Cluster robots

[Stuart Livings]

Spawning a new thread for this, since it appears to have captured the
imagination of a few...

Motion:
- Pager motors/rigid legs?
- Wheeled gearmotors?
- Wheeled micro stepper motors?
- Micro motors vibrating (rotating) legs directly?

Physical characteristics:
- Smaller usually means cheaper, but there's a balance.
- Smaller means less battery power.
- Should be resistant to damage (general public mishandling, falling off
a desk, etc), 3D printed two-part case?
- Motors should be attached in a manner to avoid vibration damaging
soldered components. Maybe foam mount?
- Recharge with minimal effort. Maybe charge through the legs?
Inductive charge?
- USB port for initial programming?

Sensors/display:
- Own battery voltage/level.
- Obstruction/proximity (overlap with communication? Infrared?).
Omnidirectional TX and unidirectional RX? Vice versa?
- Minimum of one LED, preferably more.

Communication:
- RF, maybe use NRF51822 or ESP8266 MCUs? Maybe use LoRaWAN
capabilities and piggyback TTN?
- Short range comms (ultrasound, infrared, maybe RF?), must be able to
communicate with robots in immediate area.
- Would be beneficial to be able to detect range and angle to nearby bots.

Build/logistics:
- The more we build the more important it is to be low cost and low labour.
- Be useful to have punters do final assembly, so maybe build and test
the PCBs externally and have the punters solder on the battery
connectors, the motors, assemble the legs/wheels and clip on the case?
- Colour the case for overhead recognition. Maybe use the LEDs to light
the upper case through translucent PLA?

Quantity:
- What are people thinking of? 10? 100? 1000?

[Nick Forbes]

I think we possibly need to consider two projects, one being an all singing and dancing cluster robot with bleading edge technology that will probably cost 10s of £s and a separate absolutely stripped to the bones one that could be assembled at open days etc. that would cost between £5 and £10 each.

If people are going to assemble things at an open day they will need to be very cheap, especially if we can't reuse the bits or they take them away with them. Might be different if we could obtain sponsership for the parts. However a higher spec robot with lots of room for expansion would be great fun when we get a hackspace to play in. My interests are in robotics so I want one (at least) of each!

Personally I think initially we should concentrate on a very simple, stripped to the bones (i.e. cheap) robot with very basic functionality, my first thoughts are:
- Use pager vibrators and three legs to save on drive motors, gear boxes etc.
- Rechargeable battery
- Install a boot loader so we don't need fancy programming tools
- Charge and program using the three legs to save on connectors, might also need a debug connector for initial development
- RGB led so we can make teams in the cluster or just indicate actions and they look cool
- IR communications - cheaper than radio
- Collision detection IR or possibly feeler switches
- My personal preference would be to use a PIC as the processor as that is what I'm familiar with.

Quantities - initial batch of 10 for dev work and then probably gear up for 100 for open days etc. however we wouldn't need to build them all at once. PCBs get cheaper by the 100, most of the other components only get significantly cheaper by the 1000 or more so we need to look at a sensible balance.

[Norman - M0JEC]

I've generated a new thread for this one as it seems to be a viable idea...

The guys at Plane Plotter said...

Have look at the OLE/COM interface that PlanePlotter presents

Using a trivially simple script you can read out the range of all the
aircraft and choose the nearest one at which point you can read out
the elevation and azimuth directly. You do not need any other
software. You just need to send the Az/El to your pointing device.

Let me know if you need any help with it.

So looking like the software exists to drive the rotator we just need a
script to pick the 'nearest' aircraft?

Norman

[Stuart Livings]

On 01/03/2016 12:11, Norman - M0JEC wrote:
> Have look at the OLE/COM interface that PlanePlotter presents
>
> Using a trivially simple script you can read out the range of all the
> aircraft and choose the nearest one at which point you can read out
> the elevation and azimuth directly. You do not need any other
> software. You just need to send the Az/El to your pointing device.

