how to move part of a shaft/axle

Hi,

A small/regular DC motor shaft is connected to a propeller. The motor shaft rotation is directly moving the propeller. This is working fine.

The need/problem:
After 1 minute of rotation, the propeller must move away from the motor, about an inch.
After additional 1 minute the propeller should move back to its original position (an inch closer to the motor.)

How can I do it?

I thought of one solution, that I don't like: To move the whole system, the motor+shaft+propeller, as one unit.

How to move only part of a shaft/axle? Is there any device to move/expand/enlarge the shaft? Some kind of a coupler? Maybe a different DC motor with a different shaft?

Thanks

There are various solutions for telescopic rotating shafts. One the simplest is two square tubes that are a nice slide fit one inside the other.

...R

hi Robin2,

The idea sounds very good, but I have several question about it:

Do the two square tubes really square?
Say, SE is the external square, SI is the internal square part. Does the SI connected to the propeller? or, How the SE and SI around the shaft?
Does the SI have bearings around the shaft, so rotating shaft is freely rotating inside the SI?
What is between SE and SI? nothing? The SE just slides over the SI?
The SE is external and we can move/push it. But how do we push the propeller?

Sorry. Many questions cause no idea how this works...

Thanks

Do you have access to a lathe? Experience with mechanical engineering? They would both help a lot...

edward-flame:
Does the SI have bearings around the shaft, so rotating shaft is freely rotating inside the SI?

In my concept the square tubes ARE the the rotating shaft. One of then connects to the motor. The other connects to the propeller.

Obviously both parts need bearings to support them and a thrust bearing on the propeller tube to take the propeller forces.

Most agricultural machinery suppliers will have full sized examples of telescoping drive shafts - I'm sure they would let you see them.

Google!

...R

See MarkT's reply - surely this is much more a mechanical than a processor problem

regards

Allan

Hi,

Again, thank you for the new idea. But reading about square shafts and sliding shafts and telescopic shafts, all came to the same point that the two parts are uncontrolled. The two shafts can deliver power to each other, and still move in/out/slide one over the other.

Arduino controls the main DC Motor (of course, not directly.) and the propeller is rotating.
I need to connect another, additional, stepper motor to move the propeller, an inch, at the right time and to the right direction.
If both shafts (external and internal square shafts) are moving together, the additional motor can not hold/grab/force the movement between them. Cause both shafts are moving...

How can an additional motor control the movement of one shaft? the propeller shaft?

Many thanks

The sliding part of the shaft has a bearing, just a regular ball bearing or a taper-roller bearing. So the shaft can rotate freely and the outer part of the bearing doesn't rotate. Then you attach some kind of linear actuator to the bearing and move it in and out, moving the shaft.

If the outer shaft is hollow all the way through, this sliding bearing can be 'inboard' or on the opposite side of the motor.

There's lots of mechanical examples where a shaft needs to turn and to 'plunge' when the ends move. Car prop-shafts, driveshafts and tractor implement drives are all good examples. Very few of them are actively driven, but a slightly similar mechanism can be seen in a gearbox where the gears slide on the shafts.

Interesting! How is the propeller attached to the motor shaft? Can your motor drive a separate shaft/propeller with a belt, so the motor is offset from the shaft/propeller? what motor speed are we using? How long does this need to run without attention and will the propeller movement from one location to the other continue for the entire time the motor is powered?

Paul

Different thought. If the motor has a round shaft, can you make it "D" shaped with a file, etc.? It needs to transmit power to the propeller, but also needs to allow the propeller to move on the shaft.

Can you do some metal and plastic machining? Not much. Form some sheet metal into a "U" shape to mount the motor and allow room for a stiff control wire to through two holes in the "U" beside the motor? Also need to fabricate a plastic hub to attach to the back of the propeller. The hub will have a groove for the control wire to ride in. Probably need to have a loop there to go around most of that plastic part.

The propeller and hub will have to have a hole large enough so the motor shaft can easily slide.

Since the motor shaft is not able to transmit power to the propeller, we must modify the propeller and attached hub by making a locking pin to go inside the propeller hub and attached plastic hub. they can still slide on the motor shaft, but the motor shaft can transmit power. A tiny piece of aluminum from a soda can laid in the hub and the ends folded to lock in place may be sufficient. Be sure they can slide easily.

Ultimately, the propeller and hub will be moved in/out by a solenoid or a by a servo with a connecting link.

If that sounds like something you can do, I can try to make some drawings and post them.

Paul

Thank you MorganS and Paul_KD7HB for your solutions.
Both solutions seems good, but I lean to MorganS' solution.

[ Currently, the motor is connected to a "T" (at the "leg", straight below,) and the propeller is horizontally inserted into the "T". ]

I will try to build the next solution based on MorganS' suggestion:

  1. Motor (M1) shaft will be square. Call this shaft S1. Length is 5 inch.
  2. The "leg" of the "T" will be round externally, and squared hole internally. Call this shaft S2. Length 4.5 inch.
  3. Around S2 we have a simple bearing. The center ID of the bearing is fixed to the S2, so it will rotate with it.
  4. Connect a stepper motor (M2) to the bearing, to the OD, which is not moving.

The actual moving operation is:
A. The M2 will push/pull the external part of the bearing, so the whole T will move an inch this side and that side back.
B. The bearing is pushing the S2.
C. Internally, S2 is square, so it will slide on S1, forward and backward. But still allowing both S1 and S2 to rotate, force is going freely from motor M1 thru S1 to S2.

Many thanks to all

edward-flame:

  1. Motor (M1) shaft will be square. Call this shaft S1. Length is 5 inch.
  2. The "leg" of the "T" will be round externally, and squared hole internally. Call this shaft S2. Length 4.5 inch.
  3. Around S2 we have a simple bearing. The center ID of the bearing is fixed to the S2, so it will rotate with it.
  4. Connect a stepper motor (M2) to the bearing, to the OD, which is not moving.

For that sort of thing a diagram (even a very crude one) is much less open to confusion than a verbal description.

...R

sounds as if you need something like a thrust bearing in a car clutch.. they work on a spline, of course.

The sliding square sections could work ok...

regards

Allan

You can get small thrust bearings or flanged bearings for model helicopters, they might be useful.

Google " Stock Drive Products".
They stock a lot of small splined shafting and the matching hubs and other hardware to match them.
Look through there web sight and you might get some ideas for something that would suit your project.