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Speed Controller

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Dave Oconnell19/06/2018 16:36:22
5 forum posts
5 photos

4a.jpg3a.jpg2a.jpgHi, I Have built an electric pottery wheel and used a industrial sewing machine motor 1hp 750w this came with digital control box and a speed control box which connects to a foot peddle by a rod (see attached photos)

All is working OK except the speed control box is very sharp and abrupt, I have geared down the speed to 260rpm from 500rpm.

My question is, is there any way I can alter the speed control to make it run Smother, the attached photos show how the arm moves across a sensor.

Hope this makes sense, Many Thanks1a.jpg

John Rudd19/06/2018 17:10:41
1232 forum posts
57 photos

Without knowing what the sensor is, I'd guess at it being a Hall effect device, whose o/p voltage varies with mag field...

How to make the control finer is difficult without seeing what the foot pedal connects to...again I'd guess the main speed control gubbins is in the motor?

Any more detail?

Edited By John Rudd on 19/06/2018 17:15:04

SillyOldDuffer19/06/2018 17:13:43
3385 forum posts
664 photos

Not sure there's much that can be done simply to the electronics - it is what it is, looks like a magnet and sensor.

But how about extending the mechanical arm to increase the pedal travel necessary to move the magnet? Or working the arm via a second lever arranged so that large foot movements are necessary to move the magnet slightly.

Dave

blowlamp19/06/2018 17:23:44
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1050 forum posts
72 photos
This video might be of assistance to you if yours is light sensitive.
https://m.youtube.com/watch?v=X6CCxv3i4No

Edited By blowlamp on 19/06/2018 17:26:38

XD 35119/06/2018 20:41:43
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1048 forum posts
42 photos

Nothing more than a hall effect switch by the looks of it

We really need to see all of the components you have to control the motor , that switch could be used for sensing the footswitch position so the speed controler is then switched on and from there pushing down further on the pedal increases speed via a variable resistor or rotary encoder inside the motor controller box.

Dave Oconnell20/06/2018 15:44:08
5 forum posts
5 photos

Thanks to all, yes I believe it is a Hall effect switch, the foot peddle pulls the arm which turns the plastic spindle across the sensor. The you tube vid looks like an idea worth playing around with, also the longer foot peddle. If anyone as a brain wave let me know.

SillyOldDuffer20/06/2018 16:15:31
3385 forum posts
664 photos
Posted by Dave Oconnell on 20/06/2018 15:44:08:

Thanks to all, yes I believe it is a Hall effect switch...

Apologies for being a pedant but it might help. I think the sensor is a linear Hall effect device rather than a switch. It produces a DC voltage proportional to the proximity of a magnet on the plastic arm. (For safety there might also be an on/off switch inside that piston thingy?)

Hall effect sensors as used in Tachometers contain a built-in amplifier arranged to trigger so that the output is either fully on or fully off. It doesn't make sense to use that type in a speed controller.

Unlike a potentiometer the Hall effect arrangement has nothing to wear out, is robust and electrically safe. The motor controller probably doesn't care how its control voltage is produced, provided it stays within range, so there are any number of ways of varying a few volts that would drive it. But because the mechanical part is more complicated than the electronics, I'd be inclined to stick with what you have, making the magnet travel more slowly for a given foot movement with a longer lever, or levers.

Just a suggestion. What works best for you depends on what you have available, not what I think.

Dave

Michael Gilligan20/06/2018 16:21:36
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11878 forum posts
518 photos

For the sake of undoing two screws, it might be worth releasing the circuit board and checking what's written on the chip ... These things are always easier when we've found a datasheet.

MichaelG.

john swift 120/06/2018 17:47:22
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309 forum posts
175 photos

looking at the video link from blowlamp

https://m.youtube.com/watch?v=X6CCxv3i4No

at 19:59 you can see what looks like the light from a red LED

I assume the speed control is controlled by the amount of reflected light from the movable flag / reflector

the mod with the graded reflector giving a better range of control

as MichaelG says looking up the device part data sheet will make things easier

may be its like this Sharp GP2S700HCP

https://cdn.sharpsde.com/fileadmin/products/Optoelectronics/Isolation%20Devices/Specs_Photointerrupter/GP2S700HCP_03Oct05_DS_D3-A02201FEN.pdf

John

Edited By john swift 1 on 20/06/2018 17:47:59

XD 35120/06/2018 20:55:02
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1048 forum posts
42 photos

(For safety there might also be an on/off switch inside that piston thingy?)

i was thinking the piston thing may have been like a dashpot unit ?

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