How rpm regulate PF Medium motor in simple way?

[Superkalle]

Hello all you PF and Mindstorms gurus.

I have the Vestas windmill in front of me, and it's really noisy and turns too fast. So I was thinking about reducing the output RPM of the PF motor to half it's original speed. Is there any really simple solution that will allow me to do that without involving NXT units or other expensive parts? Note that I don't want to change gearing as the design is fixed and the motor needs to be slowed down on account of the noise.

Another question is if there is a way to more generally silence the motor. Can it for example be encapsulated in silicon rubber or something like that without damaging it (dissipation of heat etc)

[Alasdair Ryan]

Hello all you PF and Mindstorms gurus.

I have the Vestas windmill in front of me, and it's really noisy and turns too fast. So I was thinking about reducing the output RPM of the PF motor to half it's original speed. Is there any really simple solution that will allow me to do that without involving NXT units or other expensive parts? Note that I don't want to change gearing as the design is fixed and the motor needs to be slowed down on account of the noise.

Another question is if there is a way to more generally silence the motor. Can it for example be encapsulated in silicon rubber or something like that without damaging it (dissipation of heat etc)

try a pf speed controler thats, easiest to do

that should drop the sound down as well (a wee bit)

Edited April 27, 2011 by Alasdair Ryan

[P4trickvH]

If it has gears, you can also change the gears, for example 10 tooth gear on motor and 20 tooth gear on the mill. That also reduces the speed by half.

10/20 = 1/2 (0.5)

Hello all you PF and Mindstorms gurus.

I have the Vestas windmill in front of me, and it's really noisy and turns too fast. So I was thinking about reducing the output RPM of the PF motor to half it's original speed. Is there any really simple solution that will allow me to do that without involving NXT units or other expensive parts? Note that I don't want to change gearing as the design is fixed and the motor needs to be slowed down on account of the noise.

Another question is if there is a way to more generally silence the motor. Can it for example be encapsulated in silicon rubber or something like that without damaging it (dissipation of heat etc)

Edited April 27, 2011 by P4trickvH

[Parax]

Hello all you PF and Mindstorms gurus.

I have the Vestas windmill in front of me, and it's really noisy and turns too fast. So I was thinking about reducing the output RPM of the PF motor to half it's original speed. Is there any really simple solution that will allow me to do that without involving NXT units or other expensive parts? Note that I don't want to change gearing as the design is fixed and the motor needs to be slowed down on account of the noise.

Another question is if there is a way to more generally silence the motor. Can it for example be encapsulated in silicon rubber or something like that without damaging it (dissipation of heat etc)

Simplest way?

http://shop.lego.com/ByTheme/Product.aspx?p=8878

It has a built in speed controller (7 step) and it'll save you money/hassle in the long run.

You could use a PF speed controller remote and a receiver too, It's possibly cheaper than the rechargeable battery.

As for noise, this greatly reduced if you use a speed controller. I have no experience of encapsulating the motor, but I doubt there would be issues though, as its designed to work whilst encased in Lego! I believe there is a thermal cut-out on it, perhaps someone could confirm this.

P.

Edited April 27, 2011 by Parax

[DLuders]

@ Superkalle: The rotating speed of the 4999 Lego Vestas Wind Turbine could be set by a 2868b "Electric, Train Speed Regulator 9V" unit, powered by a 70931 "Electric, Train Speed Regulator 9V Power Adaptor 230V (Continental European type)."

On the electrified 2 x 2 plate at the "north end" of the Train Speed Regulator, connect a 60656 "Electric, Power Functions Extension Wire with one Light Bluish Gray End (length 20cm)." The Light Bluish Gray end of the wire connects onto the Train Speed Regulator, and the Dark Bluish Gray end connects to the (Dark Bluish Gray) Power Functions Motor wire. There is a longer version of the Extension Wire -- the 8871 "Power Functions Extension Wire 20" (50cm)."

I don't know anything about "silencing" a Power Functions motor.

[Superkalle]

Thanks guys for your replies.

@Alasdair Ryan: Your style of reply does not fit well in a forum for AFOLs. Please try to post in a more mature maner.

@Parax: Thanks for the tip about the batterybox. However, it is a tad to expensive for the simple task I want to accomplish.

@DLuders: Good idea, hadn't thought of that either

I should perhaps clarify that I don't need to be able to vary the speed - all I want is to reduce the RPM of the motor by half. Actually, when I initially thought about this my idea was to add a resistance to the wire, and thus reducing the voltage to the motor. But converting power into heat isn't a very nice solution I suppose. Maybe if I could just take out a few batteries to get a lower voltage to the motor. Could that work?

[Alasdair Ryan]

Thanks guys for your replies.

@Alasdair Ryan: Your style of reply does not fit well in a forum for AFOLs. Please try to post in a more mature maner.

