Testing: HeliMax Voltage 500 Aerobatic Quadrotor

By Terry Dunn

The Voltage 500 is a new ship from HeliMax that promotes quad flying in its purest sense. No camera gimbals, no GPS waypoints, no 3D terrain mapping--just flying for the sake of flying.

Many people think of multi-rotors as beasts of burden. Whether that means carrying cameras or performing some other helpful task, the utilitarian focus is the same. It is easy to forget that multi-rotors can actually be fun to fly all by themselves. The Voltage 500 is a new ship from HeliMax that promotes quad flying in its purest sense. No camera gimbals, no GPS waypoints, no 3D terrain mapping--just flying for the sake of flying. [Full disclosure: I added a camera for a few flights, but just a little one. I swear.]

You may recall that we took a look at a pair of aerobatic quads last year; the Stingray 500 and the Invertix 400. Those two quads take very different approaches to achieve sustained inverted flight. The Stingray uses a constant speed motor to drive propellers with variable pitch. The Voltage 500 follows in the footsteps of the Invertix by utilizing fixed-pitch propellers on motors that can reverse in flight.

What You Get

The Voltage 500 ($430) is a 500mm class quad (diagonal measurement from a front motor shaft to the opposite rear motor shaft), which is rather large as quads go. This ship has a double-deck fiberglass main frame and arms made of large diameter carbon fiber tube. At the end of each arm is a red-anodized aluminum mount holding a 1400kV brushless motor. The Voltage has a very wide stance with plastic landing gear legs located below the motors.

The quad's 500mm size and contrasting colors improve visibility and reduce the pilot's workload.

Most of the assembly is complete out of the box. All of the hardware, except for the props are bolted into place. The onboard electronics include a power distribution board, flight controller (FC) and four Electronic Speed Controls. These parts are all wired up and anchored into place.

A painted Lexan shell covers the main frame. The Voltage has a clean look even when naked, but the shell really tidies things up. More importantly, the contrasting colors on the shell and the props provide visual cues for orientation of the quad in flight. It always helps to know which way your aircraft is pointing.

The only things required to complete the Voltage are a radio receiver and flight batteries. There are numerous options to fill both slots. On the receiver side of things, the FC will interface with Futaba S.Bus, JR XBUS, or Spektrum DSM2/X/M systems. When using S.Bus or XBUS, a single 3-conductor wire links the FC to the serial input of the receiver. When using the Spektrum systems, one or two satellite receivers are plugged directly into the FC and linked via the computer interface application.

I used a Futaba R7008SB receiver which requires just a single 3-conductor link to the flight controller board.

There is a wide selection of batteries that can be used with the Voltage. The battery is held to the bottom of the frame with Velcro straps, so there isn't much of a physical size limitation. In addition to the two straps, I added strips of self-adhesive Velcro to the frame and batteries for a more secure attachment.

HeliMax included two Flight Power brand batteries with the review kit: a 25C 4S-2500 and a 25C 4S-3300. This quad can also be flown with 3S batteries. In addition to the provided packs, I've flown the Voltage with ElectriFly 30C 3S-2200 and 25C 3S-3200 batteries. I'll get into the performance differences of these batteries later.

Prepping For Flight

I used a Futaba R7008SB S.Bus receiver linked to my Futaba 14SG transmitter. The R7008SB has S.Bus and S.Bus2 slots. Either will work in this instance. I used Velcro to mount the receiver on the bottom plate, between the rear booms.

I wanted to ensure that the two antennae were oriented for good signal diversity (about 90-degrees apart) and away from any signal-blocking carbon fiber. I glued two small plastic tubes to the plate to act as mounts for the antennae. This location accomplishes both objectives and also keeps the antennae well clear of the props.

I glued two plastic tubes to the frame to help orient the receiver antennae and keep them out of the props.

Basic set up of the model profile in my 14SG transmitter took about 10 minutes. There are only a few parameters to define (control rates, exponential and flight mode) and the Voltage's manual spells it all out very clearly. Yet, as you'll see, I soon returned and made tweaks to the stock configuration.

The Flight Controller has two flight mode options: 3D and Stability. 3D mode works like rate mode found on other FCs. That is, making a pitch or roll control input will command the model to rotate in that axis at a defined rate – with no limits to how far it can go. This allows you to do complete flips or rolls. What makes it "3D" is the reversing ability of the motors. When the throttle stick is above the half-way point, the motors provide positive thrust. Below halfway, the motors change direction and provide negative thrust, allowing the quad to remain inverted indefinitely (or do insane tricks).

The brushless motors can reverse direction in flight to allow the Voltage 500 to sustain inverted flight.

Stability mode works like attitude mode on other FCs. In that way, the pitch and roll axes have maximum bank angles defined (default on the Voltage is 45 degrees). The amount you move the control stick determines how much of that maximum angle the quad assumes. More importantly, when you return the stick to neutral, the quad resumes level flight. It's a nice safety net that many beginning quad pilots rely on--experienced flyers do too.

Even though the Voltage will only tilt up to 45 degrees in stability mode, the motors can still reverse. While I can't think of any reason that you would want to engage reverse thrust on an upright quad, the point here is that throttle response is consistent for both flight modes. In many cases, pilot will want to use stability mode as a "bailout" for when they are about to crash in 3D mode. Whether you are upright, inverted, or hurtling towards the ground in 3D mode, switching to stability mode will command the quad to assume an upright hover and save the day.

