: mini pond/fountain pump workings

[DaveC426913]

urgent: mini pond/fountain pump workings

Well, it's not life-or-death but, I've got a deadline for tomorrow to finish this thing I've been working on for months and I've just came bang up against what might be a showstopper.

I'm building a pond widget that is powered by an 11W mini pond pump, http://www.homedepot.ca/webapp/wcs/stores/servlet/CatalogSearchResultView?D=910305&Ntt=910305&catalogId=10051&storeId=10051&langId=-15&Dx=mode+matchallpartial&Ntx=mode+matchall&recN=0&N=0&Ntk=P_PartNumber&showreviews=true". My widget uses the pump for its axle, not for its waterflow. i.e. I've got gears on the pump's axle.

I've just discovered a very strange behaviour in the pump and I'm not sure what to make of it. It seems as if, occasionally, the magnetic motor reverses its direction. It seems that, say if the motor encounters too much resistance turning clockwise, it will just reverse direction, rotating counter-clockwise. It can flip back and forth like this continuously every few seconds.

If this is true, I am scrood. It frankly never occurred to me that a pump might change its direction. (operating as a water pump, this behaviour would have no negative effect, since the turbine blades are symmetical. No matter which way the pump turns, the water would still flow the same direction. That lends credence to the idea that this might be designed behaviour - which is bad for me.)

Can anyone corroborate or disspell this idea?

I've got to find a solution in the next 24 hours or months of work will be wasted...

 

[Danger]

I've never heard of such a thing. Have you tried contacting the manufacturer of the pump for tech support?
My only top-of-the-head suggestion is to sideline the pump and substitute a waterproof motor such as for a submersible vehicle. Or, put the motor outside of the aquatic environment and run a flex cable to your gear mechanism.
Sorry that I can't be of more help, but this is pretty short notice, and I'm both tired and drunk.
I am, in fact, going to bed now. I'll check back before your deadline expires, but I sure hope that someone else can help you in the meantime.

 

[Dadface]

If it is designed behaviour then what is the purpose of it?The first thing that comes to my mind is that it reverses to expel pond debris which might clog up the works.Is the reversal feature programmed in or is it triggered by an increase of resistance?If the former is the case then perhaps you could bypass the programming circuitry, if the latter is the case and if you have to demonstrate your widget in a real pond with real debris(not pure water) then perhaps you could remove the turbine blades.These are just some first impression thoughts.Good luck with it.

 

[DaveC426913]

If it is designed behaviour then what is the purpose of it?The first thing that comes to my mind is that it reverses to expel pond debris which might clog up the works.

This is my thought, yes.

Note, btw, that the reversal of the turbine does not reverse the direction of water flow. This is why I never noticed the behaviour; it is only evident when one attaches something to the axle.

Is the reversal feature programmed in or is it triggered by an increase of resistance?If the former is the case then perhaps you could bypass the programming circuitry, if the latter is the case and if you have to demonstrate your widget in a real pond with real debris(not pure water) then perhaps you could remove the turbine blades.These are just some first impression thoughts.Good luck with it.

I'm sure that it's caused by resistance. Definitely not programmed.

Unfortunately, the turbine blades are what I use to attach the driver gear to the axle. The gear is also what causes the friction.

 

[Bob S]

This is a very interesting problem. I suspect that this is an AC motor, not an AC-DC (or universal brush) motor, running on AC. Single phase AC induction-type motors are brushless, and need some starting phase shift (either inductive or capacitive), which in your size (11 watts) may be a shaded pole motor. I have made shaded pole motors run in either direction, but only when I cut off the "shades" (copper coils shading about 1/3 of the poles). I suspect that shaded pole motors could run in either direction if the copper shades were very thin, which means minimal starting torque. Is this a reciprocating (piston) pump with flapper valves? Too much pressure (head) may stall the motor, and give the motor a kick-start in the reverse direction.

 

[berkeman]

As a quick temporary fix, maybe install a ratchet mechanism on the shaft, so that it can only turn the way you want it to. If resistance makes it reverse, then when it tries to go backwards and can't hopefully it just goes back to running forward.

You could use the what are you-macallitt thing off of a coaster bicycle brake/axle...

