I'm looking for a capable robotic arm on a budget. However, I've been
unable to find anything between hobbyist arms (such as Lynx,
CrustCrawler) and the lowest end of the industrial arms, such as ST
Robotics. Am I missing something? I'd like an arm with some speed,
reach (say 24", and lift capability (~ 1kg), and the hobby arms don't
quite cut it.
On Jul 26, 10:55 am, firstname.lastname@example.org wrote:
Try giving more specifics about your requirments and we prbably can
offer some potential solutions.
1 What is your " Budget " ? $ 300 , $ 3,000 , $ 100 ?
2. What is your accuracy requirements.
3. What is your "ulitmiate goal for the arm" i.e lift a quart of
beer , or twist off the bottle top
4. What is your time budget and engineering experience ?
if you have $300 then get a Scorbot on Ebay its a very capable 1 kg
lift arm with controller, if you lurk the Scorbot III listings you'll
find one every couple of months and they usually go for $300 -400
If you have less money but more time then you can build and arm from
aluminum and metal. To get the 1 kgs lift you can not use RC hobby
servos, instead you will want to use surlplus Pittman motors and
gearboxes. Attache these to a pully system and you will get your 1
For $3,000 you should be a ble to get a Puma or Milicron Arm that
will lift a few Kg and control it with great accuracy.
What can you tell us ?
Under $1k would be great, but if $2k or so made a difference I can
probably go there. $3k is probably over the top unless it really was
the perfect solution (hardware and software library-wise).
I can probably work within a range of accuracies. However, this isn't
an area of robotics I've read up on so I'm not sure what to expect.
If i just imagined what would be most useful, I'd say I'd like to be
able to get the end-effector to a desired position within 5-10 mm.
But like I said, if that's too high of an expectation, I can work with
The arm will be painting. It needs to be able to lift/select a brush,
dip it in paint, and apply that paint. Ideally I'd be able to make
brush strokes (place, drag, and lift) as opposed to just dabs, but I'm
I have time, but not much engineering experience. I'm good with my
hands, and build things out of wood, but haven't built any
electronics. That said, I have decent programming experience (rusty,
but usable), have a strong understanding of 3D computer-aided design,
and understand computers very well. I expect this to be a long-term
project, but am also anticipating a hefty programming requirement (see
below). As such, I had hoped to buy a complete arm instead of
starting from scratch.
Another requirement is that I'll want to be able to programmatically
and dynamically control the arm, hopefully using a language such as
python, ruby, or java. I expect I'll need inverse 3D kinematics so
that I can direct the end-effector to specific locations. Ideally,
the arm would include software libraries that supported that as my
math chops aren't up to that task.
Thanks for these suggestions, i'll look into them. It could be that 1
kg is more than I need... 0.5 kg might do it. I'll have to do some
If I were to go the build-it-myself route, are there 3rd party control
libraries out there I could use to control it, and to hopefully do the
inverse kinematics? Also, how much money would be saved going this
On Jul 27, 6:29 am, email@example.com wrote:
What kind of painting is it to do? Paint a house?
A wall? A window frame? Or paint a picture?
Part of the solution might be a special purpose
effector rather than a hand. Can you use spray
painting for example instead of a brush?
If that's what you need, look into robotic tool changers:
Each tool (brush) has a standard collar attached to it, and the
arm has a powered tool changer which can grab and release those
On Jul 27, 7:26 am, firstname.lastname@example.org wrote:
Then may I suggest not a robotic arm but a printer plotter machine?
Instead of a pen you use a brush.
Are you wanting to use tubes of paint or pots of paint?
There are probably electric paint dispenses (or maybe
use electric liquid soap dispensers to store the paint
to squirt out different amounts to be mixed.
I thought of that. However, I'd also need to be able to control the
height of the brush. I know that I've seen rapid prototyping hardware
that works with a basic plotter type mechanism (say, ejecting material
in a bead) onto a platform that moves up and down. In this respect, a
plotter type (I suppose this would be a 'Cartesian' robot?) might
I am also after a certain visual aspect to the device, and the arm
would be a lot more interesting to watch than the plotter. But I'm
not ruling it out. Would that kind of device be a lot less
expensive? Easier to build and/or buy?
I'm considering supporting different kinds of paint. One would
originate in tubes. Another would have to be picked up from small
pots onto the brush. Your idea would work for the former.
Thanks for the link. This idea makes a lot of sense and I hadn't
thought of it.
A cartesian/gantry robot would be much easier to control than the
classic articulated arm you're thinking about. If the painting
doesn't need to be vertical, then a SCARA arm would be another good
configuration to consider.
With any of these, I suspect the main control difficulty will be
maintaining the correct distance/pressure between the brush and the
painting. That's why a cartesian or SCARA arm might be better than a
fully articulated one. Cartesian is nice because painting coordinates
directly map to joint coordinates... Inaccuracies in the SCARA
control might give a more human effect, though. Since the main joints
in a SCARA arm are horizontal, they can be powered by smaller motors...
On Jul 27, 9:03 am, email@example.com wrote:
Yes a LOT less expensive and easier to accurately control.
You can always incorporate the "human effect" mentioned
by Daniel with simple software.
