MUGEN Mk II

The main idea behind MUGEN Mark II was to address the major issues encountered with the first build: a loose airframe and a weak landing gear.

But I also tried to reduce the overall vibrations and their impact on the Arducopter, and added a 2 axes stabilized GoPro mount.

A folding airframe

As we would like to bring MUGEN on mountain hikes, a folding airframe was searched… and found: the X525 folding airframe is cheap and effective !

the X525 airframe (can be found for $30 on goodluckbuy.com or ebay)

Some notes about this airframe:

  • The aluminium tubes are thicker than those provided with the jDrones kit, so they are heavier, but less prone to damage.
  • The folding mechanism is quite basic but it works.
  • The landing gear is not useful for us, since we’d like to have a GoPro under MUGEN.
  • I saw in some user forums that the motor fiber glass mounts could get torn apart easily, depending on the motor power/torque.

So I bought this airframe and once stripped of the landing gear and the motor mounts, I had a base to design MUGEN Mk II.

Now, I had to design and build what was missing: a new landing gear, some robust motor mounts and some plates for the battery and all the electronic modules to fit in (Ardupilot, GPS, receiver…). A new mount for the sonar was needed too.

Custom parts and landing gear

I opened up Solidworks, modeled the X525 airframe and then began to model the new parts I wanted to create.

Here is what I came up to:

For those new parts, I spent a lot of time to choose the right material. I finally used some acetal/delrin white sheets to make those parts with Ichiro.

I found Acetal/Delrin to be a material of choice for this application: light, resistant, and unlike PMMA, it won’t break easily when it bends. Like PMMA, it can be easily cut with CO2 lasers.

The landing gear and the motor mount were cut from some 3mm thick sheets, while the rest is cut from 2mm thick sheets.

You can download the blueprints of the parts here:

The files are in PDF format, at a 1:1 scale. You can use them for example to have the parts cut at Ponoko or at a local laser shop !

And you can drop me an email here if you find it useful ! (^_^)

Those blueprints are shared under a Creative Commons Attribution ShareAlike 3.0 license.

 

Here are some close ups of MUGEN Mk II to show how the parts are assembled together:

I used some rubber grommets to absorb some of the vibrations transmitted by the motors to the airframe:

The initial power distribution board is put between the two folding airframe plates. The arducopter and the RC receiver are installed on the first upper plate.

The GPS is positionned on the second upper plate and protected by its own plate.

Both upper plates are assembled using some big rubber mounts to absorb vibrations.

The lower battery plate maintain the Lipo in place and the GoPro mount is also fixed on it.

The mount I used is the jDrones version, its stabilized on 2 axes with some tiny servos. It should be used with a GoPro without it’s protection shell. But I couldn’t take the risk of damaging the GoPro and I choose to keep the protection case in flight.

Finally, I put the sonar on the back of MUGEN, on a mount that allows the sonar to be far enough from the arms and motors to prevent electrical and EM noise, and strong enough to prevent oscillations/vibrations.

The idea behind the landing gear was to absorb most of the shock in case of emergency landing/crash. So I naturally reused a 1:10 scale RC car oil filled shock absorber for this purpose.

This gives of course a heavy landing gear, but it might be the best solution I found to prevent damages and it proved itself quite useful during the flights!

Power bench

As I already had some tools to fine tune RC motors for planes and helicopters, I decided to put MUGEN on my own RC power bench to benchmark its performance…

My custom power bench is based on the Eagletree Micropower line of products/sensors to measure power, and on a modified weight scale sensor to measure thrust.

I tested four of the Lipo batteries I had in stock. Two were old batteries I used for RC planes, and the other two were the brand new ones we bought for MUGEN.

I considered 1.6kg as a total weight for MUGEN, that is more than it’s current weight (less than 1.5kg), but I was trying to take into account the modules required for FPV.

Here are the results:

So, my old Lipo batteries (ZippyH 3300 & 4000) are not performing that well…

On the other hand, the brand new Turnigy 2.6 and the Zippy 3000 manage to supply 700W of power, and even more for the Zippy.

That’s great and the thrust/weight ratio is more then enough to do what we want.

The motors were sold as 20A/210W/1380g thrust capable at max power with a 12×45″ prop (see motors info here). I measured them at 17.5A/180W/950g, so even if there’s still quite a difference here, the motors are still very capable of putting MUGEN high in the air.

Let’s take off!

This summer, we took MUGEN on moutain hikes to make it fly. We used the GoPro and the basic flying modes of the ardupilot were tested with success.

Here is a brief presentation of MUGEN (audio in french only, sorry):

And here are some flight sequences…

MUGEN Season 3: teaser

We had great times making MUGEN Mk II fly!

The airframe proved to be very efficient and practical, and the landing gear prevented damages on numerous occasions. Although it’s heavy, I’m quite happy with the current design in the end.

Having spent more time designing and cutting parts then training and flying, I’m still not good at piloting MUGEN, and for example, I still didn’t manage to have the waypoint function properly. I should improve on this point, and then let the other friends take the commands!

The main problem that should be addressed next, is how to get a proper video recording while in the air.

The current solution isn’t good:

  1. the jDrones mount is too weak to handle the weight of the GoPro + it’s protection shell. On a heavy landing, on of the tiny servo broke.
  2. the vibrations transmitted to the GoPro makes the video jitter. The videos are terrible @30fps, and it’s still a problem @60fps.

So those will be the main issues that should be fixed next…

Other things I’d like to include are some lights (cool!) and a low-battery alarm to show when batteries aren’t good enough to fly.

If you have any questions, feel free to ask…

Have fun! (^_^)

— 2014 update : MUGEN has gone flying elsewhere, so the adventure ends here…