Designing a Heavyweight

[Eventorizon]

[ATTACH=CONFIG]5438[/ATTACH]
I have built an ESC for Beta's weapon (Etek run off 14s lipo-60v) using these 200A bolt on terminal packages.
http://uk.farnell.com/ixys-semicondu...27b/dp/1427322

IXYS also do the same package with a higher rating also.

Damn! That is insane! Reminds me of the ESC's that were built for Tornado back in the day... but even bigger!

Grant, given Beta never aired on BB does that leave it open for a UK competition or is it still tied to Battlebots?

[grant_ploughbot]

It can compete on the UK scene where not televised as with all the UK machines who attended. They have been very good in being as flexible as possible for us. I will probably only bring beta out every now and then for testing, and it would need to be on a reduced power on a non magnetic floor. It may also punch holes through the UK arena floors so that will need to be tested.
I have since done a lot of testing with this ESC, which is taking 1200A for a short period, then 500A co Tunisia after that. They don't get warm so far.

[Rapidrory]

Those are some beautiful ESCs, however I'm looking to produce a slightly lower end PCB based solution, something to handle Bosch 750s and the like. I really need to research the layout of more controllers; anyone got pics of the insides of one of the lower end Wottys or something similar? My aim is to get it all fitting on at most a double sided 10cm x 10cm pcb, as then it can be printed cheaply in china. Hopefully further research will show whether that's possible or not..

[grant_ploughbot]

The Wotty uses smaller package 3 legged Fets rated to about 350A each, however due to the package size they're more like 80A each I would expect (hence he uses a number of them!).

[Rapidrory]

My setup at present uses large surface mount 340A fets with a package rating of about 200A... The 320A rating in this case just means lower on resistance so less heat, which helps. My fet drivers only supply a measly 125mA to the gates though, so i'll be upping that to the proper 1.2A H bridge driver chips that most other people seem to use.

[grant_ploughbot]

That should still be plenty. Although I'm using 2A drivers, a pair are run of a 63mA dc-dc converter and runs 3 Fets in parallel each driver

[Rapidrory]

Yeah, I'm also running a 63mA dc-dc converter and it barely gets warm, but it's more about how sharply it can switch the Fets; I'd imagine the 2A drivers switch the Fets a whole lot more quickly than my 0.125A drivers, given that the gates can take a couple of amps to switch at their full speed.. Another downside of my drivers is they keep dying after a few fights, and I have no idea why... They're the same used in TZ85s so I'll have to properly scrutinize their circuit layout to make good of the current batch of boards; I've already had offers for the lot of them and could use the money :P

[Rapidrory]

Bought one of those 24V 800W scooter motors for another project largely so I could have a look (I'm not paying so its fine :P )

Opened it up and it looks to be suitably beefy. It doesn't have a cooling fan and has fine mesh over the cooling holes so the only battle hardening it would likely need is some magnet retainers. Runs really smooth and seems to have plenty of power, but can't really make a judgement on that until I've fitted it to something. Certainly looks good for £50 though..

One thing I did consider is that the way the brushes are setup means that you could easily take a second set of wires out of the motor and run it off a pair of smaller ESCs then rather than one large one (something that is sometimes done for various larger motors).

[typhoon_driver]

Yup that's a motor

[Ellis]

Didn't realise those are 4 pole. Neat.

[maddox10]

That's a chinese MY1020. I'm not unimpressed with the build quality.
An annoying bit is the way you have to mount the bushes over the collector.
And of course, the feeble leads provided.

The magnets are the same size as those of a Bosch 750, to give a point of reference.

[Eventorizon]

Well, provided the magnets were retained/epoxied, that looks like suitable basic HW drive motor. Old Skool maybe but so long as its functional. You could even run it off a TZ85A :P I think...

[Rapidrory]

Well, 2 TZ85s wired to each set of brushes maybe... not so sure one alone would handle it under combat conditions :L

Also, as with a lot of motors the nut holding the sprocket on is reverse threaded... A fact which I forgot whilst I was turned it until the thread stripped The motor thread is fine though so looks like i'll just have to buy another nut.

[Rapidrory]

Ok, so that's weapons, ESCs, and motors covered... got a question on batteries this time (I seem to be hi-jacking this thread a little, but it's still more or less on topic :L)

What batteries would people suggest for a heavy? I'm talking mainly for drive here (though may be needing some for a spinner at some point). This would be using those 800W motors which for the time being I'm assuming perform similarly to Bosch 750s.

Batteries are one of the components that are hard to scrounge, so usually represent a large chunk of the cost of my bots.. as such I'm looking for something that's fairly cheap while not being unnecessarily dangerous. Currently looking at 6S 5Ah 20C Lipos, but am guessing you'd need 2 of them to provide enough capacity and current. Was wondering if that'd be good enough, or if there's a cheaper option..

[daveimi]

I got a couple of big sla's and a charger from component shop for fifty quid delivered if that's any help...