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米Teen唔鐘意玩現成品,喜歡由零件開始砌。99次失敗唔係問題,最緊要係有1次成功!

米Teen總部設在聖公會白約翰會督中學506室,在午膳後和放學後集會。有興趣參與的同學,請與會長或導師聯絡。

米Teen專頁

506室內 2020-11-01 10:16:17
溫度 28℃ 濕度 95%
街景 2020-11-01 10:16:43
街景
5樓室外 2020-11-01 10:16:21
溫度 28℃ 濕度 7%
街景 2020-11-01 10:14:48
街景

「米缸」米Teen的智能魚缸

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米Teen X 良師啟導計劃 -- 本校每年都有良師啟導計劃,老師會親自帶領個別學生像師徒般傳授知識。今年度(2019-2020)米Teen與良師啟導計劃合作,參與的學生負責設計及製作一個約6呎x1呎x1呎的電腦控制環境及監察的智能魚缸。整個製作都是由基本材料組成,成員可以學到DIY和各種技術,計劃內容包括有各種STEAM的元素。

本計劃仍在進行中,以下內容會不斷更新。

規格(2020.4.7更新)

魚缸:外部量度84"x14"x17",用4分厚玻璃,內部容水量83"x13"x14"
水容量:~248L ~546磅重
底架:2"x2"一分厚鉛水角鐵、燒焊、上防鏽漆及半啞磁油
控制:各系統由獨立的微電腦控制
系統:餵食系統,恒溫系統,過濾系統,燈光系統,數據收集

組長

餵食系統:4C楊尚餘
恒溫系統:4C趙心怡
過濾系統: 4C張喆熙 4D鍾卓林
生物化學: 4C黃逸朗 4C張喆熙
外觀設計: 5B鄧凱兒

工作進度

構思計劃
	2019.10-11月
焊製底架
	2019.12月-2020.1月 
訂造魚缸
	2020.1月
安裝喉管及過濾系統
	2020.2月-4月
恒溫系統
	2020.3月-4月
餵食系統
	2020.3月-4月        
...............
完成
	希望在7月完成

4C楊尚餘

餵食系統

共有兩個設計方案,兩者皆用stepper motor推動餵食裝置,由Arduino UNO控制。

  1. 方案一
  2. 最初的設計靈感來自扭蛋機,經實驗後發現魚糧因設計問題而卡住系統,因此參照水車設計改為垂直設計,經過重重實驗而改成現在的摩天輪設計。此設計可避免因糧食卡住的問題同時增加靈活度。

    初型扭蛋機設計 二代水車設計

    修訂後的設計類似摩天輪,共有6個飼料倉格。在指定時間,程式會啟動stepper motor將摩天輪轉動60度,令倉格內的飼料跌進魚缸中。

    設計飼料倉格 三代飼料倉格設計 3D打印一個飼料倉格需要90分鐘 鐳射切割和3D打印的飼料倉格 三代摩天輪設計 方案一:類似摩天輪的設計

  3. 方案二(研發中)
  4. 設計的靈感來自輸送帶。類似輸送帶的設計,利用齒條搭配 stepper motor以推動擋板餵食魚糧。在指定時間,程式會先倒出一定份量糧食,然後啟動stepper motor配合齒條推動食物。

    方案二:初型活塞設計


4C趙心怡

Heating system

Nichrome wires are used for the heating element of our fish tank. Nichrome(Cr20Ni80) is commonly used for making heating elements of electrical appliances because 1) nichrome has a high melting point, which prevents it from melting from the heat produced and 2) nichrome has a high resistivity and therefore a high resistance, which leads to faster generation of heat.

In order to maintain the water temperature of the fish tank, we need to compensate for heat loss into the surroundings by supplying an equivalent amount of heat to the water.

Calculation:
Heat loss is due to the difference between the temperature of the inner surface of glass (water temperature) and that of the outer surface of the glass (room temperature). It is calculated with the formula Q=U*A*ΔT. Q is the heat loss per second. U is thermal transmittance, which is the rate of heat transfer through matter. A is the size of the area in which heat loss occurs. ΔT is the temperature difference.

Since the optimal water temperature for fish is 24-27°C, we set the upper limit of water temperature as 27°C. And since the lowest temperature in Hong Kong is around 10°C, we set the lower limit of water temperature as 10°C. Therefore, the maximum temperature difference ΔT is 17°C.

U of glass= 4W/m2°C
U of plastic= 0.2W/m2°C

The 4 sides and the bottom of the tank are glass, while the top is covered by a plastic sheet.
Height of the tank=42cm
Length=214cm
Width=35cm
Area of the 4 sides and the bottom(glass)
= 0.42×0.35×2 + 2.14×0.42×2 + 2.14×0.35m2
= 2.84m2
Area of the top(plastic)
= 2.14×0.35 = 0.749m2
Maximum heat loss through glass
= 4×2.84×17W = 193W
Maximum heat loss through the plastic sheet
= 0.2×0.749×17W = 2.55W
Total maximum heat loss
= 193+2.55W = 195.55W

Since there will be further heat loss into the glass and heat loss due to the water circulatory system, extra energy needs to be supplied in order to fully compensate for heat loss. Therefore, taking the design of commercial products as reference, we decided to supply a total of 216W through 12 sets of nichrome heating wires each of diameter 0.5mm.

