Project help.

So I working on a project that involves a cylinder with 1/4 of it removed that turns to drop food, then turns back every 8 hours. I also have three small flaps that will be controlled by servos triggered by rfid. It's a timed cat feeder with restricted access, basically. Only certain cats will be able to eat at certain "feeding stations".

This is something like what I am going to do, but Mine will have three of these cylinders, side by side, on a rod that drops food through pipes into three separate bowls.http://www.youtube.com/watch?v=cHsRC4yNpPw

There will probably be over 20 lbs of food in the container when full. I know that with a tapered design, not all the weight will be right on the cylinders, but I don't knot how to calculate required torque. The bar will be held on both sides of the set of cylinders by mounts with bearings for easy turning and to avoid putting too much downward force on the motor shaft.

here's a crude drawing.

+

The cut out portions of the cylinders will have walls. I just didn't put them to make it easier to interpret the drawing. There will be a "hopper" above these that is sort of segmented into three equal segments and reduced to fit the opening size of the cylinder. (tapered rectangular prism. like a squared of funnel.)

Should I use a servo? high torgue? stepper?. Those are pretty much my only option because I need the control . Thanks, everyone.

It looks like the discs only need to turn part of a circle and then back to the original position. That sort of motion would be ideal for a servo and servos are much much easier to install and control as well as being cheaper than stepper motors + stepper motor driver boards. The controller is included inside the servo.

I would think about using a separate servo for each disk and then the servo could be one side of the disk's bearing.

I think you will need to experiment to see what torque is needed. I suspect the biggest force to overcome will be food that jams at the edge of the disk as the aperture closes. Buy a cheap standard sized servo and see how you get on before investing in anything expensive.

...R

I’ll look into that. I have another question. My ATmega is going to need 5V, rfid readers need 3.3V and servos, ideally, 6V. I’m trying to think of a way to bring 6V onto my board, then split it twice to get my 5 and 3.3. I recon I’ll need a bit of amperage for four servos, three readers, and the controller. they have 6v, 3A adapters but all the ones that I find from trusted sources are over $20 per. should I just bite the bullet on the price or could I use an old laptop adapter with a 6v, 3a ubec? My ideal adapter is one from servocity for $24. If it would be way better to go that way, I have no problem. Just checking.

tercelkisor:
I'll look into that. I have another question. My ATmega is going to need 5V, rfid readers need 3.3V and servos, ideally, 6V. I'm trying to think of a way to bring 6V onto my board, then split it twice to get my 5 and 3.3. I recon I'll need a bit of amperage for four servos, three readers, and the controller. they have 6v, 3A adapters but all the ones that I find from trusted sources are over $20 per. should I just bite the bullet on the price or could I use an old laptop adapter with a 6v, 3a ubec? My ideal adapter is one from servocity for $24. If it would be way better to go that way, I have no problem. Just checking.

I think doing the laptop adapter and UBEC idea might be the best one; also get a 5V UBEC for the ATMega, and for the 3.3 volt needs, use a regulator (LM1117 3.3v for instance).

Regarding the "edge of disc" catching food - you might try rounding off the edges (and inner corner) of the 1/4 cutout; it might help.

cool. So you think a ubec would be better than a 5v regulator on the board? I haven't put anything together yet but I do plan on rounding over some key edges .

I'm looking at these adapters

http://www.amazon.com/Laptop-Adapter-Charger-Toshiba-Satellite/dp/B003U8CRGY/ref=sr_1_3?ie=UTF8&qid=1412137731&sr=8-3&keywords=laptop+power+cord

and these ubecs

Would there be any issues with an adapter like this?
thanks!

or maybe this one?

its 12v while the other is 19v.

You need a separate power supply for the servos so they don't interfere with the Arduino. Just make sure the servo GND is connected to the Arduino GND.

If the RFID readers don't need much current they can be powered from the Arduino 3.3v pin.