This looks dead easy...

> So looking like the software exists to drive the rotator we just need
> a script to pick the 'nearest' aircraft?

Yep, and I think we could even avoid the need to use OLE/COM, since
PlanePlotter appears to be able to send UDP packets, which are
themselves trivial to process in a programming language of our choice.
Some MCUs (e.g. the Pi) could run the UDP stack and a simple (Python)
script locally, meaning that it could be remote from the PlanePlotter
machine.

I have all those bus driven servos, too, so we wouldn't even need the
large antenna tracker, we could do it on a smaller scale and have
several pointers, e.g. pointing at the ten nearest planes!

Stuart

[Norman - M0JEC]

Cool, I'll leave you to play with that one?

Maybe we can use my 'big' rotator as a test rig and then use the smaller
ones for demo etc?

UDP/TCP is how I currently control the big rotator anyway.

Just a thought.

Norman

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[Nick Forbes]

I don't think your new thread worked. When I look at Google Groups everything about the Plane Pointer appears under the Robot Cluster thread, the only thing that is different is the subject line has altered part way down the thread. Might just be me, or is this happening to others.

Nick

[Stuart Livings]

On 01/03/2016 12:10, Nick Forbes wrote:
> I think we possibly need to consider two projects, one being an all
> singing and dancing cluster robot with bleading edge technology that
> will probably cost 10s of £s and a separate absolutely stripped to the
> bones one that could be assembled at open days etc. that would cost
> between £5 and £10 each.

Agreed. Our focus last night was on the cheap ones with the explicit
intention of getting people to make them and add them to the NADHack
cluster, i.e. not take them away.

> My interests are in robotics so I want one (at least) of each!

Same here :D

> Personally I think initially we should concentrate on a very simple,
> stripped to the bones (i.e. cheap) robot with very basic
> functionality, my first thoughts are:
> - Use pager vibrators and three legs to save on drive motors, gear
> boxes etc.

My biggest concern about this approach is that the play area needs to be
absolutely level, otherwise the robots will follow gravity. It is very
cheap, of course :)

http://www.aliexpress.com/item/FREE-SHIPPING-Vibration-Pager-Vibrating-Vibrator-Micro-mobile-Motor-6mm-x12mm-diameter/565241701.html
and
http://www.aliexpress.com/item/100pcs-lot-12MM-2-8-MM-Micro-Button-coin-pancake-Type-Vibration-Motor-2-V-5/32387232857.html

Both good examples of bulk buy vibration motors, about $30 for 100 or
$60 for 100 robots (2 motors each).

> - Rechargeable battery

18650 cells (much larger than we spoke about last night, about 65mm long
and 3Ah) are about 1.2USD each at 100 off.
16340 cells (16mm diameter, 34mm long and 1.2Ah) are about .9USD each at
100 off, or $90 for 100 robots.

> - Install a boot loader so we don't need fancy programming tools

Agreed. Using IR or RF for programming through the bootloader is a big
benefit, if we can keep the communication simple we can use the on-chip
UARTs and minimise the code footprint. In-protocol checksums are a good
way of ensuring that we don't corrupt anything.

> - Charge and program using the three legs to save on connectors, might
> also need a debug connector for initial development

Can definitely charge using the three legs (see below*) but if we can
program using IR (once the bootloader is on) then we can do contactless
reprogramming.

> - RGB led so we can make teams in the cluster or just indicate actions
> and they look cool

Definitely agree. I like the idea of having four (or eight, or
whatever) RGB LEDs to light the case for external robot recognition. If
we can recognise four colours then four LEDs gives us 4^4 or 256 unique
colours, but we'd lose 75% due to the rotational symmetry, i.e. we'd
only have 64 unique patterns. With eight LEDs in a ring and four
recognisable colours we can 8^4 / 8 = 8^3 or 16M unique robots. Putting
the LEDs in an asymmetric pattern (e.g. a U shape instead of a ring)
gives us better recognition (unique plus orientation) and you could do
1024 robots with six RGB LEDs, 256 robots with four RGB LEDs.

