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prong
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Joined: 19 Jun 2004
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hmmm i think servo switching is pretty underrated. While i am biased towards servo switching because that is what i use to save money, i do not think it has all the disavantages you mention.

that said proper speed control would be nice, but when i am building a couple of bots i need them to all together to cost less than the IBC, so servo switching is the best way for me.

Servo switching is pretty easy to make, a bit of aluminium, drill a few holes, screw everyhting on. The first one you make will be the hardest while you get all the postitions right, but after that you just copy the first one.

As for prone to mechanical failure, i have not experienced this at all, and i am using 20 year old servos and microswitches, all allready heavily used. I find there is not much to break, the switches might fuse is you try and run too much current through them, but an IBC will blow if you try and run too much current through it, they are both about setting it up correctly for your use. And if a spinner etc hits the actual servo switching, then sure it most likley will fail, but so will anythign else. The most important thing is having a good servo switching design, so nothing can get jammed or damaged from g forces and i have found there will be no issues.

hmmm variable speed control, this is servo switching's real disatvantage, as you can run a motor very slowly with a speed controller. To a small degree you can provide some speed control by rapidly turning your switch on and off, but this is not much of a subsitute. In the end i do not mind though, i have grown up driving non proportional tank control radio control cars, and it is all about the timing, you go full power and let it off at the right time and you can be very accurate, it just takes a lot more practice.

With mixing throttle and steering, after having a think about it i see no reason why you cannot set up your switches to do this, it is more complex than tank control though. That said i prefer tank control, after driving radio control cars with tank control as a kid is just feels like the natural way to drive, and i think it gives you greater control.

Failsafe, while you can buy those hobby ones or cheaply make your own i do not think it has to be that complex. I have a radio control plane that uses a servo to adjust flaps on the V tail. These flaps are not actually hinged as such, the ends just bend, and they are quite springy. At full extend the servo can move the flap all the way but it has to fight the springyness. If you turn off the controller or lose signal the spring in the tail has enough power to push the servo back to almost its starting position. If this idea was applied to servo switching you could easily have a spring etc that when the reciever loses signal then the servo is returned to the centre postition, automatically turning off the servo switching. This also has the bonus that it would return the servo even with reviever power failure, and because the servo has to work harder to move it will help damp slight interference. Unless i missed something here this gives a very simple and cheap failsafe that passes the failsafe test.

With braking i guess you mean electric braking? as in shorting of the motor wires when they are not being driven to give breaking and more accurate control? My servo switching setup atm does electronic breaking, how it is wired means that is the motor is not being powered it has its contacts joined. This is just done using standard 3 pin microswitches, two per servo. I have found that the electric breaking gives much greater control of the robot.

I do not understand what you mean by no weapon control? Why can't the servo switching turn a weapon on and off the same as it does to the drive motors? I use 4 channel servo switching on my robot, two of those channels are two way weapon control, allowing me to raise and lower the drill arm and run the drill forward or reverse. The only robot i can think of off the top of my head that would benefit from proportional weapon control would be pinscher, to accurately control the grip speed. I am sure there are others but it seems that most weapons are on or off type things, or driving something slow where you only want full speed anyway.

I think that the only real disatvantage of servo switiching is lack of speed control. Also in theory they are more vunerable being a mechanical system but i have yet to experience any problem. While speed control would be nice, i think the money spent on one speed controller would be better spend on making a few extra bots. Also in no way am i against the IBC, it is a very succesful speed control system, just for my use i find servo swithcing best, so i thought i would give my reasons why Smile

Post Mon Oct 25, 2004 4:44 pm 
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Nexus
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Joined: 17 Jun 2004
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Pinscher would benefit from speed control but a suitable ESC would be expensive so hard to justify.
Only had one relay fry on it so it would need to handle at least 30 amps at 24 volts.
Can see a big advantage when lifting and controlling other bots but as far as closing speed it might be a disadvantage.
Example being the grabbing of Arachnophobia. THat move was basically instinct and was done by a couple of quick flicks once it was acelerating.
The whole move was done in about half a second so I wonder if it could be done the same with speed control, but for sure it would suit but would guess it would come in handy for subtle movements more but having that sort of control would be very nice indead
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Post Mon Oct 25, 2004 6:22 pm 
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chrisjon65
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Joined: 15 Jun 2004
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servo switching will do fine for any bot Very Happy ,i dont understand what brett meant when he said if you dont have a failsafe you cant compete in the robowars events Confused
this being the case am i to assume that a 'no ibc no compete' rule applies Confused .......unless there are other ways to satisfy the organisers...
please explain !! Wink
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Post Mon Oct 25, 2004 6:33 pm 
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Valen
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Joined: 07 Jul 2004
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nothing about an IBC
basically when you turn the radio off your robot must stop, everything.

