All terrain mobile platform

Good point about the limited writes.
That why vendors of industrial computers that use flash drives say that you must use an OS like Windows CE or Windows XP Embedded (as
opposed to normal Windows XP) because they don't regurlarly hit the disk. There are also distros of embedded Linux that would work.
BRW

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[Terrain Traversibility] Can someone speculate about the relation ship between the hight of the obstacle to drive over (i) Wheel radius (ii) Distances between wheels (front/back side to side) (iii) Number of wheels (iv) Mechanical design of wheel attachment (See also : http://www.abc.net.au/newinventors/txt/s1181148.htm http://www.magneticpie.com/LEGO/techNotes/MecTherMob.html#Mobility http://www.magneticpie.com/LEGO/techNotes/MecTherMob.html ) (v) ...

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[Localization] (i) Can someone suggest how to localize the "outdoor" mobile platform within 10cm accuracy ? (ii) Which GPS receiver serial output and which antenna with (Low cost) ? (iii) How to improve GPS accuracy (without using expensive DGPS base station) ? (iv) How to make inertial unit that can work on all terrain mobile platform (low cost) ? (v) How to combine odometry + inertial data + GPS readings to improve localisation accuracy? (vi) Any help on "Simplified" version of maths of combining/fusing odometry + inertial data + GPS readings (math for dummies kind of info and examples)? (vii) ...

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Gee. . .I don't know that is a lot of information. Each answer may require one or more books to discuss. Each one could lead to thousands of pages of books to hash out. You need to tackle each one one at a time or divide it among the team members. Gordon McComb and some others have some nice books that would help you out a lot.
(1)10cm accuracy -- Civilian GPS can't do it. Maybe 10 feet at best. You can place a fixed GPS reference unit at a point on the field. After 24 hours it'll be down to less than a foot or even a few inches. You can only get the accuarcy over time using civilian GPS units. The robot then can retreive the fixed reference and use it in conjunction with it's own GPS unit to help determine position. (2)Which GPS reciever, antenna, low cost -- Not all three are possible, the active antennas are expensive, you can get some GPS units surplus for lower prices, but sometimes people have trouble using them. there are a lot of GPS units to choose from, try going for a middle of the road price, those seem to yeild the most bang for the buck. I hate to suggest one as they obsolete these models faster than the stores get them in to sell. (iii) How to improve GPS accuracy - - you can't really. But expensive Psuedolites give the best accuracy. You are basically making your own local GPS positioning system. <v) -- that has been the source of thousands of pages of work and discussuins by many people. No simple easy answer. It depends on so many factors. But a hint is to have the quad encoders run as close to the motor itself as possible in order to get the higest resolution helps a lot. Wheel slippage over rough slippery terrain is always going to be a issue. Turns always result in some wheel slippage. (vi) --sorry Kalman filters are the way to go. You'll have to learn the math and concepts. I did an article for www.dprg.org on building up a gyro/acellerometer project that references other people's work on the issues. www.newmicros.com has PID and some other examples if you go the ISOPOD route.
Large outdoor robots get expensive real fast. But you can get creative. You know I think if you find a few of those kids ride in battery powered cars, and some creative hacking could result in a nice cheap outdoor robot. Four cars would make up a nice start for a 4 wheel drive robot.
<Roberto> wrote in message > [Localization]

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The best way (probably only way) of doing this is to use a SCAAT Kalman filter as at http://www.cs.unc.edu/~welch/scaat.html under dissertation. This is not difficult maths if you have some maths training. It uses Jacobian matrices. But for a complete beginner at maths the thesis would be impenetrable (give it a try). There is no way of doing this with 'simple' maths, but you should be able to understand what the maths is doing.
A normal Kalman filter has to work with an 'observable' set of measurements (data from sensors), this means that the measurement must completely specify the position of the vehicle. With SCAAT it is much easier, as each single measurement (which is not 'observable' because it does not specify the position of the vehicle), can be incorporated into the filter one at a time.
It basically estimates the expected measurement, and compares it with the actual measurement, and adjusts the internal Kalman filter notion of position to be in keeping with the actual measurement in a statistically sound way.
I am implementing a SCAAT Kalman filter for a automated guided vehicle and would be happy to open source the code. It is not yet finished, and I have problems with the design of the filter, but the code is all present. It is written under GNU/Linux in C++, using Blitz++. I am keen to have other people use and test the code.
Let me know if you are interested.
Jack
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THANK YOU for the reference and your offer to share your C++ code for SCAAT. We are now looking at the http://www.cs.unc.edu/~welch/media/pdf/scaat_dissertation.pdf and we are also looking forward to hear from you when we can work with your code.
Kind regards,

