than us working on near-space recovery systems too. Can I recommend the #highaltitude irc channel on irc.freenode.net? Most of the UK's near-space balloon launchers can be found there.
Ed
I do near space stuff myself (cuspaceflight.co.uk). I mainly do electronic and control, but also specialise in recovery after a pretty educational summer job (vorticity-systems.com).
So, your projects are pretty close to my heart! You'll notice the 'meteor' project on our team page - it's precisely what you're describing. It's been on the back burner a bit as all the effort is going into Martlet and Aurora at the moment.
Control - it's harder than fixed wing because the parafoil (or whatever) is not rigidly coupled to the inertial measurement system that the flight computer uses. It's flexible, it vibrates, it twists. The suspension system has lots of oscillatory modes.
This means you have lots of added crud to filter out. Starter for 10: commanding a bank angle rather than a turn rate is a good thing to do. One is a function of the other, but a bank angle is subject to less noise than a turn rate.
Other problems. The 'added mass' effect of parafoils. Fairly complicated aerodynamics, but essentially a parafoil accelerates both itself and the air around it when deployed. If there is no air around it (in near space) you end up with a moment that causes the parafoil to drop forward relative to the payload, and eventually it will wrap itself around the payload and you have a problem. Simulations for parafoils on Mars, with its thin atmosphere, found the same result. It's a no-go. You'll have to get some decent dynamic and static pressures going before you deploy a parafoil.
Batteries are fine. Put everything in a polystyrene box - it can easily be kept around freezing. If the batteries have to dump some juice into actuators, they'll quickly warm up too.
Maybe one of you guys can explain to me why a parafoil is that much different to control than a RC plane with a rudder only autopilot? The parachute will have forward motion (not as fast as a RC plane but that is good with the 1Hz GPS refresh rate. It will only loose altitude but that is the whole idea and I do not want to maintain altitude as with and RC plane. I only want to use left and right motion which a rudder only autopilot just does on a RC plane.
Jim - your goal is the same as mine, looking forward sharing info together
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