The Crocodile's Bucket & Chain Water Pump

We are The Crocodiles and this is our ‘bucket & chain’ style water pump. We are a group of Product Design Engineering students and were given the brief to construct a water pump which lifts 5 litres of water up a height of 600mm, in under 5 minutes, using the 24v motor provided. The winning team would be the one which completed this task in the most efficient way possible – voltage and amplitude were measured, as well as the total time taken. We decided that simplicity was the key and started work on a Bucket & Chain system.

Step 1: Concept & Planning

After discussion, research and idea generation we came up with a concept for how we could make a bucket and chain pump that would fit the tank provided (pictured below). Our idea consisted of a simple wooden frame, two belts and five water containers – equidistantly spaced along the belt for maximum stability. One of the main features of our design was an adjustable arm that allowed the system to collect water at various gradient increments, meaning that it could be adapted to suit the water level of the tank. Here is a rendered image of our concept (made in SolidWorks):

Step 2: Materials

Materials:

Pine (frame)
MDF (swing arm)
Screws: M5x40mm
Bearings: 26x10x8 mm
Aluminium (gear-axle connection, brackets)
Sheet Acrylic (gears)
Grub Screws
Foam (spacers)
Styrene (guide plates)
Rubber Belts
Tin Cans (vessel)
Zip Ties,
10mm Steel Rod (axle)

Sourced:
Plastic Robotics Gearbox (Maplins)
24V Motor & Power Source

Step 3: Constructing the Frame

We decided to construct our frame out of 62x37mm pine beams because they were readily available in our workshop, had a relatively good strength to weight ratio and wouldn’t be affected by the time spent underwater in the tank.

1. Cut the required lengths (as measured from our general arrangement drawing) of pine
2. Drilled holes for the bearings
3. Clamped into desired form to prepare for fastening.
4. Fastened together using wood glue and screws (hand drill), into a form of A-frame (as shown in SolidWorks image)
5. Repeated for other side of frame.

Step 4: Adding the Swing Arm

The swing arm would allow us to adjust the gradient of the system.
This is how we constructed it:

1. Marked the curved shape onto a sheet on mdf
2. Cut using band saw
3. Drilled 10mm holes spaced 100mm apart along the swing arm
4. Drilled one 26mm hole at one end of the arm for the bearings
5. Repeated for second swing arm

Step 5: Attaching the Cups to the Belt

1. We sourced two belts that met our spec from the website [http://www.bearingboys.co.uk] and next had to attach five cups to the belts.
2. To do this we made five brackets by cutting and bending 3mm thick sheet aluminium.
3. Drilled two holes in each bracket for attaching to belt
4. Drilled two more to use with zip ties
5. Fastened to belt using small bolts countersunk into spaces between the teeth, equidistantly around the belt.
6. Attached the cups to the holes in the brackets with the zip ties

Step 6: Making the Gears

We sourced some 10mm steel rod to use as the axles and next had to make gears to fit the belt.

1. Measured the spacing between the teeth on the belt with digital callipers.
2. Used SolidWorks to draw out a stencil for the gears
3. Laser cut this shape out of 4mm sheet acrylic (x8)
4. Cut a rough spacer plate out of foam to place between two of the gears (x4)
5. Cut two guide plates out of 2mm thick styrene, for either side of the gear sets. This was to insure that the belts wouldn’t slip, causing the system to fail.

Once we had made these gear ‘sets’ we had to find a way to connect them to the axle without slipping. To do this we had four aluminium lathed parts that would effectively allow us to grub screw the gear sets to the axle. These are also shown in pictures below.

Step 7: Assembly of System

It was then a case of assembling all the aforementioned components into one system that would fit  the tank.

1. The bearings were push fitted into the holes on the frame
2. Gear sets fastened onto axles
3. Belt configuration placed onto gear sets
4. Axles slid into bearings, into frame
5. Swing arm locked into place with aluminium rod

We then placed the system into the tank to check that everything was ready for testing.

Step 8: Motor and Gearbox

We decided it would be more time effective to buy a gear box, rather than make one ourselves.

1. We sourced a plastic robotics gear box (from a Maplin store) to allow the motor to turn the axle.
2. The gear ratio we were looking for in order to turn our axle was 260:1, which this gear box provided.
3. We then connected the motor to the gear box and mounted this to a piece of MDF.
4. This was then lined up and the motor shaft was grub screwed to the axle.
5. The whole system was then mounted to the frame.

Step 9: Finale

Unfortunately the robotics gearbox failed us as the little plastic gears couldnt handle the amount of torque we required and started to shear. By the time of the event we were still unable to fix the gearbox, however we did manage to run the pump by connecting a hand drill directly to the axle. Here is a brief video of the pump in action.