@Parax: Thanks for the tip about the batterybox. However, it is a tad to expensive for the simple task I want to accomplish.

@DLuders: Good idea, hadn't thought of that either

I should perhaps clarify that I don't need to be able to vary the speed - all I want is to reduce the RPM of the motor by half. Actually, when I initially thought about this my idea was to add a resistance to the wire, and thus reducing the voltage to the motor. But converting power into heat isn't a very nice solution I suppose. Maybe if I could just take out a few batteries to get a lower voltage to the motor. Could that work?

ah ok i wont bother helping next time

[Brickdoctor]

ah ok i wont bother helping next time

He means you need to hit 'Shift' at the proper times and add in some punctuation. Because it's in the forum guidelines.

[roamingstop]

I should perhaps clarify that I don't need to be able to vary the speed - all I want is to reduce the RPM of the motor by half. Actually, when I initially thought about this my idea was to add a resistance to the wire, and thus reducing the voltage to the motor. But converting power into heat isn't a very nice solution I suppose. Maybe if I could just take out a few batteries to get a lower voltage to the motor. Could that work?

It depends what PF box is being used to run the system. Checking BL it is the technic AAA one, so yes, using some wire to connect across the battery terminal might work... but I seem to recall that the motors have a form of stall protection in them, and so may complain when the voltage is not at 9V.

Actually with PF there are 4 lines; GND, +9V, C1 and C2. The voltage on C1 and C2 actually do the speed regulation, so in principle you could afford to drop two 10k resistors between the 9V and GND, and take an output between the two supply power to C1, but it would need a custom cable - (Philohome has more details on PF functions).

You could also butcher a PF M motor and strip out the orbital gears, and replace them with something which goes slower; or use the Lego education PF Generator / Motor (natural resources element pack).

And finally - looking at all the gearing which goes on in the 4999 instruction book; im sure you could reduce the ratios even more... Go on, be a bit creative with Technic solutions

Edited April 27, 2011 by roamingstudio

[Bartholomew]

Hi folks, I'm new :)

First of all: Nice place here, I feel comfortable.

Second: I'm a native German speaker, so please be patient if i use strange words when explaning something. Corrections are strongly approved!

@roamingstudio: You've linked the 6*AA battery box.

The voltage on C1 and C2 actually do the speed regulation, so in principle you could afford to drop two 10k resistors between the 9V and GND, and take an output between the two supply power to C1, but it would need a custom cable - (Philohome has more details on PF functions).

If I interpret Philo's figures Philo right, then that won't work. I do think the motors take their power completely from C1 and C2, and totally ignore the 0V and 9V lines, as the LEDs do (I'm sure about them, as there are schematics at Philo's site).

I do think that you mean that the motors have integrated driving transistors. This theoretically possible design brings no advancements compared to the driver-transistors-in-control-element-solution, and so Mr Ockham says it's not very likely.

I think that normal PF speed and direction control works via pulse width modulation. That means that C1 and C2 are electronically connected to 0V and 9V for a short time x and then turned off for another short time y, whereby x+y=T is constant, and will be around 1/20000 s. For direction change, C1 and C2 can be electronically or mechanically toggled (can one say "commuted" in this context?).

So, if the battery box has no electronic that won't work with the lower voltage you get when you use less than six cells, reducing the motor speed this way will work. A trial surely won't damage any parts.

But do not simply wrap old used-up cells in aluminium foil and short the contacts this way, because used-up alkaline cells tend to leak (this is also the main reason why you shouldn't use cells of different type or age in the same battery box, because the one used up first has an increased risk of leaking while the other cells keep on pumping current through it).

but I seem to recall that the motors have a form of stall protection in them, and so may complain when the voltage is not at 9V.

I've read the newer battery boxes have a safety current limitation, not the motors. The old motors had a (P)PTC (those are current sensitive, not voltage sensitive), and i dont't think they've changed that in the new motors.

[Superkalle]

And finally - looking at all the gearing which goes on in the 4999 instruction book; im sure you could reduce the ratios even more... Go on, be a bit creative with Technic solutions

I thought I was creative when I wanted to rewire the whole contraption

No, but seriously - there are two issues that go hand in hand - too fast and too noisy. Changing ratios will only fix one. I was planning to use the Windmill at an exhibition where it will stand in a fairly quite area and the way it sounds out of the box is just too much (I'm actually surprised how much the PF motors sound ).

So, if the battery box has no electronic that won't work with the lower voltage you get when you use less than six cells, reducing the motor speed this way will work. A trial surely won't damage any parts.

Hi Bartholomew. As this was your first post I'm going to start with saying "Welcome to EB". And thanks for your interesting observations. I need to try this. I'll take the battery box to work and get some soldering/wiring done (no used batteries )

In the meantime, if anyone has tried this themselves and allready know the results, please post here.