We talked about displaying patterns, e.g. a digital clock, so if you
used three robots per segment you'd need 21 robots to make a single
7-segment display. Clocks require approximately 4+two-halves segments,
so we'd need approx 100 robots to make a digital clock. If you forego
seconds (which the robots couldn't keep up with anyway) you can do it
with 2 + .5 + .5 segments, or approximately 64 robots.

> - IR communications - cheaper than radio

Agree that it's much cheaper but range and interference are more of a
problem. 100pcs of discrete IR receiver (e.g. TSOP1738) are $50 but
bizarrely cheaper from Farnell :) For the purposes of this email I'll
assume that transmitters are equivalently priced so 100 robots are $100.

> - Collision detection IR or possibly feeler switches

I'd love to do this but think this might be cost prohibitive. Using
infrared doubles the IR budget (but does allow us to use directional IR
for other purposes).

> - My personal preference would be to use a PIC as the processor as
> that is what I'm familiar with.

I personally like the AVRs but absolutely happy to choose any platform.

> Quantities - initial batch of 10 for dev work and then probably gear
> up for 100 for open days etc. however we wouldn't need to build them
> all at once. PCBs get cheaper by the 100, most of the other components
> only get significantly cheaper by the 1000 or more so we need to look
> at a sensible balance.

I think we could be in the region of $10 per robot at 100 robots, which
is an astonishingly low $1000 / £650. I'm happy to pledge a decent
chunk of that if it's something we as a group could realistically commit
to designing and manufacturing...

Stuart

*Footnote about charging... the charging area could be a lattice of
aluminium/copper electrodes with an AC power source. The legs could
then be fed through a diode rectifier to the charging circuit. For
swarmed feeding behaviours the charging area could be considered a food
source :)

[Stuart Livings]

This happens if you reply to another email.  The email client puts a header in the new email indicating that it's a reply and threaded mail readers (e.g. the Google Groups interface or a thread-aware mail client if you're reading the mail on your PC as I am) will ignore the subject change and join the two 'threads' together.

The solution is to send a new email to newbury-...@googlegroups.com without clicking 'reply' or 'forward'.

Stuart

On 01/03/2016 13:50, Nick Forbes wrote:

I don't think your new thread worked. When I look at Google Groups everything about the Plane Pointer appears under the Robot Cluster thread, the only thing that is different is the subject line has altered part way down the thread. Might just be me, or is this happening to others.

Nick

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[Matthew Bucknall]

A few thoughts:

- General public + soldering irons perhaps asking for trouble. Not sure whoever is handling first aid will appreciate the inevitable deluge of 2nd/3rd degree burn victims.  Less chance of trouble if final assembly can be limited to plugging/clicking/screwing things together.

- Assembly could be made more fun by allowing for some customization - Stick on googly eyes etc.

- Pager motors are certainly cheaper than geared motors, but if Harvard University's Kilobot project is anything to go by, *controlled* vibration based movement is pretty darn slow and probably isn't very interesting to watch in real time.

- The cheapest geared motors I've been able to find are these (http://goo.gl/uiqAw3) but they're a bit chunky. I wonder if just a couple of venerable FA-130s (http://goo.gl/DiaQ0Q) with rubber bands hooked between their output shafts and a pair of 3D printed wheels would suffice?

- For power, how about using solar panels and some suitable overhead lighting? Small panels are about as cheap as suitably sized rechargeable batteries (http://goo.gl/9l6HHN) and there would be no need for the robots to recharge.

Matt.

[Matthew Bucknall]

Just re-posting this under the correct thread (apologies for the duplication):

A few thoughts:

- General public + soldering irons perhaps asking for trouble. Not sure whoever is handling first aid will appreciate the inevitable deluge of 2nd/3rd degree burn victims.  Less chance of trouble if final assembly can be limited to plugging/clicking/screwing things together.

