Maker Pro
Login Join Maker Pro
Or sign in with

Menu

Connect With Us

Network

Maker Pro

small, accurate rotary encoders?

M

Mike Noone

Hi - I'm looking to measure the angles that a 6 legged robot's joints
are making relative to each other. I'm thinking a rotary encoder might
be the best option, though I'm also looking at using a pot.

Problem is I don't have much space to work with - I'd need something
that was maybe max of 1.5cm diameter or so, and ideally no more than
about 1cm in depth. I need at least 1 degree resolution, but ideally
I'd like about 5-10 times that. Output doesn't really matter too much -
it will be interfaced with a microcontroller that has both analog and
digital inputs.

Anything out there that will fit my needs?

Thanks!
 
R

Roger Hamlett

Mike Noone said:
Hi - I'm looking to measure the angles that a 6 legged robot's joints
are making relative to each other. I'm thinking a rotary encoder might
be the best option, though I'm also looking at using a pot.

Problem is I don't have much space to work with - I'd need something
that was maybe max of 1.5cm diameter or so, and ideally no more than
about 1cm in depth. I need at least 1 degree resolution, but ideally
I'd like about 5-10 times that. Output doesn't really matter too much -
it will be interfaced with a microcontroller that has both analog and
digital inputs.

Anything out there that will fit my needs?

Thanks!
Click to expand...
Critical question, is whether the unit can establish a 'zero' point, using
some other method (moving the joint to a 'limit' perhaps during boot up)?.
This makes the difference between having to use an 'absolute' encoder, or
a 'relative' encoder. Now, if you use a 'relative' encoder, 1 degree, only
needs a 90ppr encoder (remember if you decode the four possible quadrature
states, you get 4* the quoted number of 'steps' round a circle). The
smallest 90ppr encoder I know of, at a reasonable price, is the Nemicon
OMS-T encoder, which is just 1.2cm across, but is 1.25cm long. I don't
know of anything quite this small, for an absolute encoder (look at the
CUI MAS-10, which gives 256 locations, and is only 13mm*17.5mm, but the
17.5, is the length).
The problem with a potentiometer, will be accuracy, and durability. You
need to look for units that are designed as position transducers, with a
correspondingly high life, or the failure rate will be high.
You might want to look at alternative technologies. For instance, the
changing signal on a magnetometer IC, with a magnet on the shaft.
I can't think you are going to get that much finer than 1 degree, on this
sort of diameter. The problem is that even tiny errors in the accuracy of
the bearings at the centre, translate to large errors, and costs therefore
skyrocket for higher accuracies on this sort of diameter...

Best Wishes
 
M

martin griffith

Hi - I'm looking to measure the angles that a 6 legged robot's joints
are making relative to each other. I'm thinking a rotary encoder might
be the best option, though I'm also looking at using a pot.

Problem is I don't have much space to work with - I'd need something
that was maybe max of 1.5cm diameter or so, and ideally no more than
about 1cm in depth. I need at least 1 degree resolution, but ideally
I'd like about 5-10 times that. Output doesn't really matter too much -
it will be interfaced with a microcontroller that has both analog and
digital inputs.

Anything out there that will fit my needs?

Thanks!
Click to expand...
I had to dredge the toilet bend of my brain to remember this company,
but
http://www.usdigital.com/products/ma2/
may be better options on the site, but sounds like mission immprobable


martin
 
B

Ben Jackson

be the best option, though I'm also looking at using a pot.
Click to expand...

A pot would be much better in that application. It's self zeroing,
it's able to tell you position immediately from power-on, and it has
a much higher resolution (limited by your ADC). Open up a hobby servo
and take a look at their pot-driven control loop.
 
R

Rich Grise

Hi - I'm looking to measure the angles that a 6 legged robot's joints
are making relative to each other. I'm thinking a rotary encoder might
be the best option, though I'm also looking at using a pot.

Problem is I don't have much space to work with - I'd need something
that was maybe max of 1.5cm diameter or so, and ideally no more than
about 1cm in depth. I need at least 1 degree resolution, but ideally
I'd like about 5-10 times that. Output doesn't really matter too much -
it will be interfaced with a microcontroller that has both analog and
digital inputs.

Anything out there that will fit my needs?

Thanks!
Click to expand...

How are you with making little tiny parts? Digikey seems to have
quite a selection of 1-turn trimpots, which might work in your app.
Obviously, you wouldn't get a full range, but a cermet pot is
"infinitely" variable - you might have to watch for repeatability,
but as others have mentioned, a zero-set at bootup should take care
of that; and with sensors, your controller could compensate. :)
Just go to http://www.digikey.com, and put "trimpot" in the search
window, and start picking through parameters.

[FWIW, ISTR hearing some dissatisfaction with Digikey's search facility
lately, but it seems to be working OK for me, at least just now.]

My idea is you could find a way to mount a little pot on the axis
of a joint, and just measure the angle by the resistance.

Good Luck!
Rich
 
W

whit3rd

Hi - I'm looking to measure the angles that a 6 legged robot's joints
are making relative to each other. I'm thinking a rotary encoder might
be the best option, though I'm also looking at using a pot.

