Using Arduino to control capstan speed of reel to reel recorder

Projects General Guidance
1

Hi. Looking to swap out the capstan motor on an old reel to reel.

I have an old reel to reel recorder that I never use.
I want to somehow control the speed of the capstan motor. I have an arduino nano that I thought I could use as a controller.

It has an AC motor inside, which seems to be difficult to hack to do varispeed/speed control.
That’s why I want to swap it out with a newer dc motor.

My plan is to ditch the reel mechanics and only rely on capstan motor to push the tape. (I will make a "cage" for the tape tape loop, so won't need the 2 reels. Just the capstan).
I can find many brushless dc motors, but I want one that has high enough torque at low rpm. Most dc motors have insane rpm that is not needed at all, and I want to make sure that hey perform well at low rpm.

I found this on the internet:
"On the capstan a roller of varying diameter from model to model is mounted - typically around 1 - 2 inches, which means somewhere between 4-5 inches of tape is transported per round (1.5 * 3.14159 = 4.7). If the speed is e.g. 30 inches per second, then that gives 30 / 4.7 * 60 ~= 383 RPM for the capstan. The reels are harder because many different reel types exist, with varying starting inner diameter."

If I then rewrite that to 15 ips, as medium speed?
If the speed is e.g. 15 inches per second, then that gives 15 / 4.7 * 50 (im in Denmark and we use 50hz) ~= 159 RPM

So that means that I have to find a DC brushless motor that can give me 159 rpm (or in that ball park).
I can then add varispeed to that pretty easily it seems (maybe with pwm or other techniques).
I am guessing

I'm thinking that the drone industry has made huge strides in the DC motor area, but they are all very fast. I need slow and reliable.
It seems that KV=rpm. So I should get a DC brushless 159KV motor.

Or should I not worry at all about torgue? It only needs to keep the tape rolling :slight_smile:

Any hints on where go looking? Any hints for making a good controller?

This is the original motor in the machine. But I only need a new motor for driving the capstan. Not the actual reels.


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Thanks

2

Um, no, all you need to do is vary the frequency of the applied AC.

3

Hmm everywhere I read about that, it seems pretty complex to do. Could you elaborate? :slight_smile:

4

It's a synchronous induction motor. The armature follows almost exactly the AC magnetic field induced by the coils. So, 50 or 60Hz produces a fixed RPM based on how many poles and how many current reversals per second.

Thus, if you for example supply the 60Hz rated motor with 62Hz, it will run 62/60 = 3.33% faster.

How much speed variation do you need?

5

Probably one octave.

6

Probably too much variation to do it that way... when you consider other types of motor, you will then encounter the problem of speed stability. How stable must it be? :slight_smile: Wow and flutter? :slight_smile:

7

Yes exactly. That’s the problem.
It must be pretty stable. Wow and flutter should not be too audible. It has its charm in delays, but shouldn’t be much more than your average tape echo.

8

You lost me there.

9

Well, a brushless motor designed to fly a drone wouldn't be designed for that.

10

I’m sure I did. I don’t know that much about it :slight_smile: I just read that somewhere online
:slight_smile:
About wow/flutter: would rather have a machine that has a bit too much wow and flutter than no machine at all. But again, I would like the a pretty stable machine.

11

You know the approximate RPM range 1500-1800 printed on the motor. What have you turned up so far? Give us some candidates to think about...

BTW synchronous motors have inherent speed regulation, brushless don't unless they have built in or additional speed feedback encoders.

12

Not quite sure I understand your post?

The rpm on the motor is not correct for the capstan. The motor poweres the capstan via a large gear (and also the reel cogs). So ignore the rpm on the motor :slight_smile: looking to put a motor directly on where the capstan should be.
And thanks for your time! :slight_smile:

13

Then please reveal the gear ratios etc. because you will have additional torque issues with direct drive. With direct drive, you hugely magnify your problem. You will lack the inertial stability of the armature, multiplied by the speed reduction chain.

At this point, a decent answer depends on more details of the mechanical arrangements.

14

Ok. Makes sense. Can’t give you any info right now. But maybe I should look for a motor that has the same rpm as the original and swap that one out, instead placing a new one on the capstan location.

I’m guessing avoiding direct drive will also make it easier to avoid excessive wow/flutter.

15

That would be my advice.

16

Will look into that. Need to see if I can find any motor candidates. Thanks for the advice so far:)

17

Have you considered digital audio editing? :stuck_out_tongue:

Most (maybe all?) direct-drive turntables use slow-speed DC motors and I think some high-end tape machines were made that way too. But in both cases it's probably a custom motor.

18

Hehe. Yes, I have heard about that new fangled digital stuff. But I prefer Amish audio!

@anon57585045
Would this be a candidate?

I says 830rpm, but don’t know if that speed can be varied up.

19

@DVDdoug
I will look into turntable dc motors. You might be on to something there.

20

Gearmotors are usually pretty noisy.