Piccolo Low Flight Time Troubleshooting GuideAs more and more folks build and fly the Piccolo, we have seen a rising number of complaints of low flight times on the Piccolo BBS. Since the Piccolo is the first foray into electric flight for many people, I have put together this page asa guide to assist in diagnosing the cause or causes of abnormally low flight times.As a "benchmark", a normal Piccolo weighing 240 grams with a seven cell 250 mAH battery should be able to fly for about 5 minutes, give or take. This assumes everything is OK and the battery used is up to the task of electric flight. Not all are. WeightA normal Piccolo (including canopy) should weigh approximately 160 grams without the battery and approximately 228 grams with a 7 cell NiCd pack. If your Piccolo weighs more than that, it will not fly as long. If it weighs significantly more than that, it may not lift off at all. To find the extra weight, look to things like the servos and battery pack. If you are not using the Piccoboard, make sure that your separate components (ie., receiver and gyro and speed controls) are not the culprit. And finally, if you are using training gear the extra weight will reduce your flight time. The rule of thumb has always been that every gram will cost you approximately 5 seconds of flight time, so you can see immediately that weight is your enemy!See also "Piccolo and weight" in the Hints and Tips section. BatteryProbably the most crucial item in the Piccolo, and any electric aircraft for that matter, is the battery pack. Do not assume that just because your pack is marked with a reasonable capacity it will be able to fly the Piccolo. There is a rather delicate balance between the pack weight and the ability of that pack to deliver enough energy to lift the heli and battery pack. The optimum balance between capacity and weight for NiCd cells seems to be 250 mAH. Smaller cells cannot produce sufficient current, and larger cells require much higher current to lift the greater weight and this reduces efficiency and can overheat the motor.Charging your packs correctly is almost as important as having the right pack in the first place. See the Battery charging and Battery chargers sections of the Hints and Tips section. Cell count is also important. Most people flying 250 mAH NiCds are using 7 cells. Most people using NiMh cells are using 8 cells since the voltage out of a NiMh cell under load is lower than from a NiCd cell. However, there is a wide variation in actual capacity at Piccolo currents between various NiMh cell manufacturers. The NiMh cells that have been found to perform well are the Sanyo 720 mAH AAA (various sources including Specialized Model Supply), the Panasonic 550 mAH AAA (from DigiKey), and the Rayovac 700 mAH AAA (from Kmart and others). Some 7 cell NiMh packs can fly the Piccolo, but if you are using a 7 cell NiMh pack and are having flight time problems, try adding a cell. The easiest way to be sure your problem is not the battery is to make sure you are using fresh cells that are known to be suitable for the Piccolo. My recommendation is to start with at least one 7 cell pack of Panasonic AAA NiCds from DigiKey. These cells are universally accepted as suitable for the Piccolo and should be able to reliably deliver 5 minute flights on a 240 gram Piccolo. This is NOT to say that other packs and cell types are unsuitable. Some are quite suitable. But in the absence of any other means of testing your pack, it is a good idea to have a known good pack handy. If you want to evaluate your present pack(s) you will need some way to discharge them at a current representative of what the Piccolo requires to hover... at least 2.5A. At that current, you will need to be able to measure the pack capacity in mAH. Some chargers that also discharge can display the capacity, or you can purchase the Astroflight Whattmeter, which has this display. Remember, though, that without some way of measuring the pack capacity, you can not be sure that your pack is or is not the culprit. Battery connectorDon't overlook the battery connector as a source of trouble. The red "BEC" connector supplied as standard on the Piccoboard since day one is NOT suitable for Piccolo current levels and can easily drop enough voltage to put you in ground effect prematurely. I strongly advise that you replace it with something more suited to the approximately 2.5-3A current drawn by a hovering Piccolo. My personal favorite is the two or three pin Deans connectors available in almost any good hobby shop. The three pin version is polarized, and the two pin version is available in polarized or non-polarized versions. Get the polarized version to make sure you never plug it in backwards!!MotorsThe main motor should be broken in properly before the first flight, per the instruction manual. Failure to do this can lead to poor motor performance, since the brushes may not seat correctly. If you have a way to measure current, the entire heli should draw about 2.5A at hover speed. Significantly more current is a symptom of overweight or a bad motor.Something else that I have found is that dirt and corrosion can accumulate on the commutator and brushes and degrade performance just enough to lower efficiency tot he