EMI !!!

Ive almost finished Xen now, and have been giving it a test run. Everything runs fine until I use the saw at the back, then the signal is lost. The problem is its run off a starter motor trigger by a solenoid. Unfortunatly, my attempts to get into the thing to clean it have been unsuccessful as the bolts refuse to budge. Admittedly, I havent fitted ANY suppression yet, although i will be doing tonight (will a 10,000pf capacitor across the terminals do it?) How do i suppress the spark inside the solenoid? and any other tips? All my sensative electronics are inside aluminium boxes.

btw, the starter motor is completely isolated from the shell and chassis as it is mounted on a non-electically-conductive material, and also how do I supress relay contacts too?
Many thanks in advance

http://www.technobots.co.uk/Technical/Guidance/EMI%20and%20how%20to%20deal%20with%20it.pdfhttp://www.technobots.co.uk/Technica...o%20deal%20wit h%20it.pdf

Try that.

Cheers Ian :)

Ive also noticed that the supply to my electronic equiptment drops a bit when large motors are switched on. Could I use a capacitor across the supply terminals to my electronics to help relieve this problem, and if so what type and how big?

Matt

Whats the problem, a relay not changing over? Generally what people do is put a 4.8volt receiver battery inline so as to up the voltage for the relay. THe will only need to be charged once in a blue moon.

nope, the onboard computer crashes. It works fine up until i use the saw, so Im presuming the problem is due to either a supply voltage drop when running the saw or interference from it. Im planning to suppress all motors, solenoids and relays and fix the supply drop problem (although the supply does go through a regulator anyway) and hopefully that should sort it :)

http://homepages.which.net/~paul.hills/Emc/Emc.htmlhttp://homepages.which.net/~paul.hills/Emc/Emc.html

might be of help

It might be worth a try to put in about 4.8volts extra. It may just solve that problem.

hmm, maybe but i dont want to risk blowing the DC-DC that runs the PC.

Heres an idea, i dont know how practical it is but I am assuming the computer requires little juice. WOuld it be possible to give it its own battery supply?

yeh, the computer uses less than 50watts as theres no mechanical parts besides the cooling fan (which is connected directly to the battery anyway)... all drives etc are solid-state. Ill give it a go on its own seperate battery and see if it is just the voltage drop thats the problem, and if so ill try a capacitor across the supply to sort of even it out.

The problem will be conducted interference. The large surge of current required by the starter motor causing the computers supply to disappear monetarily.

What fixes these problems nearly 100% of the time is to run your power (motors & weapons) on a separate battery entirtely to the control and radoi electronics. The electronics then controls the power stuff via opto-isolators. NEVER connect the two together electrically - they must be isolated.

This has been the solution to numerous people who have emailed me for help with this kind of problem. My site that gary cairns pointed to above contains information on how to achieve this, with links to sections on optoisolators.

Good luck!

cheers guys...
Diodes fitted to all solenoids and relays, suppression capacitors fitted, no problems so far :S fingers crossed!

btw, since the weapon motors use solenoids to trigger them and are not pulsed, could i fit extra suppression capacitors to them to provide more of a buffer? Its the starter motor im most concerned about.

starter motors draw so much current that any other circuits will have its share of the battery leeched.

The best suppression for starter motors I found were the drive mechanism from a circuit breaker - if you take one apart there is a set of copper plates with air gaps - connect both motor contacts to the 2 outer plates.

Also, to diminish the amount of current the motor wants to take, allow the motor to rev in excess of 10,000rpm - by the use of gearing - and it will not only speed up very quickly but generate a lot of internal resistance, hence reducing current flow.

Starter motors are designed to develop a lot of power under heavy load. I seem to remember from old conversations about starters that they were dangerous to run unloaded, as without an engine to turn over they could run too fast and potentially break due to centrifugal forces. That might be worth remembering if you gear them down too much.

Also, what sort of computer are you using? Most Intel-compatible systems are run with very tight tolerances and will crash easily if fed with noisy power supplies or too much EMI. PICs are much more tolerant if you can do the processing you need with them.

Yeh, its a pentium. fraid I cant use pics for my purpose really. the computer recieves its signal over a wireless network link. The reason I went for this approach is;
A) I program for PCs
B) I wanted the robot to have the potential to eventually have an autonomous mode with a bit of AI (such as judging where a target is, or if its a mobile target, how its likely to move, and also by following the movements of a target, determine the best way to attack, such as by cornering it) which would be a pain with PICs
C) With the onboard camera, I was thinking maybe setting up a http server on the computer so you could control the robot from anywhere using a web browser (provided the robot is in reach of an available access point of course)
D) Using this method, I also have a huge amount of outputs, both pulsed and simple on-off triggers for upgrades
E) and finally, I was also thinking of having a mobile-phone mode where i could actually ring the robot, the robot would pick up and ask for a security code, type it in and away you go, using the keys like you would for playing games on your mobile, using tone-recognition.
Even tho i probly wont get round to doing some of my ideas and most of them have no purpose anyway, i like to have the posiblity of doing it if i want :)
btw, its more like just a home project than a combat robot.. although Ive begun making my featherweight combat robot and have plans for a light/middle (depending on how the weight goes... still in the brainstorming process at the mo for that one :) ) so i might see some of you guys soon :) although the lack of car is a bit of a problem too at the mo... but im working on that lol

Is it a Mini-ITX system by any chance? I run one of those as my fileserver. You can get in-car power supplies for those at mini-itx.com, they should run other motherboards as well provided they dont need much power. They must have to deal with quite a quite a lot of EMI from the ignition system so might be better for running off the same battery as your motor, although Id still recommend going for a separate battery if you can.

Aye, you hit the nail on the head... Its actually a compaq i found in a skip, which had all the features i needed on the motherboard. so i stripped it down, fitted it inside an aluminium box, bought myself a solid-state hard-drive, a wireless nic and a dc-dc converter, and bobs your uncle. Yeh, it has its own battery (well, it shares it with the wireless video system too)

(Message edited by pyromatt on August 14, 2005)