Is there any circuit that I can buy that will allow me to power my receiver from my SLA batts ?
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Is there any circuit that I can buy that will allow me to power my receiver from my SLA batts ?
Yes Its called a BEC Battery Eliminator Circuit
Basically it will take an input of a certin voltage and out put 5v constant. If you have a soldering iron and a farnell/maplin/rs/rapid electronics catelogue you should be able to build one very very cheeply.
http://www20.brinkster.com/antweights/5%20Volt%20Regulator.htmlhttp://www20.brinkster.com/antweight...Regulator.html
Here is a guide from my website. Its very simple and with 16v capacators will only work to about 12v but if you put in higher voltage caps you should be able to power it from 24v. However I do not advise this. I would advise using a 2 step regulator to first drop the voltage to 12v and then down to 5v. You can find the information for this here
http://www.teambigbro.co.uk/regulator.htmlhttp://www.teambigbro.co.uk/regulator.html
If you should prefer to buy one you can purchase a 4.5v regulator from technobots reletaviely cheeply (but not as cheep as you can make one):
http://www.technobots.co.uk/en-gb/dept_408.htmlhttp://www.technobots.co.uk/en-gb/dept_408.html
But if you want really no hastle and dont want to worry about anything else with it simply the best BEC out there is found here:
http://www.robotcombat.com/marketplace_elect_other.htmlhttp://www.robotcombat.com/marketplace_elect_other.html
This is expensive but is a mighty fine piece of kit.
Hope this helps you.
Regards
Ian
i have got the robot combat BEC and after 3 weeks of waiting it arrived on a huge box with it just rattling around in a bit of newpaper, and to top it all it doesnt work
make your own simon might be best
craig
Thanks guys. Think I will purchase one. Me and delicate circuits dont really mix. Im more of a blow torch than a soldering iron type of guy :)
Simon- Theres a diagram of how to make a simple 1 on the Bigger brother website...I can nearly understand it so it must be simple!:) and my team mate Ed wallace made one and it worked quite nicely...
Dave moulds
Team Turbine
Oh sorry - Didnt see your post there Ian.
Dave moulds
Team Turbine
I would advise against using a BEC. It may work for you, or you may end up with the most horrific EMC and radio comms problems imagineable.
I have conversed with many roboteers about this subject, and in conclusion, a rechargeable radio receiver battery is the best option, with a link that allows it to be recharged from the SLA.
If you have opto-isolated control lines between your receiver and speed controller, then using a BEC simply allows the noise to bypass the optos.
See my EMC page for more info about conducted interference. I think Ill add a section specifically on BECs and why theyre not a good idea.
Good luck anyway!
Hi Paul, Nice to see you back on the forum.
I have used a BEC succesfully in the past, with two linear voltage regulators and a ferrite-core inductor, but I now find I can run all the radio & logic circuits for several hours on a 9v PP3 battery . Its smaller than the BEC used to be.
Hi Jim, from the east side of Didsbury to the west!
Yes, the thing about the interference problems that BECs can introduce is that they are very specific to the robot they are used on, the wiring, position of screening materials, antennas etc. Theyll work fine on some machines and not on others.
Thats why I say generally, from the design outset, dont use them. However, if youve finished your robot and it works fine with a BEC, then thats great - dont take it out!
Adding series inductive filtering to the regulator circuit like you did will help to keep sharp transients getting through the regulators, but it wont cure problems much if youre already having trouble. Its amusing that your PP3 battery ends up smaller than the BEC anyway!
I said above that I would add a section to my website on BECs. Ive just looked and noticed that there is already a whole page about them there already!
Its here: http://homepages.which.net/~paul.hills/Emc/Bec.htmlhttp://homepages.which.net/~paul.hills/Emc/Bec.html
Just goes to show how large my site has grown that I cant remember whats in there!
http://www.koolflightsystems.com/ultimatebec.htmhttp://www.koolflightsystems.com/ultimatebec.htm
this will handle up to 3amps continuous and on the better versions 6v
Note that most commercial BECs are designed for RC planes that generally do not have 100 Amp electric motors. Our motors and cables tend to create a bit more radiated and conducted interference than RC planes motors!
