Well the summer is over. Getting too cold and the daylight hours are getting too short for evening bicycle rides and other outdoor activities so time to pull the indoor activities back off the shelf.

One of the projects is a propeller clock and I need a little help with the math to determine the optimum diameter of the clock.

Here are the parameters:

3 mm LEDs
8 columns x 8 rows
12 character display

So the distance to display all of that is 3x8x12 = 288mm.

That is the length to display all of those characters in lone line. Am I missing anything by arranging them around the circumference of a circle?

My diameter would be 288/pi = 91.1mm

Can someone please confirm my calculations are correct and I am not missing anything?

 

Well the summer is over. Getting too cold and the daylight hours are getting too short for evening bicycle rides and other outdoor activities so time to pull the indoor activities back off the shelf.

One of the projects is a propeller clock and I need a little help with the math to determine the optimum diameter of the clock.

Here are the parameters:

3 mm LEDs
8 columns x 8 rows
12 character display

So the distance to display all of that is 3x8x12 = 288mm.

That is the length to display all of those characters in lone line. Am I missing anything by arranging them around the circumference of a circle?

My diameter would be 288/pi = 91.1mm

Can someone please confirm my calculations are correct and I am not missing anything?

Your calculation seems correct. But I'd still make a drawing of the LEDs arrangement, to make sure they don't interfere among themselves when arranged in a circle.

 

Your calculation seems correct. But I'd still make a drawing of the LEDs arrangement, to make sure they don't interfere among themselves when arranged in a circle.

Not sure if I get your point. It will just be a single column of LEDs.

One thing I think I need to be careful of is the spacing of the columns. I am thinking that the LEDs closer to the center would require the propeller to be moved a bit further than what is required for the one close to the outer edge of the propeller or the inner ones might overlap. Or then again maybe I am not thinking correctl.

 

In your other thread(original thread on the clock) I posted a link that the guy had it all simplified out.

 

That's the diameter of the inside row of LEDs. You need another 21mm (7*3) on the radius, making total diameter 133.1mm.

 

Spinnaker, would you mind refreshing my memory as to the configuration of the clock that you're referring to?

Is it something like this?:

​

Or is it something like this?:

​

 

​

The above is planned.

 

Then the extra diameter is needed, post #5.

 

That's the diameter of the inside row of LEDs. You need another 21mm (7*3) on the radius, making total diameter 133.1mm.

Then the extra diameter is needed, post #5.

Not sure I understand. What do you mean by "inside" row? There is really only one row. Where does the (7*3) = 21 come from?


When you say "inside" do you mean the LED closet to the center?

 

You have a row of 8 LEDs extending outwards. For the innermost LED to be able to display 12 eight dot wide characters that innermost LED must descibe a circle of the diameter you calculated in post #1. Then there are another 7 LEDs extending outwards from that innermost LED. That is 7 LEDs times 3mm for each LED making an extra 21mm on the radius.

 

I think I got it. So I need to allow enough space for the inner most LED? So what I really needed to do was calculate the circumference needed for the inner most LED?

 

It is the nature of a circle that smaller radius equals smaller circumference. The dots produced by the innermost LED will be more closely spaced than the dots from the LEDs further out.

 

Another question. How do plan to sync the propeller and the MCU? Are you going to use an encoder?

 

Another question. How do plan to sync the propeller and the MCU? Are you going to use an encoder?

Just an I/R sensor for the "home" position. Then a timer there after.

The pic will be stationary to make it easier to troubleshoot.

I have one of these.

https://www.ebay.com/itm/Slip-Ring-...347560?hash=item468273f2a8:g:32AAAOSwzXtbPgcW

They only have 6 wires so the plan is to use a shift register on the spinning board. I just hope I can transmit fast enough.

I also have a few of these with more wires but no hole in the center. But for the life of me I can't figure out how these work expect perhaps with some kind of belt drive. Says 300 RPM but I will bet it can be pushed.
https://www.ebay.com/itm/300Rpm-Cap...=item1a16fbd426:g:cV0AAOSwCJxaTaXY:rk:14:pf:0

I mean even if it is for a wind turbine (which I think how some of these are sold) you would think the blade would mount to the plate but then how do you drive the generator??

And if you want to use it for robotics how do you get the servo to spin the arm (or whatever you are moving)?

 

I think I now understand how the second type is used for a wind turbine. It isn't the turbine part. It is the wind vane part. Now that I think of it it does not make any sense why you would want to connect to the blade. Still don't see how it would be used in robotics though.

 

Just an I/R sensor for the "home" position. Then a timer there after.

The pic will be stationary to make it easier to troubleshoot.

I have one of these.

https://www.ebay.com/itm/Slip-Ring-...347560?hash=item468273f2a8:g:32AAAOSwzXtbPgcW

They only have 6 wires so the plan is to use a shift register on the spinning board. I just hope I can transmit fast enough.

I

Slip rings are really noisy, I don't think clocking a shift register through one is going to work.
There are mercury-wetted versions, might give you a fighting chance.

http://www.mercotac.com/

 

Slip rings are really noisy

yeap ... they're very noisy. I think that it would be much easier to mount the arduino (or some other MCU) on the rotor. And if you want to guild the lily, you could add bluetooth connectivity to it to adjust it on the fly.

 

yeap ... they're very noisy. I think that it would be much easier to mount the arduino (or some other MCU) on the rotor. And if you want to guild the lily, you could add bluetooth connectivity to it to adjust it on the fly.

It might take some effort to balance it though.

 

Slip rings are really noisy, I don't think clocking a shift register through one is going to work.
There are mercury-wetted versions, might give you a fighting chance.

http://www.mercotac.com/

That was what I was worried about. Also simply transmitting via the unshielded wires at a high frequency might be a problem.

 

It might take some effort to balance it though.

Balancing the entire assembly is something that needs to be done regardless of the presence of the MCU or not. But I grant you that it might make things slightly more difficult.