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Showing results for '"for beginners"' in content posted in Electric Flight for Beginners.
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The ESC ( Electronic Speed Control ) is exactly that - it controls the speed of the motor.As seen in the main intro section, it connects between the battery and the motor, and also has a lead which goes off to the receiver throttle port and this usually supplies power to the whole onboard radio system, as well as receiving commands back from the receiver as to the throttle position. Two other main features of most ESCs are 1) The BEC ( Battery Eliminator Circuit ). This eliminates the need for a separate radio system battery, and cleverly "drops" the high voltage from your main flight battery down to around 5V which is what your radio needs. It is carried along the same wire as the one that plugged into the throttle port, so nothing is normally plugged into the main battery port of the Rx. This is great for saving weight - and dont worry, this radio voltage will be maintained long after the battery has dropped so low as to not power the motor any longer, so although you may experience a "dead stick" if the battery does drop this low, the radio will still allow you to guide the model back to the strip. 2) The LVC ( Low Voltage Cutoff ). This little circuit within the ESC cuts the power to the motor when it detects that the flight battery has run down too low.Batteries especially LiPo batteries will be ruined if they are allowed to discharge too far, so this clever gizmo prevents this from happening. Note that on some ESCs you have to "program" the type of battery you are using into the ESC, and this is much easier to do with the ESCs which can deploy a "programming card " Other ESCs can automatically detect the battery cell count when first detected, and will automatically adjust this cut off point. However, other features of the ESC can usually be programmed also, such as an electronic brake ( useful for folding props back on gliders ) motor timings, and so on.....and here the programming card really comes into its own. Check when purchasing an ESC that.... 1) It is a brushless ESC for brushless motors... brushed ESCs do still exist, but will NOT work on your brushless motor, The opposite is also true. 2) The maximum current capacity of the device. Before you purchase the ESC, you should have already worked out the maximum current that will be flowing in your setup. Choose an ESC which is "rated" for at least this amount, and little bit more for headroom. I often go as high as 50% more , so for example, if I know my motor and prop will be "pulling" say 20 Amps at WOT ( Wide Open Throttle ) then I will likely buy an ESC rated for 30A. There is absolutely no reason at all that you could not use a huge 100A ESC on this, except for the weight penalty...so for the few extra pounds difference in price, play safe and "go large " 3) That it will work with the planned number of cells you intend using in your battery. Many of the smaller ESC will be limited to just 3 or 4 LiPo cells as a battery maximum, so if your rig is going to be using more cells than this, get the appropriate ESC.Incidentally....regarding "twins" -in almost every "multi-motored" model its best to use a separate ESC for each motor. If you still wish to supply the radio using the BEC, then its best to disconnect the BEC power ( red lead ) from one of the ESC BEC units that are connected to the Rx throttle channel ( usually with a Y lead ). It is not uncommon for two BECS to "fight" one another if both connected . There are many more clever features in ESCs, and also some models dont have the BEC we mentioned earlier. These often also deploy something called OPTO Isolation, where the actual commands beteween the ESC and the Receiver are communicated optically - as in fibre optic technology - and this can help eliminate any electrical noise and interference created by the ESC from actually affecting the operation of your radio. Where an ESC does not have a BEC unit, then obviously you will need to arrange for an alternative supply for the radio sytem. This thread here, has a lot more on this aspect. However, as a beginner with electric flight, you are likely starting off with a more simple rig, and in most cases, the ESC with a built in BEC will do just fine.Connecting it all together. The motor has 3 wires to connect with the 3 wires from the ESC output. These can be connected in any configuration you like, with no ill effects. If the motor, during testing runs the "wrong way" then simply swap over any two of these wires. The ESC also has another two large gauge wires - usually red and black, and these are for connection to the battery - in the right polarity! Edited By Tim Mackey - Administrator on 15/06/2010 22:32:56 -
As we learned in the intro section, model aeroplane electric motors are generally divided into two main categories, so lets a take a look at these in more detail. Inrunners and Outrunners - within each category there are variations of....1) Maximum power capability, 2) Typical RPM range achievable, and3) The fuel ( battery ) required to drive it…… Sound familiar? It should do, because these factors are also used in selecting an IC engine. Inrunner style motors ( where the moving bits are all inside the “can” ) are generally high revving motors more suitable for fast high speed models, and EDFs ( Electric Ducted Fans ) and will be used with small propellers or rotors in the case of EDF. Think of these like the 2 stroke engine. Most Outrunners ( the actual outside case revolves around a fixed stator ) are slower revving motors with greater torque, and are good for swinging medium and large size propellers. Think of these like the 4 stroke engine. So, knowing the type of model you wish to power, the first decision is relatively easy - Inrunner, or Outrunner? -and with that out of the way lets look at some more crucial data needed to select the right one. This data should be available with all good motors, and its nigh on impossible to make a proper choice without it. Kv ( RPM per volt of fuel ) This determines how fast the motor will spin given a voltage from the battery, and the higher this figure, the higher the revs and the higher the current consumption of the motor....... and power ( Watts ) the motor will produce. Need a motor to power your super fast hotliner? Then choose a high revving model, of around 2000 Kv or more, which will be good for spinning that small diameter, high pitch prop required for top end speed. Vintage biplane ? You want a relatively larger diameter prop spinning slower to produce more thrust than actual top speed, so choose a lower Kv motor of say 800 Kv or maybe lower. Maximum Power ( Watts ) or Current. Excessive current will kill motors, so you need to get one which will work at the expected current. Most motor data sheets will tell you the maximum current allowable, and this will be determined by the voltage of the battery used, and also the prop size. More volts = more current ( and Watts ) and bigger props ( diameter /pitch /or both ) = more current and ( and Watts ) A good general guide as to the power required for different models is General sports models, older Warbirds and trainers etc 80 - 100 Watts per pound of AUW ( all up weight ).More modern Warbirds and aerobatic machines etc 120 watts per lb. Fast models, pattern ships, and jets 150 Watts per lb, with very high performance models requiring around 200 watts per lb. Fairly obviously, larger heavier models requiring good performance will require larger motors capable of producing lots of power ( Watts ) … just as an IC model will also. So in summary… lets look at the following model. A high wing Trainer, originally designed for a .30 size IC engine. Its AUW is around 4.5lbs, and would have probably had something like a 10 X 6 prop. Outrunner. 450-500 Watt capable. Medium RPM ( Kv ) = around 800 - 1000 Kv. Now, that wasn’t too hard was it Edited By Timbo - Moderator on 23/08/2009 14:13:25
