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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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Electronic Speed Controller Tech - DIY & Commercial
This Thread is for anyone interesting in learning more about Electronics in General and ESC's in particular to discuss such things..
To Kick it off, heres some messages moved from a Builders Thread.
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Its good to see someone having a go at making their own controllers.. I did it when I first got interested in robots (not realising what I'd let myself in for), and enjoyed the learning very much..
Like nearly everything, what looks simple at first glance proves to have a lot more to it than you first think, but by the time you are out the other end you can look back and go "Well, NOW I really understand how they work".
Which is sort of a major point of building robots anyway.. Enjoy, If I can be of any help, feel free to ask in a tech ESC thread where everyone can benefit
Earth Loops are a common problem in nearly all electronics. Audio, Digital, Radio, and Power, if you dont keep all the current flows going where you expect, then you can end up with the weirdest symptoms that can take hours to track down. Think of the current as a water flow, and voltages as pressures. If you have multiple paths for the water to flow through between different pressure sources, then transistors get reverse-biased, chips throw wobbly's, and power back-feeds can baffle you.
Try to have a single earth point that all different voltages are referenced to.. (this applies to robot builders as well, not just the ESC's). Dont allow current to flow through the frame, motor casings, radio receiver servo leads or anywhere unpredictable. return all grounds to a common point.
Depending on what you are driving your relays with, you will probably need a reverse-biased diode across the coils as well to clamp inductive-kick spikes when you turn them off. The negative voltage spikes can throw digital logic into unpredictable states and have you scratching your head. a diode across the coils will stop 95% of this _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Thu Jan 06, 2005 10:07 pm |
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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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Remember that normal ("Linear") regulators can only *reduce* their input voltage to a lower (regulated) one.
You need to keep their input at least 1-3v (depending on the regulator) higher than the output voltage that you want.. so for 12v out, you need to keep the input at least 14+ volts.
To increase a lower voltage to a higher one (called a "Boost" regulator), you need a much more complicated (and expensive) "switchmode" voltage regulator with the associated magnetic coils, high speed diodes and switching capacitors which works by pulsing the input voltage into the coils and caps and then smoothing off the resulting "spikes" (ringing) into a higher smoothed voltage than the input.
To be able to both reduce ("buck) and boost the input voltage automatically depending on whether it is higher or lower than the desired output voltage, you need an even more complicated "SEPIC" (Single End Primary Inductor Converter) design that can buck or boost as appropriate. This is what the IBC has, and by the time you include the regulator, coils, caps, diodes etc, it adds nearly $50 to the cost of your ESC.
Much Easier to just make sure your input voltage stays above 14v for your first design..
If you want to avoid blowups, it might be worth looking at some new FETs from International Rectifier (the same people who make the IRF1405 Fet), These new Fets are what Ajax is planning on using in his Fet power Switch, and I might start work on a new ESC design based on them myself once I've had a bit more of a read of the datasheet and made sure there are no "gotcha's" to using them.
They have in-built protection from Thermal Overload, Current Overload, and in-built high-side drivers (meaning you dont need a HIP chip). There are two types. an IPS0551 and an IPS5551 (low and high side). They're fairly pricey at around $10 each, but look like the might be worth it if they're relatively un-blow-upable.
Then again, for a first and simple ESC design, you're probably better off sticking with low-side PWM only and using the relay for reversing.
Enough rambling for now.. I just meant to tell you about the regulators.. _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Thu Jan 06, 2005 10:20 pm |
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