I was trying to uses a 30A RC plane speedo to power the compressor but it kept cutting out. Also tried it on 24V set to half speed for 12V compressors but the BEC shut down at 18V so I cut it off. Although it worked on its own it would not work with the drive connected and had terrible interferance. Could have been something to do with not having a voltreg on it and powering the 5V side from the Rx battery. The speedo was rated at 6-12 Cells but the only limiting factor is the BEC, beyond that it will work upto a max of 30V where it would try and clamp the supply.
I still want a 12V compressor to work off a 24V battery that can be controlled from the Rx & a pressure switch. So Im currently building something. Surly someone else outthere must have already done this. If so how did you do it?
I was planning a 24v compressor driven system before I discovered that the motors/gear ratio made the robot uncontrollable so Ive since cut down to 12V.
However, when I was using 24V the method I was going to use to solve the fried compressor problem was to use two in series, hopefully giving a faster recharge time and definitely giving 12V per compressor.
Of course, this wont be an option if youve not got the space or weight which, having seen the interior of Big Nipper, seems likely. :)
My brother was lightening it last night while I try and fixup the electrics. Therere may be space but we dont have the weight. He lost 1.5kg, only another 2kg left. Mind you when we started the base plate on its own was nearly 20kg! And it doesnt help when the valve is nearly as big as the ram.
Using the IBC controller I few things came up. First was we bolted the heatsink to the chasis. As it turns out the heat sink is connected to the battery +ve. Big flashes when a ground lead touched the chasis. Problem solved by using insulating kits for the MOSFET that didnt have them fitted. It also turned out that the weapon channels can only switch upto 12V as there is a voltage clamp on it and I wanted to connected it to the 24V solinod directly as it could supply enough current. Actually I connected it anyway as the instructions didnt give a max voltage limit and the valve kept clicking every time the battery was connected and I thought the IBC was not working. It turned out be clamping it to 12V so I had 12V across the coil when off and 24V when on. This was easily fixed by altering the clamp to the battery voltage.
Back on subject. A range check with the BEC built into the IBC controller gave no noticeable reduction in range from using a 4.8V Rx battery. Although the IBC doesnt have opto-isolators on the Rx wires. Range was alot further than big nipper. That is without the Compressor running.
Mark,
If you want to drive a 12V solenoid from 24V without it overheating, try just chopping the 24v supply to it at 50% duty cycle. The average voltage will then be 12V and the solenoid will not overheat. This assumes that the solenoid is already rated for continuous 12V operation (check that - some are rated only for a few seconds, or require a chopped/AC supply anyway).
The chopping frequency must be high enough so that the solenoid doesnt chatter on and off of course - a few kilohertz should be OK (less than 20kHz may give you problems with audible screaming of the solenoid - thats up to you!).
You can use a MOSFET or BJT to perform the chopping. If you need a circuit I can draw one, but you may be able to work that out yourself.
Congratulations on getting the range with a BEC - I consider you lucky with that!
Paul, The solenoid is 24V but the compressor has a 12V motor. Same thing just need 10A at 12V but thats exactly what Ive now done. Got a PIC12C508A to get the signal from the RX and convert it to a PWM output through a MOSFET to the compressor motor. It also has a auto zero upon powerup for the RC input and a softstart function to reduce EMI from the motor. The pressure switch is then connected through an LED to another input of the PIC to light when upto pressure.
The PWM freq is only 2.08kHz but with 32 steps (only first 16 used upto 50% duty cycle) gives a smooth startup. This gives me 7uS for the PWM rountine and 8uS inbetween to read the Rx input with 16uS resolution. Now that was a challenge.
It seems to work ok so far.
Mark, well done - that sounds good. Do you hear any audible noise from the 2kHz chopped drive?
At low speeds yes. The output waveform shows clearly its in the discontinous mode but above around 10% the compressor is so noisy you cant tell anyway and it starts to enter the continuos mode. After its recieved 50 pulses within +/- 32uS it takes this as the zero position and theres a little subroutine that then sweeps from 200Hz to 1kHz and back with a 3% duty cycle to create an audiable tone to let me know its received this signal and is ready to turn on. To my suprise this actually moves the motor slightly but as its a compressor it doest matter.