[vmln8r]

@Alasdair Ryan: Your style of reply does not fit well in a forum for AFOLs. Please try to post in a more mature maner.

We get that a lot here.

Anyway - this isn't particularly simple, but you may want to try the speed regulator along with an older 9V motor. I have a few of these and they are comparatively whisper-quiet.

[Bartholomew]

Thank you :)

Testing is complete. I used my 8043 excavator which comes with the standard PF battery box that roamingstudio linked.

In order to short the contacts, I first insulated both poles of fresh alkaline cells with adhesive tape, then wrapped the cells in metallised paper from chewing gums (and I didn't even watch that much McGyver when I was young :D ).

Result:

Works like a charm :) Less speed, less noise, less torque with every cell wrapped in chewing gum paper. I stopped with four bridged compartments, because I ran out of gum (and the IR receivers are not likely to work with 1,2V remainig voltage anyway, as I use Eneloop rechargeable cells).

If the motor has problems turning the rotor because of lack of torque, I recommend using a cell more to prevent stalling. I do think that even at lower voltage a stalling motor can overheat and thus be permanently damaged, but I'm not sure since I haven't measured the corresponding current yet.

I can't open the battery box (momentary lack of matching screwdrivers as prying tools) to check if there is any kind of overcurrent protection installed, maybe I catch that up next saturday.

P.S.:

be carefull not to accidentially short two neigbouring compartments, as you could short a working cell this way if vou've got an unlucky alignment of working cells and shortened cells. Iv you've got a continuity tester, you can simply check the wiring of your battery box to avoid this (but if you own such a tool, you know that anyway).

Edited April 27, 2011 by Bartholomew

[DLuders]

@ Bartholomew: So, did you essentially replicate the procedure outlined in this TechnicBRICKS post?

[Blakbird]

I have the Vestas windmill in front of me, and it's really noisy and turns too fast. So I was thinking about reducing the output RPM of the PF motor to half it's original speed. Is there any really simple solution that will allow me to do that without involving NXT units or other expensive parts? Note that I don't want to change gearing as the design is fixed and the motor needs to be slowed down on account of the noise.

Another question is if there is a way to more generally silence the motor. Can it for example be encapsulated in silicon rubber or something like that without damaging it (dissipation of heat etc)

The noise of the PF medium motor comes primarily from the integrated 2 stage epicyclic gear set rather than from the motor itself. Reducing the speed will not do a lot to change the noise output. If you want to reduce the noise, the only obvious way is to open the motor casing and apply some thin grease. This will work, but you risk damaging the motor since they are not easy to open.

Regarding the speed, the simplest way to reduce the speed is simply to reduce the input voltage. For example, use 3AA batteries in series instead of 6 and you'll approximately halve the speed. You can do this by leaving 3 batteries out of the case and replacing them with paper clips. Otherwise, as others have suggested, you can change the gear ratio externally.

If you want a quieter motor, the 43362 is very quiet and is also geared.

If you slow it down a LOT, then it gets quite quiet. On the V-8 I displayed at Brickcon, I used a train regulator to slow a PF-medium motor down to about 1/10th speed and I could hardly hear it at all.

[nychase]

If you slow it down a LOT, then it gets quite quiet. On the V-8 I displayed at Brickcon, I used a train regulator to slow a PF-medium motor down to about 1/10th speed and I could hardly hear it at all.

Thats a really nice V8 you got there

I recently tried this setup and was troubled to find out that the Train Regulator only modulates the speed in steps. I grew up with a vast assortment of HO trains which offer infinite speed variations so I dont know why lego never did the same (mixing lego and trains at that age would have surly suffocated any hope I had at being normal )

Edited April 28, 2011 by nychase

[shimon]

Hi.

In my last project: an AH-64 i had pretty much the same problem with the top rotor.

And although it seems nearly impossible to reduce the sound of the motor without changing the input current or voltage, i had an idea..

The mechanism is simple:adding rubber belt system, the trick is that it also reduces speed but it also gives the rotor its own acceleration because it is not depend on the motor (sorry my bad english)in a result the motor isnt struggling and giving less power and the whole mechanism will work more quietly(just an idea) in my AH-64 it worked like a charm.

In the 4999(the gear mechanism that goes to the rotor) it has 3 reductions 12\20, 8\24, 8\24 just simply replace

the 1st set of gears:12T and 20T or you can try replace everything with theese: in the axle which is connected to the motor put 2 of theese "bushes" http://www.bricklink.com/catalogItem.asp?P=4265c and the next axle put theese http://www.bricklink.com/catalogItem.asp?P=4185

And the smallest rubber belt: http://www.bricklink.com/catalogItem.asp?P=x71 between... im not sure 100% that it will work on a vertical structure. but surely it is the easiest and cheapest way.

[Superkalle]

Thanks guys for all the tips.

