Wednesday, May 14, 2008

FMA Direct Cellpro 10s Charger Review

The FMA Direct Cellpro 10s is a balancing lithium battery charger, capable of charging a single battery up to 10 cells, or two batteries simultaneously up to 5 cells, with power up to 10 amps. It can handle lithium polymer, lithium ion, and the M1 lithium cells from A123 Systems. Let's dig in and put it through its paces.
Specifications Chemistry
Lithium polymer, lithium ion, lithium manganese, and A123 M1 Pack capacity
100 mAh to 65 Ah
Input voltage
10 to 16V DC, reverse polarity protected

Input current
Up to 25A, can be limited between 1A to 25A

Charge rate
Up to 10A (300 watts)

6 5/8 x 3 3/8 x 1 5/8 inches

Street Price
$189 USD

FMA Direct was kind enough to provide a sample unit for review. The charger comes with 4mm bullet connectors on the power input leads, as well as alligator clips, which can be used to connect a car battery or other power source. Also included are two 5s-to-4s converters that let the 10s work with any generation of Cellpro batteries. Finally there is a plug blocker which can be installed across the main charging terminals, allowing charging through the balancing ports only (up to 4 amps). Five dollars extra buys two sets of 4mm charging leads without connectors, so you can solder Dean's ultra connectors, PowerPoles, or whatever you prefer for charging at above 4 amps.

It's hardly news that the state of balancing connectors in this hobby is a mess. It seems that every major manufacturer of batteries has its own balancing tap, and a few even share connectors but differ by polarity. Fortunately FMA has taken a comprehensive approach by offering optional adaptors for all the major connectors in use. I evaluated two adaptors: one board has both PolyQuest and ThunderPower connectors up to five cells, the other has Align/ElectriFly and Kokam up to four cells. Since beginning the review, FMA has introduced new adaptor boards which handle 2 to 6 cells each. There's a lot of flexibility to this system, and you'll have no trouble connecting up your collection of batteries.

The charger itself is smaller than I expected, given its power rating. The construction is very solid with metal heatsinks along the sides. The top has a large, backlit LCD display, and cooling holes for the fan, which only runs when needed. I found the manual clearly written and easy to understand, with a lot of detail about different connection possibilities and error codes.

Like FMA's Cellpro 4s , control is simple. There are two buttons on the right side which control all functions. The Mode button is used three ways: short presses cycle through the six presets from the main screen, or change values in the other screens. A long press enters the menu mode, where continuing to hold the button gives a choice of battery chemistry, charge rate, and exit to the main screen. Lastly, a quick double press on the Mode button changes the charge rate in whole amps, rather than tenths of an amp. The second button, labeled Start/Stop, does just that.

While this style of programming works, it is a little unintuitive, and I sometimes made mistakes. Given that the hardware only has two physical buttons, I would have preferred a more traditional arrangement, where Mode (button one) is only used to change between screens. Then the Start/Stop (button two) could be renamed to Set, and used to change values, changing them faster if held down. This is just a personal preference, and not a serious issue. I got used to the interface quickly and it's now second nature.
One thing I applaud is the user-upgradable firmware. Although the required USB interface is optional, new versions can be flashed at home, for free. The Windows-only software checks online for the latest versions, and describes the changes in each, another nice touch. The update takes a couple minutes and was reliable in my experience.

The PC application has a number of other functions, like displaying individual cell voltages live, and a graphing mode while charging which is very cool. You can also configure and name your presets, which is fast and easy using the keyboard. Lastly, there are a number of settings which are not available from the charger front panel. In particular, the ability to limit the amp draw on the power supply is very useful and could prevent damaging your power source. I wish this setting could be set on the charger itself, or that the $20 USB interface was included in the purchase price.
I tried a variety of LiPo packs with the charger, from 2S 300 mAh packs up to the biggest I had on hand, 3S 2100 mAh. Because these packs are relatively small, I installed the plug blocker across the main terminals and charged entirely through the balance connectors. I find this very convenient as there's less to connect and fewer wires in the way. You can either set the amps manually or select 1C, 2C, or 3C charging (if your batteries can handle these higher rates). Since the Cellpro 10s detects the number of cells automatically, using 1C mode is dead-simple - it just does the right thing with no fiddling.