- Assembly could be made more fun by allowing for some customization - Stick on googly eyes etc.

- Pager motors are certainly cheaper than geared motors, but if Harvard University's Kilobot project is anything to go by, *controlled* vibration based movement is pretty darn slow and probably isn't very interesting to watch in real time.

- The cheapest geared motors I've been able to find are these (http://goo.gl/uiqAw3) but they're a bit chunky. I wonder if just a couple of venerable FA-130s (http://goo.gl/DiaQ0Q) with rubber bands hooked between their output shafts and a pair of 3D printed wheels would suffice?

- For power, how about using solar panels and some suitable overhead lighting? Small panels are about as cheap as suitably sized rechargeable batteries (http://goo.gl/9l6HHN) and there would be no need for the robots to recharge.

Matt.

[Norman - M0JEC]

Sorry about that My e-mail client sees them as different threads. (and this one as yet another thread!)

 

I’ll try not to make that mistake again in the future.

 

Norman

 

From: 'Stuart Livings' via Newbury Hackspace (NADHack)

To view this discussion on the web, visit https://groups.google.com/d/msgid/newbury-hackspace/56D5A04A.5020403%40livings.co.uk.

[Ben Norris]

Yeah, you can't just change the title. There is some other id lurking in the headers that says its all the same thread.

[Stuart Livings]

No apology required, Norman!

[Matthew Bucknall]

This thread seems to have lost momentum a bit - If we're going to be getting anything in bulk from China in time to have stuff ready for May, we ought to be placing orders about now... Is anyone interested in taking on any of the design work for the project?

Matt.

[Stuart Livings]

Definitely interested, next few weeks are absolutely insane for me.  I had a look at building a kit list and struggled just on the drive system.  I can really see why the Kilobot uses pager motors :D

I'd much rather use wheels if possible for a more positive drive, including the ability to go uphill.  However this looks 'difficult' with off the shelf parts.  The larger gearboxes (the 100rpm yellow ones previously identified on this thread) look to be too big and slow for our uses, we really want something much smaller.

I did wonder if some of the micro stepper motors have appropriate drive characteristics for direct drive of small wheels, but Aliexpress (etc) don't list any stats for the motors.

I'd like to create something very compact and very flexible, and I'd like to build them in a way that they're marketable in the long term future.  I think there's a market for the Hackspace to sell micro-robot kits for fundraising if they're appropriately flexible.  For those kits to be viable, though, they need to run on imperfect surfaces and I don't think vibration drive works for enough surfaces.

Open to all comments as usual :)

Stuart

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[Matthew Bucknall]

I have a box full of micro stepper motors (http://goo.gl/Jzvbi5) at home intended for driving the feeders for my pick and place machine project - I haven't gotten around to evaluating what sort of torque curve they produce yet, but I can rig one up over the weekend to see. Trouble is with steppers is they're a bit heavy on the juice - Not an issue for PnP machine feeders, but maybe an issue for small mobile robots. Still, with a couple of those 3V 10 ohm steppers + the rest of the electronics, you'd probably get an hour or two of continuous movement out of a CR123A battery, which I guess is good enough. Of course to drive the steppers you're going to have to come up with a cheap way to implement 4x H-Bridges.. No current limiting required though, so you could probably just use N/P FET arrays or 'abuse' some gate drivers.

Matt.

[Stuart Livings]

I think we can save a lot of energy by unpowering the stepper motor when we're not using it.  Most stepper drivers hold one of the coils to hold position and that's not something we're overly bothered about.

Could we use one of the logical level multi-channel single-chip H bridges to meet our needs, noting that we don't yet know if we *can* direct drive...?

To view this discussion on the web, visit https://groups.google.com/d/msgid/newbury-hackspace/4c518e3d-bc50-4c9a-bf21-09724787458c%40googlegroups.com.

