無刷馬達的基本概念

YannChen

我再談談無刷馬達的基本認識
一些基本公式我先列出
Kv=RPM / Volts
Watts=Volts x Amps

= Work / Time


= Torque x RPM
Watts = Kp x D^4(4次方) x P x RPM^3 (3次方)
Power (Watts) = Kp * D^4 * P * RPM^3 (where Kp is the prop constant (1.25 for general usage), D is the diameter of the prop in feet, P is the pitch of the prop in feet, and RPM is in thousands.)
Kp of various propellers
Propeller Brand Kp
Top Flite, Zinger, Master Airscrew 1.31
APC 1.11
thin carbon fiber folders 1.18
市面上大部分的馬達都會附上Kv值,或者RPM，從此公式你可預知馬達的最大功率
問題一
How much power is absorbed by a 10x6 propeller that is turning at 9500 RPM?
Recall that:
Power (Watts) = Kp * D^4 * P * RPM^3
The question did not provide a value for the propeller constant, so lets assume that Kp is 1.25 (a good general pupose value).
Therefore:
Power = 1.25 * (.83 ^ 4) * .5 * (9.5 ^ 3)
Power = 1.25 * .48 * .5 * 857.38
Power = 257.21 watts
問題二
Propeller 12 x 8, 多少的 RPM 能運轉功率達到 500 watts
I'll choose a 12x8 propeller.
Lets assume a Kp of 1.25 and solve for RPM using our power equation as shown:
Power (Watts) = Kp * D^4 * P * RPM^3
500 = 1.25 * 1 ^ 4 * .67 * RPM ^ 3
500 = .8375 * RPM ^ 3
RPM ^ 3 = 597.01
RPM = 8.42
問題三
Power (W) = voltage x current = Volts x Amp
A = Power / voltage = Watts / Volts
Substituting our power absorption equation for Watts gives us:
Amp = Kp * D^4 * P * RPM^3 / Volts
But the RPM of our motor is actually equal to the Kv of the motor times the input voltage.
Therefore:
Amp = Kp * D^4 * P * (Kv * Volts) ^ 3 / Volts
Amp = Kp * D^4 * P * Kv ^ 3 * Volts ^ 3 / Volts
Amp = Kp * D^4 * P * Kv ^ 3 * Volts^2
公式與算法有很多種，說太多各位定會很無聊。這些理論上只是給我們一個idea

當然實際上馬達在轉動時一定會有 Loss
INPUT Power 與 OUTPUT Power 一定是不同的
Ohm's Law:
I = V / R
-or-
V = IR
RPM = Kv x V
RPM = Kv x (V – Volts loss)
RPM = Kv x (V - I x Rm)
I: amp
Rm:Ohms

The RPM of a motor is equal to its Kv times the input voltage minus losses due to armature resistance.
The losses due to armature resistance are computed as the input current multiplied by the armature resistance.
假設所用馬達的Kv = 1,000 and an armature resistance of .05 Ohms.
What will the RPM be if the power into the motor is 10 volts at 10 amps?
RPM = Kv x (V - I x Rm)
RPM = 1000 x (10 - 10 x .05)
RPM = 1000 x (10 - .5)
RPM = 9500
說了這麼多，相信有人要說看不懂。要再講我可以寫一篇文章。在此只是提供一些基本的馬達常識，幫助你尋找要的無刷馬達。市面上現有許多可用之測量表，如AstroFlight Watt Metters可以幫助我們很多要的答案。況且現在有很多馬達都已堤供更詳細的Data.
希望對大家有所幫助。

Richard5257

太深奧了~~~看無~~

唉呀~~~豬

偶ㄝ看無~~~~

龍崗小吳

我沒想那麼多耶！
我都是用功率表來量量看，電池、馬達受不受的了！再用轉速計量量看轉速，再用網路上的計算公式(只要套入槳、轉速、電壓、電流即可)，看看推力有多少。

7871497

夭壽~~~豆芽菜都快看不懂ㄌ  現在有搞ㄌ豆芽菜長毛毛蟲 更是霧煞煞~
把無刷馬達複雜話ㄌ起來~~

solomon

原帖由 龍崗小吳 於 2007年5月17日 11:14 PM 發表
我沒想那麼多耶！
我都是用功率表來量量看，電池、馬達受不受的了！再用轉速計量量看轉速，再用網路上的計算公式(只要套入槳、轉速、電壓、電流即可)，看看推力有多少。

可以分享「網路上的計算公式」嗎??