DIY 50Kg赤道儀進度

[hope]

赤經軸也開始組裝了,其實與赤緯軸只是大小不同,赤經軸較大,但只有一端有輸出軸,鎖住赤緯軸:



左邊長的是赤緯軸,右邊短的是經緯軸:



大略組合後是這個模樣:



工作到這裡,因加工精度的問題,須要對減速機外尺寸做修正,麻煩事開始了.

[hope]

今天將赤經赤緯軸組裝起來,好多的螺絲,每根軸都用3個滾珠軸承(兩個減速機自帶,一個是外殼加上的),以增加力臂,使加重之後軸變形減少,用10mm厚鋁板做成的外殼,加上減速機,重錘桿,不含腳架是30Kg,好重啊,加上可伸縮的立柱腳架40Kg,不含電機就已自重70Kg,若加上鏡筒30Kg,就達100Kg了,看來真要帶出去玩,已不太可能了.
重是重,但強度十足,鏡座還沒做,還沒能架上鏡子,但從外觀看來,架個100Kg也不會是問題.
電機及導星控制器還未找到.

組好的上座.


露在外面的二級減速機,赤經赤緯都是1:3600減速比


30mm直徑的重錘桿


與大家熟悉的LXD-75比大小,LXD-75含電機為5.5Kg


伸縮式立柱腳架伸長時的高度,立柱架是國產10X12座機的腳架.最後會把腳輪拆除.

[Wah!]

好重型! 比我還要重一大半!!
反而腳架看來不夠大呢?

[hope]

這個腳架是下截腳座是鑄鐵,中截是實心桿3支,上截是10mm壁厚的剛管,強度是夠的,只是與這鬼東東比起來小一點,但好處是伸縮式的.

[Wah!]

最底下只是三個輪子,如何固定它在地面?

[hope]

3支腳會再加長,腳輪會拆除,否則要晃動的.最後想鍍成枚瑰紅色.

[Wah!]

拆了輪子,如何移動這個"巨人"?

[hope]

練成SUPER MAN

[sharpgun]

3支腳會再加長,腳輪會拆除,否則要晃動的.最後想鍍成枚瑰紅色.

看來你真的想搞個paraｍｏｕｎｔ。。

[clover]

這個腳架是下截腳座是鑄鐵,中截是實心桿3支,上截是10mm壁厚的剛管,強度是夠的,只是與這鬼東東比起來小一點,但好處是伸縮式的.

鑄鐵 .....強度一定好勁~~

[Tarepanda]

為何不把輪子設計成可輕易組裝的?
要移動時才安裝上去
到選好觀測位置才拆一來固定呢?

[Chanlunlun]

這個腳架是下截腳座是鑄鐵,中截是實心桿3支,上截是10mm壁厚的剛管,強度是夠的,只是與這鬼東東比起來小一點,但好處是伸縮式的.

Dear Mr. Hope,

Your mounting is very strong, at the same time very heavy ( you metion that it weights 100 kg ). I have following questions :-

1. May be I'm wrong but it seems to me that the stand doesn't equipped with suffucuent strength to stop the mount from vibrating. Imagine a weight of 100 kg ( !!! , not counting the weight of the telescope) with a height of 4 to 5 feet above floor, the moment of inertia of the whole setup, with pivot on floor, approaches 150 - 160 kg m^2. The stand merely cannot withstand such great moment of inertia to damp out any simple harmonic motion thus created by even a slight bumping on the mount.

2. The latitude angle adjustment mechanisim of the mount seems to be a little bit weak, will the mount just oscillate about this small support ?

3. You are using two worm gears coupled together in series. The gear ratio I gusee at least approaches 6000 to 10000 : 1. You need a motor of around 7 r.p.m for normal sideral tracking and 100 r.p.m for 16 X slow motion. Accounting for the internal friction of the two worm wheels you need a very big motor. If you are using a stepper motor the vibration will be huge, and you need a lot of electrical supply. How can you solve this problem ?

4. How could you solve the problem of slewing the telescope to your target, especially when your gear ratio is up to 10000 : 1 ?. If you are using a 500 X speed for slewing you need a motor speed of 3500 r.p.m. A motor with 7 rpm for tracking and 3500 rpm for slewing, I'm afraid, is not available on market at the moment. You need a special technique ( pulse width modulation ) to drive a d.c. motor. Obviously stepper motor could not provide such great range of speed.

5. The mounting is obviously not a portable one. Are you intending to build an observatory to house it ? Or you will use it in open area provided that the whole setup is water and storm proof ?


Actually we had built a similair mounting for our 10 inch Newtonian. We have selected a gear ratio of 60 for quick slewing to target by hand. The whole mounting is placed on top of the roof and the whole telescope and mounting is weather proof. They just stay there for several years unprotected from rain and storm. Above 5 questions were actually asked by us before we started our work.

The telescope is still in use now. It functions well despite the fact that it has been subjected to rain and strom for these several years. ( 5 years till now )

Hopefully my question is able to keep you shortening the path of being success.

