Hey Everyone

I've been messing with making a quad to carry a GoPro for indoor commercial use. I wanted one that was not necessarily 'finger safe' but 'impact safe' and after several iterations including a 'Bucket Copter' (Yep made out of kids toy buckets - Flew for 15 seconds then never stayed up again) I hit on the idea of using 8" PC Fan Guards mounted on Poly Screws to solve the issue.

I started with the super cheap frames from China. The current version has Emax MT2213 motors and 30amp ESCs. The mount for the GoPro is two Carbon Sheets and dampers with ear plugs in them. Its Rock Solid to the frame so needs smooth control but the platform is very stable in itself. APM 2.5 Board of course. LiPo 2200mah 4S 45c Battery. Props are 3 blade 6". Flight time is currently at 8mins to about 25% on the battery

My problem is that I have no fabrication or design experience but have a degree from the university of 'How Hard Can it Be?' Right now its getting pretty hard. The ESCs get pretty hot as do the motors after about 8mins. I'm pretty much tied to the 6" props because the largest Fan Guards I can find are 8". I want to go to bigger motors but am restricted to the props size and weight increase quite a lot with the Turnigy series. The other issue is that bigger motors are making the gap on the guards over 50mm and the screw system is only rigid up to that distance (broke a few)

I moulded some guards out of plastic but they were incredibly brittle and reduced airflow quite a bit. Also they weight benefit was not enough to get worried about.

So...any suggestions as to how to get this thing to have more grunt, not start smoking, have bigger props (with bigger guards) and more. I'd be grateful of any input you guys can have as I've hit a bit of a brick wall. Nothing I try at the moment improves on the current spec. Total cost of the rig was around $250 so I have a little more budget to throw at it but the aim was to come up with a viable rig I can use for work that wasn't the cost of my DSLR Octocopter.



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Comment by Magnus von Rosen on August 11, 2013 at 1:00am

* 30 Amps sounds like a lot for such a small rig? Have you measured the amps the motors draw with those props? 

* Maybe if you put the ESCs under the props, strapped to the bottom fan guard, flat side up? That would probably double the cooling capacity.

* A smaller battery might help, I expect it is a big part of the load? If you are getting 8 minutes on 25% of the capacity, you could probably get 15 mins out of a 1200mAh battery = half the weight?

Other than that: Cool project!!

Comment by Tero Koivunen on August 11, 2013 at 1:02am

I think you need bigger prop or higher kv motor. (Emax CF2812 etc.)

Low kv and small prop means that motor/esc are not in "comfort zone" -> bad performance.

4s battery is also little bit overkill, 3s shoud be enough.

Comment by CliffN on August 11, 2013 at 1:08am

3s 5300mah and 850KV-950KV is what im currently using. but you could use 1300KV-1600KV on a 7-8 inch prop

Comment by Ewen Rankin on August 11, 2013 at 1:18am

Great comments Guys. With the guarding it means at the moment I am stuck with 6" 3 blade props. I get more lift with the 3 blade and its way more stable

3S batteries don't lift it at all, the revs on the motors are too slow even at full throttle to get anymore than 'ground effect lift' and the 20amp ESCs started smoking with the 4s attached hence the 30amp. I'll definitely move them under the props if I dont get too much of a negative on lift. Will let you know. Motor heat is a bigger issue.

Keep going chaps. I really appreciate the help

Comment by Rob Burrows on August 11, 2013 at 1:36am

Mmm, interesting problem...If you want to stay with the small props, what about going with a smaller sized battery (less weight) and 40 amp ESCs (not much more weight).  Will let the whole system not have to work as hard.

Another idea would be smaller, lower kV motors matched to the 6-inch prop size and a 5S battery.  I don't know which motor would work for this, but you could probably find something by hunting around.  Of course you'd probably need new ESCs to handle this as well so it might be the more expensive option.

Comment by Ewen Rankin on August 11, 2013 at 2:01am

Thanks Rob. Will have a hunt around. Weight is my killer so yours and Magnus comment about battery might be a good option. I have some 40amp ESCs in a drawer as well. I'll buy a lower mAH in 4s and 5s and have a play.

Until I can suss out Prop guarding, I am stuck with 6" props and nothing I have tried so far tops the PC Fan Guards. Really stable and rigid but only 8" across

Comment by mP1 on August 11, 2013 at 4:34am

Why dont you just make your own guards out of fence wire or whatever ? Im talking about the stuff that comes rolled up in lengths somewhere between 5 - 10m. I use it to make my own legs for my copter with foam tubing to house the wires.

Comment by Ewen Rankin on August 11, 2013 at 4:39am

Fence wire deflect too much if your thinking of what I am. The Prop guards are more to stop impacts causing property damage and rotor damage. So some rigidity is required.

Comment by Timo on August 11, 2013 at 5:26am

I think the problem is that your propeller are spinning to slow. You can solve this by either higher kv motors, larger props or a higher voltage.

But higher voltage is not possible with your motors.

So you have to think about buying new engines or finding a way to mount larger props. Larger props would be the better solution because this although increases the efficiency.

Reducing weight is always something that helps, but I think using a smaller battery doesn't really pay off for you because compared to the weight of the copter the battery is not really heavy and you have already only 8 minutes air time.

And by the way, do you know ecalc? It's a great tool that helps me a lot with such design decisions.

Comment by Project Nadar on August 11, 2013 at 5:37am

You ll need something in the range of 1300-1800 kv for those props. you can try the little expensive motors robbe roxxy 2216 series which are about 1800kv and can spin a 6 inch prop on 4s.  


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