If you need to charge at 4 to 10 amps, connect both the main leads and balancing taps for each cell. As a safety feature, the Cellpro 10s will not charge without the balancing connectors hooked up. Although that makes perfect sense for LiPo packs, it is a drawback for A123 users who either use solderless end-to-end packs or didn't bother to add a balancing tap to their brick packs. There are mixed opinions on whether M1 cells require balancing, and FMA has taken the cautious route here.

Initially I tried the Cellpro 10s using a computer power supply with banana plugs added to the 12V rails. However it was not able to maintain 12 volts during a charging cycle, and when the charger detected the insufficient voltage it halted the charge. I don't think the Cellpro is particularly picky about power supplies, but a switching unit between 12 and 15 volts is best.

To work around this problem, FMA sent me their top-of-the-line power supply . This serious looking piece of hardware delivers up to 28 amps at 13.8 volts on its main terminals, and can simultaneously supply 7 amps to a cigarette lighter jack and a pair of clips for bare wires on the rear panel. It has a quiet fan which runs all the time, and in all my testing it never even got warm. I'm very impressed with its quality of this unit. FMA offers this power supply separately or in a bundle with the 10s if you don't own a suitable source of DC power.

They also sell a 5 amp supply which would be adequate if you only use small park flyer packs. In my testing, I was able to charge two 3s 1500 mAh packs at the same time, drawing 4 amps from the power supply. Consider this a way to squeeze by on a budget though, as you won't be able to really let the 10s shine. Any larger than 1500 mAh and I recommend a more powerful 12V source.

As I mentioned, the 10s can handle all three popular lithium variants. It does this by changing the cutoff voltage appropriately: 4.2V per cell for LiPo, 4.1V per cell for LiIon, and 3.6V per cell for A123. If you charge two packs at once they must be of the same chemistry. The 10s does not charge NiCD or NiMH batteries, which doesn't bother me a bit, since I haven't used either in a couple years. In fact, I planned to try a safety check to make sure the 10s wouldn't start a charge when connected to a NiMH pack, and couldn't even find one in my workshop.

The 10s is essentially two chargers in one when used with packs up to five cells. I found it convenient to put a couple 3s 2100 mAh packs through my T-Rex and charge them together in under an hour. You need to start and stop both packs at the same time, but I didn't find this to be an issue. The only possible drawback involves charging two batteries of very different capacities, whether they are of different sizes, or the same size packs depleted to different levels. Once one battery is done, the charger will slow down to 1A to complete the other.

Pictured are the various information screens the 10s offers during a charge. When charging a total of more than four cells, the display alternates automatically within the individual cell voltages screen.

One question that's come up on the forums is whether to buy the 10s or two Cellpro 4s chargers. This is largely a matter of personal preference. If you can't see ever going beyond 4s packs, the two independent chargers are a bit cheaper. On the other hand, the 10s has more features and more room to grow. Helicopter pilots in particular often want to step up from their 450 sized models into something bigger, and that typically means at least 5s or 6s LiPos, or up to 10 cell A123 batteries.

Tuesday, May 13, 2008

ElectriFly Yak 55 Follow Up

In my original review , I described building the ElectriFly Yak 55 ARF, a flexible and durable ARF from Great Planes. So how has it held up over time?

The truth is, I have punished this plane quite a bit. It has survived countless hard landings, and has the hot glue repair seams to prove it. I've gone through four of the plastic spur gears, which get chewed up easily by the metal pinion gear. And the original foam nose has long since disintegrated. I bought spares, but it seemed that each crash pushed the stick mount a little more into the body, to the point where the propeller wouldn't clear the cowl. It was simpler to leave it off. I made at least two major mistakes with this plane. The first was flying it with an older, non-computer radio, where I could only reduce the control surface throws mechanically at the servos. This still left the plane way too volatile for me to learn on, and resulted in more crashes than necessary. Since moving over to a Futaba 7C with dual rates and expo, I've found it significantly easier to control. This is still not a beginner plane though - it's small, fast, and easy to lose your orientation. I wish the bottom had more distinctive coloring from the top. The second mistake was using such a heavy battery. I started with an 11 volt 1500 mah LiPo pack, which at 4.4 ounces did serious damage to the fuselage in crashes. The firewall completely shattered, and the floor of the fuselage (which is actually the top of the one-pice wing) crumpled. If you're sticking with the stock motor and gearbox, I'd start with a 3S, 950 mah battery instead. It may be tricky to get the center of gravity right, so try moving the receiver and ESC as far forward as possible. Another good idea is to put a spongy piece of foam behind the firewall, which will protect it and the battery in a nose-first crash.

