Need Help with a 2 speed motor control for small dc motor!! NEWBIE, please help!

[jarrettbailey]

Hi-

Brand new to the forums here, and a novice electronics person. I am an inventor (of sorts) and I always have visions for thing and then realize I don't have the knowledge to finish them. So I am hoping that you can help me figure this out.

I am building a version of a Leslie speaker system (a dual speaker system with rotors for upper and lower speakers) that is powered by 2 dc motors. I have not decided what motors to use, but I need small motors with fairly high torque (the slow speed for the rotors is around 30 rpm). What I need to figure out is 2 things:

1 - what type/size motor I need (e.g. 9v, 12v, etc, also other specs)

2 - how to build/buy/adapt a 2 speed controller (one which I can adjust the speeds) that will allow me to operate the two motors simultaneously to turn the rotors for the upper and lower speakers.

Any suggestions, schematics, ideas, etc will be greatly appreciated. This has been the biggest obstacle to overcome for me. The mechanical part of this is easy for me. I am a machinist by trade, and mechanics is what I deal with. Electronics has always been hard to deal with however. Please help if you can. I'm going to try and include a sketch of what I am talking about to this as well.

Thanks!

 

[SherpaDoug]

Look at these as a starting point.
Motor Driver 1A Dual TB6612FNG - SparkFun Electronics
Mini Metal Gearmotor 100:1 - SparkFun Electronics
If you spend some time you can get cheaper stuff on the surplus market, but the guys at Sparkfun may help you out if you buy their gear.
To control speed you need an oscillator like a 555 timer chip on an Arduino controller, both of which Sparkfun sells as well.

 

[jarrettbailey]

Thanks. That does look like a starting point. The sparkfun site doesn't offer technical assistance though. Only another forum to try to find help from. So... any more info would be helpful. I am a true novice when it comes to this type of stuff, so any info is appreciated. How do you incorporate the speed control to that driver that you linked me to? Also, the 2 speeds that I need are 40 rpm and 390 rpm (or thereabouts). Not sure that motor will work since it's top speed is around 140 (at 6V)? Also, what kind of power supply do you use with this, and how do you incorporate that? Sorry, I am full of questions. I appreciate all the help.

Thanks!

 

[SherpaDoug]

This is a similar motor with a different gearbox for higher speeds:
Mini Metal Gearmotor 24:1 - SparkFun Electronics

For a really simple speed control you might look at a model train throttle.
This is built for two trains (two motors): **broken link removed**
though right now this pair of individual throttles is cheaper: **broken link removed**

 

[jarrettbailey]

Hey guys-

Ok, here is a schematic that I used ( a friend of mine actually built the circuit for me) to build a circuit for a similar project with bigger DC motors. First of all, only part of the circuit works (and I will send pics of the actual circuit later so that maybe you could help me figure out how to get that working), but it was made for 2 5A DC motors. Pretty sizeable power supply. For this smaller project (and probably for my original one) I won't need that kind of power. But can someone help me make this schematic something that would work with 2 small dc motors, and only 2 speeds (this schematic is for 4 different speeds)? Any info is appreciated!

 

[SherpaDoug]

That looks like a reasonable design. For this application I think you can leave off the circuitry around the dynamic brake half of the speed adjustment pots and diodes. Depending on the power level you may be able to use smaller transistors, but using those large ones will work and they only cost a little more money.

To choose the power supply and motor size you need to estimate the power required. For that you need to determine the torque x speed you require. Until you have an idea of torque all any of us can can do is guess.

 

[jarrettbailey]

Well, I am thinking something like this for the motors:

**broken link removed**

But any other suggestions would be welcome.

Thanks

 

[SherpaDoug]

That looks like a fine motor. But to be sure we need more info on the mechanical load. Torque, bearings, friction, inertia, etc.

 

[greentree]

Hi*
you can use 555.