Help Me decide on my motor/controller setup

[WCRiot]

Hey all,
I found this forum searching Google. I read several post before I started my own thread. Let me explain my project:
I have a small semi-automated welding station which consist of a small benchtop lathe and tig welder.
This is the lathe I have, it has a 3/4 hp motor: **broken link removed**
This is the welding unit that I have: **broken link removed**

I have a mechanical gear reduction mechanisum on the motor to slow the lathe down but that didn't slow down the motor enough. So, I hook up a power supply to the lathe motor to slow it down even more.

The problems with this setup are: the speed of the motor changes slightly and the operator has to constantly time the rotation and adjust the power supply voltage to regulate the speed of the lathe to 6 r.p.m.

So we definitely need to change the speed controller to something more precise. But, we are also considering on changing the motor so that we can ensure this precision. What do you think I should do?

So our situation is this: We have a low RPM speed requirement. We do not apply any load to the rotating shaft. The only load on the motor is from the resistance of the gears, friction and the weight of the lathe head. So we don't need alot of torque or power.

Any help to get me rolling would be really appreciated.

 

[WCRiot]

Help Please

 

[KMoffett]

The welder is irrelevant ...how about more info on the current motor and lathe setup...pictures...links...power supply info.

Ken

 

[WCRiot]

The welder is irrelevant ...how about more info on the current motor and lathe setup...pictures...links...power supply info.

Ken

The picture of the lathe is above. Ill have to take some pictures of the setup within the next two hrs.

I believe the power supply is a 0-15v 2A Hewlett Packard. Ill confirm this within 2 hrs.

I would not say that the welder is irrelevant. Because I think that I need to build some shielding for the motor. When the welder starts, I believe the frequency of the welder might be causing some conflicts

 

[KMoffett]

No picture! ??? And, you are right that high frequency RF generated by the TIG could cause problems. By irrelevant I just meant the first step is looking at what options there are to reduce the lathe speed.

Ken

 

[WCRiot]

Pictures as promised

**broken link removed**

**broken link removed**

**broken link removed**

**broken link removed**

 

[WCRiot]

I talk to Baldor tech support and here is what they told me.
They said using a power supply to adjust the speed of a DC motor is not a precise method for low speeds. He said we need a DC Driver. Because we are using a low voltage DC motor he recommended Baldor model number BC141. it hooks up to the wall and outputs 0-90v Dc to the motor. This will replace the power supply. We would still need a potentiometer to adjust the speed of the motor.

**broken link removed**

They cost about $150-$200. The tech was very confident that this would work. He said the other option is to get a controller with tach readout that will automatically adjust output voltage. He said this would cost more like $700

What are your thoughts?

 

[KMoffett]

He's right. My guess is the that there are tach-feedback motor controllers out there for much less that $700, but "I" can't point you there. Sorry.

Ken

 

[evarobotics]

If you want to vary the speed and still keep it accurate, you need some form of motion controller. Google that and you'll get bazillion hits for all sorts of motors. It will include encoder or taco feedback, and you may need to change the motor. Look around the robot supply shops (battle bots and the like). I imagine you could find something for around $200.

If you want to have 6rpm now and for ever, well at least for a while, you have two options for regular speed control.

1) DC Motor running at it's rated speed, from a regulated supply, with a gearbox to give you the speed reduction. The motor speed and gearbox size will depend on how big a gearbox you can fit/afford. The idea here is to add inertia to the system (flywheels work well to). Get the motor pumping with a large reduction and any small changes in supply voltage won't have a big effect on your work piece.

Even adding a larger flywheel/pulley to the lathe chuck would help. The faster you can run the motor the better.

2) Use an AC Motor, again with a gear box to reduce the speed (a 200:1 reduction on a 6 pole motor I believe). This will give you better speed regulation because the speed is based on the mains frequency, not the voltage, but speed changes require a different hardware reduction.

Both these methods will protect your workpiece when the TIG fires up as well.

Good luck