I ended up taking out three batteries and shortcuting - a friend at work helped me an elegant solution with using a single paper clip set in tension between two poles. See below how it was done.

And IMHO, the way the Vestas turn now is the way it should be - more majestic and with a nimble electric whining sound.

[Bartholomew]

@Superkalle: Nice pictures :)

@David Luders:

No, I deduced what I wrote about the C1/C2-Lines from what i had read at Philos site, without testing things myself.

Meanwhile, i've made a resistance measurment of the 0V/9V-contacts from an PF medium motor - they are not connected to anything in the motor.

So, in the sketch with the blue and red wiring you've embedded in your post, dashed lines definitely means unused lines (but they're still looped through to the connector terminals to allow easy daisy chaining).

I've done some further measuring on my 8043. The results:

6 cells:

Standby current drain of LED in PF battery box: 5,8mA

Standby current drain of single IR receiver (computed): 14,5mA

Total standby current: 34,8mA

Standby voltage (35mA): 7.85V

Motor with minimal load (clutch in neutral position): 75-85mA

Motor with little load (Bucket): ~130mA

Motor with heavy load (lifitng jib): ~330mA

Stalling motor: ~620mA ~7,37V

Two stalling motors: ~1080mA ~7,05V

Three stalling motors: ~1500mA ~6,83V

Four stalling motors: ~1800mA 6,54V

With rising current, the battery voltage drops, and so four stalling motors don't drain 4*620mA=2480mA, but 1800mA.

If a stalling motor is kept powered, the current drops due to motor-internal protection electronic (the PTC gets warm and rises its internal resistance).

If I stall all four motors and keep them powered, the IR receiver overcurrent protection kicks in, resulting in cyclic contraction and relaxation of the separate geartrains. This does not happen at lower currents, i.e. if I reduce the number of stalled motors to three, or the total cells (and such the voltage and indirectly the current) used. As not all motors relax together, I know this effect comes from the receivers and not from the battery box.

Four cells:

Total standby current: 20mA 5,14V

Motor with minimal load (clutch in neutral position): 65mA

Motor with little load (Bucket): ~120mA

Motor with heavy load (lifitng jib): ~250mA

Stalling motor: ~410mA

Three cells:

Total standby current: 11mA 3,85V

Motor with minimal load (clutch in neutral position): 60mA

Motor with little load (Bucket): ~110mA (slow)

Motor with heavy load (lifitng jib): ~220mA (very slow)

Stalling motor: ~315mA

Two cells:

Total standby current: 2mA 2,57V

Motor with minimal load (clutch in neutral position): 47mA

Motor with little load (Bucket): ~80mA (slow)

Motor with heavy load (lifitng jib): stalls

Stalling motor: ~210mA

One cell:

Total standby current: 0mA 1,28V

Not enough voltage for battery box LED (will need about 1,7V), nor for the IR reveivers.

Edited April 28, 2011 by Bartholomew

[Philo]

Hi all,

Yes, reducing voltage is the simplest way of reducing motor speed. Roughly speaking, motor speed is proportional to voltage (for a given load). Using a resistor won't work well: if load increases, current increases so voltage drop in resistor increases, so motor speed decreases... Generally it ends up in a stall!

I have photos of PF AA box open, with a method to permanently reduce voltage: http://philohome.com/alimservo/alimservo.htm . The good point of aluminium paper wrapped on stick is that it is reversible!

@Bartholomew:

I've read the newer battery boxes have a safety current limitation, not the motors

Both battery AND motors are over-current protected by PTCs

@Blackbird: The motors I opened did have grease in gear train. And the older 71427 is even quieter than 43362!

I ended up taking out three batteries and shortcuting - a friend at work helped me an elegant solution with using a single paper clip set in tension between two poles. See below how it was done.

Ah! the ubiquitous paper clip!!! very clever

[Bartholomew]

Thanks for the correction, Philo, and generally for your great site :)

I still have problems disassembling my battery box (there will be some catches that bother me), but since there are schematics on your site, I don't have to anymore.

Also kudos to Blakbirk for his Technicopedia. I'm looking forward to the 1996 update :)

Edited April 28, 2011 by Bartholomew

[Superkalle]

Ah! the ubiquitous paper clip!!! very clever

Thanks for the link to your article. Very intereseting read.

Yeah, paper clips are good for most things

The tricky parts was to figure out how the batteries are connected in serial in the batterbox, that's why one battery is left out on one side, and the papperclip is crossing over two battery compartments on the other.

But the alumnium covered battery I really like. Simple and elegant. I'll probably use that method the next time.

[Philo]

But the alumnium covered battery I really like. Simple and elegant. I'll probably use that method the next time.

As mentionned by Bartholomew, it's better to use a wood or plastic stick instead of a dead battery that would leak and ruin your battery box. I have used hot glue rods for a similar (though somewhat opposite) purpose: