Small motor speed control + battery holder - how/where?

[tinnews]

I want a really simple small motor battery box and speed controller. I have one that is beginning to disintgrate. It can be very crude and simple, a box to hold three/four AA batteries, a connector and some way of controlling the output. The existing box has a 10 ohm slider potentiometer.

I can find suitable boxes and connectors and battery holders from such as Rapid Recall and CPC but the 10 ohm pot is difficult. A slider works better from the usability point of view but even rotary 10 ohm pots are difficult to come by.

Can anyone suggest either somewhere I can find 10 ohm slider pots or, maybe, something ready made that would suit? I guess there may be old-fashioned 'wired' model cars that had this sort of controller. Or maybe there's something I've not thought of at all that might have this.

[meow2222]

A few options...

1. battery taps: just connect the motor to 6v, 4.5v, or 3v using connectors or a rotary switch
2. Diode droppers: use diodes connected to one end of the batt pack to drop aound a volt each. For finer control, also add a schottky diode dropping 0.5v at the other end.
3. Switched fixed resistors do a similar job, but will give poorer motor regulation
4. Make your own pot using resistance wire to get the 10ohms you want. Either make from scratch or rewind a wirewound one.
5. USe an adjustable voltreg, eg LM317. The circuit is pretty simple, but yes its a bit more complex than the above, and needs a heatsink.

NT

[tinnews]

This had occurred to me too but any rotary control isn't as neat/easy as a slider. I looked for slide switches with more than a couple of positions but found nothing.

Eek, that's getting a bit desperate! :-)

That's a possible approach, I probably even have all the bits lying around, I even have a few higher resistance slider pots. I was just hoping for a simpler solution!

[Lobster]

'ere, you're not allowed to ask queries like this without telling us what it's for...

(not that I'll have a clue as to the answer even then...)

David

[George]

So get a 20 ohm pot and a 20omhs resistor and put it in parrallel with the pot ie the two outer tags.

[Dave Plowman (News)]

A 10 ohm resistor suggests it is simply in series with the motor to set the speed. An extremely crude way of doing it - wasting battery power and lowering the available torque at that speed due to a higher source impedance.

I'm sure if you do a search on motor speed controller - qualifying it by the type of motor etc - you'll get lots of circuit suggestions. Ebay might also be a source of ready made units. Or Maplin, etc.

[Andy Dingley]

Radio control toy and fillet it. Even if you tape the transmitter to the receiver, this is still cheaper than almost anything that involves the slightest degree of "assembly".

If it's high current, then model boat controllers are about 20 quid for up to about 15A, (Mtroniks Viper is cheapest and simplest, IMHE) You can bodge up a pulse generator to dummy out the radio from one chip and a pot (circuits all over the intawebs)

[tinnews]

Nothing remotely near that available from the usual sources, 1k or 10k and up. Even doing what you say with a 20 Ohm pot isn't going to work as well as a 10 ohm one.

[tinnews]

Yes, it's very crude (but also very simple), efficiency isn't much of an issue.

I did have a look around (at Maplin in particular) but didn't come up with anything particularly useful looking.

[tinnews]

I think this might well be the answer, I'd half considered it already and, as you say, it'll be cheaper than almost any other solution.

[George]

What?

20 ohms resistor in parrallel will bring it down to 10 ohms.

The lowest available pot I think is 100 ohms?

[Bob Eager]

Won't be very linear, will it?

[dennis]

However when its half way it won't be 5 ohms, but 7.5 ohms (if my mental arithmetic is working in this heat).

[The Natural Philosopher]

Plenty of brushed controllers on Ebay. You also need a servo tester. Good kit from

for a cheapo controller and for the servo tester. Wire that up to a slide pot and all you need is a battery holder.

[tinnews]

Yes, a 20 ohm resistor in parallel will bring the resistance from end to end to 10 ohms but it's the slider which is connected to the motor to adjust its speed when it's (for example) half way between the ends it'll see much more than 5 ohms to the supply. Taking it to extremes your logic would work by putting a 10 ohm resistor in parallel with a

1M ohm pot, that definitely won't work as a motor speed control.

[mick]

Rotary ones here:

?N=1002379+109436&_requestid=164514or this may work... (same site)

[meow2222]

How cheap can you get that then? Hard to believe its the cheapest option.

NT

[The Natural Philosopher]

I was up to 14 quid or so using a premade servo tester and speed controller

[tinnews]

Thanks for the pointers, looks like just what I need.

[meow2222]

Lot more than any of the ones I suggested, hence my puzzlement.

NT