Problem is I don't have much space to work with - I'd need something
that was maybe max of 1.5cm diameter
Click to expand...

Maybe wrap a monofilament around the joint, with spring tension, tied
to
a sliding potentiometer? Even connecting a rotary encoder in addition
to providing mechanical rotation is a tricky job.
 
O

[email protected]

Hi - I'm looking to measure the angles that a 6 legged robot's joints
are making relative to each other. I'm thinking a rotary encoder might
be the best option, though I'm also looking at using a pot.

Problem is I don't have much space to work with - I'd need something
that was maybe max of 1.5cm diameter or so, and ideally no more than
about 1cm in depth. I need at least 1 degree resolution, but ideally
I'd like about 5-10 times that. Output doesn't really matter too much -
it will be interfaced with a microcontroller that has both analog and
digital inputs.

Anything out there that will fit my needs?
Click to expand...

The HMC 1512 from Honeywell might be worth a look, it senses magnetic
field direction down to 0.05° and they're pretty small! you'd need a
little magnet too but there's plenty of places that sell them now :)
 
L

Luhan

Hi - I'm looking to measure the angles that a 6 legged robot's joints
are making relative to each other. I'm thinking a rotary encoder might
be the best option, though I'm also looking at using a pot.

Problem is I don't have much space to work with - I'd need something
that was maybe max of 1.5cm diameter or so, and ideally no more than
about 1cm in depth. I need at least 1 degree resolution, but ideally
I'd like about 5-10 times that. Output doesn't really matter too much -
it will be interfaced with a microcontroller that has both analog and
digital inputs.

Anything out there that will fit my needs?
Click to expand...

The usual solution for non-industrial designs is to use a pot. I've
seen some really small ones among the kazillion of them out there.

Luhan
 
M

Mike Noone

it's able to tell you position immediately from power-on, and it has
a much higher resolution (limited by your ADC). Open up a hobby servo
and take a look at their pot-driven control loop.
Click to expand...

Hi Ben - my worry with using pots is that they will wear out with
repeated usage. Maybe there are some pots designed to be constantly
turned?

-Mike
 
M

Mike Noone

How are you with making little tiny parts? Digikey seems to have
quite a selection of 1-turn trimpots, which might work in your app.
Obviously, you wouldn't get a full range, but a cermet pot is
"infinitely" variable - you might have to watch for repeatability,
but as others have mentioned, a zero-set at bootup should take care
of that; and with sensors, your controller could compensate. :)
Just go tohttp://www.digikey.com, and put "trimpot" in the search
window, and start picking through parameters.

[FWIW, ISTR hearing some dissatisfaction with Digikey's search facility
lately, but it seems to be working OK for me, at least just now.]

My idea is you could find a way to mount a little pot on the axis
of a joint, and just measure the angle by the resistance.

Good Luck!
Rich
Click to expand...

I can handle little parts. Problem is that cermets, in my experience at
least, are designed to be used to adjust a setting, and then left and
forgotten. I think they would break down with constant usage.

-Mike
 
R

Rich Grise

Hi Ben - my worry with using pots is that they will wear out with
repeated usage. Maybe there are some pots designed to be constantly
turned?
Click to expand...

Well, like he said, open up a hobby servo, and get another one of
whatever they're using.

Good Luck!
Rich
 
M

MassiveProng

Well, like he said, open up a hobby servo, and get another one of
whatever they're using.
Click to expand...

Use a chopper wheel, and an IR LED emitter, and an IR LED receiver,
and set up a slit wheel (chopper).

Double the xceiver set, and you can double the slit pitch rotational
resolution (or is that quadruple?)

Anyway... VERY accurate.
 
J

Jamie

Mike said:
Hi - I'm looking to measure the angles that a 6 legged robot's joints
are making relative to each other. I'm thinking a rotary encoder might
be the best option, though I'm also looking at using a pot.

Problem is I don't have much space to work with - I'd need something
that was maybe max of 1.5cm diameter or so, and ideally no more than
about 1cm in depth. I need at least 1 degree resolution, but ideally
I'd like about 5-10 times that. Output doesn't really matter too much -
it will be interfaced with a microcontroller that has both analog and
digital inputs.

Anything out there that will fit my needs?

Thanks!
Click to expand...
an absolute/Gray code encoder is what you need how ever, the space
and resolution you're looking for may put the kibosh on that!

in your case, use some precision pots into ADC of a PIC or something
like an Atmega that has lots of ADC's on them and perform a commutations
link to your master CPU.
 
You must log in or register to reply here.

Similar threads

M
small, very accurate shunt resistors?
Replies
15
Views
2K
The Phantom
T
flippineck
Small IR gooseneck spot heater?
Replies
1
Views
940
Martaine2005
Martaine2005
P
Small signal model of emitter follower circuit
Replies
3
Views
990
Harald Kapp
Harald Kapp
roughshawd
Small motor with 104 cap bridge between terminals.
2
Replies
21
Views
2K
davenn
davenn
V
The EASY Way to check a small SMPS transformer
Replies
3
Views
941
Bluejets
B
Top