Sunday, August 02, 2015

Blade mCP X BL

For those that happened upon this post, I was introduced to r/c flight about 2 months ago with a Hubsan X4. As fun as a quadcopter is, it got boring rather quickly, and at about the same time, I discovered 3d helicopter aerobatics, and decided to pick up a beginner's heli to learn.
Now, there are broadly 3 types of r/c helicopters available. Coaxial helicopters are commonly found in big box stores, and their distinctive feature being the two pairs of rotors they spin. These are supposedly very stable and easy to fly. The next step up from them are Fixed Pitch (FP) helicopters. They spin just one pair of blades, and are highly popular as many are small enough to fly indoors and many, like coaxials, are self-leveling like quadcopters, but more agile than coaxials. I've never flown either of these two types.

The last type of helicopter, are Collective Pitch (CP) helicopters, which allow the pilot to alter the pitch of the blade in flight, as well as the regular controls found in other helis. Of the 3 kinds of helicopters, this is the only kind of heli that can do true aerobatics, like flying inverted.

It is also extremely difficult to fly.

Generally, the recommended path is to fly a coaxial to learn the various orientations of flying a helicopter, then move up to a FP before a CP. With the helicopter's tail pointed at you, it is rather easy to fly as the controls mirror the motion of the helicopter.

Things start to get trick when the helicopter is pointed at you - the controls on the right stick are now totally reversed. Flying with the helicopter to its side also poses its own challenges, and that's before flying inverted when things go really mad. And that you still have to control the pitch to maintain the correct amount and direction of thrust, as well as the yaw of the helicopter.

No, not easy at all.

Now the reason why I decided to just fly a CP bird is because ultimately, that's what I hope to fly. Unlike the FP and Coaxials, which utilize the speed of the rotors to hover, with CP helicopters you usually spool up the rotor to a fixed RPM, and rely on the changes in pitch of the blades to produce thrust in the correct direction you want.

As such, on the controls, leaving the left stick in the middle equates to no pitch at all, with the left stick in the down position maximizes the negative pitch. For FP and Coaxial helis, the same control governs RPM, so that's one major difference there - if you accidently push down on a CP helicopter, it's going to piledrive into the ground. In addition, CP helicopters are very unstable - or rather, extremely stable.

With most Coaxials and FP helicopters, if you do not give it any cyclic controls (the controls that bank/pitch the heli), the helicopter will actually revert to level flight, which makes it really easy to fly. Some consider this unstable, as the helicopter will constantly be fighting you to return to level flight.

A CP helicopter on the other size, remembers the last attitude you placed the helicopter in, and good, stable CP helicopters will maintain that attitude. Which means if you are pitched forward, it will maintain that attitude unless you tell it otherwise!

What means, is that if you want a CP helicopter to simply hover in a spot, you'd need to continuously give it tiny corrections so that it stays in place. Whereas with Coaxials and FP Helis, the will just level and hover, depending on how much throttle you give it.
After a few weeks with the quad and barely learning orientations, I'd bought a r/c simulator software called "Accurc" as well as a Specktrum DX4e to learn how to fly collective pitch birds. But the sim is hardly representative of the real thing, and the hunt was on for something to fly in real life.

Being new to the heli world, I checked out what brands are easy to find spares here in Canada (while I was still in Australia lol) and Blade Helicopters appeared to be available in lots of the hobby shops nearby. Nearby means about a 40 minute ride on public transport. Unfortunately, the smallest CP helicopter that Blade has, that is also very crash resistant, the Nano CPX was discontinued. Even their next bigger helicopter, the mCP X has long been discontinued. The smallest helicopter I could get, was an evolved version of the mCP X, the mCP X BL - a 2S (aka two cell) micro helicopter equipped with two brushless motors.

This helicopter has lots of power to do aerobatics, but unfortunately, power in the hands of a newbie is just endless crashing.
I remember my very first flight with this helicopter, barely twenty seconds in, I'd already flow it into the ground. One skill every pilot has to learn, is to know when to hit the throttle hold switch. This shuts off the motors in the event of a crash. With the motors not spinning and the light weight of the helicopter, a crash into grass usually means just putting some of the links back, pushing the canopy back or something minor.  Flying it into a hard surface is another story, as I'd learnt - the rear boom that houses the tail rotor is hollow, and twisted into two pieces, while the motor's wires were torn out.
Several hours of flying later, I'm now able to mostly fly a battery pack without crashing, which is yay! And so long as I fly over grass, the crashes with throttle hold generally see no damage, apart from needing to put parts back that were popped out. I'd also bought a so-called computer radio with the helicopter. These more advanced radios allow you to setup how responsive the helicopter is. Now as mentioned above, CP helicopters are usually flown with the throttle fixed, and the left stick controls the pitch of the blades.

For example, earlier today, I experimented setting the throttle at a much lower setting, and that really helped calm the helicopter down, making it easier to control.

The first dozen or so flights were really quite bad. So far I've broke a canopy, two tail motors, two landing skids, one of the servos and even bent the main frame. The repairs are not too expensive, but some parts are annoyingly expensive like the tail motor, which is over 20 dollars a pop, whereas the plastic components can be replaced for only a few dollars.

The more I fly the heli and the less I crash it though, it seems the running costs are improving. It's probably a stage everyone goes through. I can't imagine flying one of the bigger helicopters, crashing one of those would cost a lot more!

That said, I have been lusting for a bigger helicopter. My mCP X BL is only about 25cm long, and is very easy to lose it's orientation if it gets far away. And thanks to its brushless motors, the power to weight ratio is very good, and easily gets lost in the distance.

A bigger helicopter would help with this, but there are several issues to consider:
a) Safety
b) Space for flying
c) Main equipment costs
d) Crash costs
e) Supporting equipment costs.

Now safety is obvious, the bigger the heli, the more kinematic energy the blades have. I've been hit by my mCP X BL from behind - how that happened, I don't remember! - but that had the throttle hold on, and through a t-shirt, I had a nice red line even though the skin didn't break. 

Space is also another thing, why I was looking for a Nano CPX is the ability to fly indoors, if I actually had the skill for it, but a bigger heli just needs space to fly.

Flying a bigger heli means batteries cost more, and spares will probably cost more. Also, a bigger helicopter with heavier mass will cause more damage on impact, versus my heli which weighs less than 50g.

Apart from the helicopter, batteries and spare costs, there is also the need to purchase supporting equipment like battery chargers and tools to work with the larger helicopters. I actually do want to work on a bigger helicopter - parts are easier to fix and adjust, and a larger helicopter should be more stable.

I'm not willing at this time to move up - while a large helicopter alone is not too that expensive, once the additional costs are summed, I cannot really justify the price point at my current skill level, so I'll be flying this little one until I get good at it and maybe, just maybe, I'll get a larger heli after that.

No comments: