Featherweight Speedos

[big_nipper]

Just looking at the IBC and has anyone else noticed it says its got reverse battery protection. Judging by it circuit diagram you will get alot of smoke if you try that. Also (I may be wrong) but 50A continuous? Will need a very large fan. But as they are usually not used for more than 5 minutes and then never at full current for that long they should be ok.

Sorry but I dont know how to program those and not looked at the code, but i didnt think it would be too hard. All you would have to do is find the code that updates the PWM output and apply a log or exp function just before it.

*goes back to the bench to figure out why his dual speed controller doesnt work yet*

[fwsorg]

If Im honest, Ive never been very happy about putting anything much more that 20A through a TO-220 case. They just dont look up to it :-). Mark- I will be modding my IBC with a slightly larger, finned heatsink, and a little fan. Im a bit of a nut about things running cool, especially batts, considering the amount Ive just forked out for mine :s

The IBC does infact have Polarity protection. We had a competitor running at Robowars 2003, KO, 4 x 12v drills on 24v with a possibility of drawing over 200amps on a moderately large drain and it only got the IBC warm, that was with out a fan on the heat sink, and Tim was making KO push a fair bit, I know, I was able to get a beautiful view of two sides of the arena .

On both of our IBC that my team owns, we have small 40mm PC fans on them to have that extra bit of protection, expecially when running T2M with its 340watt winch motors (When you see your team mate who is around 80kg sitting on top of a feather weight doing over 5MPH in the pits doing a wheel stand on your feather weight, youll under stand why we have a fan on the IBC )

Brett was running BullDoze, a heavyweight on an IBC using wheelchair motors at 24v and it was getting fairly warm, but it with stood the punishment.

Ed, if your going to make up a finned heat sink, let me know on the prices you can get them made for, you might be able to sell them as IBC Upgrade part with fan attached

[fwsorg]

Will do that. If there is sufficient interest, I dont mind doing a small batch on the mill. It would only be fairly simple tho- anyone with a block of ali and a free hour (and a mill) could make one.

Its important to note that its the MOSFETs that get the abuse on the speedo, and its a rule of thumb that a reduction of 10 degrees at the junction of a semiconductor approximatelly doubles its life, and especially with people drawing 50A through those poor little to220 packages, cooling is important. For a few grams extra, a fan has got be to worth it. I have built a speed 300 motor powered fan, which really howls, and, once i stick it on my modded heatsink, should ensure long life and excellent performance- forgot to mention above that as the mosfet heats up, its on resistence increases, thus making it heat up even more- its all wasted power that could be going to your motors instead of damaging your mosfets.

Stay cool

Ed

Ive checked the circuit again and all I can say is if you think its got polarity protection then try it. The MOSFET are not protected (acording to there published circuit) and will generate a short across the battery. The only protection they have is before the voltage reg for the ICs. This should be made clear or someone will try it and be very dissapointed. If it does have a diode protecting it as it says it does then a diode at 100A with a 0.7V (at best) will produce 70W of heat!! Far more than you will get with just the MOSFETS and would take this power away from your motor. Again all I can say is try it but be prepared for the cost of repair.

[jim]

Ive just had a look at the circuit diagram available via robotcombat.com and I agree with Mark. If there is reverse polarity protection then its done by something not shown on the circuit diagram. The same document states that theyre reverse polarity protected though, so if they do burn when you accidentally connect them the wrong way round, I would expect them to repair it free of charge.

If anyone has a link to the source code for the IBC I will take a look at it - I cant find it on robowars.org.

http://www.robowars.org/docs/ibc-docs-v0.1.pdfhttp://www.robowars.org/docs/ibc-docs-v0.1.pdf

thats all there is i think

[knightrous]

Its only a cheap diode placed in the battery circuit, so if you do cross polarise, it will protect the main important parts of the board and only blow a small 15 diode which takes 5mins to unsolder and replace. Saves you loosing $$$ because the diode wasnt there.

You can infact short circuit the diode afew times with out it blowing, weve had one person do it a few times and they still keep working.

[leorcc]

Instead of starting a new thread I am going to bump this one.

Has anyone here got a Scorpion XL in their featherweight and what are your experiences with them? Good and bad reviews all welcome.