Less noisy alternative to servo. Muscle / nitinol wire?  - Page 1
Forum section: electronics / projects

author: perik
author_rank: Newbie
timestamp: November 09, 2019, 10:54:14 am
content: I´m looking for a less noisy alternative to using servos for a project and I was thinking of using musclewires (Flexinol / nitinol wire) as an replacement. I havnt worked with musclewires before and wonder if this is possible or if they are very slow (I know they are driven by heat so slow cooling might be a problem)Basically my project need to pull and push a small weight with a thin ironstick as arm. I need something that goes two ways. When I applies current to it I want it to pull and when I decrease the current again I want it to gradually go back depending on the current. Im using a pwm signal from my raspberry pi to control the current.I wounder if anyone has some experience with doing the same? Basically replacing a servo with musclewire?For example this one:https://www.sparkfun.com/products/12096I guess the thinner the wire the faster it reacts since it cools off faster?

author: soldar
author_rank: Super Contributor
timestamp: November 10, 2019, 08:49:43 am
content: An electromagnet should work if you control the current gradually.

author: perik
author_rank: Newbie
timestamp: November 10, 2019, 08:56:46 am
content: I had electromagnets in mind for a while but in my case the heating is a problem. As well as I need to pull and push around 3 cm

author: beanflying
author_rank: Super Contributor
timestamp: November 10, 2019, 09:40:21 am
content: Not all servos are that noisy when you get into the really tiny ones. Do you need no noise or just really low noise? You could also take a look at things like the steppers used on CD drives or even the internals of a hard drive.This will get you started for a look. Single gear reduction (standard servos are 5-8 reductions) only and even drop the motor voltage a touch to reduce the speed and noise.https://www.horizonhobby.com/helicopters/aircraft-servos/20-gram-performance-linear-long-throw-servo--15mm-lead-spmsh2025l

author: artag
author_rank: Super Contributor
timestamp: November 10, 2019, 10:24:31 am
content: As usual, it's a tradeoff of power, cost, speed, noise. You can get quiet geared DC motors - try Maxon. The more expensive servos are also quieter : it's a question of how good the tolerances are on the gears, so metal-geared servos tend to be better.Thermal actuators are quiet, slow, and take a lot of power. That's fine in some applications.Steppers are noisy if the steps are large. Use small steps above audio frequency and they're a lot better : try the drivers from Trinamic.CD drives, as beanflying says, are also good : you can hear a CD drive move but not usually at the individual step level. They use a very long pitch leadscrew so the step rate is low.Pneumatic and hydraulic actuators are extremely quiet but the pumps and air-release valves are not. Try the murata micropumps or the piezo aquatic aerators for silent operation (the muratas produce surprisingly high pressure) and pump the air both ways (as you would with hydraulics) rather than letting it escape.

author: soldar
author_rank: Super Contributor
timestamp: November 10, 2019, 04:24:34 pm
content: Quote from: perik on November 10, 2019, 08:56:46 amDepends on amount of force and power needed, acceleration, precision, etc.3 cm is very doable with an electromagnet with a sliding nucleus. Also, you can have an arm that amplifies the travel range. Heat should not be a problem.You could use an actuator using compressed oil.Depending on the application you might benefit from having position feedback.Many variables.

author: perik
author_rank: Newbie
timestamp: November 10, 2019, 10:16:41 pm
content: Quote from: beanflying on November 10, 2019, 09:40:21 amIdeal no noise but guess it is not possibleQuote from: beanflying on November 10, 2019, 09:40:21 amGood idea! But I need lots of servos so prefer buying instead av deconstructingDo you have an example of what kind of steppers this is?Quote from: beanflying on November 10, 2019, 09:40:21 amSorry for stupid question butSingle gear reduction- is that the same asBearingthat sayssinglein the specs? At the moment I have got some cheap SG90 servos. They are pretty noisy though. If you know some other cheap servos in with lower noise you are welcome to recommendQuote from: soldar on November 10, 2019, 04:24:34 pmwhat is a sliding nucleus? I did some tests and to get a strong electromagnet the heat was actually a problemQuote from: artag on November 10, 2019, 10:24:31 amsince in the project im working i need a lot of servos, around 100 or even more so will try to get a decent servo but with low cost. Because of the amount Im using at the same time I also need them to be more quiet. At the moment I have got some cheap SG90 servos. They are pretty noisy though. If you know some other cheap servos in with lower noise you are welcome to recommendQuote from: artag on November 10, 2019, 10:24:31 amI understood first now that steppers cannot be controlled with pwm signal. Maybe also a more expensive alternative compared to servos ...

author: soldar
author_rank: Super Contributor
timestamp: November 10, 2019, 10:45:23 pm
content: Quote from: perik on November 10, 2019, 10:16:41 pmI meant solenoid. You can get solenoids with linear-moving plunger or with rotary movement.Again, it depends on many factors. Probably not suited if you need fine control of position where other solutions will give you better control.https://www.electronics-tutorials.ws/io/io_6.html

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 10, 2019, 11:43:41 pm
content: "Flexinol" wires are nice, but require a fair amount of current to operate. Yes AFAIR, the thinnest they are, the fastest they react (but obviously the less tension they can handle before breaking). You may need to experiment a bit.There are a lot of linear actuators out there, eg:https://www.robotshop.com/en/micro-linear-actuators.htmlthey tend to be pretty expensive though. You may be able to find much cheaper ones on Aliexpress or the like.Servos are a bit noisy while rotating, but once in a fixed position, they will normally not make any significant noise unless you are approaching their max rated torque (in which case they can get into the typical "pumping" state.) Of course the servos (or true linear actuators) will be more accurate position-wise (if that matters in your application, maybe it doesn't) than Flexinol.

