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mlw posted on 
The sub-$500 robot is designed to be a platform anyone with a moderate skill
set and limited budget can build. The idea is that this can be built by a
highschool student or class with basic understanding of electronics and
computers and a little supervision from a teacher.
The price is *VERY* important as schools have *NO* money these days.
Overall complexity must be minimal. There should be a very easy to
understand build and operation process. At any point in time, the state of
the system should be "knowable." The whole system's operation should be
able to be debugged and "viewed" using a single debugging session.
The above requirement is why I do not want any programmable
micro-controllers on the system. While we may disagree as to whether or not
this is a reasonable requirement, please understand that this is an
important requirement.
Each component in the system should be easily testable independent of the
system. I.e. the wheels will use a mouse for encoders, so any program what
display mouse movement can test the motors.
I am using a POSIX style OS (Linux) because it is free and IMHO is better
suited for the task. While it is not a RTOS, it does have much better
response time characteristics and the various delays on a system that is
running a set of well define programs is manageable.
I am not using FreeBSD (or any other BSD) for a couple reasons. Device
drivers in linux are both easier to construct and load (IMHO) and more
plentiful. Linux also has better support for video and other I/O.
I am not using Windows for a few reasons. Product activation, each time you
materially change a Windows XP system you need to ask for microsoft's
permission to use it again. In a robot I will likely be reinstalling the OS
multiple times and is just not worth it. Response time, Windows is not as
responsive as a UNIX type system. Bloat, Windows is very large, a UNIX
system can be trimmed down as needed. Stability, Windows is not stable
enough to run for long periods of time.
I am using a mini-ATX or mini-ITX motherboard because it will be familiar to
almost anyone attepting this.
I am still considering the final I/O system. Right now I am using a Velleman
K8000 I2C board, and am not too happy with it. I am looking for a cheap
8255/8253 I/O board, but while I suspect there are vendors that can supply
it for less than $60, I haven't been able to find one. I may end up
building the I/O system off the parallel port.
I am using 3 separate power supplies. One 70W ATX power supply which costs
$35 at mini-box.com, one 12V 1.25A DC/DC converter, and one 5V 3A DC/DC
converter. I'm sure I can get a dual output supply for less.
Any cost cutting ideas and comments would be very welcome.
Robot Parts List $587.00
Motherboard $100.00 Mini-ITX with built in video, network
and sound
RAM $35.00 256M DIMM
12V ATX Power supply $35.00 12V 70W ATX
5V DC to DC Converter $35.00 For electronics
12V DC to DC Converter $35.00 For electronics
12V Battery $35.00
12V Charger $10.00
Ride around toy $40.00 Steel shaft w/2 motor wheels
(find at discount, surplus warehouses,
ebay, yardsale)
I/O Card $65.00
Electronic parts $50.00 ICs, wire, protoboards,
Wireless Router/WAP 802.11g $30.00 Belken or Linksys on sale with rebate
PS/2 Ball Mouse $3.00
Refurb 40G Hard Disk $29.00
Hardware $50.00
USB Camera $35.00
set and limited budget can build. The idea is that this can be built by a
highschool student or class with basic understanding of electronics and
computers and a little supervision from a teacher.
The price is *VERY* important as schools have *NO* money these days.
Overall complexity must be minimal. There should be a very easy to
understand build and operation process. At any point in time, the state of
the system should be "knowable." The whole system's operation should be
able to be debugged and "viewed" using a single debugging session.
The above requirement is why I do not want any programmable
micro-controllers on the system. While we may disagree as to whether or not
this is a reasonable requirement, please understand that this is an
important requirement.
Each component in the system should be easily testable independent of the
system. I.e. the wheels will use a mouse for encoders, so any program what
display mouse movement can test the motors.
I am using a POSIX style OS (Linux) because it is free and IMHO is better
suited for the task. While it is not a RTOS, it does have much better
response time characteristics and the various delays on a system that is
running a set of well define programs is manageable.
I am not using FreeBSD (or any other BSD) for a couple reasons. Device
drivers in linux are both easier to construct and load (IMHO) and more
plentiful. Linux also has better support for video and other I/O.
