Picking your brains.

**turps** · 22nd October 2009, 18:52

Hi all,

I've recently re-immersed myself in all things robot combat after several years and I've decided I want to build a featherweight. My favorite robot when Robot wars was on TV was Killertron and I'd like to build a machine loosely based around the same design but perhaps with 2 wheels rather than 6, a lower ground clearance, an axe capable of righting the machine and most importantly a different colour.

After looking at a few threads on this forum I have a few ideas of how to do things and I've spotted a design for an axe using a 300w electric scooter motor that looks pretty awesome.

Here are a few questions that I have though:

If I were to use Magnum 775 gear-motors for the drive and a scooter motor for the axe, what batteries would be best?

What ways are there to control the axe without using a servo linkage? I don't really want to use a speed controller either.

Is lime green any better than pink?

Charlie.

**joey_picus** · 22nd October 2009, 20:33

Welcome to the world of robotics Charlie

I can't really comment on the batteries, I can however advise on the axe controlling...if you don't want a speed controller the best way would be to use something like a Team Delta dual ended R/C switch, wired to switch two bigger relays that actually switched the axe motor (I suspect a 300w scooter motor draws a bit more than 12A at stall) and use microswitches wired to the R/C switch to turn off the axe at each end of its travel to stop the mechanism wrecking itself. Agent Orange used something a bit like that I believe, only with more servos and bodging, and it'd be fairly cheap as well (the RC switch would be the most expensive bit, about Â£30 with shipping, the rest could be picked up from Maplins or similar for fairly little)

As for colour, personally I favour flourescent yellow for when you just can't use subtle shades

22nd October 2009, 22:02

hi i'm new here so dont ask me much!

**typhoon_driver** · 23rd October 2009, 13:15

I'm not familiar with the drive motors, could you give a link with their specification?

**RogueTwoRobots** · 23rd October 2009, 13:23

http://www.robotpower.com/products/magnum775_info.html

**Ellis** · 23rd October 2009, 14:07

I was thinking about using those motors too, but since I had let slip the whole drill motor thing to my dad, he favoured the cheaper, not as good option :x

Sorry that was totally off-topic, I just felt like a rant on my dad, lol.

**calumco** · 23rd October 2009, 19:32

hey,
this isn't really a related responce to your thread lol, but my dads the same when ever i buy robot parts i've got a general rule where i always say it cost half the price of what it actually cost.

its alright for him to waste large amounts of money going to watch men kick footballs around a large grassy area, but its frowned upon when i buy expensive robot stuff.

**typhoon_driver** · 23rd October 2009, 22:11

My parents don't ask anymore.

Ok batteries, you have a number of options.

- SLAs - very old school. You would be looking to the batteries designed for alarm system back ups. I wouldn't even bother if I were you though, heavy and difficult to get current out of.

- Nimh/nicad racing packs - I think this is probably your best bet. Two 7.2V packs in series will happily run your drive plus axe mechanism.

- A123s - This would require you to build your own packs from cells. A 4 or 5 cell pack would happily run your machine and provide you with higher currents.

http://cgi.ebay.co.uk/10-Pcs-New-A123-3 ... 2a01f91692

Not too difficult to build your packs if you follow the information provided by John Reid on the terrorhurtz site.

- Lipo - I wouldn't bother. You won't need the currents these can provide and they're pricier.

**turps** · 25th October 2009, 20:04

Hi guys, brilliant advice, thanks. I've just realised a small mistake I've made though. The magnum 775 is only 14.4 volts where as most of the scooter motors are 24 volts. I wouldn't really want to over-volt them too much as they aren't cheap. Is there a 24v version that I've not found?