Ice Cream Machine Motor Control

[supremelord]

Hi guys,
I am currently making an ice cream machine. I had this DC motor lying around and figured it can do the job of mixing the 4L of ice cream.
It is a 24VDC / 14A / 250W / 2500 RPM
Now I need to be able to reduce its RPM from 2500 to probably something like 30-50 RPM. I have been reading about PWM circuits but I am having difficulty finding a good site that can explain the theory properly and allow me to build the circuit to control the motor.
I would really appreciate it if anyone could point me in the right direction and possibly point out possible schematics.

Thanks!

 

[crutschow]

A 250W motor at 2500RPM has a calculated torque of about 0.7 lb-ft, which is likely about as much as it can generate even at slower speeds without overheating. An ice-cream-maker crank requires a lot of torque, particularly as the ice cream hardens, and I doubt that 0.7 lb-ft. is enough for that without a gear reduction. I suggest you look for a gear box that will handle the motor torque and provide the required speed reduction.

 

[supremelord]

Ok I was looking into that but I figured a 250w motor would be sufficient.
Where would you suggest I get the gears from? And what ratio would I need?
The gear that is currently attached to the motor shaft has 11 teeth. If I understand the theory behind gears I would need a 50/1 gear ratio to get it to spin at about 50 RPM?

And, would it be possible to run the motor on 12v instead of 24v to reduce the RPM without loosing torque?

 

[4pyros]

You need a motor with a built on gear box, or as we call them a gear head motor. That will get you to about 250 RPM so you will need external gearing to. You should get an AC powered motor too. The motor you have will need a 24 volt DC at 20 amps supply,not cheep,and many gears also not cheep. Get the right motor. Andy

 

[Boncuk]

If you can't find a proper reduction gear you might use a belt drive with a transmission ratio of 50:1 to 83.3:1.

Boncuk

 

[supremelord]

Would a standard AC drill motor work? And where would i be able to get the gears? I dont have much experience with gears that is why i wanted to stick with dc motor and PWM circuit. I just find it funny that the motor would not have enough torque since it was originally used on a scooter... I could alway simply reduce the size of the machine to maybe mix 2L of ice cream so the motor I have will work?

 

[crutschow]

Reducing the voltage will reduce the torque.

A scooter typically has a chain and large sprocket on the wheel to increase the torque. Do you have that available from the scooter?

An AC drill motor may have difficulty operating at the low rpm you need.

 

[supremelord]

No i dont have any of those. I think i will just buy an old ice cream maker of ebay for 20$ that has a motor on it and use that. My only problem is i need it ASAP.

Well Theres one good thing out of all this, i now have a 30 amp PWM circuit ready for when i might need it and a 250w motor lying around haha.

 

[cr0sh]

One thing about regular ice cream makers is that they typically use shaded-pole AC induction motors. As the ice cream solidifies, it takes more and more work for the motor to churn it. At a certain point, the motor can't turn any more, stalling it. With a shaded-pole motor, while this presents a larger load on the circuit, it generally won't trip the breaker (ie, it isn't a short) because of the way an induction motor works (its basically a form of a transformer in which one side rotates). However, with your DC motor (which is likely a brushed DC motor), such stalling would show as a almost "dead short" - very high current draw - and if your controller isn't built for it, you could end up with a dead controller (or even a fire). So - your system (even before gearing) becomes more complicated with such a motor (same thing with an AC drill motor - most of these kinds of motors are brushed as well - series wound, IIRC - a stall there can trip a breaker, too).

Regarding gearing: take a look around, there's a ton of things out there that use gears, or has gearboxes that can be repurposed. As Boncuk noted, you can effect a gear-down with a belt drive (quick and easy method would be to use swamp-cooler parts). If you need a custom gear system (not easy to engineer properly, btw) - if you live near a large city, look in the yellow pages (or equivalent) for industrial motion-control, bearing, belt, and chain suppliers. There's always Grainger and McMaster-Carr (if you have the money!). Tons of online sources for gear reduction units, gear motors, etc (even ebay!).

Also - take a look at local thrift stores (if you have them). There, you'll find all manner of appliances with gear boxes, motors, etc for little to nothing (rotisserie spit turning motors, or mixers - might be perfect). I also can't tell you the number of ice cream maker machines I've seen at thrift stores before (they are typically gotten rid of after one or two uses, because making homemade ice cream isn't cheap, compared to store bought ice cream. People tend to realize this after the first batch or two - heavy cream isn't cheap).

