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Servo for a cat feeder?

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IceQubed

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Hey, I was wondering if anybody has any suggestions for which servo to go for - I am making an automatic cat feeder with the same basic design as the cat mate c50 (google image search it, it is a simple rotary design). The servo will turn the top half, revealing the food in the tray. I don't want an expensive servo, it doesn't need to be massively precise or efficient speed is not an issue.

The main thing I'm looking for is power - it needs to be able to turn the upper tray, and I might even gear it so that it can rotate the full 360 degrees. I don't really want to spend a massive amount of money, and obviously don't need enthusiast-level gear.

The servo will be run off a battery pack (probably 9v) and controlled with a PIC chip.

Thanks!
 

Sceadwian

Banned
Typically servo's that have been modified to rotate 360 degree lose their ability to move to a set position.
You'll at the very least want to use a small DC power supply, a 9 volt battery will be extremely wasteful and not last very long at all. I don't understand why you're looking for power... don't rotate the tray rotate the upper cover which would be light plastic, use a small solenoid to lock the cover in place when the servo isn't supplied with power. Any inexpensive hobby servo should work fine.
 

alec_t

Well-Known Member
Most Helpful Member
...or you could probably get a suitable dc motor with reduction gearing out of a kid's toy vehicle etc. A simple bang-bang function is all you need, rather than a proportional servo.
 

Sceadwian

Banned
alec, something has to provide feedback for tray position, doesn't have to be proportional simple limit switch(s) perhaps
 

KeepItSimpleStupid

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Most Helpful Member
I once did a 4 position system (not for a cat, but rotary) that worked out well. The motor used was a 24 VAC synchronous motor.

Each position had a roller microswitch that ran along the edge. When the switch was in the detent, the motor would stop.

To advance the system, you just supplied power across the limit switch until the motor started moving (opto isolator) and you released.

For this system I needed absolute position indication, so I used 2 hall effect sensors with stud mounted commercial magnets used for this purpose to get a binary pattern.
 

IceQubed

New Member
I am not able to use mains power for this project. It shouldn't need a massive amount of power, but that is the most important thing.
 

Boncuk

New Member
Why overcomplicate things?

Use a simple solenoid to open the food dispenser. No counting, no motor and no accurate stopping position required for the solution as drawn.

Boncuk
 

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IceQubed

New Member
Hmm, so I should use a basic motor, using roller microswitches to find the position? I guess this has some advantages.
 

IceQubed

New Member
Why overcomplicate things?

Use a simple solenoid to open the food dispenser. No counting, no motor and no accurate stopping position required for the solution as drawn.

Boncuk
Thanks for the image, however the design needs to be able to supply both wet and dry food, multiple times.

EDIT: I think that the RE-385 General Purpose Motor, costing £5.99 at Maplin.co.uk is probably the type of thing I want to go for, using roller microswitches to stop it.
 
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ronsimpson

Well-Known Member
Most Helpful Member
Now that you are not going to use a servo.....
If you want a 360 degree servo look for a wench or sail wench servo. There are a number of 3 turn wench servos out there. One version turns 360 plus a little. I think it comes in 1T, 2T,3T......9T versions.
 

crutschow

Well-Known Member
Most Helpful Member
One way to avoid using switches to determine location is to use a stepper motor. The motor will move an exact number of counts that you program into the micro.
 

IceQubed

New Member
Yeah, stepper motors seem to be good too, although I will probably be using a chip like the picaxe C08, would that be complex to use with it?
 

Sceadwian

Banned
Boncuk, the reason for the use of a circular tray with many compartments is so you can fill the tray once a week and it advances once a day to the next try so you can meter the cat food.

Personally, I have three cats, they get two scoops every morning before I go to work. If you can't take the time out of a day to feed your cat then you might want to not have pets =) As for convenience sure I can understand it a little, but because I'm the one that feeds the cat they know where food comes from, it's kind of a mini pet bonding moment everyday.
 

Reloadron

Well-Known Member
Most Helpful Member
Given a choice I would likely build a screw feed system similar to what you see here. The link being just an example. Buy a few pieces of PVC pipe and build the screw. Attached a simple geared DC motor and have the motor turn on and off at intervals. Dry food is not a problem and you will need to get creative with wet food. You don't need stops or positioning. If you want to get fancy design in a rotating hopper system.

Ron
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
You only need one roller limit switch. You just need multiple detents. There is no reason to know the day of the week, but if so, you could advance manually until day reached.
 

IceQubed

New Member
This is designed to supply the cats over a weekend - I always feed my cats daily by hand, but this is for when we are on holiday. A screw type device will not work as it needs to supply both wet and dry food.
 
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