[Matthew Bucknall]

Indeed - Note I said continuous movement...

The reason I mentioned using FETs/gate drivers over single chip H-Bridge chips is that the latter will almost certainly end up more expensive - I've already been through this exercise to keep the build cost of my component feeders down. More than happy to be proven wrong though!

Matt.

[Matthew Bucknall]

...I don't know if you would consider 28BYJ-48 geared steppers to be too big: http://goo.gl/UqWgeu

They are a bit slow, but definitely strong enough to steer a small robot about and being unipolar, they are easier to drive. They are also easier to fit 3D printed wheels/gears onto because the output shafts are fairly chunky and have the advantage of being keyed.

Tic Tac Turtle uses one to operate its rack-and-pinion pen mechanism, driven by a couple of NUD3105DMT1G dual channel relay drivers. People often drive these motors with ULN2003/ULN2803 darlington arrays which are dirt cheap. Trouble is, with the motors being rated at 5V, Darlington drivers drop too much voltage to allow getting away with a 3.4V nominal lithium battery power source - That's why I'm using MOSFET based drivers.

Will report back on micro stepper motor torque as soon as I get a chance.

Matt.

[Norman - M0JEC]

I would agree that these could become a 'fund raising' tool, and the ability to be used on most surfaces would be a big bonus.

 

I'm not sure how expensive they are but don't some 'lego' kits come with motors for wheels/gears etc? Is it worth considering if they might be suitable for the robots?

 

If not then something similar?

 

Norman

----- Original Message -----

From: 'Stuart Livings' via Newbury Hackspace (NADHack)

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[Stuart Livings]

I think those steppers are a good size but they're way too slow for drive.  You're in the region of .25rps, so a 100mm circumference wheel is around 25mm/sec.  We might be able to adjust the gearing but that's a lot of work.

I looked around AliExpress to see if there was a bulk buy on cheap RC tanks to use as the chassis (the answer is no :() and found this one...

http://www.aliexpress.com/item/1-72-2117-German-Tiger-RC-Remote-Radio-Control-Battle-Tank-RC-toys-Military-for-Boys/32565187934.html

What's most notable about this RC Tank is its feature list...

"rise, fall, turn right, turn left, advance, retreat and hover"

That last one is a feature missing from most tanks I've been exposed to...

:D

I like your thought about unipolar steppers.  It occurs to me that if they're small and low enough current we might even be able to direct drive them from the MCU...  MCUs can typically sink 20mA or so of current (obviously varies quite a lot) but I'm guessing the inductive nature of the load makes this a non-starter...

I did find these: http://www.aliexpress.com/item/Wholesale-20pcs-N20-12mm-3V-280-rpm-Mini-Micro-Brushed-DC-Gear-Motor-For-Diy-Electric/32302497101.html

They're a bit more expensive at just over $3 each but there's plenty of torque for our purposes and they free run at 300rpm, which should give a fair turn of speed if we want it.

They are quite big, 10mm (tall) x 12mm (wide) x 30mm (estimated length) which, if you offset the drive motors and drive diagonally opposite corners on a four-wheeled robot, puts the robot around 50mm square.  Ten robots side by side would be 50cm wide, 100 robots would probably need a play area around four square metres.

Still not completely happy with that idea, I'd like to be more compact if we can, price seems to get high pretty quickly...

Stuart

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[Norman - M0JEC]

Maybe it's a misprint and it should say Hoover?

 

I'd be really impressed with a tank that can Hover....

 

Norman

----- Original Message -----

From: 'Stuart Livings' via Newbury Hackspace (NADHack)

To: newbury-...@googlegroups.com

Sent: Friday, March 04, 2016 12:22 PM

Subject: Re: [NADHack] Re: Cluster robots

To view this discussion on the web, visit https://groups.google.com/d/msgid/newbury-hackspace/56D97DFE.8050702%40livings.co.uk.