Calculation:
The resistance of each wire can be calculated with the formula R=ρL/A, where R is resistance, ρ is resistivity, L is the length of the wire and A is the cross-sectional area.
ρ of nichrome = 1.09×10-6Ωm
L of the wire = 1.5m
A of the wire = (0.0005/2)2π = 1.96×10-7m
Therefore, R= 8.32Ω
By measuring the resistance of the 1.5m nichrome wire with an ohmmeter, we obtained a result of 8Ω.
The power of each wire can be calculated with the formula P=V2/R, where P is power, V is voltage and R is resistance.
V=12V
R=8Ω
Therefore, P=18W
For 12 sets of wires, total P =18×12= 216W

The nichrome wires are each contained within a 1.5m long glass tube. However, the glass tube is in danger of cracking if the wire is heated to a great extent in a short time. Therefore, to ensure the safety of the heating system, we carried out an experiment in which a single 1.5 m nichrome wire of 0.5 mm diameter is heated, with a voltage of 12V. The wire was simply placed on a table under room temperature and pressure. Throughout the experiment, there were no abnormal signs and the surface of the glass was warm to the touch. The positive result shows that there is no danger of glass cracking and the system is safe to use.

The heating system makes use of proportional control. Proportional control is a control system technology based on a response in proportion to the difference between what is set as a desired process variable and the current value of the variable, which means that the greater the difference, the greater the response and the smaller the difference, the smaller the response. In our case, the power supplied to the heating element decreases as the water temperature approaches the desired temperature. This helps maintain a stable water temperature and ensure rapid response, which enhances accuracy. When the temperature of water exceeds the appropriate temperature, the system will be turned off to prevent overheating.

Nichrome wire in glass tube Sealing the end of a glass tube 1.5m heating tube Group of heating tubes

過濾系統

水泵一:HAILEA海利HX8860 130W 5800L/h 揚程4.1m
水泵一的流量為5800L/h,馬力太強,水流過猛,去水速度跟不上,不宜使用。
水泵二: HAILEA海利HX8830 45W 2900L/h 揚程2.3m
水泵二的流量實驗結果:13.2L/36.75s,約為1293L/h,適合使用。
過濾箱一(頂層):平分水流的灑水蓋,過濾棉
過濾箱二(中層):活性碳
過濾箱三(底層,左):培養消化菌
過濾箱四(底層,右):打氣石(HAILEA ACO-9610 4出口 10Lit/min 0.015Mpa),水位監察器,水泵

Diameter of holes: found by doing experiments to test the flow rate against the density and diameters of the holes. Some adjustments were made to optimize the results. Acceptable result is obtained using 3.5mm drills to make the holes.

No. of holes: determined by calculating the surface area of the pipe opening and the diameter of each hole.

Distribution of holes: to make water flow in a certain rate and to clear suspended particles in all heights.

Function of overflow tube: to let excess water flow out and to control the amount of water in tank.

HX8860水流太猛 HX8830水流適合 製作過濾系統的入水喉管 製作過濾系統的分隔層 電子水閥 吸水管


4C黃逸朗

硝化細菌

  1. 氮循環
  2. 硝化細菌在氮循環中扮演很重要的角色,負責把泥土中對生物有毒的氨硝化至可以繼續讓植物吸收氮的硝酸鹽。而在我們的「米缸」中,魚缸裏的魚排出的糞便中也含有對生物有毒的銨。因此我們使用硝化細菌來令氨轉變硝酸鹽,而被植物吸收。

  3. 使用方式
  4. 直接使用,每100L水加90ml細菌,每日一次。

  5. pH值對硝化作用的影響
  6. pH值會影響水中分子性氨(NH3)與離子性銨(NH4+)的濃度平衡,其中只有分子態氨能用於硝化作用。在總氨量一定狀況下,pH值越高,氨濃度比例越高。因此用於硝化作用的反應基質濃度越高,硝化速率越有利。換言之,硝化作用在中性或鹼性環境遠比在酸性環境中更能快速進行。此外,pH值會直接影響硝化酵素的活性,通常最適pH值約為7.5~8.2之間,依溫度不同而有所差異。由於硝化作用中會產生硝酸,造成水質酸化,會使pH降低,影響硝化作用。

  7. 溫度對硝化作用的影響
  8. 溫度主要會催化硝化反應的酵素活性,最適溫度約在35~40℃之間(28~32℃為「米缸」使用的細菌建議溫度),但還需視溶氧濃度取得一最高效率平衡。一般以不超過30℃,不低於20℃為較佳區間。

魚缸製作過程

切割角鐵 固定角度,預備燒焊 清理焊渣 上防鏽漆及半啞磁油 上防鏽漆及半啞磁油 魚缸底架的木板修邊 噴油 底板開去水喉位 鑽孔固定魚缸支架 鑽孔固定魚缸支架 初次入水測試 測試電動去水閥 安裝水管 安裝水管 測試整體的水流循環

welcome

 Album 

米Teen唔鐘意玩現成品,喜歡由零件開始砌。99次失敗唔係問題,最緊要係有1次成功!

米Teen總部設在聖公會白約翰會督中學506室,在午膳後和放學後集會。有興趣參與的同學,請與會長或導師聯絡。

米Teen專頁

506室內 2020-11-01 10:16:17
溫度 28℃ 濕度 95%
街景 2020-11-01 10:16:43
街景
5樓室外 2020-11-01 10:16:21
溫度 28℃ 濕度 7%
街景 2020-11-01 10:14:48
街景
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