Need electronics help

[ScotY]

I would like to build a circuit that would provide variable speed control of a small
electric motor. This is for a homemade optical helicopter tach and you can see pics and a schematic here:

http://www.rcgroups.com/forums/showthread.php?s=&threadid=62023&perpage=15&pagenumber=2

I don't require the LEDs in this circuit and it would be much better if the rpm could be controlled with a rocker switch, although I have no idea if this can be done.

Can anyone help with ideas or suggestions? Please keep in mind that I am electronically challenged. :D

[steve lewin]

Bear in mind that I am "helicopterally" challenged i.e. I know nothing about helicopters and their tachs. What do you mean by "controlled with a rocker switch" ? You want to switch between 2 preset speeds ?

The schematic seems very simple. If you can explain exactly what problem you are having with it I'm sure spmeone can help.

Steve

[Mr.RC-CAM]

Using a switch to vary the motor speed will really make this a complicated project. Why not just build the simple speed control that is shown in the link you provided?

RC-CAM

[ScotY]

Hi Steve,

Thanks for the offer for help! Here's what I want to do in non-helicopter terms:

I would like to run a small motor with the ability to control it's speed using a pot. It would be better if the pot was replaced with a rocker switch, momentary on/off. I'm not sure if that is the right way to say it. It would be ideal if the rocker when pushed up would increase the rpm and when pushed down the rpm would decrease. I do need variable speed control, not just two speeds. I would ideally like to use a two cell lipo pack to run it, as I have one on hand. I also would like to have a power switch, on/off in the circuit but that should be easy enough for even me to figure out. :D

The problem I'm having with the circuit is I don't know what the purpose is of the transistor thing. I'm assuming I could just use a pot to control rpm but don't know what value to start with. Is the transistor necessary and what type do I need?

Thanks!

[steve lewin]

As RC-CAM says using rocker switch control like that would make the project vastly more complicated.

The pot shown in the circuit will already regulate the speed. The transistor controls the current through the motor. What type of transistor you need will depend on how much current your "small motor" takes. If you have more detailed info on the motor it may be possible to tell if it will work from 2 Li-Poly cells and get a better idea of what values would be required.

It's really only an experimenter's circuit. If you're not comfortable playing with electronics then it's probably not for you.

Steve