Advice on quiet actuation

[SeagullOne]

Hi everyone.

I'd like to ask some advice. I'm trying to come up with a "sensory safe" actuator for an "autism therapy robot."

I'm considering either really small motors (the kind that don't make any audible noise when applied power to [gears omitted]) or muscle wire like nitinol or flexinol.

I'm leaning toward small motors because while some memory alloy actuators are super quiet and luxurious on the senses (with pull forces of up to almost 8 pounds), they are not efficient and take time to cool off, resulting in robot movement that will not look very natural.

I have thought about heat-sinking the muscle wire, but if it's sunk all the time, will that keep the wire from contracting? It's heat that makes it contract, so it would just make it even more power inefficient, right? So I would need to find some way to sink it with control. Don't know if I want to even bother though.

Anyone recommend a small motor that is quiet (almost silent) when it spins? I know they're out there from experience, and I'm looking myself, but I thought I'd consult the forum.

I'm still thinking about my requirements as far as how big or small the robot should be and how much weight it will be lifting. Right now I'm guessing the motor ought to be under 5 ounces at most. I'm thinking of using tiny belts and pulleys instead of gears for a speed-reduction train (gears are almost certainly out of the question for my application right now). Servos simply will not work.

The application for this motor is joint movement. For now, I'm focusing on of the articulation rather than the mobility of the robot.

I'm also planning to add further features to the robot to reduce noise, but first I want to start with the actuators themselves. The quieter the better, the easier on the ears.

Thanks in advance. Happy to provide any more information if it will help with the advice.

[Soeren]

Hi,

[...] some memory alloy actuators [...] are not efficient and take time to cool off, resulting in robot movement that will not look very natural.

Silent motors mean high quality balanced motors = expensive.
Low speed brushless motors may be the cheapest way to get low noise, as there's no brush noise, but either way, expect to pay for silence.

SMA wire can be sped up by using 2 or more wires separated by air and each of a smaller diameter (than if using a single wire).
Running them in a tube with a small fan turned on when they have to cool will help as well. Besides, humans don't move as abruptly as motors do, so SMA wire or small air muscles will give a more natural movement.


Another side of it is, whether someone suffering from autism will react to it at all.
Autists will mostly react to known stimuli (usually from family and such) and will tend to ignore new inputs, which may even get them to go even deeper into themselves, as new and previously "un-classified" stimuli can be quite a scare to them. It will probably have to be judged on a per person basis.

Actually, slow facial movements may be more comforting than more realistic movements (to an autist), as they sense the world a little different from most of us. Perhaps SMA wire will be just the ticket to useability

[bens]

Hello.

I apologize if I'm stating the obvious here, but if you do go with brushed DC motors, make sure you use an ultrasonic PWM frequency (20 kHz is usually good).  Otherwise, you will likely hear the PWM frequency as an audible motor whine.

- Ben

[SeagullOne]

Thanks Soren! This is very encouraging, as it seems I'm just having more trouble with motors than shape memory alloy.

Thanks Bens. At this rate, I'm thinking using motors at all might be a bit risky. Your advice on PWM frequencies and their relationship with motor whining is appreciated.

The robot is not actually going to have many facial expressions. I was even thinking about having a one-face robot that doesn't change its expression but maintains an overall friendly appearance. The muscle wire I'm thinking of using is for overall head and arm movement. No doubt it will have to be a small bot, but that will be part of its friendliness.

The robot's programming can be adapted to make it move with different levels of complexity--via GUI settings--so while it is programmed to move in certain ways with certain gestures, evening the programming is modular so it won't always utilize every form of body language, making it easier to interact with.

I actually have autism myself, but I'm much closer to what they call "high functioning" so I'm always very curious about what individuals from all ends of the spectrum experience and how my application can make them comfortable. Your elaboration, Soren, is very much appreciated.

One of the major goals of the emerging robotics aspect of my business is to create a robotic platform (not necessarily one mainstream product) that can be adapted and refitted to multiple clients. Some things I realize, however, are universal such as sensory noise, which is why I really want to find a way to tackle the actuation. Robots like Keepon, for instance, seem to actuate without any noise--aside from being small, soft and having a harmless appearance and nature. I also, however, want to allow my robotics platform to nurture those on the higher ends of the spectrum as well, and not just what is known as classic autism. In this regard, I'm aiming for a unique invention.

Patent pending by the way.  

[Soeren]

Hi,

The robot is not actually going to have many facial expressions. I was even thinking about having a one-face robot that doesn't change its expression but maintains an overall friendly appearance.

OK
If you make it capable of any facial expressions at all, be sure to make it a smile and don't use it all the time (or it will loose some of its strength).
Eyes would best be on the large side, especially the pupils (small pupils reads as hostile, large pupils as friendly).

Some things I realize, however, are universal such as sensory noise, which is why I really want to find a way to tackle the actuation. Robots like Keepon, for instance, seem to actuate without any noise--

I didn't know Keepon, but just spend a good half hour getting acquainted with it - Thanks 

Most videos are stripped of sound or dubbed afterward, so it's hard to judge the noise, but I came across this:

My Keepon’s motors are somewhat noisy but the noise is covered by moderate levels of music.

(My emphasis)
Link: http://toysrustoys.org/reviews/my-keepon/


I stumbled upon this link that you might wanna check out for ideas and/or inspiration:
http://www.myu.ac.jp/~xkozima/carebots/robot-ponhist-eng.html
and this PDF: www.ri.cmu.edu/pub_files/2008/3/AmbidextrousMichalowski.pdf

aside from being small, soft and having a harmless appearance and nature. I also, however, want to allow my robotics platform to nurture those on the higher ends of the spectrum as well, and not just what is known as classic autism. In this regard, I'm aiming for a unique invention.

Patent pending by the way.  

I hold my thumbs for you
But if you're serious about the patent, be very careful about what you reveal in a public forum.

[SeagullOne]

Thanks, Soeren, for that information. I'll be looking through it with interest.
I hadn't known Keepon's actuators were a bit noisy after all. In any regard, a friend of mine who also has autism once complained that the servo whirling of of my robots was unbearable, so hopefully SMA wire will serve a more suitable application than motors.

I hold my thumbs for you
But if you're serious about the patent, be very careful about what you reveal in a public forum.

Of course. I've filed already. Thanks.

[Soeren]

Hi,

[...] a friend of mine who also has autism once complained that the servo whirling of of my robots was unbearable,

Servo whine is unbearable, if they're operated continuously, but that's to be expected from a tiny motor, a gearbox and controlling electronics with a low price tag.
I'd imagine, that in your friends case, it has more to do with his apparently good hearing, rather than autism, lthough the latter may enhance the annoyance.

I have some motors that are close to inaudible (at least to me - might be my hearing loss though ). They're very well made (read: expensive), balanced and made for the pro market - you might find something similar at a surplus site. A motor that goes for a few bucks new OTOH, is bound to be crappy in comparison.


If it's supposed to be stationary, shadow pole motors are very silent and I would imagine a small "slow" brushless DC motor would be very quiet too (but probably difficult to find) for battery operation.

Solenoids with some "rubber" damping of the full in position and PWM to control position might be another fairly silent "motor" (I think the Keepon uses at least one solenoid, as it goes *clunk* when it "ducks").

Sound shielding with high density felt or some elastic foam can do wonders against mechanical noise (but they need air to cool, so use in moderation). Elastic motor mounting will keep noise from wandering through a mechanical structure.

It's a great project and the many options for experimenting is just the icing on cake