The making of 30 in telescope - 39, motor drives completed

夸克星 註冊時間: 2003-10-09 文章: 2207

Dear ATMs,

Finally the electric slow motion drive was completed and the whole system, including the electronics inside appropriate housing, was installed and test run today. The motors are running smoothly under the commands from the control panel. At last we no longer need to hand push the heavy scope during star observation. We may also track the target easily by pressing appropriate button even in high powers.

The two motors are controlled by the so-called pulse-width modulation (PWM) technology. The most important advantage of this technology is that it saves a lot of electrical energy during motor motion and it means that the motor could run the whole night through without changing batteries. This is important for star observation in rural areas, where electrical supply does not exist.

All the external electrical connections are made by RCA cables ( used in hi-fi equipment ) and RCA sockets. They are cheap and readily available at anywhere. If the cables are damaged they are able to be easily and economically replenished. These kind of connections are very stable and rugged.

Our next step is to install the GOTO system onto the telescope – yes, you bet it, it』s a big job !

Best regards
Chan Yuk Lun
15-3-2006

主序星 註冊時間: 2005-07-26 文章: 158 來自: kunming

呵呵，陳sir開始進入機械化了。。。。。。 Very Happy

主序星 註冊時間: 2005-07-26 文章: 158 來自: kunming

好像上半部也改動啦？

不知使用效果怎樣？

紅巨星 註冊時間: 2005-04-19 文章: 311 來自: TaiPei,ShangHai

我有疑問!
1. 所有部件會不會都太薄了,既然使用馬達加皮帶傳動,這本身就有一定的定位拉力,就應放棄手動的轉動固定方法,何不把緯軸改採滾珠軸承,用大圓木軸,阻力大也不能平穩轉動,即便用簡單的套軸,也比圓木片板強多了.

2. 底座軸承看不到,但我猜想一定要用圓盤軸承,直徑最少要40公分,否則就要加長軸心,用兩個軸承才能順利轉動.

3. 機械力學的應用在這個系統好像用得較少!

hope

夸克星 註冊時間: 2003-10-09 文章: 2207

Dear Mr. Hope,

hope 寫到:

我有疑問!
1. 所有部件會不會都太薄了,既然使用馬達加皮帶傳動,這本身就有一定的定位拉力,就應放棄手動的轉動固定方法,何不把緯軸改採滾珠軸承,用大圓木軸,阻力大也不能平穩轉動,即便用簡單的套軸,也比圓木片板強多了.

hope

Thanks for your concern.

1. The wood circular plate is resting on a pair of teflon bearing plate, this is the famous Dobsonian design. The telescope is very smooth upon rotation. The other end of the altitude bearing is a ball bearing. We are using a three points supporting system in the altitude axis.

2. hand slewing is a must. When viewing deep sky objects in field the whole telescope must be slewing fast enough so as to save valuable telescope time.

3. The plywood is very thin. We do this with a very good reason - to save money and in particular, the weight so that we could take the telescope to field. Don't worry, the telescope is strong enough. We repeatedly tested it again and again - it could withhstand quite big wind breeze and the optical alignment wouldn't change upon slewing in any part of the sky.

4. You are correct - there is some clearance in the belt in reverse motion. But the waiting time is just about one second, we completely accept this.

hope 寫到:

我有疑問!

2. 底座軸承看不到,但我猜想一定要用圓盤軸承,直徑最少要40公分,否則就要加長軸心,用兩個軸承才能順利轉動.

hope

1. The azimuth bearing is 4 nylon rollers rolling on a base plate. There is no need to use "Lazy Sussie" type table bearing for two reasons - A. it is not stable, and B. it cannot hold the weight of a 30 inch telescope ( these bearing designed for table serving, not for great thrust ). Nylon rollers are very smooth, and designed for taking up great thrust.

hope 寫到:

我有疑問!

3. 機械力學的應用在這個系統好像用得較少!

hope

It could be that the ugly outlook of the telescope produces an illusion that there is no mechanical designing involved. Just the opposite, very great amount of mechanical enginnering has been placed onto the design of this 30 inch big telescope -

1. Think about this - a traditional 30 inch telescope weights 5-7000 kg if resting on equatorial mount. Now we made it only 40 kg, without great input of mechanical enginering this could not happen.

2. The telescope is VERY SMOOTH upon hand slewing. We have been paying great deal of engineering on the design of bearings on both axis. The altitude bearing is a three point supporting system by two teflons and one ball bearing. The azimuth bearing is a 4 point roller system for maximum stability and minimum friction. The telescope is surprisingly stable despite the use of very thin plywood.

3. The two driving motors also involves unthinkable amount of mechanical designing and fabrications. We made all the metal components ourselves. As usual such costum fuction motors are not available in market. So we made all the connectors, motor frames, releasing cluthes.....by a small lathe in our optical shop.

4. We have to design a practical GOTO system for the telescope because we don't want to waste time in targeting in field. I always emphasis the valuable telescope time, this is especially true for big telescope. The GOTO system is still under designing stage but will soon be completed.

5. Last but not least the motors have to be served by very small amount of current yet producing great enough torque since in the field there is no electrical supply. Every thing is run on batteries. This call for special electronic driver circuit which is called the "Pulse Width Modulation" to save energy. We have designed the circuit but fortunately we soon discovered that there is commercial kits available in Ap Liu StreetBut we still need to couple it to the driving motors. The coupling need lots of mechanical engineering.

6. Of course we intended to fold the optical path in the future and this, again, needs designing on to how to hold the giant flat secondary without flexture, on a thinplywood structure.

If we have a fixed observatory the enginnering problem will be simple - steel work and AC power supply. Unfortrunately this telescope is intended to be a portable one ( we now even think about to carry it to Yunan for star observation ) and since we are restrained to use thin plywood only ( money, student abilities, weight constraints ) mechanical design involved is much heavier than a conventional one.

Engineering, in my humble opinion, is a job to maximized the effect from minimum resources. I think we are just doing this.

Thanks for your questioning. We are being benefited from your opinions and comments, as always.

Best regards
Chan Yuk Lun

紅巨星 註冊時間: 2005-04-19 文章: 311 來自: TaiPei,ShangHai

看來我在內地玩DIY,會比在香港有優勢一點,材料與加工費相對都較低,資源也豐富一些,比如用2mm鋁板做的50CM直徑160CM長度的3截式伸縮鏡筒才花RMB:600元,所以往往會往深一點的地方去想,在台灣,我不可能玩這些,最多玩玩10公分鏡,對香港的居住面積及物價及加工費我還算清楚,Chanlunlun兄在香港玩鏡如此的想法是對的,畢竟我沒在香港長住過,對某些事習慣上會有不同的想法.所有的設計都要實踐後才能定奪結果,上篇只是我光看外觀的想法.但最後的結果還是Chanlunlun最清楚,加油啊!但如同上次帶到雲南,這30吋鏡更難實現了.

我的40公分鏡也打算做DOB型式(與赤道儀式共用),對於赤道儀式已定案,但DOB式還在想如何能好運作又方便收藏,可能會抄襲Chanlunlun的做法喔!到時可別投訴我~ Laughing

~

hope