Please suggest some silent motors - I decided to get Steppers

[cosminprund]

Please suggest some silent motors. I want to build something relatively small with two wheels and differential drive but I want it to be as silent as possible. All the servos I've seen are loud. My planetary gearhead motors are loud - and I've read some comments around here that all planetary gearboxes are loud and make that drilling machine noise. I don't need this thing to go fast or carry allot of weight, I'll be using LiPo batteries and they're anything but heavy.

A link to something would be grate but I'm also happy with search term suggestions.

--
Cosmin Prund

[Soeren]

Hi,

Be aware that if you want silent, you gotta pay "aloud".

You all know a Dremel (the real deal, not the even worse clones).
The professional equivalents are pretty expensive (I recently got an offer: "Take 3 of those and you get them for US$10,000" and that was sort of an entry level model).
The reason for such high prices are... Precision engineering, loads of precision ball bearings and everything balanced to a point where you hardly feel it running when holding it.  You do hear them when they go 50,000 RPM though   

You can get silent, but unless you're getting it second hand (or by Dumpster Diving(tm)), you'll need to find a company that are prepared to sell to a private customer and that may be just as large a problem as finding the right motor.


You might wanna take a look at the following links, but do keep in mind that it's easy to write "low noise" or "ultra low noise" if you don't tell how many dB they put out, so before placing an order, get this number in writing.

http://www.directindustry.com/industrial-manufacturer/micro-gearmotor-79255.html

http://www.alibaba.com/product-gs/201614804/AM25_series_DC_tubular_motor.html

[cosminprund]

I've never seen "dB" quoted for an motor or gearhead (and not because I wasn't looking!). If I need to quote an number I'd say 30-35 dB at 1m (guesstimating numbers based on http://en.wikipedia.org/wiki/Sound_pressure_level#Examples_of_sound_pressure_and_sound_pressure_levels)

The only "silent" motor that mighty google finds is not for sale  (I've googled for "silent gearhead motor"). Googling for "silent gearhead motor -maxon" as to avoid pages related to the phantom gearhead motor from Maxon only finds junk.

I guess I need to rephrase my question: I want an relatively silent motor. I don't want to hear the motor if it's running two meters away from me. Have any of you ever played with such an motor, or is that alot to ask?

[paulstreats]

Motors can be pretty silent themselves, its generally the gears that generate a lot of noise. If you use stepper motors, you wont need a gear set therefore removing most of the noise, and provided youre not moving superfast it should just give off a soft hum not audible 2 metres away.

[cosminprund]

So stepper motors are acceptable solutions for "drive motors"? Aren't the wheels going to skid because of the stop/start/stop/start way of moving? If this is not an issue then an 1.8 degree stepper seems really nice - if skid is not a big problem it doesn't need an encoder!

[HDL_CinC_Dragon]

stepper motors do not need to have a start/stop/start/stop way of moving. If they do then it means the programmer messed up.

[paulstreats]

It depends on the size of the wheels and the amount of steps the stepping motor has.

if the circumference of the wheel means that each step takes 2 cm movements then it will appear as a sudden start/stop sequence meaning that skidding could be a problem. but if the wheel circumference divided by the number of steps is low enough then it will appear as a constant movement. (the lower the number the smoother the motion)

[Soeren]

Hi,

if the circumference of the wheel means that each step takes 2 cm movements then it will appear as a sudden start/stop sequence meaning that skidding could be a problem.

Just drive it with the correct ramp and use a sine or sawtooth shape, then even 2 cm is possible without skidding in most cases.

[Soeren]

Hi,

I've never seen "dB" quoted for an motor or gearhead (and not because I wasn't looking!).

Then you were looking in the wrong places 

If I need to quote an number I'd say 30-35 dB at 1m (guesstimating numbers based on http://en.wikipedia.org/wiki/Sound_pressure_level#Examples_of_sound_pressure_and_sound_pressure_levels)

Info lacking...
@ speed=?
@ load=?
And perhaps you should throw in...
Max. price you're prepared to pay=?
Number of motors you'll be buying=?

The only "silent" motor that mighty google finds is not for sale  (I've googled for "silent gearhead motor"). Googling for "silent gearhead motor -maxon" as to avoid pages related to the phantom gearhead motor from Maxon only finds junk.

Sorry, I allready translated silent into low noise without much thought, since no regular motor can be silent (as silent means: Not emitting any audible sound at all).
Try a pagefull of this: http://www.google.com/search?num=100&hl=en&lr=&safe=off&rls=com.microsoft%3A*%3AIE-SearchBox&rlz=1I7GGLJ_en&as_qdr=all&q=DC-motor+sales-price+%22low+noise+%22

I guess I need to rephrase my question: I want an relatively silent motor. I don't want to hear the motor if it's running two meters away from me. Have any of you ever played with such an motor, or is that alot to ask?

