complete noob with electronics! help with basic motor control, please?

[zaebra]

hi! this is my first post, and i'm hoping you all can help me with a project.

i'm making a nerf pistol from scratch, since hasbro hasn't made a semi-automatic or fully-automatic clip-fed pistol yet. i'm handy with the physical building part, but i need help with the simple electronics.

the pistol will have two components. the main component will be a pair of high-rpm drive motors rotating in opposite directions, exactly the same as a pitching machine. the other component will be a much smaller and slower rpm motor that feeds the darts into the drive motors.

i'd like to power the whole pistol with a pair of trustfire 14500 3.7v 900mAh batteries in the handle. the motors don't need to have a variable speed setting, since they'll be hardwired to be either on or off at their respective speeds.

so, here are my questions:

1) how would i split the power from the batteries to the two different components? would it be as simple as running two positive wires from the + pole and two negative wires from the - pole?

2) how would i power both drive motors simultaneously? just split the wires?

3) how do i control the speed of the three motors as simply as possible? would i use a resistor in the wire leading from the battery to each motor? if so, how would i calculate the RPM of the motor to tell me what resistor (or whatever component i need to actually use) to use?

4) (bonus) is there a way to easily create a momentary circuit, where one press of the trigger cycles the feed motor a certain amount of time and then stops (unless the trigger is still pressed)? this last part is probably less simple than i would hope, so i might just be stuck letting go of the trigger at "just the right time" to stop it from feeding more darts into the drive motors.

thank you all very much in advance for any help you can offer!

 

[donkey]

you are new so HI there and welcome

1) connecting to multiple components IS as easy as connecting wires to the batteries, think of your home entertainment unit it has a dvd and a t.v. both running from 1 outlet, just using 2 different wires.

2) as stated above you can just split the wires, but there are 3 motors in the description you gave.

3) a resistor is one way of controlling speed however it will generate heat, depending on the resistor that could be enough to melt the enclosure. a method used more commonly is called PWM and there are kits available to get you started. you can look up motor speed controller to start researching.

4) there is a way to do this I can think of one using a micro but I am sure a 555 timer might be better for this.

once again welcome to the forums

 

[CDRIVE]

4) (bonus) is there a way to easily create a momentary circuit, where one press of the trigger cycles the feed motor a certain amount of time and then stops (unless the trigger is still pressed)? this last part is probably less simple than i would hope, so i might just be stuck letting go of the trigger at "just the right time" to stop it from feeding more darts into the drive motors.

Actually, this would be the easiest to do. As Donkey said, a 555 'One Shot' should do fine.

Chris

 

[donkey]

yeah I just like micros atm. but thats like taking a nuke to a fist fight in this case

 

[zaebra]

i'll take a stab at the 555 pwm motor control and a 555 one-shot timer. i have positively zero experience reading electronics schematics, but i'm hoping to find pictures online and/or someone helpful at radio shack to decipher them.

thanks for the help!

 

[CDRIVE]

i'll take a stab at the 555 pwm motor control and a 555 one-shot timer. i have positively zero experience reading electronics schematics, but i'm hoping to find pictures online and/or someone helpful at radio shack to decipher them.

thanks for the help!

On par with that miracle would be Moses parting the Red Sea.

Chris

 

[CocaCola]

On par with that miracle would be Moses parting the Red Sea.

A tidal change exposing land during a drought (or low water table) is much more likely than finding someone at Rat Shack that knows anything about designing electronics... They do know a decent amount about cheap RC cars, batteries and cell phones though...

 

[zaebra]

where would i go to purchase the components, if not radio shack? i'm hoping to keep the project affordable.

 

[CocaCola]

where would i go to purchase the components, if not radio shack? i'm hoping to keep the project affordable.

Radio Shack and affordable electronic components is an oxymoron...

For the casual hobbyist I find Jameco to be one of the more user friendly and not overwhelming... Even with the smaller selection of parts I order from them quite a bit as they leverage some good pricing on what they do carry...

www.jameco.com

For a much larger selection that might overwhelm the newbie but is far more complete...

www.mouser.com
www.digikey.com
www.alliedelec.com

 

[CDRIVE]

Can we get back on Earth here? This is the proverbial "Cart before the horse". Before you loose sleep over where to purchase the parts, it might be helpful to know what parts you have to purchase. This is usually determined after someone has given you a circuit.