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Just the basics please, and relevant to the likely things encountered by beginners when dabbling with electric flight Edited By Timbo - Moderator on 25/08/2009 22:00:05
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Hi Guys, On my new Easy Glider I am having difficulty joining the wings. Obviously where the wings join it is molded something like a jig saw piece to join the two wing halves. It seems I will have to use exessive force to join the two halves and I am afraid I would break the foam. Grateful for any ideas. Cheers, Bob
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Unless you have been living under a stone, you will almost certainly have heard of a "Wattmeter". This invaluable, and inexpensive piece of measuring equipment is the best way of ensuring that your electric powertrain is correctly matched. All components within an electric powertrain are designed to operate within specific parameters, and we need to ensure that our system is going to produce the power we are looking for. The "Wattmeter" ( I will call it a meter from now on ) is used for bench testing your setup before you commit themodel to flight. Heres how it works. You will have seen in the main intro section how the motor and battery and ESC all connect up. The meter is temporarily inserted between the battery and the speed conrollers main cables and will provide you with a readout of exactly how much current your "rig" is consuming, how many watts of power the system is providing, and also how many volts the battery is maintaining when under full load. Normally the rig is secured safely on the bench or whatever, and the throttle is advanced ( ensure you stand behind the prop / fan and that if the worst happens and the prop flies off, it will not damage anything ). Let the motor run for around 30 seconds or so, and make a note of the figures mentioned above. They will likely fluctauate alittle during the test, but you will get the trend. One of the main things this will show for you is the power - in watts - that the set up is producing. Watts are derived from multipying the volts of the battery ( under load ) by the Amps consumed. W =I x V ( I is the symbol for current, or amps ). The more volts you have the higher the watts, the more Amps you have the higher the watts. Assuming that the battery you select is not likely to be changed for a higher voltage version, then altering the propeller is the biggest single factor in altering the current that the motor will consume. Lets say your motor is designed for a 6 X 4 prop, on the chosen battery, but you want to try and get a litlte more thrust, or climbing performance from your setup. Using the meter, you could now fit a slightly larger diameter prop, and monitor the current being drawn. Now you can see the amps that the motor is pulling, and therefore ensure you do not "prop up" to the point where the maximum figures allowable are exceeded. These maximum figures are also applicbale to your battery, and your speed controller, and indeed exceeeding any or all these could prove very expensive, or even dangerous. The modest cost of a suitable meter will be re-couped the very first time you use it and discover that your power figures are beyond the maximums allowed. Various models and features are available these days, including a less versatile "clamp style" ammeter which as the name suggests, simply clamps around the poer leads, so negating the need to actually "break into" the cabling and fit extra connecters etc. However, these will not show all the data that an "inline" meter will, and also be aware that many of the cheaper clamp meters will only measure A/C ( alternating current ) - we need to measure D/C ( direct current) Heres a whattmeter And heres the clamp meter.... Edited By Timbo - Moderator on 23/08/2009 16:36:47
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OK here we go with the very basics you need to know - I am only discussing Lipo here, cos far and away this is definately the most popular form of electric fuel today. LiPo ( Lithium Polymer ) batteries come in all sizes, capacities, and voltages.The "S" in the pack description refers to the number of cells in Series, and the "P" is the number of cells in Parallel. If a battery does not contain cells in parallel this letter is usually dropped from the "name". 2s 2p = 2 cells in series, and they are in parallel with another 2.3s = 3 single cells in series. Easy right! Putting cells in parallel keeps the voltage the same but doubles the capacity..... ( the length of time the battery will give power for, or the amount available as a maximum. ) 1 X 2000m/a cell = 3.7V 2000m/a 2 X 2000m/a cells in parallel still = 3.7V but now its 4000m/a capacity, and so on. Putting cells in Series increases the voltage each time, each cell is 3.7V ( nominal ) so...2s battery = 7.4 and a 3s = 11.1V and so on. Capacity remains the same throughout. Motors require power to turn, and the more they are "loaded" with bigger and bigger props, the more current they will take from your battery....lots of it ! If you are using a high power motor and want lots of speed, big props, heavy large models, or long flights and so on then you will need a battery with lots of CAPACITY . The Voltage of the battery only drops a little with this loading, and the voltage will determine how fast the motor turns ( RPM = Revs Per Minute ). Increasing the voltage by using more cells will not only make the motor spin faster, but will cause more current to flow also, and the power goes up as well. Of course, sometimes you dont actually want a high revving model, so beware about using high voltage batteries in this case. As you will see in the MOTORS thread, the motor choice is also very important. Batteries must be properly charged, and "balanced" to ensure each cell in the pack stays at the same level as its neighbour. You CANNOT use a charger that is not specifically designed for Lipos to charge the batteries. You can read a lot more about batteries and chargers from these threads and articles BATTERIES HERE and HERE ..... CHARGERS HERE. And all about the "C Rate " of Lipos over here in an old thread. Edited By Timbo - Moderator on 30/08/2009 23:47:10