 

[supremelord]

The thing is I am on a very tight budget since I am a student and I am broke..
Up to this point I think that my only option would be to go look around for a used ice cream maker and remove the motor from it, like you said they are all over the place. That is unless I can figure out within the next 2 days where to get the gears how to install them and get this thing working. This project is due in three weeks and the end of semester stress is starting to kick in!

But, getting this motor to put out more torque using gears really interests me and I will definitely look into it because if I don't use the motor for the ice cream machine I will probably end up wanting to use it for something else.

Thanks so much, you guys have been great help.

 

[supremelord]

Hi guys,
I found three greatly priced DC Motors that could possibly do the job, which one would be the best?

**broken link removed**

Surplus Center - 35 RPM 24 VDC MOLON GEARMOTOR

Surplus Center - 30 RPM 24 VDC VON WEISE GEARMOTOR

 

[cr0sh]

I'd say either of the latter two "Surplus Center" motors; those things have some pretty serious torque for their size, so be careful as you play with them (ie, if you attach a mixer paddle to them, don't try to stop it from spinning or anything where your hand can get caught - it might not stop!). You should count on the current needs of either of those motors to be several amps while under load; as the ice-cream solidifies, it might be able to bring the motor to a halt, or at least place it under a -very- heavy load. With this in mind, take care to select an appropriate power supply, as well as have some kind of cut-off system when it is under load (monitor the amperage in some manner, or place a light-bulb in series with the motor, etc). Also, you will want to couple the shaft of the mixing paddle to the motor in such a fashion so as not to put too much torque on the gearbox bearings (unless they look designed for such a thing); set the paddle in its own bearing, and attach the motor's shaft to the paddle's shaft with a flexible coupling or some kind of spider-coupling. Good luck with your project!

 

[4pyros]

Lord; As said before you should get a main powered motor so you dont need a power supply! Why do keep looking at the LOW voltage motors?

 

[supremelord]

I can get a DC 24V up to 15A power supply on ebay for 30$. If I pushed it to its limit I would possibly be able to get 360w out of my motor, I just want to make sure that either one of the surplus motors can handle this.
I understand that an AC motor might be better but I cant seem to find one at the same price range and torque capacity.

Now for the DC motor, I am looking to make some smooth ice cream, so once it gets thick enough for the motor to stall the ice cream should technically be ready. What I thought of doing to protect it would be to install a breaker that would pop at like 14 Abe mps to make sure the power supply does not overload.
My other problem will to find a way to attach the shaft to the mixing blade. I want to it to be easily detachable so I can easily take it all apart to clean.

Now my problem is that I have no idea of the peak current of any of the Surplus motors so I don't know to what I can push it yet... I don't want to buy one of them, wait two weeks to get it to find out it wont be able to do the job

 

[4pyros]

Whats wrong with this motor?Surplus Center - 110 RPM 115 VAC GARAGE DOOR OPENER GEARMOTOR

 

[KMoffett]

I would not expect the garage door opener motor to be rated for continuous duty operation...heat, bearings....

Ken

 

[4pyros]

Would an icecream maker run 24 hours a day?

 

[KMoffett]

No, but it will likely run for 1/2 to 1 hour. That would be continuous compared to running a garage door up an down once in a long while.
Won't saw it can't do it, just that I think there would be a better choice.

Ken

 

[cr0sh]

I can get a DC 24V up to 15A power supply on ebay for 30$. If I pushed it to its limit I would possibly be able to get 360w out of my motor, I just want to make sure that either one of the surplus motors can handle this.
I understand that an AC motor might be better but I cant seem to find one at the same price range and torque capacity.

I would say that if you could find at least the AC motor unit to a household ice cream mixer (or a rotisserie spit, or some other similar slow-rotating gear-boxed shaded-pole AC induction motor meant for moving large food-based loads), you might be better off. This is simply because of the stalling issue, which I explained before.

Now for the DC motor, I am looking to make some smooth ice cream, so once it gets thick enough for the motor to stall the ice cream should technically be ready.

That's technically how all ice cream is made; its made until super-thick (which may or may not stall the motor - depending on its power and gear train strength), then the paddles pulled out and either eaten soft, or put into a freezer to solidify.

What I thought of doing to protect it would be to install a breaker that would pop at like 14 Abe mps to make sure the power supply does not overload.

This may or may not work; I know this for a fact. It will depend on how powerful the motor is, and how strong the gear train is; if the gears are metal and helical mesh, that's a potentially much stronger gear box than say one made from regular square-mesh spur gears made of plastic. But even a metal gear train is no guarantee - I recently had a smaller 24V Pittman gear motor with metal square-mesh spur/pinion gear combos break the teeth off one of the pinions due to the power of the motor. My main mistake was in not having any kind of stall protection (I was performing some manual tests on a steering mechanism on a robot platform); the motor was much more powerful than the teeth of the gears, and snapped them off easily.