[Matthew Bucknall]

I'm using N20 motors to drive the wheels on Tic Tac Turtle albeit a 100rpm variant with magnetic encoder on the back. Rather than drive the wheels directly, I have a small 3D printed pinon gear on the output shaft of each motor which drives a larger gear integrated into each wheel (also 3D printed) to allow the motors to be offset. I have both motors above and in-front of the wheels to keep them clear of the pen and its associated mechanism, but you could have one to the front and one to the back of the robot (as with the 4 wheeled arrangement you described) - That would get the robot footprint down to about 32mm square.

I still wonder if a rubber band hooked around the output shaft of a small motor and a wheel (so the rubber band acts as both a drive belt and tire) would do the trick? An FA-130RA-18100 has an output shaft diameter of 2mm and a stall torque of approx 36 g-cm @ 3V, so with a 30mm diameter wheel that's a reduction of 1:15 and a stall torque of 540g-cm per wheel. At maximum efficiency, the same motor provides 6 g.cm at 9710rpm - Obviously that sort of speed is too fast for this application, but it should be possible to reduce the motor's speed without sacrificing torque by servoing it off it's own current ripple.

Another alternative I've gotten into my head is some sort of harmonic drive based on a vibration motor, but I haven't worked out the details yet and it's probably a bit silly anyway.

All that aside, some inspiration: http://www.gettyimages.co.uk/detail/news-photo/japans-citizen-watch-engineer-yasuji-hirosawa-displays-the-news-photo/57031691

Matt.

[Stuart Livings]

N20 motors seem like a pretty cost effective way of doing it, but hitting the right wheel speed seems tricky.  Because the maths hurt my brain I created a spreadsheet to calculate key things like wheel diameter, torque, etc for a given set of input parameters:

https://docs.google.com/spreadsheets/d/1I3GxhbrbNWwj0DFw2npI4gNuZZX1wPN-B0iPBGo89Ls/edit?usp=sharing

Please send me a request via google-docs if you want access to the sheet.  I'll try to respond quickly.  I *think* the maths is right, please feel free to correct anything you believe to be wrong.

In the worksheet you enter the robot mass, the height of an obstacle you want to 'stall' climbing over, the motor speed (under load), the robot speed and the inclination angle you want to stall at (i.e. the slope angle at which it's ok for the robot to be unable to climb).

The sheet calculates a bunch of stuff but the important ones (in bold) are the wheel diameter, the wheel torque, the wheel speed, the reduction ratio (for one and two stage reduction) and the motor torque.

It surprised me how tall a wheel needs to be to overcome a 5mm obstacle (my target) at a 30 degree angle of attack.  This obstacle gives you a 75mm diameter wheel, not at all viable for a microbot.

Dropping the obstacle size to 2mm brings much more reasonable numbers out of the sheet.  Of particular interest are the wheel diameter of 30mm and the shaft speed of 100rpm.  Both of these are doable with off-the-shelf (AliExpress) N20 motors with reduction gearboxes, available to buy in large quantities at under $3.50 each.

Buying the 300rpm version would allow us to 3D print a 1:3 reduction onto the wheel, alternatively we could direct drive from the 100RPM version, potentially 'unwrapping' the tight packaging on the gearbox to allow us to lay the motors side-by-side.

This still puts the robot around 50mm square, larger than I had in mind (and much larger than the ones in Matt's link!) but viable, I think.  3D printing or laser cutting chassis becomes viable at these sizes and the size means that hand assembly is doable.

Stuart

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[Matthew Bucknall]

Useful spreadsheet. I think you probably have more 'rugged' terrain in mind compared to what I had imagined. 150mm/s is a lot faster than I had imagined too, but I guess it all adds up to making the robots more versatile. Given the quantity of motors we're looking at, I'm sure a better price than $3.50/piece could be negotiated through Alibaba.com.

