Smaller than 1k potentiometer

[rec-tec]

Hi all

I am throwing myself at the feet of the learned (a little too sycophantic - at least I'm trying)

I am building a thing. I have tried a 10k pot, a 5k port and a 1k pot. Is there a smaller one? Like a
0.5 k pot as there is too much twisting of the pot before it does what I want - so the amount of sensitivity is very limited (ie it is only working over a very small range of rotation), if that makes any sense.

As you can tell I know very little about electronic stuff - but I know exactly what I want to do.

Please could some kind forum member share a link to a pot (with low resistance - have I just shown my ignorance of terminology)

By the way, I am trying to control the speed of a 3-6v motor. Don't tell me I need a rheostat - if so what, where?????

Very best

Cheers

RT

[James Perrett]

I remember trying to do this with a Lego motor and a pot many years ago. The problem is that the motor usually requires a high startup current which goes down when it is running. So you'll have to set the pot to almost full on to start the motor up and then adjust it down again to get the speed that you want. You will usually want to wire the pot up as just a variable resistor rather than a potentiometer.

We also need to know the current rating of the motor. If it is something like 0.5A at 6V then it will have a power output of 3W. Your pot will need to be rated at a similar value. As you've guessed, a low value wirewound pot (often called a rheostat) is what you need or, better still, an electronic PWM controller.

[Folderol]

Have a look for pulse width circuits. They are far more efficient than a simple pot and also give a much better torque performance.

Model railway enthusiasts use these a lot as they can get the locos to creep out of a station very realistically.

[Hugh Robjohns]

Yep, if you're controlling a DC motor then a PWM controller system is definitely the way to go.

H

[damoore]

If you are doing something else though, and need to spread a smaller range of control through the range of the pot, you can do that by putting a resistor in series with the wiper to set the minimum resistance and another in parallel to set the maximum (less than 1K). It won't give you a linear "taper" though which may or may not be a problem.

Digikey seems to have pots going down to 1 Ohm though the signal level ones you probably want start at 500 Ohms.

[ef37a]

http://www.maplin.co.uk/p/mfa-motor-spe ... unit-wc76h

You would need to replace the dinky pre set pot with something chunkier.

I also think you do not need to change the track value so much as the track "law"?
This can be cheated by shunting the wiper to one or other end of the track with resistors Try something 30% of track resistance to begin with.

Dave.

[Folderol]

Sorry, but from (almost forgotten) experience, you'll never be satisfied with the results. At low revs the motor will stall at the drop of a feather, and speed will be all over the place depending on the load as soon as there is any resistance at all in series with it.

I just looked on ebay, and proper motor controllers are going for about £5 these days.

If you just want to have fun, you can do a reasonable job with an NE555 timer and a 2N3055.

As a rule of thumb for best torque, use a supply voltage about 1.5x the motor rating, and make sure you never go above 75% on the control.

[rec-tec]

How kind you all are for respectful and prompt replies

I wish I knew more about electronics. I can just about change a battery

The motor is for part of a music project - the kinetic part (weird I know) and I will let you know how it all goes, providing I don't burn out the motor(s)

The last poster mentioned something about have fun with something that I presume to be some kind of modules (a bunch of numbers) would this be suitable for someone who has only just learned which end of a soldering iron to hold (I apologise for not name checking the poster, but I forgot when I got to this point, early onset....)

Anyway cheers and I will checkout the various options and will update. Once (if) complete I will share the music bit of it as I am due to do (some kind of performance - if all goes to plan)

Many, many thanks

Rec-tec

[rec-tec]

Me again

I have just seen a PWM (?) motor controller for 99p + 55p p&p

I think I should go for a better one. Is it fairly easy to wire them up. I presume that they just come with simple instructions, as far as I can see it is only a matter of inserting power input to some connectors and wires to the motor to others

I think I might like to buy British, even though it is a fiver.

Any advice

Cheers

Rec-tec

[Folderol]

Me again

I have just seen a PWM (?) motor controller for 99p + 55p p&p
Rec-tec

At that price I'd suggest it's just a PWM chip, not a complete unit!

[Martin Walker]

Me again

I have just seen a PWM (?) motor controller for 99p + 55p p&p
Rec-tec

At that price I'd suggest it's just a PWM chip, not a complete unit!

Post a link rec-tec, and then we can advise in more detail whether or not this will be beyond your electronic capabilities

Martin

[rec-tec]

Cheers guys

I am in your debt for your assistance

I hope these links work

http://m.ebay.co.uk/itm/3A-DC-6V-12V-24 ... nav=SEARCH

Or

http://m.ebay.co.uk/itm/10x-DC6V-30V-12 ... 1059968908

Which I think I may find more useful, if the numbers accurately reflect the speed.

Take a look and let me know what think or if you consider one better. Bear in mind that the low cost means it may be worth a punt?

Cheers guys

Rec-tec

[James Perrett]

They seem ludicrously cheap for what you appear to be getting but, on the face of it, they look like what you need.

[rec-tec]

That's what I thought James (thanks for prompt reply)

One of each then - but they will probably take a month to arrive!

Thanks to all for suggestions (and not focusing on my ignorance!)

I will (may) post back with out comes

Don't you just love this forum!!

Cheers

Rec-tec

[Folderol]

Hope it works out OK, be interested to hear how you get on.

[Martin Walker]

Indeed - feedback required please

However, it's amazing what you can buy from Hong Kong nowadays for tuppence halfpenny and a slice of malt loaf.

I bought my first item (a battery tester for the princely sum of £1.85) a few weeks ago, simply to use its integral analogue meter in a steampunk synth DIY project. Nothing in the UK for under £5!!

Strewth - it's now down to just £1.70



https://www.amazon.co.uk/dp/B000L9C27O/ ... TE_3p_dp_1

Martin

[MikeGorman]

There is yet another option you can look at. You can go the mechanical rather than the electronic route and use a gearbox to slow down your motor. This also tends to increase the torque supplied by the same motor as well.

There are loads of solutions out there, especially from the scale model world, but a quick Google search had this one pop up that looked quite interesting.

https://shop.pimoroni.com/products/micro-metal-gearmotor-extended-back-shaft?utm_medium=cpc&utm_source=googlepla&variant=3073681089&gclid=CNH2w93F2M8CFRQ8Gwod6hsNow

Regards

Mike

[rec-tec]

Thanks for the suggestion Mike

Martin - weird I too bought the self same battery tester, but things from China take ages, so not yet received.

Cheers

Rec-tec