point that you cannot hover as long as usual. Short of dis-assembling the motor, try going to the local hobby shop and look in the car section for a motor spray that is intended for cleaning the commutator and brushes. Spray it into the little holes in the plastic end of the motor and see if that improves things. Talk to the guys in the shop and see if they have any favorite brands. And finally, I have found that it takes a LOT more time to break in the brushes than commonly thought. My motor was suffering from low flight times and upon disassembly, I found that the brushes were still not fully seated and there were areas in the middle that were not touching the commutator. I had broken it in for at least two hours at 3V. I suspect that 10-15 hours may be a more reasonable figure. GearingA stock Piccolo will fly very well on the 9 tooth main motor pinion (the middle one). Using the 10 tooth pinion will increase the current required to hover and reduce flight times by decreasing the motor and battery efficiency. The tail rotor pinion will not have a large impact on flight times, but using too large a pinion can decrease motor life. The best choice seems to be either the 8 or 9 tooth pinon.Gear LashThere must be some play between the gears or you could be wasting significant energy in friction. There are references to using a piece of paper between the gears as a spacer when you set the lash, but I find it just as easy to eyeball the lash and merely make sure there is a small amount of play. Too much is better than none. If the main gear can move back and forth a very small amount before it contacts the pinion teeth, and it can do that for the entire 360 degree rotation (the gear might be a bit out of round), you should be fine.Rotor SystemIf you are using the stock Ikarus blades, you can assume they are OK for now. However, if you have cut them or are using other aftermarket blades, try putting a set of stock blades back on and see if the performance improves. If it does, you may want to try changing the pitch of your blades experimentally. The airfoil section used on the Piccolo blades is quite sensitive to small pitch changes and can develop little or no lift if the pitch is just slightly too low. To adjust pitch, put a small piece of tape between the blade and the blade mount... in front of the hole to decrease pitch and behind it to increase pitch. Use single layers of Scotch (Tesa) tape at a time and see what happens to the performance.If you have a method of measuring rotor speed (like a tachometer), you can verify that the rotor is achieving the correct speed to lift off. A 240 gram Piccolo should lift off at approximately 1100 RPM with stock blades. Cut blades can lift off in the 1350 RPM range. PiccoboardThere can always be something wrong with the Piccoboard, but this is relatively rare unless it dies completely. However, the Piccoboard needs to initialize correctly in order to produce full power at full throttle stick position. Initializing with the transmitter throttle stick in a position other than zero can reduce the total throttle travel available enough to prevent the Piccoboard from producing 100% power. See below, also.TransmitterOne common cause of low flight times is that the transmitter is not commanding the Piccoboard to 100% power. The symptom of this is reasonably long flight times but an inability to get out of ground effect for very long. The Piccoboard sets the speed control zero points to the throttle and rudder stick position seen during initialization. However, it does not set the overall throttle travel. For that reason, if the transmitter does not produce enough throttle channel movement from zero to full throttle, the Piccoboard may not reach 100% power by the time that the transmitter stick reaches the top of its range.If you suspect that your transmitter is the problem, try this simple test. Assuming that your transmitter trim is enabled at high throttle positions, this will easily find out if the Piccoboard is not reaching 100% power: 1. Put the throttle trim to the center and initialize the Piccoboard. 2. While holding the Piccolo, put the throttle stick to full throttle and listen to the rotor speed. 3. Leaving the throttle stick at full throttle, move the throttle trim to full up and listen to the rotor speed. If it increases even a little, you were not at 100% power to start with. If this is the problem, and if you have a computer radio, merely increase the ATV value until the Piccoboard reaches full power (ie., the main motor stops increasing speed) slightly BEFORE the transmitter stick reaches the top. If you do not have a computer radio and the main motor is still increasing in speed when the throttle stick hits the upper stop, there is not much you can do unless your transmitter has an internal mechanical throttle stop... some do, such as the Futaba Skysport. Remove it and you should have sufficient throttle travel. SummaryFor decent flight times, your Piccolo needs to be at a reasonable weight, have good batteries and a healthy motor with the right gearing, and the Piccoboard has to be able to reach 100% power output at full throttle stick deflection. Double check everything carefully and see if one of these items is the problem. |