Review: LotusRC T580 Quadcopter

A TURNKEY HOVERING CAMERA PLATFORM

Dated: 26 Mar 2011

It seems that multi-rotor hovering craft are all the rage right now. A quick search on YouTube for "quadcopter" or "tricopter" will produce an amazing list of videos that show all manner of such machines.

Most of these craft are scratch-built and require at least a small understanding of electrical wiring. They also often require a bit of trial-and-error to sort out. The array of motor, control-board and configuration options is mind-boggling (and perhaps good material for future articles here at RCModelReviews).

However, there are some people who won't want to spend hours carefully constructing, testing, tweaking and improving their own home-built machines. They'd rather just buy a "ready to fly" system off the shelf.

That's where the LotusRC T580 quadcopter comes in.

What's in the box?

The machine itself comes in a large flat box that offers excellent protection against damage during shipping. My own unit came all the way from China with no additional boxing and, despite the best efforts of the Chinese soccer team (who obviously used it for goal practice), arrived in perfect condition.

Assembly is pretty straight-forward although it's worth noting that there are no instructions provided in the box -- you'll have to hunt these down online.

Bolt the landing gear on to the bottom of the craft, mount the propellers (taking care to get the right direction props on the right motors of course) and you're done.

Your RC receiver fits inside the black plastic dome and four servo leads from the T580's controller board deliver power as well as connecting the basic control signals (rudder for yaw, roll, pitch and throttle). Yes, you can fly this quad with even a basic 4-channel RC system.

My overall impression of the construction is that it's good quality.

Nice clean plastic moldings plus beautifully anodized aluminum parts combine to make the little quad look very well made. My only gripe might be that the props aren't well balanced and the arms are made from pultruded carbon rather than spirally-wound. The pultruded carbon tubes split easily and may be damaged in even a relatively modest crash.

What's more, despite being shipped with an impressive looking quality-control check-list, I found that one of the props and motor-bell assemblies parted company with the rest of the craft after just a few minutes' flying. Turns out the grub-screw was not properly tightened in the factory. And, when I checked the other motors, one had the grub screw missing completely. This is not an isolated case either - others have reported similar oversights. Check yours *before* you fly.

Once the thing is together, all you have to do is add your own 2200mAH 3S lipo battery (even a 20C pack will do but I'd opt for at least 25C to be safe). When your battery gets low, the T580 will start beeping its low-voltage warning but I'd advise using your transmitter's timer to land and replace the battery before it gets that low.

Flying the T580

This thing flies just like one of those coaxial helicopters.

Thanks to the onboard gyros and accelerometers, the T580 will simply hover all by itself. All you need do is correct for any drift and work the throttle to adjust the altitude (and you don't even have to do this sometimes -- as I'll explain later).

Given the price of the T580, I'd recommend that if you're totally unfamiliar with helicopters (even the coaxial type) then it might pay you to spend $30 and go buy one so as to develop your basic skills and orientation. Although the craft is very stable, those unfamiliar with "nose-in" hovering or who aren't used to using their rudder as a primary flight control may take a while to "get the hang" of flying it.

In calm conditions, the T580 is a piece of cake to fly. It simply hangs in the air and tiny corrections are all that's required to arrest drift or adjust its altitude. However, if the wind gets up the craft does seem to become rather wobbly -- sometimes over-correcting for wind (or pilot) induced disturbances. Strangely enough, adding weight makes things worse rather than better.

A barometric "altitude hold" system is also built into the Lotus and it tries to keep the craft at a constant height above the ground if you don't touch the throttle for more than 2 seconds. Unfortunately, mine didn't seem to work at all well and when the system kicked in, my T580 would often simply start climbing quite quickly or start falling rather quickly -- sometimes suddenly dropping several metres without warning, requiring rapid manual correction to avoid a hard landing. I have seen other T580s where the altitude hold was functioning properly and they seemed to stay within a meter or so of the original height.

Now for a few words of warning...

The T580 is a mild-mannered quad which is incredibly easy to fly -- until you push it too hard -- whereupon it becomes an unpredictable little craft that will tumble to the ground with little warning.

Many people have reported "unexpected flips" followed by a crash. So what's going on?

Well, after accumulating several hours of time on the T580 without a single flip I think I know the secret.

Firstly, the T580 is not designed to race around the sky at speed. If you try to fly it too fast or do steeply banked turns, it will flip.

Secondly, although the manufacturer claims that it will lift a payload of up to 580g, the more weight you add, the more likely it is that the T580 will end up on its back with a broken prop or motor shaft.

However, stooge around with relatively little payload, avoid harsh or sudden stick inputs and the T580 will work "as advertised".

Why is this?

The goal of the designers who created the T580 was to produce a simple, stable, very efficient quadcopter that anyone could fly around with ease. To that end, they have succeeded quite well.

Unfortunately, this has produced a number of trade-offs, and the size of the safe-flight envelope is one of them.

To get its incredible flight-duration (over 10 minutes on a 2200mAH battery pack), the T580 uses very large props turning relatively slowly and driven by low-KV motors. This means less of the battery's valuable energy is wasted in the form of drag or heat. The downside is that these huge propellers driven by their tiny motors can't respond very quickly to corrections from the flight-controller system.