I have seen electronic magazines with these setups as
do it yourself projects. Often for automatic cutting of
If you really want to emulate human painting, industrial robotics
hardware is up to the job. A tool changer for brush changing, a force sensing
wrist (see "http://www.ati-ia.com/products/ft/sensors.aspx "), and
a standard low load robotic arm will do the job.
You could probably use the Lynxmotion hobbyist robot arms if you
could add decent force feedback. You want to servo the brush into
about the right position, then use force feedback in the direction
perpendicular to the canvas during painting to bring the brush
into contact. Then maintain that force level during the brush
stroke. Break contact with a positional move. One axis of force
feedback would be enough for this.
The hard part is that hobbyist-grade software usually isn't capable
of things like positional control in two dimensions with force control
in the third, out at the end of a jointed arm. And hobbyist robots
tend to come with crappy sensors. But the technology is well understood.
It's used industrially for grinding, drilling, sanding, and polishing
applications. References are available.
Once you have force feedback working, you can use it to dip the brushes
into jars of soft paint in a controlled way.
Further up the planning hierarchy, you can get paint-by-number software
which will take in a picture and generate a paint-by-number plan. Then
you need a stroke planner, and sequencing for picking up paint, cleaning
the brushes, and brush changing.
I have seen commercial robotic arms draw pictures of people with great
speed and dexterity. As a hobby robotic arm they are too expensive but
if the arm is making money for you then that is a whole other ball
The hobby robotic arm i played with was too slow, weak and required
you add all your own sensors. I could make my own sensors but the
slowness and weakness took all the fun out of it.
One of the more common devices in industrial robotics
is a 6 degree of freedom force sensing wrist. This detects
positional and rotational forces in each of three axes. The
wrist is a slightly flexible part equipped with strain gauges,
usually with some onboard electronics to bring out the amplified
signals in a useful form. This is overkill for many applications,
but it's generic, so it's a common solution industrially.
Simple force sensors are widely available, and not too
expensive. The general idea is that you bond a strain
gauge to something with a bit of springyness.
for a $9.90 force sensor to play with. Range is 0 to 3Kg,
and it's easy to interface to an A/D port, so that's about what
you'd need to measure the force on a paintbrush.
Academic robotics went to force sensing in the 1980s, and
by the 1990s, industrial robots tended to have force sensing.
The general idea is that you use preprogrammed positioning to
get to about the right place, then fine-tune using force sensing.
I did some of this stuff using industrial robots at Stanford
back in the 1980s, when the technology just barely worked. Today
the parts are much better.
Thanks for the link. Those look like easy to use force
sensors -- far easier than trying to measure force via
motor stall current.
Is there any comparable easy to use rotational force sensor?
I'm thinking of something with two aligned axes sticking into
a blob of some sort and some wires sticking out of the middle.
Look up "torque sensor".
What you usually get is something that looks like a shaft
collar with electrical connections. You can get bare strain
gauges and wrap them spirally around a shaft to make a torque
for a torque sensing system used for winding rubber band airplanes.
Thanks again for all the discussion. I've done more looking into
cartesian setups, and can definitely see how this would be easier than
an arm. I also noticed that some of them seem to not require support
on two sides (e.g. the Y is only supported by the X side), which makes
watching the process easier. Certainly the addition of torque sensors
and tool changers would improve it as well.
Given that, can you suggest some good starting points for building and/
or buying a cartesian robot? The shopbot link leads to a variety of
cartesian bots made for CNC. Is a CNC setup the best route to pursue
for prebuilt, or will someone out there prebuild general purpose
cartesian bots (or which I can design and/or purchase my own end-
effectors)? I'd like something rugged and quick, but still within
If not prebuilt, where would I look to to find some of the structural
components for such a machine? Would I have to design all of these
myself and have them machined?
I will also start looking up old electronics magazines to see what I
can find project-wise.
Finally, is there a generic software library for controlling such a
On Jul 28, 11:19 am, firstname.lastname@example.org wrote:
The tone of your post is you don't know much electronics?
I think you would need to find a complete project to copy
if that is the case and those questions should be part of it.
There is probably some stuff on the internet?
Do you do any programming if so what language?
A project should come with explanations as to how to read sensors
or send movement commands to the stepper motors but all the
rest would be up to your imagination and programming ability.
True, not much. I know some general concepts, and am not afraid to
get into something and figure out how it works, but I've never built
something electronic from scratch.
I'm certainly looking there primarily, but several people mentioned
plans in the mags so thought it was worth a look.
I have plenty of programming experience, so am less daunted there. C,
C++, Java, and Perl are the bulk of it, but I'm happy to learn
anything new in that area.
Someone's link above to cnczone.com was a great find...lots of people
doing home-built CNC, and I think I could adapt one of those to do
what I'm looking for. So perhaps I will end up building it from
scratch after all (with plans, though).
On Jul 27, 9:19 pm, email@example.com wrote:
There was a short article about RepRap in "Make Magazine" recently.
It's more for 3D but looks quite interesting. Open source...
And I think a 3D scanner called David was mentioned on this group:
Have robots. Will travel. http://www.robot-one.ca
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