author: jmelson
author_rank: Super Contributor
timestamp: November 10, 2019, 11:48:11 pm
content: Quote from: perik on November 09, 2019, 10:54:14 amServo motors can be almost totally silent (even in a quiet room) such that you can only hear the bearings.It just requires proper servo control laws that give smooth current to the motor and eliminate dithering.Jon

author: artag
author_rank: Super Contributor
timestamp: November 10, 2019, 11:53:02 pm
content: You can buy the CD steppers with leadscrew on ebay very cheaply - eghttps://www.ebay.co.uk/itm/392331862778(you will find cheaper ones than that). There are others with finer leadscrews if you need slower movement. Search for 'linear stepper'.Steppers do need dual h-bridge drivers to operate them. If you use proper stepper drivers you will get all sorts of advantages but for a low-voltage stepper like the ones above you can still do them pretty cheaply with something likehttps://www.ebay.co.uk/itm/173044559728I can't suggest any _cheap_ quiet servos - I'm afraid the only quiet servos I've seen are expensive ! But there may be other mechanisms like the CD sliders. For more powerful units, headlight positioners are worth considering. They're also stepper motors with a leadscrew. Mirror motors are more often just a geared DC motor and a cam.If you have large numbers then pneumatics might be an answer : valves can behttps://www.ebay.co.uk/itm/254229792066rather than something expensive from Festo. Actuators might be syringes, or small balloons. Pump might be a fish tank aeration pump. The thing about pneumatics is that you'll typically have one pump and lots of actuators rather than lots of motors, so it doesn't get noisier - unless you need a bigger pump, or let the air out too noisily.Muscle wire has quite a small extension with heat, so if used in extension mode needs to be wrapped around pulleys to get enough length. If used in a bending mode they will give more movement, but then you need thicker wire.You might learn something fromhttp://www.osloom.org/.I haven't seen updates for ages and I guess has been abandoned but they used muscle wire to avoid patents on many other forms of heddle actuator. It looks as though it had an acceptable level of performance but I don't know what happened to it.Most of these aren't very accurate without feedback. But they're OK for pushing from one limit to another.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 11, 2019, 12:11:43 am
content: Another silent actuator is the wax piston. Slow and inefficient, but very strong.https://en.wikipedia.org/wiki/Wax_motorTwisted fishing line (only some types, not any line) can actuate, too, when heated.

author: beanflying
author_rank: Super Contributor
timestamp: November 11, 2019, 01:46:06 am
content: Quote from: perik on November 10, 2019, 10:16:41 pmThe SG 90's are among the noisiestThe CD types Artag linked above are the sorts of stuff inside a CD drive so either wreck one to get a freebie or buy one for very little (fun to play with regardless). You just need a driver board to suit.Look closely at the photo of the Horizon servo I linked it only has a single bearing at the oposite end to the drive. Not really an issue given the power but it will help it run more smoothly. I run the next size down and smaller in some of my indoor R/C toys (sub 2g servos).A reason to go servo over geared steppers is micros like the arduino already speak servo but you need another board to talk stepper

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 11, 2019, 03:16:34 am
content: Maybe put the garden variety servos in a soundproof box. You can extend the mechanical motion out through small holes in the box.Implementing this approach will require attention to the paths of sound transmission. Much will come through the mounting points.

author: DrDisco
author_rank: Newbie
timestamp: November 11, 2019, 09:19:47 am
content: Some small steppers with some trinamic drivers. Should work out. The trinamic drivers have a stealth chop feature. That will silence the motor right down.They are quite expensive, but there are Chinese dev boards you can buy in the same form factor as the conventional a4988 Polulu modules:https://www.aliexpress.com/item/32886021442.html?spm=a2g0o.productlist.0.0.479f50c2Xsl2fZ&algo_pvid=f8e16a04-8a46-4601-8c2b-a3339f76c234&algo_expid=f8e16a04-8a46-4601-8c2b-a3339f76c234-11&btsid=5e5ae011-27f9-44c6-8dcf-356585bc0018&ws_ab_test=searchweb0_0,searchweb201602_2,searchweb201603_52

author: RoGeorge
author_rank: Super Contributor
timestamp: November 11, 2019, 09:39:24 am
content: A stepper motor does not produces any noise if driven with sinusoidal current. Most of the cheap stepper drivers does not produces sinusoidal currents, thus the stepper is humming/buzzing. Texas Instruments has a few motor driver chips very good at producing clean sinusoidal waveforms.However, servos are usually driven by DC motors, and gears are noisy, unless special gear profiles and special materials are used.

author: beanflying
author_rank: Super Contributor
timestamp: November 11, 2019, 09:47:59 am
content: Things to bear in mind from the OP when he added it.QuoteCost and complexity are a factor. As a simple PWM from most micros will drive a commercial servo it makes more sense over a stepper unless you want to spin custom boards.

author: artag
author_rank: Super Contributor
timestamp: November 11, 2019, 12:17:49 pm
content: Another common 'linear stepper' mechanism ishttps://www.ebay.co.uk/itm/401829445368Anybody know what these are used for ? they seem very widely available.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 11, 2019, 03:05:49 pm
content: Looks like the mechanism used to move the magnetic heads in floppy disks. The force was rather small, much smaller than in a small servo like SG9.

author: mikerj
author_rank: Super Contributor
timestamp: November 11, 2019, 04:07:49 pm
content: Someone has made an RC style servo that uses Nitinol wire. It's faster than I thought it would be.