My solution to the weight problem, and something I wanted to try anyway, was to upgrade to a brushless motor. I happened to have an ElectriFly RimFire 28-30-1450 outrunner on hand, which turns faster than I need, but actually worked out great. I found I was able to switch to a 7.4v 1500 mah battery, which both saved weight and slowed down the motor. Having temporarily run out of the original 11x47 props, I downgraded to a 10x4.5 with good results. Thrown from underneath with full throttle, this plane takes off fast! The tricky part was how to mount the motor, given that ElectriFly doesn't make a stick mount for outrunners. By complete luck, it turns out the plastic housing for the factory motor/gearbox can be used. The two tabs which held the brushed motor line up with two of the RimFire's mounting holes. The third happens to line up with the tube used for the spur gear shaft. It just took a few seconds with a hobby knife to pare down the lip on the mount, and then fitting an extra long screw to run through the tube. The motor now sits flush with the old mount, and is mounted backwards for use with a prop saver. I used hot glue to attach the mount to the plywood stick, as well as the original side screw. The result is more power than the factory setup, with much less weight. An added bonus is that the propeller turns freely now, which makes it even less likely to break on landing. The geared, brushed setup left the prop quite stiff, even without power (I didn't have the ESC programmed for brake accidentally). This added to the stress on the motor mount, which needed to be periodically reglued. After several months of punishment, my Yak 55 had reached the point of barely flying anymore. I thought the last straw was getting stuck in a low tree, which took a direct shot with a football to retrieve. The tail had split again, and the bottom was starting to fall apart. I put the plane aside for a few weeks, then gave it one more shot. After an hour with the glue gun I was able to get it flight ready again, if barely. One more flying session though and the whole front was completely demolished. The bad news is I'm going to have to retire this plane. The good news is that I'm buying another one and starting over with brushless power from day one. I'm also going to reinforce the tail with carbon rods from the old body to stiffen it. Knowing the weak points should help make the new one last, and using the smaller battery will make a big difference. I cant wait to get the new plane up in the air. The Yak is dead - long live the Yak!

Esky Lama V4 Helicopter Review

The Esky Lama V4 is an inexpensive indoor electric helicopter. For less than $100 USD online, you get a completely assembled and ready-to-fly helicopter, four channel transmitter, LiPo battery, charger, and a spare set of blades. The Lama does not come with training gear or an instructional video like similar models from Tower Hobbies and Horizon Hobbies, but it only costs half as much.

The first thing you'll notice is the two main 13" rotors, each of which has its own 180-sized motor. This coaxial design cancels out the torque of the blades without the need for a tail rotor. This supposedly makes the helicopter more stable and easier to fly for beginners. Turning the nose left and right (i.e. yaw) is accomplished by changing the relative speeds of the top and bottom rotors. While this works quite well, there is a drawback in that turning changes your total downward thrust, so moving the rudder stick can change your altitude. Forward/backward motion as well as left/right roll are determined by two servos which tilt the swashplate. The stock battery is a 7.4V, 800 mah LiPo pack which is good for about 10 minutes of flight. It takes about an hour to charge with the supplied charger/balancer. I was happy to see that this two cell pack has a balancing connector for charging, rather than using the main discharge lead and potentially leaving the cells uneven.

