Hi all,

I've decided to join the rare species called "the WA bot builder."
Here's what i'm thinking:

Robot name: Lizzie

Weight Class: Feather 13.6 kg

Drive : XU-1 Drill motors & Red wheels

Chassis: Compressed foam

Armour: 3mm Bis-alloy

Weapon: EV Warrior powered 1kg axe, reduced by V-pulleys by a factor of 10.

Batteries: 3x 2.2Ah SLAs

Tx, Rx: Spektrum DX-6

Control: Some

Currently I have the XU-1s mounted in half a frame.

I've weighed major items, and it comes pretty close to 12Kgs, which leaves me with that magical "air" armour for the moment.

I'm a bit worried abouit the current pull of the starter motor. It might total the batteries, (they weren't all that healthy to begin with so they are expendable.) Oh well, one way to find out.

Last edited by Fish_in_a_Barrel on Sat Feb 02, 2008 11:28 am; edited 1 time in total

Not all starter motors are created equal, old heavy series wound non-geared with plain bushes vs. more resent PMDC ones with planetary reduction etc.



The problem is switching it to reverse it without burning up your last few weight points.

4 Jaycar 100 amp SSR’s would do it but that starts to get heavy and expensive.

This would work a lot easier in a 60 lb lightweight design.

I used an Oatley 250w gear motor in a feather weight hammer bot and it has as much power as the bot can handle, a 6 pole planetary Bosch starter in a feather would be very entertaining to watch.

Good luck with the build and yes don’t think about any Armour you definitely wont have any weight left over for that.

I've hacked up the starter motor today, (yep an old series wound one,) so that the axe handle will make a 180 degree revolution. Larger swing angle means more energy into the axe.

Although I'm considering a hammer instead of an axe for more of a smashing action, opposed to a cutting action. I haven't seen to many holes put into bots via an axe in the videos.

With any luck I'll weld up a motor mount tomorrow. Then I'll find out how much room I have left for batteries and controllers.

For my controller I think I'll just hack some servo pot's for a PWM reference voltage. I'll stick to the KISS principle.

I won't make any promises, but it looks like I'll be making the trip to Robowars 4. I've given myself until christmas to have Lizzie finished, otherwise she won't be coming with me, (following advice not to bring anything untested to a comp.) I'll see how it all goes.

i dont think youll be shoving holes in robots unless your fighting a .5mm thick steel shelled bot or something. to get it right id just make it as long as you can make the axe with it still being strong and then give it a test and keep on loading on the weight until you see it start to noticably slow.

i think the axe head doesnt really matter really. spike would have more point loading but id assume in the end both deliver the same energy into the opponent.

oh and wrt wiring i believe you can do it with a pair of limit switches and only two relays. ive still got to actually test it out, but my shoddy wiring ability thinks it should work.
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You probably have this covered already but its usually messier reversing the rotation on series wound motors.

Just reversing the polarity wont work.

The starters off early Magna’s and VL comodores should be cheap and plentiful, they are very light for their power and have 6 ferrite magnets and planetary reduction.

You would still need to bring the leads out but current draw would be a lot lower than a series motor with no reduction.

No point trying to run a car starter off relays.

SSR’s minimum on PMDC geared motors and heavy old car solenoids on series motors would be my thoughts.

I will keep that in mind Rotwang. At the moment I'm taking things one step at a time. If everything is working, eg. moves, attacks and doesn't fall apart, then I'll start making improvements.

I appreciate your comments, and if I'm happy at the end, then the next thing to improve will be the control system (most likely to an IBC) and changing to a PMDC starter motor. Then I may even have some weight left to armour the IBC.

Does anyone know if Windhammer still visits these forums?

The most recent post from Windhammer was about a month ago regarding selling an IBC.. but if his email is still current you can send him an email or Private Message (PM) and he should be notified.
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He's already sold it, jeff now has it. I can contact him via msn if you need anything.
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YEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAH

I've sent him a PM last week, but I haven't heard anything. I was just after someone local for a bit of testing/advice. I noticed that the WA thread in the state forum died off about 2 years ago. I did talk to Big AL but he doesn't seem to keen at the moment.

There doesn't seem to be any other Perth people frequenting these forums, unless someone can point them out to me.

Probably because its a long way to come from Perth to Melbourne for an event and most of the WA builders who have been through here have been young fellas without the resources or experience to put on an event themselves
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I guess that puts me in charge of the WA event/arena building comittee?

Its nowhere near as much fun as fighting robots, but unfortuntely you need a place to play before you can play with these machines.

You can start out with some thin polycarb sheets across the front of a garage.. If you want to invite the general public, things get a lot trickier
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I was trying to find the easiest way to make my series motor run backwards. So I decided to run it in series forwards, and parallel backwards.



R1 is the motor solenoid, rated for the motor current (probably higher than 200A). The other relays will probably be mosfets.

The reverse power supply will probably be mosfet PWM to limit the current, and I will probabbly need to supply the field windings and armature windings seperately, because they will have different resistances. However you can see the basic idea.

Oh, there will also be an interlock to prevent forward and return turning on at the same time.

Can anyone see any mistakes before I spend money on it?

thats a lot of switches and diodes .

an easier way to make a series wound motor go i reverse is to put a full wave bridge in series with the filed windings .i think i have a diagrme some where i will post it when i find it . i have done it sucesfully on smaller blower fan motors but you would need some big arsed diodes for a starter, i would probaly go with a H bridge of small mower or motor bike type solonoides for reversing direction these could be controled by two relays .

You are going to need some prety good bateries to run this thing , im not even sure that some of the expensive nicad packs that some of us run would cope with it for long.

The diodes will come from 35A bridges, and 60A relays are only $8. The reason that I have done it this way, is to get full power forwards. Or as much power as the batteries can provide.

For this model I will be using SLAs for the current draw. If I was to move to cell packs it would probably be A123s which should be able to carry the current. Well they would be able to if I moved to a PMDC stater.