Cooling System
We decided on a liquid cooling solution over air-cooling because it is far more effective (water transfers 30 times as much heat as air) and is much cleaner. That is, because we are planning to use the robot outdoors, there is plenty of dust in the air. Thus air cooling is not desirable as it may have an adverse effect on exposed electronics.
If water cooling is too complex to implement, we can use air-filters on the fans to secure the cleanliness of the air that flows through the electronics. In addition, the electronics has to be placed in an area where air flow has to be well controlled; it must come in and out only through the fans (usually means a system of push and pull fans). Also, don't forget to attach the proper passive dissipator (heat sink with plenty of space to let air through in between).
Here we include both the mechanical design and electrical board control section at the same page for easy access.
Mechanical System Design
The water-cooling system consists of the following must-have components:
* cooling block. Figure above is the inside part of the cooling block. note the channels and the O-Ring grooves which are important for water proofing.
* tubes: to connect the components.
* radiator
* fans
* water pump
* reservoir
* cooling liquid: use a high performing, low-conducting, non-corrosive coolant for a mainanance free cooling system.
* 'Electronics': cooling system control board.
We can also include a flow-meter and a temperature sensor to monitor the system. We bought all the devices from [http://www.koolance.com. koolance.com].
It is important to note that we have a board to provide power to the fans and pump, and take data from the flow-meter and temperature sensor and it will be discussed in the section below.
The heat dissipated by the COM Express modules is first transferred to the liquid coolant through the processor heat-spreaders that is attached to the cooling block that contains the coolant. The heat-carrying coolant first goes through a radiator that has two fans pulling air through the radiator surface. These fans are the components that actively taking the heat out of the system. Note that the radiator (and the fans) can be placed as far away from the processors as necessary. The water pump is connected to the system to ensure the flow of the liquid and the reservoir is where we originally add the coolant into the system and taking the air (bubbles) out of it.
Because the computer system does not need a steady flow of air to cool the processors, we can easily put it in a water/air-tight area inside the robot for proper protection. The figure below illustrate how the electronics are placed on a separate secured room than the radiator and fans but are connected through a pair of aluminum holders.
Cooling System Control Board
Design and implementation is available here.
How to Fill Water into the Cooling System
The setup is the following:
* need bucket of water * For our system we need about 1L worth of liquid. * We have to configure the tube such that the air bubble is forced to leave the system through the reservoir.
Water Proofing Test
We keep the system running overnight the system to check for leaks, put it in different configurations, shake it violently. No water comes out.