Plenty of motors covers that and you probably have several of them allready.
Eg. hard drive motors are very low noise, clicking/scratching noise from a HD is from the head positioning voice coil "motor" (or you need to back up very soon ).
Old floppy drive motors (the DC motor driving the disk, not the head positioning stepper).
VHS recorders, better CC tape decks, just examine anything that moves in your home - some of the motors are way below 30..35 dB.
I do have a few motors that are very close to silent, driven within specs, but as I mentioned, then we're talking precision engineering, air/needle bearings and careful balancing, both statically and dynamically.
Geared down BLDC's are yet an option, come to think of it. I do have a paired set for a future 'bot, but I have to reduce the gearing, since they're as slow as servos (but with bone crashing torque, since they are 24V motors at almost 1 kg a pop).

Don't you have an old HD with way too few GB's, that you just couldn't get yourself to ditch?

[madchimp]

So stepper motors are acceptable solutions for "drive motors"? Aren't the wheels going to skid because of the stop/start/stop/start way of moving? If this is not an issue then an 1.8 degree stepper seems really nice - if skid is not a big problem it doesn't need an encoder!

You could even do half stepping or even smaller if you had the right stepper driver. If you want to go smaller than half steps you would probably be better off building your own stepper driver as they get expensive.

[cosminprund]

Thanks everyone that posted. I decided to get stepper motors: I want to learn the use of those any way. I'll be getting them new so I get them with datasheets and in known good condition, those I might hack an old HDD just to see what torque that motor may provide. I remamber I did open up an HDD or two, to get to those pretty disks/platans but the motor didn't seem like an easy to hack motor; I wasn't looking for motors at the time, so I might be wrong.

As for the price yeah, I allways tell people to expect high prices when they have "special requests" - but it turns out stepper motors are very reasonable in price, and with an "built in" pseudo-encoder! The few brand name motors that have encoders and gearboxes are expensive (+250 euro for motor, gearbox and encoder). I'm sure they're grate but this is an hobby so I'll skip the expensive stuff for now.

[Ro-Bot-X]

Good stepper motors (as in torque and 200 steps per rotation) you can find in dot matrix printers used in accounting. The only problem is that the 2 motors in one printer are not the same! So you need 2 printers of the same model to get 2 pairs of steppers. The specs for the motors you can find online (I've done that) and to drive the steppers (most of them are bipolars) you can go 2 ways, generate the step sequence in the microcontroller then use a dual H-bridge (like the L293 or L298) for each stepper, or you can use a stepper controller IC (like the L297) plus the dual H-bridge.

[madchimp]

A lot of the older HP printers (500-700 series probably others) also have a couple steppers in them (unipolar i believe) of course again you would need two printers to get a matched pair but most of the 500-700 series have the same motors so you wouldn't need identical printers. Older HP scanners also have a stepper in them (bipolar i believe).

[paulstreats]

ive got some similar to these:

http://www.sparkfun.com/commerce/product_info.php?products_id=8420

the only problem is that they are 15.4v rated, i use them with 12v but anything below and you cant get any real performance from them

[cosminprund]

I'll make the final decision on the motor somewhere around next week (I've got this Farnell discount code if I make a 29 line order by March 6). I'm pretty sure I want something that runs on less voltage, I'd stay around 6V - maybe less! I'd need to do the math and figure out if those tiny 5V steppers are capable of carrying themselves around + the MCU + the LiPo + + + + ......

If the 5 or 6V stepper can't do it then I'll go for something bigger since my 12V NiMh home made battery pack (actually 2 packs of 6V each) weights allmost 800 grams

[paulstreats]

I hope that youre not looking at those 18degree motors they have for cheap. They are going to be more hassle than they are worth trying to get smooth motion from them. It may be possible but the power they provide is likely to be greatly reduced when taking them further than microstepping

the 7.5degree motors may seem a bit of hassle but are likely to produce a decent speed if necessary and as Soeren said above providing the power is ramped up/down correctly with pwm you can control the steps/jolts into a smooth motion.

[cosminprund]

No, I'm looking at the 1.8 and 0.9 deg steppers. I might get an 7.5 stepper for other stuff but never the 18 deg steppers! I'd get no use out of an 18 deg stepper because it can't turn 45 deg; The 7.5 one can! And the 0.9 deg steppers I assume are 1.8 deg steppers that can do half-stepping.

[Admin]

If you use stepper motors, you wont need a gear set therefore removing most of the noise, and provided youre not moving superfast it should just give off a soft hum not audible 2 metres away.

Not true . . . steppers need gear boxes too, assuming they don't have the torque/velocity output you need.

Also, steppers, if not done right, can cause a lot of vibration on your robot. A friend of mine build a robot using a stepper, and his robot had a sheet of metal as part of the chassis. The metal vibrated so much it was quite loud! The stepper resolution will also affect the frequency and amplitude of that vibration.

You may want to try other techniques, such as putting lubricants in the gear box. Also, wrap the gear box in sound-insulating material (but don't wrap the motor or it will overheat).