Sir Mix-A-Lot was designed or the purpose of being embedded into a refrigerator. Due to the size and the number of components used within this project there was a significant amount of mechanical design and construction required.

Design Solution


The Fridge was adopted from a cabin up in Shawnigan. The donated 'Hudson Bay' company fridge had put in its time and was lucky to move onto such a prestigious honour as becoming the ultimate drink fridge.


The fridge started of as a stand alone circa 1960’s Hudson Bay harvest gold refrigerator/freezer. Sir Mix-A-Lot did not require a sub zero operating temperature – in fact this would be detrimental to some of the liquids inside, due to freezing. Sir Mix-A-Lot also required a substantial amount of room. The constraint led us to removing the barrier between the fridge and the freezer. The vegetable crisper at the bottom of the fridge was also removed to increase the usable area inside the fridge.

Hole in Bottom of Fridge

Sir Mix-A-Lot requires access for communication and supplies. To keep that aesthetics of the fridge, it was decided to route these lines through the bottom of the fridge. This allowed us to connect the pumps to the external circuitry, as well as supply power to the carbonator. The carbonator also required a pressurized water inlet as well as a CO2 line. The only other thing that needed to be routed though the hole was the connection to the LCD mounted in the freezer door.


The insulation was changed from a fiberglass to Styrospan This was done for two reasons: safety and thermal reasons. The Styrospan was safer to handle and manipulate that the fiberglass since there where no glass partials. The Styrospan also hand a higher thermal temperature coefficient. After changing the insulation inside the fridge doors the back covers to the doors where changed to aluminum sheeting. This gave the fridge a cleaner look when the doors where open.


The fridge was also painted a flat black for esthetic reasons. This was done using spray paint due to its ease in covering an area such as the outside of a fridge. Spray paint also has a fairly decent look when it has been done correctly.


The LCD needed to be mounted at a height such that it was easy to use. It was decided that mounting the LCD in the freezer door would get this result. It would be directly at eye level so that it was easy to read. This also was right put the user right in front of where the drink would be dispensed.


The LCD required that a hole be cut in to the front of the door of the freezer. After this was done the LCD still needed to be mounted in such a way that people would be able to press on it with a substantial force with out moving it or breaking it. This needed to be done inside the freezer door. Two vertical bars where mounted on the back of the LCD and then the bars where attached to the edge of the freezer door.


Moisture is a concern when ever working with expensive electronics. The cords from the LCD needed to be run inside the fridge and out through the hole in the bottom of the fridge. This meant that there was a hole through the flashing on the back of the freezer door. This could potentially allow moisture to condense on the LCD – damaging it. To solve this problem a vapor barrier was created between the inside of the fridge and the LCD.


The pumps used in the Sir Mix-A-Lot were off the shelf replacement windshield washer pumps used in automotive applications. Twenty pumps needed to be installed in and organized manner to the walls of the fridge.


It was decided that we would mount the pumps according to the circuitry such that there would be four busses each containing 5 pumps. Four 1” x 2” by 914mm bars of oak where cut, so that 5 pumps could be mounted via screws to each. The pumps and bars where then attached to the sides of the fridge using heated high strength glue. Each pump also had two electrical leads that needed to be wired to the access hole in the bottom of the fridge. To maintain organization the terminal wires were bundled using zip ties and stick downs. This lead all of the wires down each side of the fridge to the access hole in the bottom of the fridge.


Each pump required both an inlet and a outlet hose. The hose used was a 4.76mm inner diameter and 7.94mm outer diameter standard vinyl tubing. A sufficient length of tubing was attached to both the inlet and the outlet. The outlet needed enough tubing to reach the dispensing funnel. The inlet hose length needed to be long enough to reach the bottles mounted on each shelf.


After initial pump testing it was determined that in order to keep the pumps primed, the height of the pumps relative to the inlet liquid supply of each pump was critical. This was due to the back flow of the liquid from the output to the input. This back flow happens until the level of liquid in the output matches that of the input. If the line from the bottle to the outlet did not dip below the level of liquid at the input the whole line would empty itself. By mounting the row of pumps such that all the pumps where below each shelf used this criterion were resolved.

The syrup used to make pop required much more effort from the pumps since the syrup was much thicker. To ensure the liquid stayed as close to the level of the funnel as possible a one-way check value was installed on each syrup line and limited the amount the pumps had to move the heavier liquid.


The carbonator was placed at the bottom of the fridge with all its input hoses coming through a hole cut in the bottom. The carbonator needs a pressurized water source like a garden hose for its water and pressurized CO2 gas. It pumps the two inputs into a reservoir and combines them to make carbonated water. The output was controlled by a sprinkler solenoid.


The solenoid used was mounted on the side wall of the fridge using several zip ties and stick downs. The 8/16 tubing had to be routed from the outlet on the carbonator to the solenoid. The solenoid output tubing was the routed to the funnel. On the output of the solenoid a plastic ball value was added. This ball valve was used so that the flow of carbonated water could be regulated to the desired rate.