I am not using Windows for a few reasons. Product activation, each time you
materially change a Windows XP system you need to ask for microsoft's
permission to use it again. In a robot I will likely be reinstalling the OS
multiple times and is just not worth it. Response time, Windows is not as
responsive as a UNIX type system. Bloat, Windows is very large, a UNIX
system can be trimmed down as needed. Stability, Windows is not stable
enough to run for long periods of time.
I am using a mini-ATX or mini-ITX motherboard because it will be familiar to
almost anyone attepting this.
I am still considering the final I/O system. Right now I am using a Velleman
K8000 I2C board, and am not too happy with it. I am looking for a cheap
8255/8253 I/O board, but while I suspect there are vendors that can supply
it for less than $60, I haven't been able to find one. I may end up
building the I/O system off the parallel port.
I am using 3 separate power supplies. One 70W ATX power supply which costs
$35 at mini-box.com, one 12V 1.25A DC/DC converter, and one 5V 3A DC/DC
converter. I'm sure I can get a dual output supply for less.
Any cost cutting ideas and comments would be very welcome.
Robot Parts List $587.00
Motherboard $100.00 Mini-ITX with built in video, network
and sound
RAM $35.00 256M DIMM
12V ATX Power supply $35.00 12V 70W ATX
5V DC to DC Converter $35.00 For electronics
12V DC to DC Converter $35.00 For electronics
12V Battery $35.00
12V Charger $10.00
Ride around toy $40.00 Steel shaft w/2 motor wheels
(find at discount, surplus warehouses,
ebay, yardsale)
I/O Card $65.00
Electronic parts $50.00 ICs, wire, protoboards,
Wireless Router/WAP 802.11g $30.00 Belken or Linksys on sale with rebate
PS/2 Ball Mouse $3.00
Refurb 40G Hard Disk $29.00
Hardware $50.00
USB Camera $35.00
godavemon posted on
Re: Sub $500 Robot and $587 need to cut costs
supply & batteries you chose. Also, I've been looking at buying usb
cameras and you can get them cheaper than 35 bucks. Target right now
is selling a logitec two packs (targeting b/f g/f chatting) for 30
bucks. So unless you have a specific camera in mind, that gives you $20
more.
Re: Sub $500 Robot and $587 need to cut costs
I have a year or so old EPIA 800 board. You can get faster than that these
days. I think I sent a link to find the power supply.
Gordon McComb posted on
Re: Sub $500 Robot and $587 need to cut costs
and sound
ebay, yardsale)
This list is missing some parts to make a functional robot of the size
and weight you suggest. Even with an excellent vision system, auxillary
proximity sensors are highly desirable -- and for schools, probably
mandatory given liability issues. Even if it's just a couple of IRPD
sensors near the bottom skirt of the robot you need an independent
method of detecting obstacles. Mechanical switches could also be used,
but these tend to get banged up quite a bit when used on a robot
weighing 20-30 pounds. They don't last long, and besides, you really
want to stop this thing *before* it hits someone. Your camera is not on
a turret, and I doubt it can see the ground immediately in front of the
robot, while also looking out.
Perhaps some rudimentary proximity detection is included in "Electronic
parts." Impossible to tell for sure.
I don't see the need for two expensive DC-to-DC converters for
electronics that in the above description shouldn't pull much current at
all. Most of the electronics hang off the ITX board and is powered by
its power supply. You can make decent DC-DC converters with some Maxim
chips, and save some money there.
I missed the part about why you have the *router* on the robot, rather
than just a wireless node.
$40 for the ride-on toy is a bit optimistic, and your encoder solution
requires a motor design that cannot always be assumed. Someone *might*
get lucky and find something similar locally, but anything on eBay will
cost $40 MORE just for shipping. Forty bucks is not a realistic price
point, and from what I recall of your earlier description is $25 cheaper
than what you paid. I think you're better off specing some known motor
that is commonly available on surplus. $20/piece gear motors are not
hard to find, though you also need to consider the wheels. You need to
rig up a more common encoder solution that will work with a wider
variety of available motors. I believe it's not wise to leave such an
important design issue up to chance.
-- Gordon
Re: Sub $500 Robot and $587 need to cut costs
That is the idea, it is incorporated in the "hardware" and "electronic
parts." These are estimates for now.
Well, that's one of those, wow isn't that interesting, things. A WAP
(Wireless access point) is actually more expensive than a router with a few
RJ45 jacks. This works out well, because it doubles as a hub if you want
more than one computer.
