Starting a new thread to show what I'm working on. I'm building a new Octocopter of my own design. The goal is to use it for Aerial Photography, lifting a mid-weight camera such as a Sony Nex5. It will of course be using Arducopter for control. ;)
I started off researching the various kits on the market, and starting getting analysis paralysis. I looked at all the options such as Droidworx AD8, Cinestar, CarbonCore, and SteadiDrone. But I just wasn't happy with the design on them, particularly for the price they ask. Combined with the fact that I can be pretty frugal, and have a strong DIY ethic, I decided to just design my own.
The basis of the design relies on many of the Hobby King quadcopter parts. I liked the design of the motor mounts, they are very professional looking, even compared to some of the high end machines. And I liked that the boom mounts are blocks of aluminum instead of plastic. Very rigid. I also liked the look of the dome on their H.A.L. quad, but since they don't sell it seperately, I bought the whole kit, it's only $34, amazing! I might end up using the rest of it someday, who knows? So, I basically emptied out their stock of Talon parts, so if you need to fix your Talon quad and the parts are backordered... sorry!
Once that was settled, I set about designing the center frame. My design required a few things, namely I want all the wiring hidden. I don't want any spaghetti showing. Particularly with the ESC's, while still allowing cooling airflow. This required the center hub to be larger than is typical. I then needed a smaller subframe to house the avionics.
You can see these plates below. The larger one houses the HAL dome. You will notice the 3 blue anti-vibration grommets in the middle. This is the APM1 pattern. I did that just because. Maybe I'll use an APM1 as a stand along gimbal controller. The second plate had grommet mounting for an APM2. The final plate is the top plate, and has bolt patterns for the Ublox GPS and the magnetometer.
This next photos shows the avionics frame built up with an APM2 mounted. 25mm aluminum standoffs are used. I don't like the plastic standoffs typically used. They get loose, and lead to vibration. They also break easily. This structure ends up being quite rigid.
Here is the avionics frame mounted on top of the main frame. Yes, the main frame is HUGE. I actually don't see the point in having a tiny center frame, and then long arms. This seems like it just leads to flex, and doesn't leave you with any real estate to mount your avionics.
This photo shows one of my design features. I put some cutouts on the bottom frame for weight savings, and then made matching cutouts on the top frames. This creates some nice conduits to run wires neatly.
Here it is with the HAL dome mounted and one of the Talon arm mounts bolted in. I'm really happy with how stiff the assembly is already.
Here it is with one of the arms mounted. These are the short 220mm arms, I also got some of the 320mm arms. One may wonder how I'm going to get away with such short arms and 13" props.... Astute readers will know what I'm planning already. ;)
This last photo shows one of the ESC's in position. This is a Hobby King F-40A, it's somewhat larger than typical 20A units which is partially why the frame is so big.
That's it for now. I had the plates cut out of aluminum to start with because it's cost effective. If it all works out, I'll probably have it redone in carbon fiber plate for the weight savings. I was a little uncertain about the weight, but it looks like the frame will come in at 1070g all in aluminum. That's about 300g heavier than a Droidworx AD8, but not too bad. It will drop about 1-200g if redone in CF.
Replies
Rob,
How are you finding the performance of this octo? I'm torn between this and a coaxial octo. Also, are you in a + or x configuration?
Thanks,
Barry
I disconnected my R motor ESC to do some testing with just 7 motors and it definitely doesn't do what I would expect. This is my first experience with an Octo but I assumed if one motor/prop failed it would at most jerk a little and then the remaining two props on either side of the failed one would just compensate, assuming there is another available power. So I unplugged the 3 o-clock ESCs and tried to take off. I'm in + mode. It would hover alright with about 60% throttle but you had to give it left roll. If you let go, it would not stabilize. It would just keep moving fairly quickly to the right. I was in stable mode and with all 8 motors it hovers perfectly. The new auto trim on ch7 was a great idea!
What concerns me is that in one situation this happened at about 100 meters distance and the reaction of it made me lose perception. I didn't have direction lights on it yet so it was a bitch to get back and make a nice landing because I got confused because it wouldn't hover. When you let go of the rollpitch you expect it to more or less hover unless you are dealing with wind. Probably the best thing to do in case of a motor failure is hit RTL but it should also fly normal in any mode.
So what could be causing this. Has anyone here tried to take off with one ESC unplugged? Does it hover, just using more throttle or does it lean?
Rob, I want to try some other propellers to see if I can increase the efficiency. I had one of the CF props break at the roof from a tipped landing. They are not as strong as the look. Fine if it never strikes anything but I think I want to try the APC's. I've only heard good things about thing. What would you suggest in size and pitch to maybe increase my efficiency. I have the same motors you have. Now I'm using those 12x6 CF props. Flies great. I just want something more durable and efficient. I will only be using this copter for filming.
Some other chances to experience what would happen if I lost a prop. If you remember, I changed out some very stiff wire a few weeks ago that was causing the solder joint to the ESC to weaken. I replaced all but just realized I forgot to replace one and it started giving problems today. It was only a couple of meters off the ground and I saw the prop stutter and stop and it tilted and started moving in that direction. I compensated but shouldn't it just level like if I had all 8 running? Every time I've had a motor failure like that, it's done the same. I saw this through various types of tuning. Today I had the RP and RD on the tight side RP .2 and RD .014. It's very sticky in the air but no oscillations.