A simple funnel used to collect all the liquids being mixed into the drink. It funned them through a small hose into the user's cup.


The funnel was a critical element in out design. The funnel needed to be mounted such that the twenty one hoses could be situated above there inputs. The output of the funnel had a hose attached that was 7.94mm that would be inserted into a recessed Plexiglas cup holder – where the drinks would be dispensed. In order to achieve these requirements it was decided to build a stand for both the hoses and the funnel to be situated. This stand was build out of ½” MDF.


After testing the carbonator and almost soaking the electronics it was noticed that the flow rate of the carbonator was over filling and splashing out of the funnel. To resolve this the flow of the soda water was reduced and a splash guard was built. The splash guard was made build out of a Tupperware container with a hole cut in the bottom of it. This is mounted upside down on top of the funnel. All of the hoses are then run in though the hold in the splash guard. This stopped all of the splashing when the soda water was dispensed.

Cup Holder

The cup holder was essentially the boundary for the user to place a glass in and where the system would dispense the particular drink ordered. It was as made out of 1/8” that had dimensions of 203mm x 278mm x 114mm. This allowed for sufficient room for a user to place a glass and enjoy the easy-to-use automated drink dispenser.Hole


The mounting of the cup holder was placed 4 ‘ from the base of the fridge. A whole large enough to fit the cup holder tolerance was cut thought he lower door of the fridge using a drill and a saws-all. Once the hole was cut and smoothed using sandpaper the Plexiglas was mounted to the door of the fridge using a heat gun and high strength glue. The cup holder was mounted to the door, and the gap between the front and the back of the door was painted so that the Styrospan was not seen.


A small6.4mm hole was cut in the bottom of the Plexiglas cup holder. This was designed to drain any spilled beverages and drops after the cup has been removed. A drainage has 4.76mm hose was glue to this hole using a grommet to keep it intact. This completed the cup holder assembles.


To ensure that the cup holder and the LCD were at a appropriate heights a stand needed to be built. This stand needed to raise the fridge by 203mm. In addition to raising the height this allowed the necessary wiring and hoses to enter the access hole in the bottom of the fridge. The stand was maid using 2” x 4” s for the legs and 12.7mm plywood for the floor. Cross members where added to increase the weight bearing capabilities of the stand to be able to hold the fridge.


Upon nearing completion of the Sir Mix-A-Lot the fridge was left turned on at the lowest temperature setting, only to find out that the thermostat only regulated subzero temperatures. This was clearly an issue as the beverage lines would freeze. It was decided to remove the thermostat and find a replacement that would turn the fridge on and off between 3o – 7.5 o depending on the setting. McFarland appliance supplied the new thermostat witch had the same dimensions as the sub zero one so that fix was relatively painless.

The thermostat is regulated using a wire sensor that has pressurized gas inside the wire. Depending on the temperature inside the fridge the gas expands and contracts turning the fridge on and off. It should be noting that since the coolest part of the fridge is near the top where the outlet of cooler air is it was decided to unravel the wire sensor and place it in a location as close to the bottom as possible. This would assure that the fridge was turned on and off more accurately.



The group members were relatively handy with tools. We had a good collection of tools to work with as well -- which made this project significantly easier. Power tools are your friend. No one was injured throughout the whole construction of the fridge which was also a relief.


The physical construction of the fridge was almost prohibitive. The theoretical engineering was not nearly as involved as the mechanical construction of the drink mixer. It is estimated that each group member spent around 100 hours on this project; and most of it was sorting through mechanical issues and physically constructing the fridge.

The biggest challenge of this project was to solve all the little problems and keep the fridge's progress on schedule. As the project proceeded and our organization and familiarity with the project increased the construction and efficiency increased in our work


The fridge is quite difficult to transport -- to ensure that the refrigeration unit continues to function properly the unit cannot be placed on its side. This poses quite a few problems when moving through doorways and performing construction on the base of the fridge. A small pickup truck was used to transport the fridge from Shawnigan to the garage where the work was undertaken in Victoria and again when the project was demonstrated in the ELW lobby. The fridge needs to be strapped heavily into the truck since it is standing upright ( quite a high center of gravity.)

Broken Carbonator

We were lucky enough to receive some corporate sponsorship from Pepsi Cola Bottling, with the donation of some cola syrup and a fully functional H2O carbonator. The unit was originally a refurbished carbonator which looked to be in perfect condition. We had quite a scare when we turned it on for the second time and it start the smoke. We had originally thought we had burnt the pump out ourselves and any chance of serving fountain pop had evaporated. We phoned Pepsi hopping there would be something we could fix and the offered to send a technician to us: for free. Unbelievable! The technician came and checked out the carbonator and decided it was toast -- it didn't seem like it was our fault and he gave us a completely new carbonator -- right out of the box. That carbonator is now working perfectly.