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Roberto,
Please email me, so that I can email you a tar file of the code.
Jack
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Thanks to all contributers. Within this sub-thread we will further investigate how to implement "Emergency Stop" subsystem:
[Emergency Stop] : The Base Computer will transmit regular watch-dog signals to keep mobile platform operational. An emergency shutdown switch will shutdown the platform unless it receives a watch-dog signal from the Base Station. We do not know how to "turn ON/OFF" the high current, main power line. Any suggestion?
We are looking forward to receive your further contributions.
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I normally use a simple homemade knife switch with a large loop ripcord handle to yank on, to kill power. it always works as a last failsafe method. I did tinker with using some IRF MOSFETS in parallel and drive them on 100% to provide a solid state on off switch, but I haven't gone all that far with this method yet. I think I'll do that for the next robot. My checklist still uses the tried and true steps like so, insert fuses, check and engage knife swtich cutoff, stand at the side of robot, second person has hand on emergency cutoff, and turn on power to CPU, and then turn on power to motor drive units. etc. Fuses or solid state crowbar circuits are a must too. Run the CPU system off a separate power system from the drive system. Thus you can test the CPU system separate form the drive system. depending on how big you build it, you need a good base to set the robot on so the wheels don't touch the ground while testing (for many many many hours). Do not ever just go full forward and then slam it into reverse, otherwise you will get a spectacular parts explosion as the drive train lets go.:) If it is late at night or on a holiday and the stores are closed and you run out of fuses, DO NOT PROCEED, give it up until you get new fuses or such items. You don't want to get injured or killed, because your not being safe. Late at night, been up 20 hours, early in the morning, that's when your likely to get hurt. Big robots are extremely dangerous.
<Roberto> wrote in message > Thanks to all contributers.

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These are good safety ideas, but none of them is an example of a failsafe implementation. You can use a normally open relay which is energized closed by your watchdog signal. You could also have brakes which are energized open by your watchdog signal. A deadman's switch is also a failsafe idea.
Mitch
Earl Bollinger wrote:

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can you post pictures of your robot(s?) that have this on them? I'd like to see some big ones. I'll post pictures of mine when I get something worth looking at built.
Rich
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Thanks to all contributers. Within this sub-thread we will further investigate alternative steering techniques:
[Steering] : The Base Station PC will read the joytick position and interpret it to two velocity data (differential steering), one for left and one for the right set of wheels. For the mechanical simplicity we are considering differential steering rather than Ackerman steering.
We are looking forward to receive your further contributions.
References: Steering : http://www.brainyencyclopedia.com/encyclopedia/s/st/steering.html Differential Steering : http://www.scs.ryerson.ca/~aferworn/courses/CPS607/CLASSES/Class%202/sld010.htm http://technologyandtrades.vcc.ca/diesel/html/differential_steering.html http://rossum.sourceforge.net/papers/DiffSteer/DiffSteer.html#d2 Ackerman Steering : http://www.me.ua.edu/me489/PDF/11-Steering-Student-6.pdf http://voronoi.sbp.ri.cmu.edu/~choset/general/labs/ackerman.html http://www.auto-ware.com/setup/ack_rac.htm
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Thanks to all contributers. Within this sub-thread we will further investigate alternative computer HW, OSs and memory/disk etc alternatives:
[Base Station & Platform Computer] : Initially we would like to control our mobile platform via joystick interfaced to a notebook PC as "Base Station" with a wireless ethernet which communicate with a computer (which will be decided later on) on the platform (Platfrom Computer).
We are looking forward to receive your further contributions.
References: Computer HW : http://www.mini-box.com / http://store.ituner.com/ituner/viamo.html
Operating System: . . . ???
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Thanks to all contributers. Within this sub-thread we will further investigate how to implement communication subsystem between Base Station and Platform Computer.
[Communication between Base Station and Platform Computer]: During the initial testing and debugging process the Base Station and Platform Computer will communicate with each other via wireless ethernet. We are expecting the wireless networks to wors fine within 50-100m radius (line of sight) without any special antenna and/or power amplifier. Later on the we are planing to have longer range (slower) two-way radio modems.
We are looking forward to receive your further contributions.
References:
Wireless Ethernet (Long Range): http://www.x.net.au / http://www.freenet-antennas.com/index.html http://www.pacsat.com.au / Radio Modems (Long Range) : . . . ??
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H-Bridge Driver Circuits: ================= Stamp-Controlled High Power H-Bridge 30v 30Amp 900W http://www.parallax.com/dl/docs/cols/nv/vol2/col/nv52.pdf . IR3221 Fully Protected H-Bridge for DC Motor 5.5v to 35v 20A http://www.smyrph.net/~david/motors/ir3221%2020A%2015mohm%202internal+2external%20FETs.pdf
High Power 24v DC H-Bridge motor driver circuit (Current rating =?) http://www.pmb.co.nz/downloads/dgc_old_scp.pdf
H Bridge Speed controller http://www.mcmanis.com/chuck/robotics/projects/esc2/speed2.html
Power MOSFETs: ============ IRF2804 40v 75A RDS(on) 2.0mOhm http://www.irf.com/product-info/datasheets/data/irf2804.pdf IRF1404 40v 202A RDS(on) 0.004Ohm http://www.irf.com/product-info/datasheets/data/irf1404.pdf IRF1010E 60v 84A RDS(on) 12mOhm http://www.irf.com/product-info/datasheets/data/irf1010e.pdf IRF3808 75v 140A RDS(on) 0.007Ohm http://www.irf.com/product-info/datasheets/data/irf3808.pdf IRF540n 100V 33A RDS 44mOhm http://www.irf.com/product-info/datasheets/data/irf540n.pdf IRF3415 150v 43A RDS(on) 0.042Ohm http://www.irf.com/product-info/datasheets/data/irf3415.pdf
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