Programmable winch?

[OwenLinton]

G'day guys!

I'm wondering if anyone has any experience related to or ideas regarding making a small programmable winch?

I'm looking to set up a rig that will lower to a set height when I press a button and return home when I repress it.

My friend suggested a servo motor due to the ability to program the amount of rotation however I haven't been able to find a continuous rotation servo with adequate torque (2.5NM - 5NM).

I've also looked at reversible motors however I'm unsure how one would set up a circuit using a limit switch to both lower it and bring it home.

Any help would be much appreciated!

Owen

 

[Pommie]

A better idea of what you are trying to do would help. Just a torque doesn't tell us much.

Something like,
Weight of object to move.
Distance to move.
Time to move.

Depending on the answers to the above something like a model yacht winch servo might be adequate.

Mike.

 

[OwenLinton]

Thanks Mike!

I'm trying to make an automated tray that will lower 0.5M-1M on a downward angle at about 35. I've set my safe number at 5KG but it shouldn't add up to that much. Not too concerned about speed but less than 15 seconds would be ideal.

Owen

 

[Pommie]

Moving something 1M at an angle of 35° is the same as lifting it 0.6M. To lift something weighing 5kG by 0.6M requires 5*g*0.6=30 Joules. To do this in 15 seconds requires 2 joules/second = 2 Watts. I'm assuming the tray is frictionless - ie is on wheels.

From the above, any geared motor that's rated around 5W should suffice.

Mike.

 

[OwenLinton]

Any ideas regarding programming it to stop at the lowered and home positions?

Owen

 

[Pommie]

Either use limit switches or use a second gearbox (after the winch) to drive a potentiometer and use a servo circuit to control it. Oatley did a suitable circuit clicky but unfortunately they are discontinued.

Mike.

 

[OwenLinton]

Sorry for the trouble but I still can't quite get a solution from the infomation you're giving me... I think the limit switch method would be easier but I can't think of a way to get it to stop the winch at a certain lowered length. Can you provide any more info?

Owen

 

[Pommie]

If you use a double pole switch in a changeover configuration you can put the limit switches in the crossed wires.

Found an image on wiki, **broken link removed**

Put the (normally closed) limit switches in the two vertical connections.

Mike.

 

[OwenLinton]

G'day Mike

I've been thinking about this problem and constantly looking for a solution but my total lack of experience is having a major effect!

Would you mind if I sent you a message for some private tuition?

Thanks for you patience!

Owen

 

[Pommie]

It's better if you ask any questions on the thread so that anyone searching in the future will be able to find it.

Mike.

 

[OwenLinton]

A valid point!

The main problem I've been having (despite numerous googles) is working out exactly how DPDT switches work, however while I was writing a post explaining my whole situation I think I might have come up with a semi-viable solution!

What do you think of this:

 

[Pommie]

What you have is similar to the change over switch idea. A change over switch is simply two switches in one.

The dotted line in the diagram just represents the fact that both switches are joined and switch together. Can you see how the polarity to the motor is reversed by the switch?

Edit, Changed the diagram. Should work now. With the DPDT switch in the up position the motor will run until the left limit switch opens. In the down position it will run in the opposite direction until the right limit switch opens.

Mike.

 

[Pommie]

Changed the diagram, see above.

Mike.

 

[OwenLinton]

I can see the reverse in polarity but now it's combining it with the limit switches that's confusing!

Say the top wire was for the upward direction of the tray and the second from the top was downward, how would you set up that first limit switch so it stops the motor when the tray reaches home?

Edit:

Disregard that, I just had a look at your diagram again and it makes more sense now! Thanks! I'll try and plan this out a bit further and test it out ASAP!

Owen

 

[Pommie]

We posted together, see it the new diagram makes more sense. I'm assuming that the motor is a small DC motor that is reversed by changing the polarity.

Mike.

 

[OwenLinton]

I'm still trying to choose a motor I think would be appropriate... During my searching I've found mention that geared motors can sustain weight while not powered or something, which is appealing, but mostly I was looking at reversible DC motors since I read that reversing the polarity of a regular motor can damage it?

What's your opinion on this? And should that circuit still work with a reversible motor?

 

[Pommie]

That circuit will only work with a reversible DC motor. I'm assuming you will by using something like a small model type geared motor. You would definitely need a geared motor so you have enough torque. Geared motors keep their position simply through friction in the gear box, especially worm gear motors.

You should fill in your location and then someone may be able to point out a suitable motor in your vicinity.

Mike.

 

[OwenLinton]

Ahh! Thanks for that info!

You might be able to help me out, I'm actually from Sydney... Any suggestions?

The top on my list at the moment is probably the MOT-203

**broken link removed**

What do you think?

 

[Pommie]

If you wound cotton around the shaft it would wind in at 6*PI*160=3 meters per minute. So it would move your 1M in 20 seconds. At a radius of 3mm it will pull with a force of 50/0.3 = 166kg. The 202 may be a better choice, at 36RPM you would be able to use a small drum.

Mike.

 

[OwenLinton]

Okay, I'll invest in the 202 and do my best to set this up ASAP! I'm looking forward to setting this rig up... Thanks a lot for your help!

I'll be sure to keep you updated on progress and let you know if I come accross any snags!

Owen