After the lecture of Durk Durksz on biogas, the WOT decided to build its own biodigester. The system is self-constructed and uses 3 regular liquid barrels, as seen on the drawing above.

In the main barrel a substrate of manure and food scraps is present, where anaerobic digestion takes place producing (among others) methane gas. The other two barrels store the produced gas. For this purpose the barrel floats upside-down in the other barrel filled with water, containing the gas at variable volume and about equal pressure.

The system stores up to 120 liters of biogas. At this moment production is about 150 +- 50 liters a week. This is monitored by a wifi-connected Arduino circuit, measuring the temperature of the substrate and the height of the barrel. These values over the last 7 days can be seen in this graph.

Since we already installed a number of rope pumps in the Netherlands, we were looking for a safety brake that is reliable and stultifies the appearance of the rope pump not too much. As users of rope pumps know, the wheel and handle swing back firmly when they stop pumping. In developing countries the user gets instructions to use the hook to prevent turning back of the handle. For public places where anyone can use the pump, the blocking hook will not be used and there is a chance of injuring the user.

Therefore, we searched for an automatic device that prevents the reversal movement.

We have already been experimenting with a kind of rattle that inserts in the spokes of the wheel. Tests showed that the forces were too high resulting in bending the rattle pin. Another solution might be a band brake. This is also tested. These solutions do not look very pretty and they are susceptible to vandalism. Also, the braking power is not sufficient and reliable enough. A third type of a one-way brake with a nail into a wedge-shaped space in the bearing bushing gave good results. Better than expected. The video below shows the principle operation, construction, and testing of the one-way brake.

The days are starting to lengthen and temperatures rise. And on the WOT-field the nature has actually been in effect. Sometime in the distant past on the back WOT-field by a WOT member with very green fingers has planted daffodil bulbs. And miraculously come each spring the daffodils appear in the open field for us to cheer.

After a quick experiment with a drill, an asynchronous electric motor, a capacitor and a lamp, we got the idea to build a generator. The aim was to connect the 3 kW electric motor to a 3.5 hp Briggs & Stratton petrol engine from a lawn mower. We fabricated a frame where both engines can be put down in two evenings. We took some pullyes and a v-belt for the transmission. The electric motor is fixed with wire ends, so the v-belt can be always be set tighter.

After cleaning up the engine the combination works perfectly. Only some vibrations appear caused by the engine. Perhaps the pulley must be fasten tighter or a damping suspension is needed. After that the capacitor must be connected to provide power. More news about the homemade power unit coming soon.

The lamp, we spoke about in the first sentence, had not a long life: After a high number of revolutions and huge light output the 60 watt bulb broke down.

From the Department of Thermal Engineering (ThW) of the University of Twente we got three gas cylinder carts for free! Ideas about what to do with it were found easily. One cart will be modified into a trolley and the other two will probably be combined into a convenient caddy.

On Sunday, January 23rd, Freddy and Rene went to Utrecht to install a rope pump at the patting zoo ‘New Rotsoord’. This pump is the very first sample of a new design: the pump has a single support instead of a whole frame. As a result, the material costs drop 20 percent and the design becomes simpler.
The construction of the pump was done in Enschede. The only thing necessary at Nieuw Rotsoord, was the installation of the pump.

The pump is placed in a concrete foundation next to a 6-meter deep well. The intention is to let the volunteers of Rotsoord make a drive gear based on a bicycle.

Once we receive a picture we will definitely post here.

It’s Christmas time! Like many buildings, the WOT site got a makeover too last week. Thousands of Christmas lights bring magic to the place.
No doubt about it: all lights are LED’s!

It’s worth watching it, especially in snow.

The WOT Diever 450 windmill is being constructed in Biratnagar (Nepal). Students from Pulchowk Engineering Campus are building the windmill for local farmers, who use it for irrigation. Besides the windmill, students have developed a Hybrid Solar Dryer that can be kept warm by wood if there’s lack of sun.

Katrin Shrestha and Brecht Mommen from Nepal visited the WOT last week. They showed us a film about running projects in Nepal. You can watch several projects too; have a look at the website of Clean Energy and Learning Centre .

Quite a large number of T-Week participants are students studying for tropical doctor. To ensure this number won’t decrease the WOT was represented at their Career Fair today. It took place at the LUMC in Leiden. WOT member Mark Westra tried to convinced the 160 students the T-Week would be a valuable experience.
Most students had heard of the WOT before and few of them already joined the T-Week. (Even parents of some students had participated, 30 years ago!)

The smell of melting iron filled the Kiwanda last Thursday night. Menno-Jan and Freddy gave a workshop welding to three students.
After a brief explanation and some cautious trials the three students were allowed to weld all by themselves. By applying tips and advices from Freddy and Menno-Jan their welding become better and better. Their first welded dice soon became a fact.
By the time the workshop was full of smoke the students could demonstrate their acquired skills by welding a watertight cup.
One of the three proved to be watertight. The proud owner immediately upgraded the cup to a tankard.