The transmitter is a very basic four channel FM model. It has mechanical trims, servo reverse switches, and a trainer jack on the back. It's serviceable but cheaply made - the battery compartment cover on mine barely stays on. Unfortunately the throttle stick is ratcheted instead of moving smoothly for fine throttle control. See our tutorial for how to remove the ratchet . The good news is that this is a standard 72 MHz setup, so you should be able to swap the receiver crystal and use your own transmitter on your preferred frequency. Flying for the first time was straight forward. There's no assembly involved at all - just charge the battery. It wasn't clear whether the factory had trimmed the controls, so I set them all to neutral and turned on the transmitter. After plugging in the battery, the gyroscope took a few seconds to stabilize, and then lit up solid green. It's important to bring the throttle up slowly to avoid stripping the gears. I was happy to see the Lama come up off the floor easily and seem to be pretty stable. Rather than taking a chance, I took note of which way it was drifting, then landed and adjusted the trims. After a few tries, I was able to get it pretty well dialed in, with the exception of yaw. I found that even with the rudder trimmed fully to the right, the heli would still turn slowly to the left and needed constant correction. An open basement with seven foot ceilings was enough space to learn how to fly, but more height would have been better. Spending a few hours on a simulator before the first flight also helped a lot in terms of orientation and anticipating what the controls would do. It only took a couple months to go from a first-time heli pilot to having a good feel for what the Lama V4 can do. It can easily fly tight circles forwards and backwards indoors, and it's maneuverable enough to land on a small table top. Forward flight seems somewhat limited, but it does move backward pretty well. In very calm weather the Lama can be flown outside, but even a slight breeze will make it impossible to hover even with full cyclic. If you're feeling adventurous, you can lengthen the servo arms in order to give the swashplate a bigger range of motion, but you'll need to upgrade to a longer main shaft to further separate the top and bottom blades. Flying the Lama V4 is really addictive. It's a very easy helicopter to learn on, and it's remarkably tough. It's endured more crashes than I can count, and the only things that have broken are the rotor blades and one side of the landing gear. The flybar has a resilient design which causes it to pop out undamaged in a crash, which is a great feature. It's important when reattaching it to make sure that the upper blades pivot freely, which largely determines how stably the heli will hover. The black plastic blades that come with the helicopter are pretty fragile, cracking and splitting after a few crashes. The Lama will still fly with some imperfections in the blades, but this tends to create vibration throughout the body. I decided to try the Xtreme replacement blades which are popular on RC Groups . These white blades have proven dramatically better in terms of toughness, and don't show any signs of damage after repeated crashes. Several times I've experienced blade clashes, where the top and bottom rotors touch during aggressive flying, but the blades were unharmed. These are well worth the money ($8-10 for the entire set) and should be your first upgrade. I also bought the "indestructible" landing gear for the Blade CX which fit the Lama without modifications. They happened to arrive the day I broke the right factory skid. The new ones are visibly thicker than the standard ones, and so far have held up without any problems. There are many other upgrade parts available, including aluminum replacements for most of the head. It's not clear whether these improve flight performance, and a complete set costs as much as the helicopter itself. Overall I'm very impressed with the Esky Lama V4. This four channel helicopter is a huge step up over the two and three channel toys out there, and is not much more expensive. When properly set up, it can hold its own with similar models from Blade and Heli-Max that cost more. The Lama is a huge amount of fun and is easy enough for someone with only airplane experience to fly.

HPI Pro-D vs Tamiya TA03F

HPI have finally got the drop on their main drift rivals Yokomo, and come out with a revolutionary drifting car the HPI Pro-D. With a carbon main chassis, carbon upper deck and orange anodised aluminium bulkheads, it's a very slick design. Only one question remains...

The HPI Pro-D

Why has it taken this long for a manufacturer to come out with this kind of chassis not one that's a re-hash of another model, but a specific drift chassis? Tamiya, by shear fluke, have already created the perfect drifting chassis, and discontinued it before people even realised that you could drift RC cars namely the Tamiya TA03F. Since the TA03F is no longer supported by Tamiya, parts and chassis are nigh on impossible to get hold of, so some competitive drift series have created rules specifically to ban this car.

So what made the TA03F so great at drifting? Well, good drifting is all about weightgood distribution. You'll find most drifters will add a lot of weight to the front bumper so that the front tires will be pushed down and grip more than the rear, and also to give a point for the rear of the car to swing around. The TA03F was created with equal weight distribution to the left and right in mind, so the motor was moved to the front of the car to avoid the drive belts. This in turn provided the necessary weight sitting on the front wheels. Perfect left and right weight distribution also means the battery must be placed across the chassis, rather than along side the centre line.Takealook:

The tamiya TA03F

So what of this revolutionary Pro-D chassis of HPI? The HPI Pro-D has the battery placed across the chassis. Moreover, the Pro-D is not belt driven, but shaft driven, which gives the driver a much more direct feel and much sharperthrottle response. To move the motor closer to the centre line, the shaft has been moved off centre. Thisimprovesthebalaceasthemotoris not so off-set. And what about looks? The HPI Pro-D looks fantastic. Drift not only requires skill, but shock and awe bling. The Tamiya TA03F, with is black plastic everywhere, is a sore loser in this department.

Our verdict: Currently this is only available in Japan, and at a price of 52000 yen (about $450) for just the chassis kit - only hardcore drifters need apply. Although this isn't overpriced considering the specification, the now obsolete TA03 will perform just as well, and these can be picked up reasonably cheaply on ebay. If any of you have a cousin or a brother with an old RC kicking about in the loft, go and have a look, it might just be one of these gems.