Ways to turn a knob with a stepper motor and an ATMEGA32u4

Hey all I am wondering what would be the best items to purchase for me to be able to turn this know (continuous) below:

As I mentioned above, I would need the stepper motor to have a continuous rotation in order for it to work with either of these dry food dispensers above.

There is a decent tutorial HERE but really doesn't give much information about how they went about building it and the mentioned Yocto-LatchedRelay seems over priced for something that can be done with just a stepper motor and some logic behind it.

I plan on using a ATMEGA32u4 with this project. I will have a total of 6 of these to control.

So any suggestions on what would be best for this type of project would be great and I look forward in hearing them! :slight_smile:

There is a decent tutorial HERE

Ah some strange new usage of the word decent to which I was previously unaware.

To my mind that is just an advert.

Yes you can do it with a stepping motor. Yes you can control 6 of them. You need a stepping motor driver for each motor, look at the pololu website for some good ones.

I would have thought the most difficult part is the mechanics and making it look good.

What about a continuous rotation servo - assuming precise positioning is not required?

OR, if it is possible to operate the knob with a back-and-forth motion, perhaps a regular servo - which would have position control.

Servos are very much easier to work with than stepper motors.

...R
Stepper Motor Basics
Simple Stepper Code

I'm just needing to know what kind of servo torque I would need in order to turn that without issues of it getting stuck mid-ways.

StealthRT:
I'm just needing to know what kind of servo torque I would need in order to turn that without issues of it getting stuck mid-ways.

You are the person with the dispenser so you are the only person capable of measuring that. There is a simple system for measuring torque in the link I gave you in Reply #2.

...R

Robin2:
You are the person with the dispenser so you are the only person capable of measuring that. There is a simple system for measuring torque in the link I gave you in Reply #2.

...R

You mean your stepper links? Don't see how I can use that as I am looking into Servo motors.... :-\

StealthRT:
You mean your stepper links? Don't see how I can use that as I am looking into Servo motors.... :-\

Have you actually taken the trouble to read the link?

Torque is the same for steppers as for servos.

...R

StealthRT:
You mean your stepper links? Don't see how I can use that as I am looking into Servo motors.... :-\

Your complete first post mentions NOTHING about servos.. and in fact mentions steppers. (...."stepper motor to have a continuous rotation" <-- which they already do,, its servos that usually need to be modded to have 360 rotation)

In your Yoctopuce link that you posted, there is a link to the motor that they used. It is in German, bit if you click on the USA link on the left hand side it will take you to the english site.

You may want to revisit your use of the word 'continuous'.

Turning these knobs usually requires a lengthy 'forward' run, followed by a short 'reverse' to disengage the ratchet mechanism.

If you only drive forward, without detecting the end-stop, two things are likely... you'll deliver a total of one serving ever, and eventually burn out or damage the drive-train.
(And in my vast gumball experience, the torque varies greatly across the whole cycle - so you may use a lot of torque and some positioning feedback to avoid grinding the candy - and machine into dust.)

Depending on your need to use those exact candy machines, i'd be thinking about some sort of augur-feed mechanism, or a more complex drive/sense mechanism.

Added: after looking at the application - cereal dispensing, id go with your original idea with max torque, or simply redevelop the dispensers to fit the motorised model.
Perhaps a rotating cup, or augur as suggested above. Remember to make the mechanism available for cleaning.

i spoke to the original creator of that web site project that i linked to and this is what they had to say about the parts that were used:

We used a small geared Maxon motor (great but expensive hi-tech stuff).

motor
RE-max 13 Ø13 mm, Precious Metal Brushes CLL, 1.2 Watt, with cables
Part-No.: 203888

gear
Planetary Gearhead GP 13 A Ø13 mm, 0.02 - 0.35 Nm, Metal version
Part-No.: 110316

Torque was on the low side: it was enough for regular cornflakes but clearly insufficient for muesli :slight_smile:

The problem is not only about finding a motor with enough torque, it's also about finding a motor small enough to fit in the dispenser.

Here are the files. The pulleys were 3D printed,
but the bracket was laser cut in 3mm acrylic glass.

Are there any servos that have a hole in the middle so that i can slide it over the turning rod and screw down to tighten on it in order to spin it as if you were spinning it yourself with the handle?

Something like this:

How about something very similar, with the ring gear as shown, but the motor set off to the side, driving a worm..?
Loads of torque, geared down by the worm.
If not exactly off the shelf, that should be quite easy to source for manufacture.

I used the round ones. I cut the knobs off of the "D" shafts that go into the paddles. Using two 5mm x 8mm motor shaft couplings, I connected them to Nema 17 12V motors with motor mounts mounted on a board. A Uno and a Adafruit motor shield run the motors. I slid everything inside a wooden box with plexi glass shoots. I made a duplex cat feeder.

The motor weren't strong enough to rotate the paddles when filled to the top with food. The cat food weighs much more than cereal. I had to install two baffles in each canister to help distribute the weight away from and above the paddles. I rock the motors back and forth. It works great now. It feeds them twice a day and it hold about ten days of food.

Torque was on the low side: it was enough for regular cornflakes but clearly insufficient for muesli :slight_smile:

Wouldn't that sort of mechanism break the corn flakes - I hate powdery cornflakes.

...R

Given the information above, what would be the best ball park guess as to how much torque would be needed in order to move "muesli"-type of cereal?

StealthRT:
Given the information above, what would be the best ball park guess as to how much torque would be needed in order to move "muesli"-type of cereal?

I have not noticed any information above that would assist someone to make an estimate of that.

Why don't you try measuring the thing like I suggested earlier?

...R

Mainly because I just got 6 of them in just today.

The handle/shaft is 2 1/2" long.
The paddle is 3" long
The base (measured from the inside) is 5 7/4"

I'm currently looking at getting the Power HD LW-20MG 4.8-6.6V 20kg.cm Water-Proof Digital Servo

They claim to have:
Torque(4.8V): 16.5 kg-cm (229.1 oz/in | 1.61 N-m)
Torque(6.6V): 20.0 kg-cm (277.7 oz/in | 1.96 N-m)
Speed: 0.18 sec (4.8V) │ 0.16 sec (6.6V)
Operating Voltage: 4.8 ~ 6.6 DC Volts
Weight: 60 g (2.12 oz)
Bearing Type: Ball Bearing x 2
Motor Type: DC Motor
Gear Type: Copper & Aluminum
Operating Temperature: -20℃~60℃
Working frequence: 1520μs / 333hz
Size: 40.7 x 20.5 x 39.5 mm ( 1.60 x 0.80 x 1.55 in)

Which I found on eBay > https://tinyurl.com/l49sswl

Thoughts?

Or quite possibly the best one thats a good mini size:

http://alturn-usa.com/products/AHLS-1510HTG+HV.htm

Remember that you need either -

a) a continuous rotation servo - to feed the 'next' bin.
or
b) one bin forward, and 'x'-steps reverse to alternate between two bins, if you're using a rotation-limited servo.
(It can't reach the next bin after it reaches max-positive position...!)

(Either way, you still have the issue of knowing when a bin has dropped... you can't always rely on time or step-count, because the load, dropped steps may differ over multiple runs.)

Also keep in mind that the bins are always being fed from the top, so you could end up with three-day-old muesli trapped in the 'next' bin in rotation if they ar not cycled or cleaned regularly.