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pennymachines
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Re: Davy Jones penny pusher - Help!

Postby pennymachines » Sat Dec 15, 2018 12:56 pm

In case you haven't seen it, here's the CAM Automatics topic.

deano67
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Re: Davy Jones penny pusher - Help!

Postby deano67 » Sat Dec 15, 2018 1:48 pm

Yes had a good read of that link, very informative, thanks.

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Re: Davy Jones penny pusher - Help!

Postby yaksplat » Wed Jan 02, 2019 3:40 pm

Take a look at this motor:
https://www.allelectronics.com/item/dcm ... ead/1.html



Just looking at this motor makes me want to build a pusher. !PUZZLED!
brushless.jpg

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brigham
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Re: Davy Jones penny pusher - Help!

Postby brigham » Wed Jan 02, 2019 4:10 pm

3-Phase DC.
Now there's an interesting concept!

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Re: Davy Jones penny pusher - Help!

Postby yaksplat » Wed Jan 02, 2019 4:17 pm

It just requires a speed controller to work, but that eliminates any need for additional gearing. I just like reading this review:
This thing has incredible torque! Out of curiosity, I put a long 10mm wrench on the shaft, and tried to stall the motor. No matter how hard I tried, it was no contest, and the motor only peaked @ 3.1A during this heroic arm-wrestling match. Crude, but informative. I'm now using these to power a 150 lb stair-climbing robot.
That's it... I'm buying one. Future penny pusher project incoming.

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JC
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Re: Davy Jones penny pusher - Help!

Postby JC » Wed Jan 02, 2019 4:35 pm

So what exactly is a 3 phase DC motor?

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Re: Davy Jones penny pusher - Help!

Postby badpenny » Wed Jan 02, 2019 5:43 pm

Crazy, t'would seem the laws of electrickery have changed.
In order to have phase, you have to have AC so that you can have two or more AC sources to measure the relative phase angles that they possess. The concept of three phase alternating electricity refers to the relational phase differential of three alternating current single phase sine waves, each displaced 120 degrees of phase angle from the other.
The advert glibly comments that a controller is required, I guess that's the misdirection.

What is it you're wanting to push with that? Yorkshire?

BP !PUZZLED!

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Re: Davy Jones penny pusher - Help!

Postby yaksplat » Wed Jan 02, 2019 6:19 pm

I'm not an electrical engineer, but I did take a few EE classes when getting my mechanical degree. So let me give it a shot with a little help from Wikipedia.

So DC electricity from a battery or transformer goes to an electronic speed controller. This sends out timed pulses to each of the three phases, controlling rotation of the motor shaft. You can vary the voltage to the controller and that will slow down or speed up the motor.

Anyone can correct me if my information here is incorrect.

From the spec sheet, this is a 334W motor at 5270 RPM

Same motor on a test setup, without the gearbox:


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Re: Davy Jones penny pusher - Help!

Postby slotalot » Wed Jan 02, 2019 9:21 pm

Sounds like a stepper motor to me ?? :!?!:

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Re: Davy Jones penny pusher - Help!

Postby yaksplat » Wed Jan 02, 2019 10:49 pm

I found a good explanation
The two are largely the same, fundamentally. However, they differ in intended application. A stepper motor is intended to be operated in, well, steps. A BLDC motor is intended to be operated to provide smooth motion.

Since stepper motors are used for motion control, repeat-ability of the steps is desirable. That is, if you start at one step, then to another, then back to the first, it should ideally return to exactly where it was previously. Various things can mess this up; slop in the bearings, friction, etc. BLDC motors are optimized for smooth torque between steps, not repeat-ability.

Stepper motors are designed to maximize holding torque, the stepper's ability to hold the mechanical load at one of the steps. This is accomplished by keeping the winding current high even though the rotor is aligned with the stater. This wastes a lot of energy, because it generates no torque unless the load tries to turn out of position, but it does avoid the need for any feedback mechanism.

On the other hand, BLDCs are typically operated with the rotor lagging the stater so that applied current always generates maximum torque, which is what a brushed motor would do. If less torque is desired, then the current is decreased. This is more efficient, but one must sense the position of the load to know how much torque to apply. Consequently, stepper motors are usually bigger to accommodate the additional heat of operating the motor at maximum current all the time.

Also, for most applications, people expect a stepper to be capable of small steps for precise motion control. This means a large number of magnetic poles. A stepper motor typically has hundreds of steps per revolution. A BLDC will usually have many less. For example, recently I was playing with a BLDC from a hard drive, and it has four "steps" per revolution.

Stepper motors are usually designed for maximum holding torque first, and speed second. This usually means windings of very many turns, which creates a stronger magnetic field, and thus more torque, per unit of current. However, this comes at the expense of increased back-EMF, thus reducing the speed per unit voltage.

Also, stepper motors are usually driven by two phases 90 degrees apart, while BLDCs typically have three phases, 120 degrees part (though there are exceptions in both cases):

Despite these differences, a stepper can be operated like a BLDC, or a BLDC like a stepper. However, given the conflicting design intentions, the result is likely to be less than optimal.


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