do that however you will.
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Post Mon Oct 25, 2004 6:36 pm 
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chrisjon65
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but is an ibc the only way to do this ????? Very Happy
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Post Mon Oct 25, 2004 6:42 pm 
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Knightrous
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I think it's a valid rule, if your robot is not safe when it loses radio signal, it shouldn't compete. Why should other people have to risk themselves? No one has said you must have an IBC to compete, only a fully working failsafing system, which means you either spend the cash and put $30 of failsafing per channel, or you buy an electronic speed controller with it all built in.
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Post Mon Oct 25, 2004 6:46 pm 
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Nexus
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I am no expert at this at all but had an idea that might work.
I have been using the fairly cheap IMX mixer which has a failsafe builtin.
If 2 servos where mixed together to give you tank steering then would this setup be acceptable as if the IMX faisafes then wouldnt it return servos to their deadband? maybe it doesnt, who knows.
Just a cheesy thought, sorry if it sounds stupid.
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Post Mon Oct 25, 2004 6:47 pm 
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Valen
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Joined: 07 Jul 2004
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no
you can get modules like this
http://www.silvertone.com.au/access.htm
SILVERTONE FS-2. IN-LINE FAIL-SAFE UNIT FOR RECEIVERS.

possibly cheaper than that

a thaught, if the servo switcher mob use one servo as a master on/off then they should only need the one failsafe switch. you *might* be able to get away with putting something like a throttle return spring on the servo that controlls your master switch. then have your radio set to command that servo to full on position.
when the signal from the radio stops the spring will overpower the servo and cut power to the bot. QED
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Post Mon Oct 25, 2004 6:49 pm 
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Spockie-Tech
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Joined: 31 May 2004
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As Jake said, I dont mind how you do it.. As long as you can demonstrate that your robot will not do anything without an active radio link I'm happy..

Spring returns on the servo's, Micro controlled Relays, Commercial Hobby Failsafe units, PCM Radio's (with built in Failsafe), Electronize Controllers, Drill Triggers, whatever..

The test will be for you to activate your drive and weapon and with them active, turn off the radio Tx.. the drive and weapon should immediately shut down and stay shut down, if you can pass that test, then you are fail-safe..

Just to clarify a point, despite being the designer, I personally dont care whether people buy an IBC or not.. I get a small per-unit royalty from Jason (who does all the hard work of production and distribution etc), but its a tiny amount and even if sales of them tripled I still wouldnt be excited by what they earn me. As it says in the manual, we designed them because we wanted them and then a few other people asked for one so we started selling them.. its not part of my retirement plan believe me.. Laughing

So dont worry about any ulterior motives forcing people into using IBC's.. In fact, I'd almost prefer they didnt since then I wouldnt have lots of people relying on a widget I designed to win a comp for them putting pressure on me..Rolling Eyes Although its nice to think that I've helped others get started in Bots in some small way..

The Failsafe rule is there because thats the international standard for competing robots, as well as being a damn good idea. There have been some occasions that I have been very grateful that rule exists I can tell you.. Shocked
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Post Mon Oct 25, 2004 6:59 pm 
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prong
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Joined: 19 Jun 2004
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I think the problem is people do not understand that the failsafe does not have to be expensive, or be any sort of electronic controller. The failsafe rule is a good rule, any robot fights with any sort of insurance should make having a failsafe a must, and in general it is a good idea for everyones safety.

Personally i have nothing against the IBC, it seems to be a very succesful unit, but for my sort of use it is not viable because of the cost, I undersand Brett that you do not make the IBC to try and make profit, i am a pennyless uni student so i tend to make my every dollar count, and for me servo switching with a cheap simple mechanical failsafe is what i will use.

The reason i keep mentioning a mechanical failsafe, as in spring loading the servo horn, is that until i posted about it the other day it did not seem to have been considered or talked about, and i think it is a very simple and cheap way to failsafe servo switching, better in fact than hobby failsafe units. It also means that building a legal to compete servo switched robot can be done very cheaply, increasing in my opinion the appeal of servo switching for anyone wanting to build in a tight budget.

Post Mon Oct 25, 2004 7:15 pm 
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Big AL
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Joined: 16 Oct 2004
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how long should i have made my bot i was thinking round about 40cm long by 30 cm wide by 20 cm tall are these good dimentions. what should i use and how thick tubing should i use as my frame

by the way what type of disks can i use for a spinning disk i was thinking of useing a steel plate with teeth could i use it is organised events
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Post Mon Oct 25, 2004 8:49 pm 
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colin



Joined: 16 Jun 2004
Posts: 102


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quote:
Originally posted by Big AL:
how long should i have made my bot i was thinking round about 40cm long by 30 cm wide by 20 cm tall are these good dimentions. what should i use and how thick tubing should i use as my frame

by the way what type of disks can i use for a spinning disk i was thinking of useing a steel plate with teeth could i use it is organised events


All of these questions don't have a right answer, they are all design choices. you need to look at what you want to acheive and then make choice's accordingly.

minimum size will be defined by how much you have to fit in, maximum size will probably be limited by weight.

you could have no frame at all... or a strong frame with light amour.

spinning disk are interesting... you could choose from heaps in that area

Post Mon Oct 25, 2004 8:56 pm 
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kkeerroo
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Joined: 17 Jun 2004
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Location: Brisbane


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Don't worry about dimensions at first. Collect all your parts and lay them out in the way you want them on a bit of card. Then move them around to see if you can get something better. Make sure to leave plenty of room for wires and such things. Then trace around the parts and use that to build the frame. I used to use CAD progarms to do this, but have been using this method the last few months. Also weigh all the parts before you assembly them to make sure you don't go over weight.

As for disc's, I have never seen a spinner not aloud into a compitition because of what it was made of. I have entered a spinner made of a bike wheel with steel bracket bolted on for teeth.
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Post Mon Oct 25, 2004 9:02 pm 
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