Best regards
Chan Yuk Lun

[hope]

1. 這個腳架只是200元買來的現成品,已有20年了,它的重量達40Kg,且不規則部份都是鑄鐵構造, 同時也看中它能伸縮(這點變成可能攜帶,雖它很重),因原來是大型相機用,所以機體體積不大,三支腳短了一點,這可以稍加長,我想腳架的問題,除極軸角度調整機構較弱,但因不是經緯儀,所以用的時候調整時間不多,且是平牙螺桿做動,我試過加上總重70Kg的物體,調整除了較吃力,但還是轉得動,且螺桿也沒被破壞,倒是角度鎖定的兩個螺栓太小(6mm),這點會再補強.
所有減速機的轉軸都是密封的,全鋁外殼,抗候性不會有問題,腳架除鑄鐵外,其餘都是鋼材,國內還有很多,都很便宜,我就是看中這腳架才有製做這赤道儀的聯想.

2. 關於驅動馬達的問題,我已選用單步角為0.9度,400分割,扭力為1N-M的無減速機步進馬達(24W),以單步0.9度,配原系統1/3600的減速比,每步為0.00025度,0.899角秒,恆星時為0.0042度/秒,每秒要16.8 step,0.042rps=2.52rpm(做為盲跟時的轉速 ).
這馬達可以到2000rpm,我想做為手動或導星,無論扭力及轉速都是足夠的,但還沒裝上試用,結果仍只是猜測.

3. 我是住在市區的,不打算也無法將它固定裝於郊外,我的22公分2700mm折射鏡共兩支,兩支收起都只有120公分長,現場組裝鏡筒不須超過20分鐘,這也是做為外攜的前置準備工作之一,腳架收起為100公分,如此我算過,用一台3缸1000 C.C的小轎車,是可以裝下的.但我在大陸孤家寡人一個,真要完成,不知何年何月才能載出去用,還要無風無雨的天氣,我觀查過最近天像好一點的地方是蘇州太湖邊,離我住的地方為60KM.

[Chanlunlun]

2. 關於驅動馬達的問題,我已選用單步角為0.9度,400分割,扭力為1N-M的無減速機步進馬達(24W),以單步0.9度,配原系統1/3600的減速比,每步為0.00025度,0.899角秒,恆星時為0.0042度/秒,每秒要16.8 step,0.042rps=2.52rpm(做為盲跟時的轉速 ).
這馬達可以到2000rpm,我想做為手動或導星,無論扭力及轉速都是足夠的,但還沒裝上試用,結果仍只是猜測.

.

Dear Mr. Hope,

Stepper motor, however, cannot run in 2000 rpm. Running at 2000 rpm, with the stepping motor you mentioned, you need to supply a 13.3 kHz signal !!! The rotor of the stepping motor just stop down at such high frequency ( called stalling effect, somebody in USA solved this problem by using very high voltage , 2 times to 3 times the rate value, to make the motor run again. But they only achieve 500 to 600 rpm, not 2000 rpm you mentioned. By the way the motor will burn quite easily.) No ordinary stepping motor can response to such a high frequency.!!! The stepping motor you mentioned, ( at 24W, must be very big in size, must have a very high inertia...) I guess, can run at a maximum speed of about 100 to 150 rpm, much slower than what you have expected.

2000 r.p.m is a very high speed for electric motor. Practically only d.c. motor ( or a.c. induction motor ) can run at such high speed. What you need is a pulse width modulation (PWM) method of driving a d.c. motor, instead of using stepping motor.

Best regards
Chan Yuk Lun

[hope]

我用的是無減速機步進馬達,在工業應用上,一般以400分割的0.9度步進馬達可接受送出10K pulse/sec,在以緩步驅動及輕載下,可以到1500rpm,但實際應用不會用到這麼高的轉速(2000rpm是廠家保證值),這個步進馬達是比一般市售赤道儀的馬達要大很多,當然也重,而一般如EQ5之類的步進馬達,因馬達內以包含1/120減速機,所以馬達包裝的輸出軸轉速很慢,馬達的步進角為7.5度,若以赤經軸的減速比為1/144(記憶沒再去回查),再配合1/120的減 速比為1/17280,而我這個為1/3600,比數為4.8,而我用的步進馬達為0.75度,與一般EQ5的7.5度,比數為10,也就是單步的可用角度值是一般EQ5的4.8/10=0.48,所以轉速要高於一般EQ5步進馬達的2倍左右.
2.52是盲跟轉數,5x為12.6rpm,10X為25.2,50X為126rpm,100X為252rpm,這個數字在一般步進馬達是可以輕易達到的.當然在實際使用,不須用到2000rpm.
我之所以用步進馬達,是想用市售國產導星套件,只要稍加修改輸出能力及pulse寬度,便可以完成,不須再設計驅動電路,免得將事情弄得很複雜,畢竟這只是DIY,不是商品,可能就只有一台,不能花太多成本.