When the T580 is disturbed from its normal "hovering" state, by a gust of wind or a significant control-stick input, the flight controller will speed up some props and slow down others -- so as to return the craft a level position. Unfortunately, if the correction required is fairly big, there is a severe "overshoot" and, instead of simply returning to "level", the craft will tilt back the opposite way. It then tries to correct for that movement and tilts back to where it was in the first instance. If the original angle of tilt was more than about 35 degrees, this oscillation will actually get larger rather than smaller and, within a few cycles, the craft will flip upside down and crash.

It seems that when the motors/props are sped up beyond a certain level, their very inertia is enough to keep tilting the craft past the level position and likewise, those motors which are slowed take too long to speed up again -- further exaggerating the overshoot.

Why don't other quads do this?

Well if you look at the fast, agile, aerobatic quads, you'll note that they have much smaller propellers that can be sped up or slowed down much more quickly.

However, with the T580, you must keep your throws low and avoid flying in turbulent or windy conditions that can precipitate one of these wobble-wobble-flip scenarios.

Another factor in some flip-over crashes seems to be temperature.

There have been reported instances of the T580 flipping without warning and these appear to be linked to heat buildup within the internal circuitry. I've flown the T580 in temperatures from 15 to 22 degrees C and not encountered this but it does get warm so I'm hoping that Lotus will address this possible issue in later versions.

If/when it crashes

Fortunately I haven't crashed the T580 yet but it's bound to happen. With this in mind, the craft comes with two spare motor-shafts, as these seem to be the most commonly damaged part in the event of an unexpected contact with tera-firma.

The shafts are hardened steel which tends to break rather than bend -- which is probably a good thing. Spare shafts are also available for a relatively small price.

Propellers are the next most-likely casualty in the case of a flip or other crash. These are a special propeller that has a threaded hub so you won't be able to just put a standard slow-fly prop on and expect it to work. However, the props aren't too pricey so, if you're buying a T580 it might pay to buy one or two extras -- just in case.

As I mentioned earlier, the arms onto which the motors are mounted, are pultruded carbon which can split very easily when stressed. If you're replacing the arms it would be good to see if you can find some spiral-wound carbon tube of the same size, so as to improve the durability.

Summary

As I've already said, I've flown the T580 for several hours now and had no problems other than the tendency to get a bit "rock and rolly" in wind.

I've kept the speed down, avoided sharp turns or harsh control-inputs, and it has flown very well.

As an aerial photography/video platform the T580 is hindered by its lack of *real* payload capability. Yes, you *can* lift 580g but every extra gram of weight you lift, increases the chances of an unexpected flip. I flew the T580 with a 2200mAH battery and a key-chain camera -- it flew great. When I flew it with a much heavier 4400mAH battery it was not so good and noticeably more wobbly, even though I was still well under the manufacturer's recommended maximum weight.

If you just want a cool quad to get into the multi-rotor aspect of the hobby or if you're confident you can fly within the limitations of the flight-envelope then the T580 is a really nice device.

If you're looking to do some casual aerial photography using lightweight and inexpensive cameras then the T580 is probably the single quickest way to get going. However, you will have to spend some time balancing the props to avoid the effects of vibration and limit your flying to relatively calm conditions.

If, on the other hand, you're planning to do serious aerial photography or video with heavy or expensive camera gear -- I'd be hesitant to recommend the T580 right now -- but...

LotusRC are one of the few Chinese manufacturers who are actively soliciting user-feedback and working hard to improve the product by fixing any deficiencies. To this end, I suspect that many of the product's current limitations will be addressed in future releases of the product. I'm hoping that I'll be able to test the next revision of the T580 and see how much they've expanded the safe flight envelope.

What is a disappointment is that the current system offers no user-upgradeable software capability and has no provision to adjust the gain/stability of the flight-controller -- perhaps this too will be added in later versions. I don't think it's too much to ask of a $350-$400 product that it has a USB connector on the side and user-upgradeable software.

Although there are obviously improvements to come with the T580, it can already be purchased from a growing number of online RC retailers such as HiModel.com.

Would I recommend the T580?

If you've got $350-$400 burning a hole in your pocket and you want something that is *really* different but don't intend ripping up the sky at speed or carrying heavy loads then yes -- it's a really, really cool bit of gear. Even with the current limitations, The T580 is a fun model that will turn heads, being quite different to the usual foamie fixed-wing or 450-sized helicopter.

If you want something more agile and capable of handling stronger winds however, then I suggest you keep looking -- or wait until Lotus make some changes.

Pro's:

• Super-easy to get flying
• Ideal for beginners to multi-rotor flying
• Incredible flight-times (10+ minutes on a 2200mAH)
• Very nicely engineered
• Great packaging
• Nifty altitude-hold (if you can get it to work)
• Some spare motor shafts are included
• Made by a company that listens to customers

Cons:

• Not suited to windy conditions
• Limited safe payload capacity
• Overcontrolling can produce a crash
• "Cheap" carbon arms split easily
• Still not 100% on the quality control
• No user-updateable software capability

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