If you would like a copy of the source code/circuit I can Email it to you.
Could I have a copy? Im just interested to see how you measure servo pulses. I did a similar thing a while ago, on the PIC16F871 but I should be able to follow the PIC12 code. EMail address is on my profile.
Hehe I see a bandwagon approaching... one two three hup!
Could you also send me a copy please? Im currently thinking about how Im going to do this and other peoples ideas are always handy. Ill probably make my first version a direction controller rather than a speed controller (i.e. bang bang controls with mixing) but then Ill expand it into speed control too.
-- Kev
Oh btw my email address is kevdgill at warm letters dot com. Thats my MSN ID as well if anyone wants to add me.
(Id like to see an email address spider interpret THAT one successfully.)
-- Kev
I bet the spiders do have trouble with it. I cant send to it either. Try this instead:
ftp://81.106.67.7/Little%20Axe/Little%20Axe.zipftp://81.106.67.7/Little%20Axe/Little%20Axe.zip
Hope it works.
Mark - Warm Letters = Hot Mail...? Sorry maybe a bit obscure.
-- Kev
Ive managed to download it from the ftp link and Ill have a peruse at some point. Cheers.
That went right over my head too Kev! Anyway, got the file via email, thanks Mark. It look reasonably similar to PIC16F code, Ill have a proper look at it tonight.
Hehe maybe I was in just too much of a weirdo mood (even for me) when I wrote that.
-- Kev
Speaking of embedded controllers (and since I cant think of a better place in the forum to mention this), Ive been browsing through my copy of the May 2004 edition of Doctor Dobbs Journal, and noted that it has a feature on using Game Boy Advances for nefarious purposes (Ive not yet read the article, but they seemed to be using one as an oscilloscope and a spectrum analyser).
As a complete system, they would seem like a cunning plan for a top-level receiver/control unit (assuming I stick some PICs in the way to handle the low-level stuff) - although I dont know to what extent a GBA would hold together in combat, even well padded and with the LCD (possibly) removed. I know my way round ARM processors, and using one in this form seems a reasonable alternative to soldering everything together from scratch.
Anyway, I just thought Id mention it, in case anyone found it interesting. (Im unsure whether its still on sale, but being a US mag its probably running behind in the UK.)
--
Fluppet
Andrew, does the writer of the article use the existing operating system in the GBA, or is the existing software completely thrown away?
I dont suppose the existing operating system is particularly suited to real-time stuff, and the graphics drivers are probably a bit overkill for our requirements!
Sorry about the delay. Ive now read the article, and its not entirely clear - they use an Xport (which sits in the cartridge slot and adds an FPGA and a promising number of i/o lines), but other than saying they use some gcc libraries to do text its not clear what of the OS they use.
Chatting to a friend whos implemented an infocom interpreter for the GBA, he says what operating system? You can apparently set up interrupt handlers for some things; I dont know whether this means the bottom page of memory is in RAM and you can set the entire interrupt handler from scratch (as you can on Acorn boxes) or whether they go through a dispatch routine, which would add a bit of latency. Doesnt sound like theres context switching to worry about, though; Im not sure whether you can turn the screen off to reduce bandwidth requirements, but Id have thought you could (if it makes a noticable difference).
It would be an interesting thing with which to experiment, and probably less of a faff than getting the two SA1100 samples Ive got soldered onto something useful (theyre uBGA). Even a 15MHz ARM 7TDM variant ought to be plenty to control a robot, given some PIC assistance - although I may be pushing my luck with using 802.11 as a control protocol without some serious buffering.
--
Fluppet
Speaking of GBA mods, the bloke at work pointed me at:
http://www.ngine.de/site/hamdoc/korth_gbatek.htmlhttp://www.ngine.de/site/hamdoc/korth_gbatek.html
- looks informative. (It seems as though theres a hard-wired interrupt handler which faffs for a bit before going to a user routine, so its quite a bit less responsive than an ARM is capable of being, but it looks as though its capable enough.)
--
Fluppet