 

[DaveC426913]

As a quick temporary fix, maybe install a ratchet mechanism on the shaft, so that it can only turn the way you want it to. If resistance makes it reverse, then when it tries to go backwards and can't hopefully it just goes back to running forward.

This had occurred to me too. It's a bit of overkill tough.

 

[Danger]

So... did you get 'er going?

 

[DaveC426913]

So... did you get 'er going?

Sigh. No. I gave it to my friend in its unoptimized state. The deadline was Saturday, which was his G-scale railroad http://davesbrain.livejournal.com/277928.html". Such a shame for something I've been working on for two years.

The motor is just way too finicky. If its axle is out of alignment by micrometers, the rotor seizes. Trying to put a pulley on that axle, which pulls on the axle, is a losing game.

So, with his help, we're going to use a non-submersible motor, located above the pond surface to drive my widget. I'll post pix of the thing.

 

[Danger]

Bummer, but I look forward to seeing the thing when you're done. (Also the rest of the train set-up.)

 

[DaveC426913]

Bummer, but I look forward to seeing the thing when you're done.

I will photograph it as it is now, and post.

(Also the rest of the train set-up.)

You can see it in the link provided above.
But that's only last year's. He's built a whole nother street this year. I'll shoot that too and post it.

 

[Danger]

Oops; I didn't realize that there was a link in there. Neat. (I think that the bridge to the bedroom would freak me out a bit, though, given my acrophobia. Stumbling across that sucker drunk would be no fun at all.)

 

[DaveC426913]

Oops; I didn't realize that there was a link in there. Neat. (I think that the bridge to the bedroom would freak me out a bit, though, given my acrophobia. Stumbling across that sucker drunk would be no fun at all.)

?
Oh. Ha hah.

For a second, I thought you were talking about a train running over a bridge into the bedroom...

Those are two unrelated blog entries. One friend had an open house of his new house, the other had an open house of his train layout. They just happened to be on the same day.

 

[Danger]

 

[dE_logics]

If you do buy a new motor, why not just take the load off the motor?

 

[Danger]

If you do buy a new motor, why not just take the load off the motor?

I don't follow.

 

[DaveC426913]

I don't follow.

Nor I.

A different motor will still require a pulley on its axle. I'll just have to brace it, is all.


Ironically, I do have the solution already in-hand. You see, one of the step-down gears that I use to reduce the RPM is a http://upload.wikimedia.org/wikipedia/commons/thumb/9/98/Schneckengetriebe02.jpg/800px-Schneckengetriebe02.jpg" , which has no tendency to distort its axle. If I could get the pump driving the worm gear directly, I'd be golden. But I can't get the worm gear onto the motor axle.

 

[Danger]

Does this thing involve a lot of torque? If not, I've had a lot of success using chunks of gas-line or vacuum tubing, aquarium hose, etc. to connect mismatched parts. Or, you could use JB Weld to build up a connecting collar (but it might take a fair bit of work to balance it).

 

[DaveC426913]

Does this thing involve a lot of torque? If not, I've had a lot of success using chunks of gas-line or vacuum tubing, aquarium hose, etc. to connect mismatched parts. Or, you could use JB Weld to build up a connecting collar (but it might take a fair bit of work to balance it).

Not really a lot of torque, no. But one of the reasons I'm using all these step-down gears is to get some torque from the motor to overcome the inertia of my widget.

The trick is that the impellor is rotating at ~1000-2000RPM, so the connection has to be quite robust, and at the same time very small to fit in the space.

I've been looking at jerry-rigging connections, yes. Your methods sound very much like mine. I put screws through the face of the pulley and used the heads of the screws to clamp to the impellor of the motor.

But I think you're right. I need to ditch the pulley and go back to driving the worm gear directly. That will eliminate and sideways torque on the impellor axle.

 

[Danger]

Your mention of the screws reminded me of one other technique that I've used. It's tricky as hell, and you have to be very careful, but it works.
You can either thread the outside of the shaft, or, even harder, drill a hole through the centre of the shaft and tap it internally.

 

[DaveC426913]

Your mention of the screws reminded me of one other technique that I've used. It's tricky as hell, and you have to be very careful, but it works.
You can either thread the outside of the shaft, or, even harder, drill a hole through the centre of the shaft and tap it internally.

It is ~1.5mm in diameter.

 

[Danger]

It is ~1.5mm in diameter.

