Good questions. Here are the answers:
Run time over 15 hours: is that motor running time or wall clock time in which the motors only run every 1/240th of the wall clock time?
I'm talking about clock time. So in these 15 hours the motor is only running for about 4 minutes.
Weight is important: You mention several kinds of somewhat heavy battery packs, but then mention the weight concern. Do you envision the motor driver and battery pack and motor and all circuitry and wiring being on the moving shaft or do you expect some of that to be connected by cable / slip ring coupling / etc. away from the shaft?
Everything you mentioned goes on the shaft. I'm very open to other kinds of lighter batteries. I looked at coin cell batteries, but they weren't practical due to their low current output. Maybe with a current pump they would work (I haven't calculated how large the caps would need to be to make a current pump work). I think 2 AAA batteries might work as long as I balance everything well. So that's why I put them down, but if you can figure out a way to make something lighter work that would be great. To help understand what is being designed I'm basically planning to do an automated way of moving these yarn hooks on this electric spinning wheel I designed.
https://www.kickstarter.com/projects/1492884446/electric-eel-wheel-5A small motor: What's the requirement? Do you have one selected? What types are acceptable with what performance? Are you considering permanent magnet DC or BLDC or ...?
I don't have a motor selected yet, but I was expecting it to be a bidirection DC motor. I used some of these for prototyping (
https://www.amazon.com/gp/product/B01J04KK38/ref=oh_aui_search_detailpage?ie=UTF8&psc=1) -- you can get them for much cheaper from china. But they actually gear things down too much and used some laser cut gears to speed things up. My plan for the final product is to do the gearing myself, but the prototype of this mechanical system worked well enough for me to have a high confidence that I can make that part of things work. I was planning to just find a 3-6V motor from
http://www.jameco.com that is about the right size hand has the lowest RPMs and using that.
The only part of the electrics I didn't mention so far is there will be a shut resistor to detect current usage by the motor. That's how I'm planning to detect when the hook gets to one end. The current spikes and I switch the motor direction.
It sounds like you're talking almost more about the battery pack to DC voltage regulation and maybe battery charging than you are about any other aspect of the circuit. If you use your AT Tiny MCU to turn on and off the motor on schedule then what is the "motor controller" doing? Does the motor need to be speed sensed / controlled by a sensor / circuit or is open loop OK with maybe just no control or constant voltage or constant current type control?
Simply apply a stiff voltage source within rating to a DC motor and it'll run at a speed depending on its load. So a power switch is all that's needed there absent other unstated requirements. BLDC motors on the other hand need lots of control circuitry relatively speaking.
The reason I'm talking more about battery and power is because that's the part I don't have working in my prototype and haven't done before. Full speed and open loop for the motor is fine. The only special requirement is that I need to be able to switch the direction of the motor. I thought about driving directly with mosfets, but thought that h-bridge controller would make things smaller and easier to design. If you'd rather design this part of the circuit differently I'd be open to that.
If we get the right motor and batteries maybe the motors motor's power doesn't need to be regulated. I think that's what you might be getting at and that does seem like a good idea if we can make that work.
I mentioned the shut resister earlier will be used to detect a motor stall and switch directions.
#2
So you want battery pack in and 3.3VDC 1A power output. Ok. Is there a reason you don't use an off the shelf battery / DCDC power module? I guess with possible charging as well as regulation custom could make sense from a customization perspective if not a cost one.]So you want battery pack in and 3.3VDC 1A power output. Ok. Is there a reason you don't use an off the shelf battery / DCDC power module? I guess with possible charging as well as regulation custom could make sense from a customization perspective if not a cost one.[/url]
I expect to make around 1000 of these for a future project so I don't want to use a module. I started looking at boost/buck converters and the only one I found was
It would work great, but I have had issues with QFN packages in the past so I'd prefer an easier to solder package (mainly one you can see if something is wrong). Then I started looking at using boost in SEPIC mode and realized there must be people who understand this better than I do and can help with it. I'm mostly a software guy and am busy with some Android and embedded micro controller code for this project. I'd rather just have someone else help here (though I will want to understand how it works before I ship).
There is also a discussion about this going on here (
https://www.eevblog.com/forum/beginners/help-selecting-switching-power-regulator/). I was planning to just do it myself, but decided it was going to take up so much time that I started this thread.