Quote:
Originally Posted by ProfessorAlekM
You would be surprised would students can do. It's really not hard to make motor controllers, I've made them myself before and I'm only in 9th grade.
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What sort of continuous output current was your motor controller capable of? How efficient is it? How durable was it, especially when abused? How long has it lasted? How does it behave during fault conditions (does it fault in a safe and benign way)?
A schematic is only a starting point for a successful piece of equipment. A schematic for a good motor controller will look a lot like the schematic for a bad motor controller. You still need an enclosure to keep the circuit board from shorting to adjacent pieces of metal and to keep the metal shavings out. You will need to have a suitable heatsink. Do you know how to select a heatsink that performs adequately yet is not too big and expensive? The higher the current in the circuit and the higher the edge rate of the switching, the more critical the track layout on the PCB is. The layout of the circuit board suitable for FRC motor controllers will not be trivial. A poorly done layout will have high inductance paths, leading to high surge voltages and possibly destruction of the switching devices. A common cure for high surge voltages is to slow the edge rate of the switching but this causes higher losses and heating and lower efficiency and possibly destruction of the switching devices.
There is already a student designed motor controller out on the market. Test results published on this forum show that it is less efficient than other motor controllers. I have been told that it uses twice as many MOSFETs as other controllers indicating that the devices are not being operated in an efficient manner. It is quite likely that the board layout was not done in an optimum way (see above).
Quote:
Originally Posted by ProfessorAlekM
Although it doesn't seem like it, the point I'm trying to argue is that FRC would be much cheaper if they would give students the ability to create and buy their own motor controllers. When you calculate it, our team has spent hundreds of the dollars on motor controllers.
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What is your team's time worth? Are you going to propose building your own controller too (because the processors are under $10) instead of purchasing a RoboRio ($435). This is a robot competition, not a motor controller competition.
It is likely that providing just a schematic will lead many teams to disaster. Not all of them will be able to obtain the proper parts and substitute a part that "looks close enough" (yes there is a difference between two parts with the same nominal rating). Most of the parts that will be suitable are "surface mount" types. Most people I have met (including engineers working in the field) do not have the skills needed to successfully hand solder surface mount components correctly.
There is at least one other individual who has posted in this thread who has indicated that they have to professional experience in this field to comment in an authoritative and credible way and they are all saying that there is a lot more to have a successful power electronic circuit than just having a schematic. My background is doing the design and development for motor controllers ranging from 5hp to 1200hp over the last 20+ years. I use many of the same design techniques necessary to make a successful FRC motor controller and it took me (and the others posting here) much longer to learn these techniques than a high school student would have. A few years ago, I visited a startup company that had a microprocessor guru/consultant who sold them on the idea that he could design a complete motor controller for them because he got hold of a generic schematic. I saw their prototypes (as well as the scorch marks on their equipment) and it was pretty easy to see what they were doing wrong. That start up closed down pretty soon afterward.