I saw the very ride around to that I bought for $65 at a liqudation center a
while back for $35. FYI, it was a "Scrambler," a two wheeled round toy with
a switch on each side for forward and reverse.
Also, while I don't want it to be impossible, I certainly don't want it to
be totally easy. The builder should need to improvise a little.
The encoder design is one of those "must" features, because I think it
really joins robotics technology to common computing and demystifies the
topic. It universally gets a "cool" from my nephews.
Besides, all you have to do is cut the shaft of the mouse wheel, and drill
the right sized hole for your motor.
As for the motors and wheels, I spend a lot of time looking for "motorized
wheels." They used to be very popular, but now I can't find any. Also, I
don't like to attach wheels right to the shafts of geer motors. Unless the
gear box is designed to do that, it isn't a good design.
aiiadict posted on
Re: Sub $500 Robot and $587 need to cut costs
drive system.
It is something I've hacked, but it doesn't work great.
I'd like to see what exactly you have in mind.
Rich
Re: Sub $500 Robot and $587 need to cut costs
See:
PS/2 Mouse PID motor control on Linux, code and description
On this news group
Re: Sub $500 Robot and $587 need to cut costs
Hmmm. I bought my USB 802.11g wireless "stick" for about $25. Seems to
me this would be the overall less expensive approach, as the router
needs a 12v (or whatever) power source to substitute for its wall-wart.
A USB wireless adapter will simply draw its power from the MB, and its
power supply.
I assume you plan on additional networked devices than just the MB, and
don't to add a hub.
It's not so much hacking the encoder as it is getting to the shaft of
the motor. You're lucky to have found a motor that allowed access to the
shaft opposite the pinion. Many motors are sealed in their case, and the
case can't be readily removed to get to the shaft. And it's not always
possible to slip the encoder around the shaft on the other end, as the
pinion gear there is usually hydraulically press fit.
I'm not saying an encoder isn't a good idea for this, but the design you
have is fairly dependent on a particular drive motor.
Overhung load on a motor of reasonable quality will likely be adequate
for a robot of this weight, considering that even in a three-point base
configuration, each motor will take approximately 1/3 of the weight. The
output bearing on motors used for ride-on toys is probably as good, or
possibly worse, than the bearing on a surplus 12 or 24 volt motor (since
these motors may have cost >$100 new). Either way the design liabilities
end up being about the same. (The armature shaft bearing is of less
concern, since it's not directly taking the overhung load placed on the
output shaft of the motor.)
-- Gordon
Re: Sub $500 Robot and $587 need to cut costs
Either way, something is drawing power. Maybe the USB stick will be a little
more efficient, but I can't see it as being all too much (depending on what
is "too much")
Also, most mini-atx or itx boards have network adapters in them and they are
more efficient than usb versions. I may want to use the usb for something
else and don't want to dedicate any USB bandwidth to the network, since I
already have a network adapter. After all, it is a whole lot more
flexability for $5.00 difference.
Well, (not part of the sub $500 robot, per se') there is also the
possibility that I may load Linux onto the actual router processor and use
it to manage a communications interface.
I have yet to see a motor that doesn't have some shaft coming out at the
opposet end.
True, but I don't think it is a hard thing to instruct people to look for.
I seriously don't agree with this statement.
The motors I am using and the configuration that they are in, a steel axle
supports the weight of the wheel and the bearing surface (the plastic wheel
shaft hole) rotates around it. It will eventually widen and probably have a
limited life, but by then you'll probably decide to make something more
elegant.
The problem with using the shaft of a gear motor is that it is a simple two
point bushing designed to ensure stability to the shaft at the maximum
torque of the motor. The robot weight (in addition to the stress of the
motor torque) will be focused on the top of the bushing closest to the
wheel and on the bottom of the other bushing. Brass brushings are fairly
soft. Depending on the weight of your robot, and/or if any impurities get
into gear box, the output shaft will eventually wobble and start destroying
teeth or binding.
You're probably right in that it will work well enough, but it isn't a very
good design. The cheap plastic wheels on my system may wear, but there is
no weight bearing stress on on the gear box, and the assembly was rated for
(I think) 65lbs. Maybe it is just an emotional decision, but I don't have
any problem destroying plastic wheels, but I don't like the idea of
destroying a metal gear box.