I haven't gotten around to testing the micro steppers yet, but given the figures you're talking about, I think it is a safe assumption that they won't be up to the task.

Matt.

[Stuart Livings]

Hi Matt,

I'm open to comments and ideas.  Given the severe constraints rugged terrain places on tiny bots it might be worth discussing increasing the size (reducing the quantity) vs decreasing the size (increase the quantity but reduce flexibility).

What are your (and others) ideas?

Stuart

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[Norman - M0JEC]

Depends on what we want to acheive?

 

If the bots are designed to interact in an 'arena' then that can be made to fit the capabilities of the bots?

 

If you're looking for something that can work in a more 'real world' situation then you may have to compromise on the design/price/quality to get that functionality?

 

Do the cluster bots need an 'end goal' or are they just to demonstrate the sort of thing that can be done in a hack space (and a nice example of co-operation?)

 

Ultimately it needs to be decided what we can put into them and what we want out of them? What is realistic, and what would be nice but might be not viable with some of the other constraints?

 

Flat arena vs obsticale course for example, maybe with an element that requires the bots to join forces for some of the tasks? If you have an incline that 1 bot on its own can't manage but 2/3/more can with the extra help?

 

Would it be possible/fun to have something where the bots are on (2 or more?) teams and under certain criteri (surrounded by four oposing team members?) can be 'switched' to the other team?

 

Maybe with each bot having a 'home' team so if the system resets they revert back to that team.

 

Just a few ideas not sure if any help, but see what you guys think.

 

Norman

----- Original Message -----

From: 'Stuart Livings' via Newbury Hackspace (NADHack)

To: newbury-...@googlegroups.com

Sent: Monday, March 07, 2016 1:25 PM

Subject: Re: [NADHack] Re: Cluster robots

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[Matthew Bucknall]

Well I don't really want to stick my ore in any further than I already have - Ultimately, what ever the project ends up being is up to who ever is going to spend time/money implementing it and unfortunately, between Tic Tac Turtle and the umpteen projects I've got going on at work, I don't have much time left to help. I can only really make suggestions.

I agree with Norman that it is perhaps worth considering what these robots are actually going to do before deciding on their capabilities. Not many applications spring to mind right now - Perhaps have the robots arranging themselves to spell out messages or maybe have them cooperatively navigate a maze?

In terms of speed, I think there needs to be a balance between not being so slow as to be boring, but also not being so fast that camera tracking becomes problematic. Maybe 50mm/s?

Incidentally, googling around for 'micro robots', I've noticed that quite a few designs use these motors:

http://ttmotor.en.alibaba.com/product/60086176621-220017843/3v_micro_gear_motor_for_building_block_in_miniature_consumer_applications.html

Matt.

[Stuart Livings]

That's a great find, Matt.  All your suggestions are welcome!  Those motors are about the right size, weight, torque and speed.  At relatively small reduction ratios (2:1 -> 3:1) and with 15mm diameter wheels those motors will achieve some pretty good speeds.

I wonder if they're available with different reduction ratios, e.g. 100-300rpm output shaft...

Who else is interested in actively developing these robots?  i.e. Is it just me? :D

Stuart

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[Stuart Livings]

Answering my own question...

Yes they do: TGPP06-D-136 is 240rpm and TGPP06-D-700 is 47rpm.  TGPP06-D-136 seems a pretty good match for our application...

Simple 2mm diameter, .5mm keyed output shaft.  Dead easy to develop or buy a wheel to fit it.

Less than 10mm long (excluding wires), too!

Stuart

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[Nick Forbes]

I'm definately interested in working on the design, work is just a bit manic this week - should be better next week.

Probably a week or two away, but if anyone gets as far as a prototype chassis, I can cut them on my laser if required, if anyone does design anything it would be best to export the file in .dxf format.

Regardless of what we eventually decide on as a clusterbot I'll probably still try and do something with pager motors. I already have some motors and it looks fun!

Nick