Chris

 

[zaebra]

i found this one for the pwm motor controller:

http://www.easterngeek.com/2008/06/simple-and-dirty-pulse-width-modulation.html

and this one for the one-shot circuit:

http://www.instructables.com/id/Make-an-LED-Blaster/step2/Build-the-555-ic-one-shot-timer/

does anyone see anything wrong with either of those? i don't really need to be able to dial the speed up and down, but it looks pretty simple to build that capability into my project, so i might as well.

one question, though.. will i need to split the power from the batteries and then run two different pwm circuits (one for each motor), or could i run power to a single pwm circuit and then just split the output into two positive wires and two negative wires (thus controlling both motors simultaneously)?

 

[(*steve*)]

Not sure why you need a monostable for, but the PWM controller using a 555 will work for small loads.

I would recommend a diode across the motor to protect the 555, and I would consider using the 555 to switch a mosfet which can power your load.

 

[(*steve*)]

Oh, now I see. You posted a new thread so that we could benefit from not having any background.

I'll fix that...

 

[zaebra]

i'm afraid i'm a complete novice, and this is my first electronics construction project, so i don't know what you mean in your first reply. i'm more confused with your second reply, though, since this is the only topic i've created here.. was that post intended for another thread, perhaps? if i've done something wrong by asking questions here, i will most certainly stop bothering you guys.

 

[CDRIVE]

if i've done something wrong by asking questions here, i will most certainly stop bothering you guys.

Whoa, down boy. Don't be so sensitive.

Chris

 

[(*steve*)]

The problem is zebra that you posted your message in a new thread, so I was unaware that you were a newbie. I was totally unaware of what was in your earlier thread that this should have been a part of.

So what I did was combine the threads so that others would not be fooled by the same thing.

When I get time I'll go back and read this thread and try to give you a better explanation. I'm a bit busy now. We've got plenty of other members who can help and I'd not be surprised if one gets in ahead of me.

Just remember to try to keep everything in one thread so that people can be fully aware of what's going on and things will be a lot smoother.

Welcome to Electronics Point.

OK, a quick explanation. (remember I've not read the rest of your thread in detail yet) A motor generates voltage spikes that can kill electronics. The fix for this (in this case) is a diode placed across the motor in such a way that it doesn't normally conduct -- it's called reverse biased.

The 555 oscillator that you linked to should do PWM for a small motor

A better solution involves using the same 555 circuit, but adding a mosfet (a type of transistor) to increase the current (and indeed the voltage) that can be applied to the motor. You may or may not benefit from this.

 

[zaebra]

i have no idea how a second thread got started; i simply used the quick reply option (as i'm doing now). i'm sorry for any confusion that caused, as i was just trying to reply to someone saying that i was getting ahead of myself by asking for sources, when i wasn't sure what to buy yet.

thank you for the technical clarifications. it gives me more info to start reading up on. i'm sure this is all extremely basic for those who have been doing it for a long time, but it's a pretty steep learning curve for newbies like me.

perhaps there's an easier way to do this.. since i'm not looking to be able to vary the speed of the motor, is there something that i can just connect in the wire to restrict the speed of the motor to a certain maximum output? if that's the case, then i can experiment with different versions of such a piece until i find the desired speed. the two drive motors in question don't need to be adjustable, just tuned. is this simple, or am i still looking at building the 555 controller? i don't know if it matters, but i'm planning on driving two high-rpm RC car motors fast enough to grab a nerf dart and throw it about 100 feet.

thanks again for the help, and sorry for the confusion.

 

[CocaCola]

perhaps there's an easier way to do this.. since i'm not looking to be able to vary the speed of the motor, is there something that i can just connect in the wire to restrict the speed of the motor to a certain maximum output?

Yes and no, you can vary the speed of the motor to some degree with a series resistor or using series diodes to drop voltage but it has negative consequences... The motor will lose torque and it might not even start up, and there is an exponentially higher chance of it not starting up if it's under load or stalling under load doing it this way... Using PWM for all intents removes those consequences, and the motor performs as it should but the speed varies...

 

[zaebra]

ah, i see now. thank you for the explanation! i'll certainly stick with the PWM as recommended.

edit: i just discovered solenoids. the ones i found on mouser and other sites only have at most 0.2" of travel, though. is there an affordable, small solenoid that has about 1.5"-2.0" of travel..? if there is, it would completely eliminate the need for the one-shot, since all i'm doing is pushing a dart forward from the top of a clip, over and over. here's hoping!

 

[CDRIVE]

is there an affordable, small solenoid that has about 1.5"-2.0" of travel..?

Someone might say it's possible but its about as likely as finding that helpful techie at Radio Shack. That's enormous travel for a solenoid. They weaken dramatically as the stroke increases.

Chris