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標題: 想問問冇刷有感馬達t數和扭力問題 [打印本頁]

作者: 呀杜 時間: 2010-9-23 15:46
標題: 想問問冇刷有感馬達t數和扭力問題
各位師兄你好:
我是新人,本是玩油車的,想轉玩電車,但看到電變,冇刷有感馬達上的數字一大堆問號就走出來????
很多問題想問問各師兄
1)電變上的A數是否越大越好?
2)馬達上的T數與扭力,如3.5T有否足夠扭力,23T是否沒足夠馬力,有沒有平衡點數字??(我應該買一個什麼T數的馬達??有12級油車速度是那個T數???)
3)電變和馬達那個牌子較好??

先謝謝各師兄

作者: bravohk 時間: 2010-9-24 19:03
小弟都曾經想問這個題, 但想到本地論壇的氣氛和網民裝備後還是放棄:
1.本地論壇什少提及物理參數,包括扭力,轉速,推重比,只有由商品附帶的"理論"研習出來只有幾何但沒有數學基礎的所謂"SETTING"
2.找舊貼你會得知類似的問題總會得到貴=所有參數都高的結論
3.即使有公式,因車重,推力等數值太小誤差百分比大到根本沒有意義

作者: kiev 時間: 2010-9-24 22:02
12級有多少馬力？

作者: 50270898 時間: 2010-9-24 22:36
Power = Voltage * Current
電池電壓假設不變, 能處理更大電流就可以處理更大功率摩打
摩打係恆功率, 高轉速時低扭矩, 低轉速時高扭矩
Tamiya 23T stock spec個盒背面有條轉速與扭矩嘅curve
另外好似只有LRP摩打有摩打功率

作者: A300 時間: 2010-9-24 22:45

12級有多少馬力？
kiev 發表於 2010-9-24 22:02

登錄/註冊後可看大圖

= 1.0 - 1.6 ps

作者: ryancmlam 時間: 2010-9-24 23:03

小弟都曾經想問這個題, 但想到本地論壇的氣氛和網民裝備後還是放棄:
1.本地論壇什少提及物理參數,包括扭力 ...
bravohk 發表於 2010-9-24 19:03

登錄/註冊後可看大圖

Agree with you observation, and because of your post, I will try to apply my limited mechanical engineering knowledge to share my views.

1)電變上的A數是否越大越好?
In general, yes. A higher current rating means the ESC can withstand higher current without suffering from overheat. The amount of heat dissipation is a function of current and internal resistance of the FET, and usually, a FET with higher rating would have a lower internal resistance. As such, a higher rating ESC will usually let the user feel it have more "punch"

2)馬達上的T數與扭力,如3.5T有否足夠扭力,23T是否沒足夠馬力,有沒有平衡點數字??(我應該買一個什麼T數的馬達??有12級油車速度是那個T數???)
T means the no. of turns of the stator coil. The lower the T, the lower the back emf and hence the rotor needs to rotate faster to get its back emf close to the supply emf. Torque is proportional to the current, normally a high speed motor will have less max. torque than a low speed one. 3.5T有否足夠扭力 is depend not only on the motor but also the overall gear ratio of the transmission. You can get a high torque at wheel shaft with a very high speed motor at a extreme high gear ratio.
If you make reference to the hobbywing esc menu, you will know the power of a 3.5T brushless motor is 600W and 17.5T is 150W .

Do you know the power of a 12級 engine ? as far as I know, the power of a .21 engine (3.5cc) is around 3 h.p = 3 * 746 ~ 2200W.

3)電變和馬達那個牌子較好??
-較好: if you are looking for a "value for money" stuff, I would say Speed Passion.

作者: ryancmlam 時間: 2010-9-24 23:05

Power = Voltage * Current
電池電壓假設不變, 能處理更大電流就可以處理更大功率摩打
摩打係恆功率, 高轉 ...
50270898 發表於 2010-9-24 22:36

登錄/註冊後可看大圖

恆功率 = constant power.
As far as I know, electric motor is not a constant power device.

作者: kiev 時間: 2010-9-24 23:27
1 ps 大約係 735W 大約係激既 4.5t 又或者係 5mm shaft 果種 3650 摩打

1.6ps 差唔多係玩 1/8 4s 摩打

不過從油初轉玩電 5.5t ~ 8.5t 較合適~~~

作者: 50270898 時間: 2010-9-25 00:22

恆功率 = constant power.
As far as I know, electric motor is not a constant power device.
ryancmlam 發表於 2010-9-24 23:05

登錄/註冊後可看大圖

power = torque * angular speed
恆功率指torque與angular speed的關係

你所指應該係輸出功率
輸出功率同負載有關
答案一定唔係恆輸出啦

作者: ryancmlam 時間: 2010-9-25 02:00

power = torque * angular speed
恆功率指torque與angular speed的關係

你所指應該係輸出功率
輸出功 ...
50270898 發表於 2010-9-25 00:22

登錄/註冊後可看大圖

50270898 hing,
if you would like to explain 高轉速時低扭矩, 低轉速時高扭矩. it could be simply explained by using the typical torque speed characteristic curve of a dc motor. The torque is inversely proportioal to the speed of rotor. 功率 is a product of speed and torque, it is not a constant, i,e, not 恆功率

作者: ryancmlam 時間: 2010-9-25 02:09
本帖最後由 ryancmlam 於 2010-9-25 02:12 編輯

Just got a graph from internet to explain the relationships amongst Torque, Speed and Power of a dc shunt motor.