The Voltage 500's flight controller has two flight modes: "3D" for aerobatics, and "Stability" for cruising…and bailouts.

The default method of configuring the flight modes in the transmitter has you set a 3-position switch where one position sets 3D mode, another sets stability mode, while the third position shuts down the motors. I quickly determined that it would be very bad to accidentally flip the switch in the wrong direction and shut down the motors during a flight. Multi-rotors do not glide very well.

The manual offers an alternative method to isolate the motor disarming function from flight mode selection, but you basically have to start from scratch and program the model as a helicopter rather than an airplane. That's not a big deal, but I decided to try accomplishing the same thing using the 14SG's programmable channel mixes. I was mostly successful. I was able to configure a two position switch to act as an on/off toggle for the motors. I keep it in the "off" position until the quad is armed and I'm ready to fly. I created another mix that assigns mode selection to a dedicated switch. I only had three-position switches left, so two of the three positions select 3D mode. The set-up works, but I'm still considering better alternatives.

I configured another option for flight mode selection per a suggestion within the manual, but I have not yet activated it. This technique assigns flight mode selection to a 2-position momentary switch. The quad is in 3D mode by default, but engaging the switch puts it in stability mode until it is released. This is useful for those who choose to use stability mode as a bailout option. I will enable this switch as I progress to inverted aerobatics with the Voltage.

Flying the Voltage

My first flights with the Voltage used 3S batteries in stability mode. While the model is sporty in this configuration, I found it to be very easy to fly. Its large size and contrasting colors are big plusses here. I think that quad pilots who are comfortable flying without any GPS assistance can transition to the Voltage without any trouble.

Even in stability mode, the Voltage 500 is a fun and sporty flying machine.

My only issue has been staying mindful of the reverse thrust capability. My usual reaction when I goof up while flying airplanes or my racing quad is to cut the throttle--to hopefully minimize damage, or at least slow things down while I collect my wits. Slamming down the throttle stick with the Voltage doesn't kill the motor. It adds full reverse thrust, which is probably the last thing I need when I'm flustered. I experienced the same growing pains when I first learned to fly collective-pitch RC helicopters a few years ago. It's just a matter of practice and familiarity. I'm getting there.

Slamming down the throttle stick with the Voltage doesn't kill the motor. It adds full reverse thrust.

I've also flown the Voltage in 3D mode (using 3S batteries), but I've not yet tried any maneuvers that require sustained inverted flight. I fly it similarly to the way I fly my racing quad, with flips and rolls mixed among high speed flight and general goofing around. The model is nimble, but not twitchy. Again, I think that the size and colors ease the pilot workload significantly. My goal is to get comfortable flying it inverted, but I'm just not there yet. I've been practicing on the Real Flight simulator and with my Blade 200QX.

Mastering inverted flight takes plenty of practice.

Even though I'm not capable of exploring the full aerobatic potential of the Voltage 500, I have friends who are. Enter Anson Hargrove. Anson is a very accomplished RC pilot with tons of experience flying multi-rotors, helicopters, airplanes, and turbine-powered jets. He does it all and does it well. Anson agreed to take the reins of the Voltage 500 and wring it out.

After a 30-second shakedown hop to make sure that he knew where all of the necessary transmitter switches were located, Anson landed the quad and had me install the 4S-2500 battery. He then took to the air again in 3D mode and performed all sorts of inverted aerobatics. I'm sure that all of the maneuvers have names, but I don't know them. Every now and then he'd settle into a stable inverted hover long enough for me to take a photo or two.

A variety of 3S and 4S batteries can be used to fly the Voltage 500. There is plenty of mounting space on the bottom of the frame.

As I watched Anson fly a few batteries in the Voltage, it was apparent that the 4S packs provide significantly more throttle punch than 3S. The tradeoff is that flight times are shorter. The manual suggests setting a timer for three minutes. That's probably a good place to start if you're using 4S batteries with aggressive maneuvering. By the same token, 7-8 minutes is not unreasonable when using a 3S-3200 battery with more conservative flight. I'm happy with the 3S performance now, but it's good to know that I've got a lot of headroom power-wise.

Using reversing motors is definitely the simplest way to achieve inverted flight on a quad, but you give up a little crispness in maneuvers that require a thrust change. Although it's nearly imperceptible in real time, the motors must slow down, change direction, and get back up to speed each time. I wouldn't call the transition mushy…nothing like that. Just don't expect the physics-defying, lightning-fast direction changes that collective pitch helicopters are capable of.

Anson Hargrove is an excellent pilot of all types of RC aircraft. He showed me what the Voltage is really capable of.

Conclusion

With all of the recent talk about "drones" in the news and the emerging commercial potential of multi-rotors, we often need reminders of how much fun they can be. The Voltage 500 strips away the ancillary stuff and offers the simple joy of flying. I've had a blast flying it while honing my aerobatic quad chops at the same time.

Terry spent 15 years as an engineer at the Johnson Space Center. He is now a freelance writer living in Lubbock, Texas. Visit his website at TerryDunn.org and follow Terry on Twitter: @weirdflight