Well, that's inconvenient...

edit: Could you sleeve it? That's one other thing that I've done in the past. Take a tube (like maybe part of a telescoping antenna or a chunk of brake line) that just slips over the shaft, leaving a lot extending, then solder it in place. You can then either solder your secondary shaft to the inside of the sleeve (if it's the same diameter as the original), or use other attachment methods that aren't possible with the original.

 

[DaveC426913]

Well, that's inconvenient...

edit: Could you sleeve it? That's one other thing that I've done in the past. Take a tube (like maybe part of a telescoping antenna or a chunk of brake line) that just slips over the shaft, leaving a lot extending, then solder it in place. You can then either solder your secondary shaft to the inside of the sleeve (if it's the same diameter as the original), or use other attachment methods that aren't possible with the original.

Hm.

Oh shoot. Duh. I just realized. Again.

The axle is stationary. It does not rotate. The rotor rotates on the axle.

That's why I am attaching the mechanism to the impellor blade, which is affixed to the rotor.

 

[Danger]

Oh, sure... now you tell me...

I've got to think on this some more.

edit: So let's see if I have this straight. This is like the old radial aeroplane engines where the prop was attached to the cylinder block, and the whole thing revolved around the crankshaft?

 

[DaveC426913]

Here it is:

 

[Danger]

Wow... neat design. So the boat goes around, and the fish goes around in front of it but also leaps into and out of the water?
I still can't see quite how the motor works, but I love the concept of what you're doing. I'm a bit confused by your gearing; it looks to me as if the fish is jumping backward.

edit: Wouldn't it be lighter, though, and thus require less torque, to mount the models on thin spring wire rather than the plastic rods that you're using? (Yes, I realize that your secondary gearing for the fish will need an axle larger than a wire, but it could be truncated.)

 

[DaveC426913]

Wow... neat design. So the boat goes around, and the fish goes around in front of it but also leaps into and out of the water?

Yeah!

I still can't see quite how the motor works...

What do you mean?
Can can juuuust see a bit of the impellor (yellow bit inside motor casing, behind belt).
The pulley is affixed to the impellor with screws (2 silver lumps on pulley).
Motor pulley drives top pulley via belt. (You can barely see the top pulley behind its mount.)
Top pulley drives worm gear on same axle.
Worm gear drives large horizontal white gear which is affixed to grey gear.
etc.

I'm a bit confused by your gearing; it looks to me as if the fish is jumping backward.

It may be hard to see in the pic. Fish is facinbg toward camera, we are looking down its maw. It will move clockwise around the yellow gear, just like the fisherman does.
Fish is currently coming up from behind its axle, and will come toward and down in front of the axle.

edit: Wouldn't it be lighter, though, and thus require less torque, to mount the models on thin spring wire rather than the plastic rods that you're using? (Yes, I realize that your secondary gearing for the fish will need an axle larger than a wire, but it could be truncated.)

Well, I want the fisherman to be rigid. He was originally on a long thin wire like a paperclip but he just flopped around too much. The fish needs to be on a rigid pole too, since it's still got one gear to drive it in circles on the yellow gear.

 

[Danger]

Okay, I've got it now. I didn't even see the pulley or belt until you described them. I thought that the drive was coming off of the top of the motor unit. Also, for some reason, the fish looks as if it's facing away from me. (Maybe it's some kind of bass-ackwards Yank fish? )
Makes sense now.

 

[DaveC426913]

Also, for some reason, the fish looks as if it's facing away from me.

The fish itself is actually PhotoShopped in from another pic. The angle on the untouched pic was even worse. What you're likely perceiving is the poor match of lighting between the background pic and the overlaid fish.

But note that you are looking down the maw of the fish. That big white area at the head of the fish is the inside of its mouth. There's an eye in the tiny white smudge down and to the right of the maw.

 

[Danger]

Right, then... I see it now.
You got to admit that the 'bass' pun wasn't too bad, though...?

Although it might not matter to the design, is there turbulence of any sort in this pond? I ask only because of you mentioning the boat flopping around on a flimsier support structure.
Also, if the boat and the fish are synchronized in revolutions around the centre, you could link a loose piece of thread between them to make it appear as if the fish has already been hooked. It would have to be disproportionally thick, though, to make it visible from a distance.