If I had in place a protection method, this likely wouldn't have occurred - but the question would've been "which protection method"? Well, the fastest would've been best. Its a real possibility that a circuit breaker wouldn't have caught the stall condition fast enough. A temperature sensor (and attendant cut-out circuitry) would've been waaay too slow, too. A fast-blow fuse might've caught it, if I sized the fuse real close to the stall current (or under). A circuit monitoring the current to the motor would've likely caught it the fastest.

So you may want to re-think your over-current protection, especially with a brushed DC motor. If your protection is too slow, then you risk breaking gears, or even burning out the rotor coils (or welding the brushes to the commutator!). Ideally, electronic over-current protection is best; if you can source an adjustable current power supply with over-current protection, you could likely use its electronic protection system as a quick electronic cut-out system (provided you adjust things right!). A quick-blow fuse is the next best option, but you have to size the fuse properly; a tad too big and it might not blow before it breaks the gear train.

My other problem will to find a way to attach the shaft to the mixing blade. I want to it to be easily detachable so I can easily take it all apart to clean.

There are plenty of options available for shaft coupling. What you might do is drill a hole thru the output shaft (remember, coupled to the motor via a compliant coupling, as I mentioned before, so-as not to cause motor bearing damage), then make the shaft of the mixing blade out of a piece of hollow (or the end bored out) stainless steel (note: any part coming into contact with food will need to be stainless steel, or some other non-reactive food-safe material), with a hole thru it. Fit it over the shaft, and put a clevis pin thru both to secure it.

Now my problem is that I have no idea of the peak current of any of the Surplus motors so I don't know to what I can push it yet... I don't want to buy one of them, wait two weeks to get it to find out it wont be able to do the job

A motor doesn't need current "pushed" at it - a motor draws a specific amount of current based on load. The values that (most?) of those motors listed from "Surplus Center" seemed to indicate the running (no load) current. You can expect the loaded current to be a multiple of this, and the stall current to be much higher; but you won't know what that stall current is until you either contact the real manufacturer of the motor, or test it yourself (with a brake system of some sort).

The number you really need to worry about to know if the motor will fit your needs is the torque rating; both of the motors you listed have fairly large torque ratings (one was 38 inch-pounds, the other was 47 inch-pounds). What these numbers mean is that from the center of the shaft, out so many inches, how many pounds they could lift (if you had a lever attached to the shaft of that length) - so, one inch away from the shaft, the one motor could lift 38 pounds, the other 47 pounds; conversely, 38 inches away (or 47 for the other) from the shaft they could lift one pound. Since your paddle isn't likely to be more than 12 inches in diameter (6 inch radius), those motors will have plenty of torque - even if your paddle was double the size, they'll still have a lot of torque.

Whether that will be enough torque to mix ice cream, though - I don't know (how much torque does it take to mix such a mixture?); but it should be possible to find out from somewhere - I would imagine that somewhere there is a book on industrial food preparation that might have such information in it.

You can sometimes gauge the maximum current draw from a motor to be several times its running current, but it all depends on the motor, too. I've seen stall currents 5 times larger than running currents on some motors, but others it is even larger. You might simply contact "Surplus Center" and ask them if they know that rating for either of the motors. Its important information to know, so you can size your power supply, as well as your over-current protection system.

I would first look into seeing if you can find what the torque numbers are for mixing an ice cream mixture; once you have a rough idea of that (and note, you might find anything from inch-ounces to foot-tons and everything in-between including metric numbers - so be prepared to do some conversion math to get the numbers needed to compare for each gear motor), then you can narrow your needs down based on the size of your intended paddle, the current draw, etc. Also remember to add a bit extra current draw needed just for the mass of the system (a few percent).

Good luck.

 

[cr0sh]

No, but it will likely run for 1/2 to 1 hour. That would be continuous compared to running a garage door up an down once in a long while.
Won't saw it can't do it, just that I think there would be a better choice.

Ken

I also don't like that gear motor for this application because of that plastic output gear; garage doors are counter-balanced by springs or weights (typically springs), and thus there isn't much needed in the way of torque to lift or shut them. Mixing ice cream, as it approaches the solidification/thickening stages, introduces a lot of torque (not to mention just starting out; an ice cream mixture is pretty thick, and with the paddle in there that would need a bit of torque to turn). I would think that the output worm on that motor, if the motor is powerful enough, would just auger out and strip that plastic gear; if the worm was plastic itself, the whole thing might melt down if the motor could continue to turn. That is certainly not the right motor for this application.