Designing a heavy-lift octocopter with Canon 7D gimbal

Hey guys,

First post here, but I'm a longtime DIYer (hovercrafts, stereos, LCD projector, gokarts, vintage cars with big engines in them, CNC machines etc etc). I'm a 27 year-old mechanical engineer, and a little rusty on electronics, but I get by.

I've been commissioned to build an octocopter for a friend of mine, and I've got two questions:

#1, do you see any foreseeable issues with the setup listed below?* is there anything that I'm missing?

#2, I want to run a gimbal for a Canon 7D; what do you recommend for controllers/rigs? a two axis, auto level, would be sufficent - with an ability to gently change the pitch on command from the ground. the yaw will be controlled by the aircraft rotating. the roll is useless, and should be completely auto-levelled. I could build the rig and rewind the motors myself, but I'd rather spend my time elsewhere.


*Here is the planned setup:

Multiwii controller:
http://hobbyking.com/hobbyking/store/__31138__Multiwii_and_Megapira...

eight motors:
http://hobbyking.com/hobbyking/store/__26963__Turnigy_Multistar_422...

eight controllers:
http://hobbyking.com/hobbyking/store/__25366__Turnigy_Multistar_45_...

right hand props:
http://hobbyking.com/hobbyking/store/__28289__Slow_Fly_Electric_Pro...

left props:
http://hobbyking.com/hobbyking/store/__28288__Slow_Fly_Electric_Pro...

TWO 8000 6s batteries on board:
http://hobbyking.com/hobbyking/store/__18210__Turnigy_nano_tech_800...

charger:
http://hobbyking.com/hobbyking/store/__20613__Turnigy_MEGA_400Wx2_B...

power supply to go with the charger:
http://hobbyking.com/hobbyking/store/__20611__Turnigy_1080W_100_120...


I punched this info into http://www.ecalc.ch and came up with some pretty good flight times (15-30 mins) with 2kg of payload. I'll be using his transmitter/receiver taken from a Blade 450

thanks,
Sim

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the frame will be made of extruded square tube aluminum, and it will have an onboard parachute as well. 

That's a great goal project, but I'd recommend getting into it more slowly.

If I were you I'd be trying to build your own smaller, cheaper quad first before launching into the big guy. If you get one thing wrong you'll have a crash or a flyaway, better to learn those lessons on something less expensive+dangerous.

thank you Andrew for being entirely useless.

All the parts are being purchased by a friend of mine - I am designing and constructing it. As he plans on using it for filming gigs, finances are not such a constraint. I could jump into the learning curve with a quad, but then once I've learned everything... I've got a quad which is useless for professional filming. I might as well just build an octo, which requires the same controller, and at the end of it, have something useful. 

I didn't ask for a risk analysis. I asked two questions that for anyone who has built a multi-copter would know immediately off the top of their head. now, I thought I came to the right place for multi-copter advice and direction - but perhaps there are no multi-copter DIY people on DIYDrones.

I'm building an octo with same motors also for a canon 5d mk2. I've not flied yet but i've almost finished. 

I plan to use wood props 13x4.5 gemfan, more stable I think. 2 x 6000mah 5s batteries.

My frame is 100% DIY, 13mm alum square tubes and CF plates., about 980mm diam.

Hey Juan

Your Octocopter is looking promissing ... I have just posted a topic on do's and dont's on getting in to this.

I too have a 5D I wish to take airborn, but as safe as possible.

Would you be willing to tell/teache from your experience.

Kind regards Jakob

great looking chopper! I'm excited to see how it goes!!

do people have project threads on here, where they outline all the equipment they've put into their choppers? I'm curious to compare components with other people, and see what has worked, and what hasn't. I'm looking forward to reading your thread Jakob.

Simeon,

you probably didn't mean to, but you sounded pretty arrogant.. Just thought I'd give you some feedback. We, DIY'ers, are usually very friendly :) From some point of view Andrew is right - not knowing background of the asking person I'd always suggest same thing. Learn first on cheap stuff and then go spend more :)

Now assuming you're not complete rookie, let me try to answer your questions :)

With regards to if you're missing something..