Every time this has happened I've had trouble landing because it feels like it's missing thrust on that side. I thought the other 2 motors would compensate within a second or less so that it was unnoticeable. I'm going to take off one of the propellers (or is it better to unplug it's signal line?) and see how taking off with 7 is like. It shouldn't feel much different?
Just had a motor mount break on me. Luckily I was just taking off for some more tuning and was only half a foot off the ground. I think if it was higher I'm not sure what would of happen with the motor flopping around like that. It put a nice gash in the boom just with a few wacks.
BTW, what happens in a situation where you lose a prop. I'm very familiar with how it works in a quad :) and usually kill the throttle right away but with the octo it's not necessarily going to fall so the throttle will stay up and even more so since you only have 7. If it's just a propeller that has broke then would the motor go to more or less full speed since it doesn't know it's prop-less? Just wondering if that would heat up the motor at higher rpm on that one motor. I think though if this was higher up it would have been interesting to see if it could survive that type of thrashing on one arm.
Probably this mount was one that got slightly bent in a hard landing.
Rob, did you find any stronger mounts? I think I want to replace all these.
These are the type I have.
http://www.hobbyking.com/hobbyking/store/__25115__Turnigy_H_A_L_Mot...
Having a great time flying this beast!! I still haven't had a chance to finalize the tuning but it's flying great nonetheless. I was having a bad vibration issue that was coming from the front motor or prop, when I pushed the throttle, so I started changing it out starting with the prop, then the collet and finally the motor but it didn't solve the problem. It just does it when I crank the throttle or yaw left or right. I finally realized it wasn't a motor at all. It was the boom itself shifting left and right in it's mount between the two CF plates. Screws on the bottom were not tight enough. I tightened them all again but still get this vibration, just not as much. I need to find a way to make them secure there. The screws are not enough. I was thinking to put some strong double sided tape on the bottom of the boom mount. Rob, maybe you didn't have much issue with this because your booms were 160mm and mine are 320mm. If you have some better ideas about locking in the booms, I'm all ears :) It really causes the APM to freak a little.
I need to do something about the flight times also. Without the rusticwave gimbal and camera, I'm getting 10 minutes before one of the beepers goes off meaning it's reached about 3.6V per cell. For now my battery monitoring is just 4 of those $2 HK 2-4S beepers. I'm concerned that with the extra weight of the camera and gimbal, which is about 1 kilo, I'm going to have very short flight times. Rob, what were your flight times usually? I was hoping to get at least 10 minutes or 15 :) I know I could add more batteries but I'm already at 3300-4S x 4 so 13.2 amps of 4S.
I had a prop slip loose on me today so I got to experience a SeteCopter. I was able to land but it wasn't very easy and I didn't even have the camera or gimbal weight. It wasn't that I didn't have the power. Without the gimbal and camera I hover at about 45%. The problem was it was hard to control in terms of orientation. IOW I couldn't fly it normally. Just had to find a quick landing spot and sit it down. Just some small damage on the landing gear.
I was trying to discover if a motor vibration I was having was due to a prop or motor so I replaced the prop but didn't lock tight the collet because they go on so stiff anyway and I also had it really tight. Never will skip that step again. :) But I worry about getting this thing back if it happens further away and with the camera and gimbal weight. Is it normal in this case to lose some yaw control if you lose a motor or prop? I was thinking I could even stay aloft with 6 motors.
For the landing gear I'm looking to double up on the standoffs (a suggestion from quadframe.us) or get these from fox. They are telling me it will support 6 kilos. I plan to use 4. I think attaching it near the center plates where the booms start would be more stable.
http://www.foxtechfpv.com/landing-gear-for-fhh800octo800-p-563.html
Looking for legs like this.
http://www.makerbot.com/blog/tag/octo-copter/
Good and stiff ones. Know of any good ones?
Thanks Rob. Yes I was rocking to check if it was moving in the correct direction. The first few flights I had it in X mode instead of + mode. All my other copters are in X but I decided to do this one in +.
I have Stab P set to 3.0. I was going to do some tuning today but smoked an ESC. Changing that and will start the tuning tomorrow or get a few flights in tonight. I like those 8400 3S but would prefer 4S. I think I will get 2 packs to test. I can always use on a plane :) With the 4 extra 3300-4S on the legs, to simulate the camera weight, it hovers at close to mid stick so I guess that is about right. Not sure how much throttle I would need to give it with 3S but maybe that would leave me a little weak in emergencies or against a strong wind. BTW, I thought 4S would be more efficient considering equal mAh. The higher voltage I think increases efficiency a little.
No chest rig but a steady hand. The location is my place and a great practice location. I only have to worry about falling in the forest which usually means a lost craft even if it's nearby :) I have 4 or 5 out there somewhere :)
The legs though will have to be replaced. It just wobbles the way it's connected to the center of the quad. I need to connect near the point the booms enter the center piece to give it a wider gait. I'm thinking to use 4. Do you know of anyone selling that type of leg? They would all be the same with a type of connector to the boom. Then the gimbal I would hang from the battery tray like it is now. I would just remove the old legs but keep the center connection of the legs to hold the battery and support the gimbal.
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