One of the things I really want to stress is "junk yard" engineering.
Hoss posted on
Re: Sub $500 Robot and $587 need to cut costs
Really? I been in electronics and robotics for many years and motors with
usable lengths of shafts out the rear have always been rare. I've seen them,
could track one down if I needed one, but not common by any means. By usable
I mean long enough to slip tubing over, attach a pully or sprocket, decoder
stripes, etc.
-Hoss
hossweb.com
Re: Sub $500 Robot and $587 need to cut costs
Wow, I have over a dozen motors here and all have at least an 1/8 of an
inch.
D. Jay Newman posted on
Re: Sub $500 Robot and $587 need to cut costs
Wow! You get to play with the good toys.
I've played with quite a few motors, and *none* of them had shafts
coming out the back end.
It depends on the motor. Many motors are made for this sort of thing.
Many will die quickly if you try it.
--
D. Jay Newman
http://enerd.ws/robots/
Re: Sub $500 Robot and $587 need to cut costs
Nope. A solid metal for a backing.
--
D. Jay Newman
http://enerd.ws/robots/
Re: Sub $500 Robot and $587 need to cut costs
That sucks. I'm using much cheaper motors, maybe that's the difference.
the Artist Formerly Known as K posted on
Re: Sub $500 Robot and $587 need to cut costs
It's not a question of cost -- it really just depends on the motor. I
have a boatload of DC gear motors, and some have an exposed aramture
shaft, and some don't -- I generally go surplus, and you're pretty much
stuck with what's available. Sometimes there's even a glut of suitable
motors with built in encoders -- you just never know. I don't think I'd
assume an armature shaft is available unless you are designing with a
specific motor in mind -- or at least have a plan b.
--
(Replies: cleanse my address of the Mark of the Beast!)
Teleoperate a roving mobile robot from the web:
http://www.swampgas.com/robotics/rover.html
Coauthor with Dennis Clark of "Building Robot Drive Trains".
Buy several copies today!
Re: Sub $500 Robot and $587 need to cut costs
I use a Linksys 802.11g card that uses the rt2500 driver for Linux.
--
D. Jay Newman
http://enerd.ws/robots/
JGCASEY posted on
Re: Sub $500 Robot and $587 need to cut costs
What is the point of a large, complex and expensive
robot for students at a high school? What exactly
is it going to teach them and how much hands on
experience is each student going to get?
One reason for building small uC based robots
is because they are cheap and yet can cover all
the stuff a student needs to learn including how
to program and use a uC which may in fact be a
requirement for anyone interested in electronics.
It is a no brainer to program a micro processor
using C or even Assembler. It takes years to become
proficient in fully understanding the requirements
and protocols to make use of a complex OS unless
you use something simple like Visual Basic.
Cheap small robots means that more can be built
so more students have hands on experience with
many different configurations including interaction
between robots such as Sumo wrestling, tag along
and so on...
As for vision you need to determine your goal.
Is this something that is high school relevant?
A Pentium based board may be a requirement for
an advanced vision system including making use
of MMX technology and PIII streaming SIMD
extensions and so on. Not exactly high school
stuff?
Have you really identified your target builder
or is this really an mlw robot which will really
only appeal to those with the same background in
programming and electronics?
Cheers,
John Casey
Re: Sub $500 Robot and $587 need to cut costs
What's it going to teach them? Motor control, programming, operating
systems, computer math, electronics, etc.
The only difference is "programming a microcontroller." I'm not sure of the
singular value of this.
This is clearly an opinion, you are free to have it, but I don't subscribe
to it.
I see a different project.
Why?
It is impossible for anyone to create anything that doesn't reflect their
background.
MetalHead posted on
Re: Sub $500 Robot and $587 need to cut costs
and sound
ebay, yardsale)
You might be able to turn that $30 hard disk into a $8 floppy drive.
Booting off the floppy to use a ram disk would avoid the cost, power
consumption and fragility of the Hard Disk. You could also set up a
loader on the floppy to run a net-boot off your wireless network. If you
are not running X and a window manager, most of that 256MB RAM will be
unused.
I looked at the Adlink site that I mentioned in another post for a
timer/8255 card and they had something close for AT bus, but nothing
close for PCI. I think that card may be an expensive one for PCI.
Bob
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