PCB assembly – Low cost reflow option

I have the ICs, a couple of good PCB design software options and a PCB manufacture now I need a way to assemble the boards. Reflow looks like my best bet but reflow ovens are expensive and I was not looking for a DIY project (although the ones out there are very impressive) so after a bit of searching I stumbled on the C & A Scientific DB-1 Stainless steel hot plate, $140 with shipping from Amazon.

I will post details once I have had the chance to try it.

Temperature Range: 100c – 250c
Power Requirements- 300W
Heating Surface- 7.8″ X 6″
Overall Size- 14″ X 8.5″ X 4″
Shipping Weight- 8lbs.

Absolute magnetic encoder BLDC commutation sequence

Summary of data gathered from the whitepaper “Commutation of a BLDC Motor with Various Pole-Pairs Can Be Simplified By Using Absolute Encoder Feedback”

An absolute encoder feeds back the absolute counts, where the absolute counts will be compared with the preprogrammed counts in the controller to activate the correct commutation sequence. In addition, the absolute encoder also adds value by providing other features such as incremental channel signals, which can be used for servo positioning, as well as finding the latest position when powering up.

In search of the right plastic and manufacturing process

Ideally I would like to find a balance between a material that will work in most conditions (80% rule) and materials for extreme conditions. The generic material should support wear, reasonable heat and cold (work inside and outside), wet environments (humidity/rain/snow), UV protection (working in the sun for 12hr). The extreme material should support high heat (firefighter), shrapnel (military), high chemical resistance (disaster cleanup), etc. I would prefer to use one set of molds for the different materials. All materials should be dent and fracture resistant, (should survive a fall or impact).

So far many have recommended glass or carbon Long Fiber Reinforced Thermoplastic (LFRT), I also started looking into Bulk Molding Compound (BMC) and Sheet Molding Compound (SMC) thermosets.

The prototype and initial short production run will be produced via compression molding, as I move to larger production runs I will most likely move to injection molding.

Open compression molding questions:

• Required pressure
• Required heat /cooling
• How to mount the molds to the platen
• How to align a two part mold
• Mold design to support required heat/pressure

I will update the blog as I get these questions answered.

Long Fiber Reinforced Thermoplastic (LFRT)

Bulk Molding Compound (BMC)

Sheet Molding Compound (SMC)

Mold

SMC/BMC molding process

Sample BMC Part

Moved to sample 100:1 planetary brushless motor to simulate target motor design

The plan is to use an absolute magnetic encoder post gear down, this provides two benefits, one we know where the shaft is in relation to the magnets on power up and on rotation and two we know where the limb driven by the motor is on power up and during movement.

50V 60A brushless DC motor controller design – Moving to the ARM Cortex-M3

I setup another breadboard using an ARM Cortex-M3 hosted on an mbed NXP LPC1768. I rewrote the controller code in C and was able to generate motor jitters; I think the mbed’s 3.3V output might not be enough to trigger the 5V Logic MOSFETs. (The picture does not include the external power source)

50V 60A brushless DC motor controller design: We have rotation.

I added the 60V 50A MOSFETs, corrected some errors I has with the Arduino code and we have movement. I also reduced the delay just slightly after each iteration of the loop, slowly speeding the motor up. I checked the temperature of the components on the board and all were under 82F. Next step adding the magnetic encoder and using the data to drive motor sequence