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Electronic Speed Controller Tech - DIY & Commercial
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Knightrous
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Joined: 15 Jun 2004
Posts: 8492
Location: NSW


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Even though I haven't explored the full potential of the 08M PicAXE chips, I'm looking at shifting up to the 18X. It seems a lot easier to do multiple functions, has plenty of room for code and I can then put mixing into just a single chip for my whole speed controller!

I'll just give the linear regulators a go for now. I'm using a LM350T regulator, if you know anything about that or have some warnings, let me know Cool
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Post Fri Jan 07, 2005 10:12 am 
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Spockie-Tech
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Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


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Only what I already said.. rememebr they can only go down in voltage, not up.

If you want 5v, or 12v, your better off using a 7805 or 7812 (the last 2 digits is the output voltage) regulator, since they dont require any external resistors to set the output voltage, so are heaps easier to use. just attach voltage in, ground, and out comes the voltage you want (Vin > Vout+2),

If you need some weird voltage like 13.8v or 6v, then the adjustable (LM317/350) series are appropriate. but for 5, 12 and 15 the 78xx series are cheap, easy and reliable.


The 18X is a more powerful chip than the 08m. I used the 18x in the relay controller that was driving Vincent at RoboWars. it works quite well, I may have thought of a new technique to improve the failsafe safety and immunity to noise at the same time, but still have to do some testing.

The PicAxe's arent that fast however (compared to a machine code PIC), so I dont know if you will get good response time if you attempt to do dual PWM outputs as well as mixing on multiple channels at the same time. The 3 channel relay decoding works well enough, but I think ots just on the edge of keeping up. if you try and do mixed PWM in the code of a single chip as well, it might get a bit sluggish.
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Post Fri Jan 07, 2005 10:23 am 
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Knightrous
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I believe the 18X can be over clocked to 8mhz and 16mhz, would this help prevent 'lag' with out killing the pic axe. I guess for now I'll just play with the 08M's. They will do the job, just means I have to buy an external V-tail mixer. Also, something that has just struck my mind, if I have failsafing on each 08M which controls on controller per side, would they both failsafe at the same time or will one side shut down Razz This sounds like fun!
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Post Fri Jan 07, 2005 10:29 am 
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Ajax
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Joined: 17 Jun 2004
Posts: 298
Location: Sydney


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The problem with over clocking the picaxe is that the main commands that you are wanting to use are affected.

PWMout
If you use a period of 249 which is 4Khz. once your've over clocked the picaxe to 16Mhz then the period of 249 freq will change to 16Khz.

Pulsein.
I have no idea what will happen tio this command. It could cause you alsorts of problems.

and you need to remember not to use any of the commands that don't work once overclocked. As changing the clocking freq in the program will also change the period freq of the pwm.

So you would need to do some testing to see what the affects will be.

Have a look at the picaxe manual1: - Getting started.
Appendix B
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Post Fri Jan 07, 2005 2:06 pm 
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ffej
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Joined: 22 Jun 2004
Posts: 595
Location: Kurrajong, NSW


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Just threw my RS80D on an oscilloscope and confirmed what I had thought was the case for a while, its not giving me the full duty cycle when I hit full stick. It seems to max out at under 90%, which is a bit annoying, because that means that I will never get the full power from the motors. Mucking around with the calibration seems to do nothing at all to the duty cycle.

I was wondering, does the IBC do the same thing? Being based on the OSMC design, I figure it might, but then, the RS80D uses the uRRC 2.0 for the reciever to H bridge interface when the IBC uses the uMOB. If anyone with an IBC (or any other PWM controller for that matter) and an oscilloscope (Brett? Im guessing you would have already tested it before) can run a few tests I'd be interested in knowing the results.
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Post Fri Jan 07, 2005 2:14 pm 
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Spockie-Tech
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Location: Melbourne, Australia


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The IBC will definitely reach 100% duty cycle if your radio is set correctly to provide the full 1/2ms pulse. I've seen it on the scope many times..

I'm surprised the uRRc v2.0 doesnt, they were both written by the same guy. You say the RS-80 calibration proceedure doesnt affect it at all ? How about fiddling with the end-points in your radio ?

Does the RS80 use the HIP4081 chips to drive the Fets ? Perhaps its deliberate as some Fet drivers cant maintain the gate charge voltage from the charge pump and can only do 95% on time and require an off-cycle every now and then to allow them to keep up the high side drive voltage (or so I've heard)
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Post Fri Jan 07, 2005 2:48 pm 
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