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Spockie-Tech
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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
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Post Thu Jan 06, 2005 10:07 pm 
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Spockie-Tech
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From: TeamVertex

I'm enjoying it I believe it's only hard because I don't have a large amount of electronics knowledge, only what I've learnt from Andrew and a few other people online like yourself and Ajax. Other then that, this would have to be my first major piece of electronics work yet.

I'm going to fix a lot of problems in one go by just building two regulators using LM350T 2v-32v 3Amp regulators. One will be powering the picaxe to give it a smooth supply of 4.5-5v and the second will be for the relay coils so that I will be able to switch them on and off even if the battery drops to 5-6v or lower during surges and such. We had some very strange side effects from todays testing, some of it shouldn't have even worked, but it did . I'm itching to get the v0.2 prototype made now!

The final battle ready versions will hopefully hand 70amps by using two-three fets with some 60A/70A automotive relays from JayCar. They should failsafe, just not as good as the IBC
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Post Thu Jan 06, 2005 10:08 pm 
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DumHed
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Joined: 29 Jun 2004
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has anyone done the servo hack style controller with any success?

Somewhere I have a bag of dead servos, and if I can make some basic controllers out of them I'll stick them into older bots like Woktronix, while I concentrate the real stuff for the new bot.

I played around with a servo board today, but it seems to jitter a lot, and basically oscillate around the middle point when it should be still.

At first I thought it could be due to interferece from the motor, but when I replaced that with a couple of LEDs it still did the same thing.

Input voltage was about 5.3v at the servo so that should be fine.
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Post Thu Jan 06, 2005 10:20 pm 
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Spockie-Tech
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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.. Shocked
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Post Thu Jan 06, 2005 10:20 pm 
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timmeh
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Are there relays that can be switched on way to make say a motor go forward and then switch it another way to make a motor go backward then all you got to do is use two servos to switch 4 microswitches?

Or do you have to just have 4 relays?
Btw would a 30amp realy handle two motors?
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Post Thu Jan 06, 2005 10:36 pm 
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Knightrous
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I don't like the sounds of regulators already Sad They never tell you anything like that on the datasheets from national companies. I'll give it a go with a regulator for the picaxe chip at least.

I have one technical question based on todays "weird testing effects" Smile I didn't put an earth lead from my radio to the picaxe along with the signal wire. Talking with Andrew, the Pic shouldn't have been able to read any of the pwm pulses from the reciever because there was no way for the pwm signals to drain back to the negative on the reciever. But some how, but the high heavens, it was working 90% of the time when I told it to work Razz

Why did this work Very Happy
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Post Thu Jan 06, 2005 10:47 pm 
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colin



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was there a common ground?

Post Thu Jan 06, 2005 10:53 pm 
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Knightrous
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Not between any circuit on the reciever and the speed controller. Current theory is: Aliens did it Razz
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Post Thu Jan 06, 2005 10:55 pm 
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Ajax
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If your lucky it can work when there is on common ground plane.

But the problem is the next time you turn it on it may not work at all.

one way to solve this problem is to connect the neg of the signal out connector to the picaxe ngative.

another way is to conect both negative power sources together

It is not recomended to have two different negatives that are floating.

If it is required then an Opto coupler is going to be needed.
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Post Thu Jan 06, 2005 11:06 pm 
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Spockie-Tech
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Did you have more than one wire connected between the two ?

If you had two signal wires connected, chances are (due to the radio PPM transmission encoding format) that only one of them would have been putting out an active (high) pulse at a time, and its possible that the other (being in a low/off state) could have been acting as a signal return for the one that was high.

feeding current back up a signal line isnt really an approved method, but given that most chips can sink (absorb) more current when low than they can source (supply) when high, its unlikely that the high output would be able to overload the low output and pull it too far away from ground (0v), so it probably would have sort-of worked.

Only explanation I can think of at the moment. if you only had *1* signal wire connected between them, then we're back to aliens again.. Wink
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Post Thu Jan 06, 2005 11:07 pm 
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Spockie-Tech
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Re: The regulators. Remember the Water-Electricity analogy.. while there are a few cases where it doesnt apply. (wires with holes in them dont leak :lol), in more cases than not its a very good analogy.

Using a water regulator, its easy to lower the pressue of a watersupply with a few simple discs and springs. If you want to *increase* the pressure however, now you need a complicated compressor to push the liquid uphill, trap it, and squeeze it. Regulators are like that. its easier to release pressure (as heat). To boost the voltage takes some funny buggering around with complicated compressors and such machines

You will find that info in the data sheet, it just wont be worded as simply as "the input must be higher than the output". It will most likely have a table of specifications of minimum and maximum input voltage ranges to be kept within if the output is to maintain regulation as set. you just have to learn to read the table.
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Last edited by Spockie-Tech on Thu Jan 06, 2005 11:20 pm; edited 1 time in total

Post Thu Jan 06, 2005 11:12 pm 
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timmeh
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I wonder if they are the same alians that blew up my ibc 3 times Shocked
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Post Thu Jan 06, 2005 11:13 pm 
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Spockie-Tech
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Re: Tim : The Relays

You can do forward and back relay control with just 2 relays.

They are called SPDT relays. SP = Single Pole, DT = Dual Throw. The have a single center contact (pole), and two possible rest positions (throw). The center can connect to either one rest postition (normally open), or the other (normally closed).

You connect the "pole" of the #1 relay to one side of the motor, and the pole of the #2 relay to the other side of the motor. Then you connect both relays normally closed conctacts to +12v, and both relays normally open contacts to ground (0v).

Then all you have to is turn one or the other relay on to go forward or backward. If you leave them both off (or turn them both on), the motor goes into braking mode) since both its sides are shorted together,
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Post Thu Jan 06, 2005 11:17 pm 
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timmeh
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What amperages do they come in?

And how expensive are they?
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Post Thu Jan 06, 2005 11:24 pm 
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Spockie-Tech
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you can get them from oatley electronics for $3 each and they are 30/40 models. they will generally drive an un overvolted drill ok before the eventually stick. hit em with 24v and they stick really quick.

Jaycar have a 60/70 amps model with wider spades that is about 7/9$ and I dont know what it will take before it welds shut.

Havent tried it, but I wondered if the same sort of capacitor they put across the car-points of old (back in the years before electronic ignition) to stop welding might help stop relays sticking when hit with arcing inductive loads (like motor coils)
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Post Thu Jan 06, 2005 11:31 pm 
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