1. I would definitely look for ways to add at GPS/Compass (not sure if multiwii supports it?). Position hold etc are good, but RTL for TX/RX failsafe is *necessary*, IMHO

2. Video tx/rx is something you will definitely need, if you're serious about aerial video/photo.

3. Camera triggering (if you're planning photo) - not sure if multliwii has it built-in?

4. Power distribution board - unless you will make one yourself - simplifies a lot

Controller/Rig for 7D - depends what do you want to do. For photo - take more or less any available servo-based gimbal. It's much more complicated if you're planning to shoot video - I would suggest wait a little bit to see something good and brushless for 7D-size camera on market. There are many DIY examples working really nicely, but I really can't name one being for sale (and in stock) already..

thx,
jk

thanks Jaan,

See, the problem is that I asked for two precise questions to be answered, and I've shown that I have the capability to build one of these, and Andrew advises me to not build what I intend to build. It would be like me driving up to someone on the street and asking for directions to a store, and his response is "oooohh, well, I don't think you should be driving that car right now - it looks pretty dangerous". I didn't ask for that. I asked for directions. I'm a mechanical engineer, I've worked on many electro/mechanical projects, and someone else is paying for the parts - I am very aware of the risks involved. If I were to build and fly a quad, I would purchase the same motors and ESCs, control board, batteries, charger etc; so what money would I be saving? the cost of 4 motors and ESCs? As for the controller; it is the exact same. So how would it be "easier" to build and fly a quad?

As for your recommendations, they are very good. I'm going to start searching google for for answers, but have you seen GPS/compass piggybacks for the multiwii board? the main purpose for the rig is video; and as both the camera, and the copter, have limited air-time, it may initially be a matter of hitting record on the ground, and then sending it up. Eventually I'll have triggers for record/stop, and possibly zoom etc. As for power distribution; I'll probably just be crimping wires together. or have a home-made bus-bar.

Do you know of any good kits for video transmitting to the ground? I've seen something where they have an overlay on the screen for battery voltage, direction etc - what is that called? I've closed the browser tab that had the demonstration I had found.

So it seems like I'll be adapting an existing gimbal camera rig to fit the larger 7D. if anyone is familiar with the multiwii, is there an additional channel available to send pitch control to the gimbal from the ground? when people build these rigs, do they have separate control over the camera's yaw, and then have a separate transmitter/receiver to control all camera movement?

Is there not a project thread where someone has documented a octo-copter build with controllable gimbal?

Hi Simeon,

I am also doing something similar for a 5DmkII. From your information I don't see the weight of the gimbal or air frame.

I'm using a Vulcan 1200 Octo frame with Tiger Motor MT3515-15 motors, turnigy plush 40A esc's and an AMP2.5 Mega controller. I've had 2 successful test flights but there is a lot of tuning and I really have to learn how to fly. I have damaged a few props already so I decided to buy a kit of spare parts and build a quad on a smaller frame from these spares to learn how to fly first. At least if I ever damage the large octo I can take a spare part straight off the test quad. The quad is also less expensive to repair so I'm learning all the small details of the software and tuning on this first.

For all my testing I'm using 13x6.5 APC props without any additional load so the copter takes off nicely at around 50% throttle. What I've noticed with these is they flex a lot under high throttle, but for initial testing they'll be fine. Under heavy load the flexing will reduce the efficiency of the props so I will switch to larger carbon fibre props when I have the camera and gimbal mounted. I suspect you'll also have the flexing issue under heavy load with the props you have selected.

My next step now is to work out the best gimbal to use with this.

Hope this helps

D

Thanks Darren, that does help. I mentioned that in the simulation I had budgeted 2kg for additional weight. With the setup I made, I can comfortably fly with more (according to the numbers). That's helpful to hear that the props flex significantly enough to hinder performance.

When it comes to tuning; I may just string it up such that it can't hit a prop. I'm also buying twice the amount of rotors for starters in case I chew through them.

Out of curiousity, with the motors and rotors I've selected above; do they just bolt straight together? or do I need some sort of additional coupling?

Let me know when you've sorted out the gimbal. there's a lot of people who are DIYing it (rewinding the motors by hand etc), but I haven't found any off-the-shelf kits for a larger camera. Although I have many hobbies that I spend a lot of time investing in, because this is for someone else, the more off-the-shelf stuff I can find, the better.

"I've been commissioned to build an octocopter for a friend of mine, and I've got two questions:"

I don't have any specific answers to your questions, but, does your friend have any experience flying multirotor aircraft?  Will a total-loss crash be the end of the friendship?  In my limited exposure to multirotor aircraft, when learning to fly, you will crash.

At least use a dummy camera weight while doing your tuning and test flights.

> In my limited exposure to multirotor aircraft, when learning to fly, you will crash.

Particularly during the tuning phase and testing/tuning the stabilize/land/alt_hold and RTL modes.

 

For example, last week I had checked, double checked and tripple checked everything. GPS lock was perfect, position hold was perfect, GPS home position was perfect (according to my GCS) but as soon as I selected RTL (return to land) it flew off in completely the wrong direction at speed and took a dive straight into the ground. Before I even think about the gimbal design and attaching the camera I have a 6 month plan of testing and trialling first.

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