If you are looking for advice before purchasing parts I suggest you post a drawing of how you intend to connect everything to eliminate the scope for confusion.

...R

Okay. thanks for the advice. Heres a picture

I can't make components in the free version of eagle. This is my first schematic. I went off what I saw online, so let me know if something is wrong or unnecessary.

You can make components in the free version. The main restrictions are in layers and only one schematic page per file.

There are 3 steps, symbol, package, device. Symbol is the schematic side, package is the footprint, and device is where you electrically connect the pins or pads. Its super fast and easy if you piggy back on a pre-made library that uses the footprint you need. Half the time the texas instruments library is missing the part I want but another device inside has the same footprint, I can just make a new symbol (make a square add pins and name/values), grab the pre-made footprint connect the pins, give it the correct part name, and done. Its pretty easy once you know how.

tercelkisor:
Okay. thanks for the advice. Heres a picture

A photo of a pencil drawing would be fine. Please keep it at or below 1280x960 to make it easy to view.

I am most interested to see how you plan to connect all the power and GND connections and that is not clear from your existing picture.

Also, you have no pinout definitions on the RFID readers.

Have you a link to the datasheet for the RFID readers?

...R

The restrictions in the free version are as I understand it:
no commercial use
board area 8cmx10cm
only 1 schematic sheet
only 2 board layers.

And probably no customer support :slight_smile: [ although you can always say you
are evaluating the product for purchase... ]

Thanks! I'm not exactly sure what you mean about how power and ground will be connected. I'll be making a pcb with either one input (6v using ubec/expensive wall wart) or two(5v and 6v with two ubecs). There will be a regulator ( or two if I ony use one power input) to give me a total of three different voltage inputs: 3.3v, 5v, and 6v. I was planning on just grounding to the ground that was paired with wherever I got the power from. Is that wrong?

this is on the amazon page: Box

thanks

tercelkisor:
Thanks! I'm not exactly sure what you mean about how power and ground will be connected.

Nothing complicated. I would just like to see a clear schematic drawing of what will be connected to what. As I said, a photo of a pencil drawing will be fine.

...R

okay. I'm sorry, but I thought that's what I had in that picture. I'm not exactly sure on specifics if that's what you want. I've never done anything this involved before. Thanks.

You have still managed to produce a diagram that does not show the GND connections.

I must leave it to you to do them correctly.

...R

I guess I don't understand what you're saying. The ground is the middle pin on the regulators and they go to the input ground that comes in with the 6v.

tercelkisor:
I guess I don't understand what you're saying. The ground is the middle pin on the regulators and they go to the input ground that comes in with the 6v.

You probably do know how to do it properly.

Many people don't and it would have been comforting to see a diagram in which both the power and GND wires were shown explicitly. (Red and Black lines :slight_smile: )

...R

Okay. This one has colors. really all I need to know is whether a 6v ubec with two regulators (5 and 3.3) is preferable to two ubecs (5v and 6v) with one regulator (3.3). I can't do separate power adapters so I just need to know which one is less likely to cause me troubles. Of course, the other option is just to skip ubecs altogether and buy those expensive 6v, 3a adapters.

tercelkisor:
Okay. This one has colors.

Sorry - you are missing my point completely - like we are on two different wavelengths.

I first started asking for a diagram because I didn't know whether you know how to connect servos to an Arduino with a separate power supply but with a common ground. And part of the problem may be my failure to recognize that you are using a bare Atmega chip and not an Arduino board.

As I said in my previous post

You probably do know how to do it properly. Many people don't

The reference to coloured wires was meant as a joke - hence the smiley.

Can a 7805 voltage regulator operate with a 6v input voltage or does it need a higher input voltage?

...R

Robin2:
Can a 7805 voltage regulator operate with a 6v input voltage or does it need a higher input voltage?

I may be thinking of the LM317, but I believe the voltage dropout depends on amperage? So with low amperage, 6V might be okay.