You can observe
1. High speed, low torque, => low power
2. Low speed, high torque => low power
3. medium speed, medium torque => high power
i.e. the power is not constant

: 登錄/註冊後可看大圖

作者: bravohk 時間: 2010-9-25 12:24
理論上大齒比配少T摩打和小齒比配多T摩打, 何者power lost較大?

作者: ryancmlam 時間: 2010-9-25 19:54
I guess the power lost should be indepedent of 大齒比配少T摩打和小齒比配多T摩打. It depends on the efficiency of the transmission.

Would any mechnical engineer pls advise

作者: pskyng 時間: 2010-9-25 20:53

難得咁多勁人..可否問一問..
若我用過高KV motor 於一個A數不足以support 的電變上. e.g 我用 60A 電變配落 4.5R motor..
後果係..
1.燒電變. (請問原因?)
2.不會燒任何野. 是否只是那motor 因為電變供電不足去不到4.5r 應有的速度?. (請問原因?)

作者: ryancmlam 時間: 2010-9-25 21:17
The motor will 去到4.5r 應有的速度 but the ESC will stop function soon because of overheat.
Normally, the overheat protection circuit will stop the ESC before 燒電變 . 燒電變 is a general term as a result of motor demanding a high current that the ESC is unable to affort. The current carrying by each FET is higher then their rated value and cause high temperature. If the overheat protection circuit doesn't work, the FET will burn out.

作者: pskyng 時間: 2010-9-25 21:23

The motor will 去到4.5r 應有的速度 but the ESC will stop function soon because of overheat.
Normall ...
ryancmlam 發表於 2010-9-25 21:17

登錄/註冊後可看大圖

oh , thanks a lot ryancmlam hing.

作者: 呀杜 時間: 2010-9-26 00:39
thanks ryancmlam

非常專業,
希望得閒可敎多D RC知識給我們,謝謝

作者: gavl 時間: 2010-9-26 00:49
本帖最後由 gavl 於 2010-9-26 01:08 編輯

想請教如果 e.g. LRP 網業上有motor 資料 power consumption 的話，咁可唔可以知道究竟需要幾多A先足夠推動？

難得有師兄出手教路, 多謝嗮!

作者: bravohk 時間: 2010-9-26 00:50
本帖最後由 bravohk 於 2010-9-26 00:51 編輯

再請教ryancmlam師兄:
小弟想透過測試車速以配搭出最接近摩打最高理論轉速的齒比
設小弟有大,小pully(前後一樣),大齒,摩打齒的牙數和直徑車輪直徑 ,及車速, 請教計算摩打angular speed的公式

作者: ryancmlam 時間: 2010-9-26 10:23

想請教如果 e.g. LRP 網業上有motor 資料 power consumption 的話，咁可唔可以知道究竟需要幾多A先足夠推動 ...
gavl 發表於 2010-9-26 00:49

登錄/註冊後可看大圖

1. Would you pls share us the link of motor spec. ?
2.要幾多A先足夠推動 depends on the loading condition of your motor, high in a heavy car and low in light car.
3. In general, the power consumption quoted is value measured understand the certain condition, and usually an average value. The current required to power up the motor depends on the loading condition, i.e. the amound of output torque required. The current would instantaneously build up to a very high value, many times fo the average value. That's why you can see there are usually 2 values of current quoted in ESC, one is contineous value and the other is instantaneous value. The ESC is able to drive the motor at the begining but, depends on the loading condition of the motor, the protection circuit of the ESC will operation and cut the esc if the loading of the motor is higher than the esc can withstand.

作者: ryancmlam 時間: 2010-9-26 10:56

再請教ryancmlam師兄:
小弟想透過測試車速以配搭出最接近摩打最高理論轉速的齒比
設小弟有大,小pully(前 ...
bravohk 發表於 2010-9-26 00:50

登錄/註冊後可看大圖

Linear car speed = v (m/s)
wheel radius = r (m)
wheel angular speed, w = v/r (rad/s)
Transmission geat ratio = n:1
motor angular speed, w = nv/r (rad/s)

If we convert the unit from m/s to km/h (1 m/s = 3.6 km/h) and rad/s to r.p.m (1 rad/s = 9.55 rpm) , the equation would become
motor rpm = n (3.6 v)/ (9.55 r) = 0.377n v/r

Assume speed of touring is 100 km/h with a gear ratio of 8:1 and wheel radius of 3cm, motor rpm = 0.377 x 8 x 100 / 0.03 ~ 10000 rpm.

You can observe that 10000 rpm is speed of a ~1400 kv motor and how come faster like that. Pls note it is a theoretical value only, if you take into account the loss due to transmission, friction, road slip etc, I guess it is in the order.

As it is just my rough calculation, may not correct, would Mechanical Engineer pls comment and share you view pls.

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