Earthwormjim's Stuff

[earthwormjim]

Nothing will be able to outpush that, so we're going to have to rip it up

Ah yes,but you are forgetting that purple robots naturally repel spinner attacks! Don't they??

[BeligerAnt]

... purple robots naturally repel spinner attacks! Don't they??

Well, Ouchie's purple feather boa seems to have warded them off so far...

[earthwormjim]

Told you so!!

[earthwormjim]

And the other robot I have been working on is a spinner.I started by seeing if I could balance a piece of aluminium,which seemed to work ok,so I tried another,then I shortened one end,and bolted a piece of steel to the shorter end as a counter balance,which worked relatively well.Then I decided to just keep it simple,and just cut a chunk of stainless steel,and use that,which seems to work quite well,but if the bar is too heavy,then the wheels dont get enough grip for it to be driveable,so a stainless steel rear bumper provides weight at the back to give the wheels enough grip.Here are a few pics of various stages of the experiment!...

First bar,aluminium,140mm dia.


Same bar,shaped and counterbalanced with steel.




Construction of final design.




Left to right...First 3mm SS bar was too heavy,second 2mm SS worked,but was too flexible,third 3mm SS bar is pretty good from what I can tell.




Rear steel bumper adds weight over wheels.


And here is a quick vid of it...http://www.youtube.com/watch?v=FUeWAZeC ... ture=g-upl
Cheers Jim.

[Shakey]

Best looking spinner ever.... Seriously good work! And scary too.

[peterwaller]

Some how Jim you seem to be able to achive functionality with style.
Your sheet material working skills are second to non.
Look forward to seeing it at an event, not necessarily fighting my robots.

[earthwormjim]

Thanks alot! The main chassis is Aluminium,which is very easy to bend,hence the carbon/fibreglass sheet reinforcement.
I am looking forward to seeing if it works well in the arena.

[earthwormjim]

Hey guys.Are brushless motor stats accurate,if a motor states that it is 1000 kv,then does it really spin 1000 times per minute per volt supplied to it?
In which case at 11.4 volts it spins at 11400 rpm?
In which case,with a 100mm dia bar,the end is spinning at 60mps,or 132mph???
I was just wondering if a reasonably accurate tip speed could be calculated?
Cheers!

[BeligerAnt]

I don't think the kv value holds for all loads. I suspect it's quoted for the motor on its own with no load (gives the most impressive figures!). As you load the motor it must spin slower, because it's doing more work (losing more energy). Any bar will have air resistance, even if not quite as much as a proper propeller. Best way to find out the actual speed is to use a tachometer.

One other thought comes to mind ... it might be possible to use spectrum analysis software running on a PC soundcard to analyse the frequency of the motor sound, which should be equal to the speed in revs per second. I've not tried this, so I've no idea whether it would work, but it might be an interesting experiment to try.

[earthwormjim]

Thanks Gary.I have just ordered a multirotor tachometer from Hobbyking,for £7 delivered!!!I couldn't resist!
http://www.hobbyking.com/hobbyking/stor ... meter.html