Thread: PWM Question

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No, on the monster guts motors, there are two sets of terminals-low speed and high speed.

Product Information

* 12 VDC has high and low speeds
* High Speed @ 12V: 53 r.p.m.
* Low Speed @ 12V: 38 r.p.m.
* High Speed @ 5V: 21 r.p.m.
* Low Speed @ 5V: 15 r.p.m.
* Working Torque - 3.98 foot pounds (5.4 N m)
* Static Torque - 13.27 foot pounds (18 N m)
* Full Load: 2000mA @ 12VDC, 1080mA @ 5VDC
* No Load: 1020mA @ 12VDC, 780mA @ 5VDC
* Click on the "More Images" link beneath the picture above to view where to connect to the terminals for high and low speeds.
* The workhorse of electric props. Used in many animatronics.

I haven't even used the PWM yet.

Oh, OK. connect the motor on the low speed terminals to the PMW output side. The PWM will vary the width of the square wave being fed to the motor. By turning down the PWM control you in essence increase the width between on pulses. (more off time than on time) You still feed it with 12V, it will be 12v all the way from full speed on the PWM to the lowest speed setting. The only difference is the change in duty cycle. (distance between on pulses) That should slow your motor down, while maintaining full current to the motor and not sacrificing torque. Hope this helps. Keith
a second thought, is there a particular reason you want to run at 5V other than trying to slow the motor down?

With 5v input you're kinda defeating the whole purpose of using a PWM based speed controller. The benefit of using PWM to control your motor is so that you don't have to sacrifice motor torque to get slow speed. Your controller will slow your motor all the way down to zero at 12v. IMHO, you'd be giving up the whole benefit of using a wiper motor in the first place using 5v and a PWM.

Originally Posted by soundmankkc

Nosferatu, Good thought, sometimes I get so involved in answering a question, I get tunnel vision. Of course stick with 12V and turn the controller down and that should slow the speed of the motor while maintaining torque. Do you think the 8 amp limit will come into play? Not sure what torque it will be pulling but I would recommend fuse protecting it to keep from burning the PWM box out. What do you think?

I would fuse it, always better to be safe than sorry. And not to try to start something here, but I seriously doubt that monster guts motor only pulls 2 amps max.

Scary Terry once tested a wiper motor and measured nearly a 14 amp draw at motor stall load!

What kind of power supply are you using? Some, like ATX's, have internal fuse protection. What kind of prop load will you have? You may be able to balance the load with a counterweight to ease the stress on the motor.

a second thought, is there a particular reason you want to run at 5V other than trying to slow the motor down?

No, my only concern is getting around 8 rpms.

I want to build a cauldron creep (a skeleton stirring a cauldron). The wiper motor will be mounted inside the cauldron, with an 8-inch arm attached. Mounted at the end of the arm will be a PVC pipe cap, turned up like a cup. The cup will hold the 'stir stick" , moving it around to make it look like the skeleton is stirring the cauldron. The top of the stir stick will be held loosely in place by a rigid threaded rod (running through the skeletons arm). From what I've read, this should be a very light load for this motor.

I would fuse it, always better to be safe than sorry.

Good idea, Nosferatu. Am I right in assuming that the fuse goes between the power source and the PWM switch?

What kind of power supply are you using?

I haven't decided on a power source yet. I have several ATX power supplies, but I haven't converted any of them (I'm fairly new to electronics, but I'm learning). I'm also considering using this:

16 Channel Camera Distribution Box - 12V 10A
12VDC@10amp supply current
Multiple outputs (16 channel)
Four auto-reset PTC fuse protected output
Power on/off switch
DC regulated, over current and voltage protected
Individual LED indicator for each out put
Dimensions:25cm×21.3cm×9.5cm

It's regulated and fused, and it has screw terminals (easier for a novice like myself).

Your prop idea sounds neat and I think the linkage - as you have described it - should be no problem for a slowed-down wiper motor. I'm not familiar with that power supply but it seems more than capable of doing the job with those specs.

If cost is an issue, you could use one of your ATX's that you already have with this PWM controller - http://store.qkits.com/moreinfo.cfm/MX033 - $19 bucks and fits inside the ATX housing . I use this setup to run FCG's and AFG's with no problems.

[quote Your prop idea sounds neat][/quote]

Actually I got the idea from DevilsChariot. It's a really cool looking prop that's not very complicated to build...the perfect first-time animatronic prop for a newbie like me.

Thank you all for the advice and information. I really appreciate it.