(This was in response to ads that had clearly specified a price, and some that had a link to pictures. Trade off is a heavier battery and bigger ESC.Send me the picture and the last reply to ads that already show a price, and don't mention a picture, this lazy bugger who didn't even fill in the subject with something about the ad is a pathetic giveaway.)ĭo you still have it ? I am interested. High rpm (high kv) is less efficient than a low Kv, higher voltage set up. Measuring efficiency as voltage changes for different Kv motors. Bigger diameter motors procude more torque (basically more leverage), but so to longer motors. Motor size and torque: Diameter vs length. Volt and amps can change, but V*I won’t change. The same motor at different Kvs doesn’t change the output torque. Kt, torque, volts, amps video: Kt = 1/kv (torque constant) not the same as actual torque: Torque = kt*I. Lower KV = more windings = supports higher voltage = smaller wire = more resistance (and waste heat/power loss) = same power at less amps. KV and efficiency video: Motor resistance (ohms) waste heat = P=I*I*R. It’s worth checking out to get an idea of acceptable combinations. Still, the e-props folks match multiple props to each specific IC and electric motor. Unfortunately, the the 36”-44” range of HG eharness props are 10-20% smaller than powered paramotor props–meaning we can’t leverage PPG forums and vendor data as information sources. Sensorless motors are lighter, less complicated, and less prone to failure. ESC manufactures improve efficiency and performance by using sensorless synchronization at high speed to alter the timing for the sequence of power pulses sent to the motors windings. While sensorless brushless motors perform poorly at low speed, their performance at flying speeds is excellent. Low cost custom KV: MAD motor, Alien Power Systems/FreerchhobbyĬharles Allen reports that APS provided a custom motor with a hollow shaft for ~$25 extra so he could use a rod to articulate a variable pitch prop. KV reduction Ĭustom rewinds change the KV rating and RPM. Probably useful to know if one of the larger diameter 35kv or 27kv motors marketed for use on paramotors is being considered. There is also a suggestion that the lower the no load kv value of the motor the greater the 100% duty cycle reduction factor. You need to determine this yourself or accept the numbers a manufacturer provides for a specific propeller.Įdit or copy the database Motor spec reality check You should have already calculated what you need for example: 25Kg of thrust at 50-70% throttle for 5 climb minutes with 12s batteries to climb to 1000’. You’ll have to use a combination of math, data table reading, and dice rolling to formulate an idea about what’s likely true. Dynamic thrust (when moving through the air) is far less. Thrust values derive from static thrust on a test stand with a specific prop. Some vendors user 1 minute, others 2 to 5 minutes or more. For example, “continuous current” doesn’t mean much unless you know the time frame. It’s worth checking Alibaba, Amazon, eBayĭon’t blindly trust published data or what’s in the table below. For example, APS sells Freerchobby motors. Some motors are marketed by others at higher prices. DC power trains are limited to max continuous power limitations (heat). Note the following:įor reference: Mosquito 10.4 kw, Wasp 10.4kw, Mossi 11.2kw: but an IC engine has a 100% duty cycle and can continuously run at full throttle. Unfortunately, comparing motors based on published specs is as difficult as walking up an Escher staircase. Other items you might care about are beyond the scope of this document, including thickness of the magnet laminations, magnet type, number of poles, wire pressure test, max temps for wire and magnets, etc. Internal resistance: Lower is better since resistance = heat. Lower KV motors have more permanent magnets to increase torque. The number before the letter N is the quantity of electromagnets in the stator, and the number before P is the quantity of permanent magnets in the motor. N and P numbers: something like “36N30P”. Design a system that does not exceed the max current for the short time specified by the manufacturer (often 60 seconds). Max current: How many burst amps you can draw at full throttle. It’s a good idea to design a system that’s operates around 50-70% of max current during climb to reduce heat and allow for power headroom. You may need “continuous” for your climb duration. Data sources are sketchy,Ĭontinuous current: How many amps the motor can handle for the number of minutes specified by the manufacturer until it overheats. You don’t have to do it naked, but you do have to do it. TBD: Intro Motor specification wrestling
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