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Grotto
Joined: 30 Aug 2005
Posts: 38
Location: Morisset NSW
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Single-motor controllers
Hey there guys,
Im having a bit of a brainstorm at the moment and Ive
come up with a weird concept and want to see what the tech-heads
think in the way of pro's and cons.
Im planning on designing a modular control system from scratch
that uses fibre-optic cable to control localised power boards with
pwm signals.
Eg central controller sending a pwm pulse train down a fibre-optic
link to a (FET) power-board attached as close as possible to the motor,
in order to shorten the leads carrying high-current switched loads. One link
and one power-board per motor. The power boards are basically a
fibre-optic reciever feeding a pic/picaxe which drives a Fet boosted h-bridge.
Bear in mind, my first bot is still only in CAD, and Im only just starting
to study Fet designs now.(OSMC project)
The advantages I see are as follows...
1) Central processor/reciever opto-isolated from current-bearing circuits.(damage prevention)
2) Blown power circuits replaced without full nervous-system replacement.(ease of maintenance/repair)
3) Easier sectional testing (ie test single motor without needing full system power-up).
4) Ability to completely (electrically) isolate receiver from motor power supply.
5) Upgrade power circuits without full nervous-system replacement.(say in case of motor upgrade)
6) Lower internally generated RF, due to fibre-optic signal wires ?!?(advice please)
7) Lower internally generated RF, due to shortened switched-power leads ?!?(advice please)
8 ) Lower power-lead losses, due to shortened switched-power leads ?!?(advice please)
9) Reduced weight, due to shortened switched-power leads and lightweight signal leads ?!?(advice please)
As for dis-advantages, I cant see any on paper but my ears are open.
And please dont count complexity of the design as a dis-advantage as
this project is (at this time) largely a learning process for me to come
to grips with fet power designs.
I'm mostly looking for advice on the feasability of the distributed
powerboard "concept" and fibre-optics as a weight-saver.
Thanks guys _________________ "The future is not set. There is no fate but what WE make."
........CEO Cyberdyne Systems
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Tue Nov 21, 2006 2:33 am |
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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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I dont have time for a detailed reply now, but in combat-robot equipment, a key-concept is "Failure Points"
ie. The more things that can go wrong, the more that probably will.
Seperate PCB's and mounting/enclosures, Fibre Optic Connectors, Multiple Power supply points etc etc.
Also keep in mind the end-users. Most combat robot builders are not electronics guru's. Basic Electronics is usually within their grasp, but not 1 in 10 would know more about a FET than "its the bit that goes boom."
If you are building it for your own education fine, but if you are seriously intending it for use in combat, look at it the same way the army looks at a gun - If you cant give it to a grunt with an IQ less than their bicep size, throw it in the sand, drown it in the ocean, leave it in the jungle for a year or two and then pick it up and fire a bullet, then its not going to be reliable in combat.
More later _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
Last edited by Spockie-Tech on Tue Nov 21, 2006 10:13 am; edited 1 time in total
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Tue Nov 21, 2006 10:12 am |
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Grotto
Joined: 30 Aug 2005
Posts: 38
Location: Morisset NSW
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Ok, replies...
Andrew12 -
Ive been playing with fibreoptics for a few months
now and have been able to manufacture a reliable connector
using an Led at one end and a photo-transistor at the other.
By drilling a small hole in the led and transistor i can cut the
cable easily and just jam it in the drilled holes, secured externally
with blu-tak, cable cut with a hobby knife.
I have been getting reliable 20-30kbit per second transmit rates
around the house & workshop
, so I'm sure it will manage a
5-10khz pwm signal fine.
SpockieTech -
I agree with the failuree point concept, but shouldnt
it be balanced with the "dont keep all your eggs in one basket" concept?
Ive no practical experiance with IBC's or any other controllers, but
wouldnt it be common for lose function to the whole IBC if a fried
motor blows the fets or bridge? A distributed design allows the bot
to continue to hobble onwards, and the localised powerboard could
be replaced quickly if you have spares on hand.
Also, this is really for personal use only so I dont need to worry about
any end users besides myself.
Valen -
Glad to see someone else warped enough to thinks into every
corner of the box. Im not planning for brushless at this stage so Im
unlikely to need boosters, just a main-power rail running the length of
the bot. Good luck with your design too, and rather than diodes, have
you thought about slo-blow fusable links or thermal circuit breakers
on the outputs instead?
Anyways, thanks for the advice all, and everything everyone says is
being taken into consideraton, no matter how badly I phrase my replies.
As this is still early stage in the design for me, so no rush on the replies
but please keep them coming.
Catch you'all later
_________________ "The future is not set. There is no fate but what WE make."
........CEO Cyberdyne Systems
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Tue Nov 21, 2006 10:22 pm |
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