elobire's build thread

**team_orr** · 19th August 2010, 12:32

looks really good so far

, the frame looks a bit on the large side though

**RogueTwoRobots** · 19th August 2010, 12:40

35 seconds of axe video, followed by two-and-a-half minutes of music and black screen? :P

Nice prototype. The axe head does look quite heavy but to get a bit more power out of it, remove the paint tin and let the axe swing through 180*, that will improve its performance.

Think of it as a segment of a spinning disc; the faster it spins, the more energy it will have. So the more travel your axe has, the more energy it can build up before impact.

**elobire** · 19th August 2010, 15:05

the hammer i had on their was too heavy for me to use, so i replaced it with a small hatchet. it swings alot better now that its under half as heavy.
the paint tin was their because it couldnt lift the axe up.
also the frame was one i made just to test out the drive, i made it large because i didnt know how much room i needed for the axe.
going to start work on the frame this weekend, got a sheet of aluminium for the base just need to find some thinner stuff for the rest of it.

will post a video of the new axe tommorow.

**RogueTwoRobots** · 19th August 2010, 15:35

Look forward to seeing the new video then with the lighter axe.

One thing to think about though, which may or may not be a problem; you said you needed the paint tin to support the axe because the motor couldn't lift it from all the way back?
That may pose a problem when it comes to self-righting. If the motor can't lift the axe when it's a heavy hammer, it's probably not going to be able to lift 13.6kg when you've been flipped and need to turn yourself back over.

What's your gearing ratio on the weapon? Were the batteries fully charged? And are you running the motor at the voltage it will be running when the robot is complete? It may be okay, because when self-righting, the arm will be acting as a lever turning the weight about the pivot point of the axe mechanism rather than lifting a weight at the far end of the lever when firing the axe as normal, but just something to check.

**elobire** · 19th August 2010, 15:51

Originally Posted by k_c_r

Look forward to seeing the new video then with the lighter axe.
What's your gearing ratio on the weapon? Were the batteries fully charged? And are you running the motor at the voltage it will be running when the robot is complete? It may be okay, because when self-righting, the arm will be acting as a lever turning the weight about the pivot point of the axe mechanism rather than lifting a weight at the far end of the lever when firing the axe as normal, but just something to check.

i dont know much about gear ratios, but i know that the driven sprocket has 68 teeth (il have to check) and the drive has 12 teeth.
and i dont think the batteries where fully charged in the video, but they where not completely flat either. going to get new batteries as well, the ones i have are too heavy, i only bought them because i was low on money at the time.

**RogueTwoRobots** · 19th August 2010, 16:06

That's a ratio of 5.6:1
Quite low I would have thought for an axe but it depends on what you've got to work with sprocket-wise I guess. Depending on sizes etc you could get quite a ratio increase by changing the 12 tooth sprocket to a 10 tooth (6.8:1) or 8 tooth (8.5:1) but that's just me thinking out loud really. If you're happy with how it performs though with the lighter head (by what you've said, the batteries seemed fine) then that's okay.
Don't worry too much about what I said regarding levers. Again that was me mainly thinking out loud; I'm not even sure if what I said was 100% right

**elobire** · 19th August 2010, 16:20

Originally Posted by k_c_r

That's a ratio of 5.6:1
Quite low I would have thought for an axe but it depends on what you've got to work with sprocket-wise I guess. Depending on sizes etc you could get quite a ratio increase by changing the 12 tooth sprocket to a 10 tooth (6.8:1) or 8 tooth (8.5:1) but that's just me thinking out loud really. If you're happy with how it performs though with the lighter head (by what you've said, the batteries seemed fine) then that's okay.
Don't worry too much about what I said regarding levers. Again that was me mainly thinking out loud; I'm not even sure if what I said was 100% right

what you said helped me understand what im doing a bit more actually.
im quite happy how it performs at the moment, although the chain keeps coming off, but i think thats because my brother sprayed WD40 on the chain and sprocket, along with the chain being loose.

also im going to have to redesign my robot slightly and have the wheels on the outside. i think some of my designs where a bit hard to built anyway.

**joey_picus** · 19th August 2010, 18:44

You definitely want to make sure the chain is properly tensioned - what sprang to mind when reading that was ORAC, which had either no tensioners at all or improperly tensioned chains, with the result that they both fell off against Killertron (and then a certain amount of fire ensued)

I think people have used skateboard wheels as tensioners before, or failing that just a small sprocket on a sprung arm would work.

**elobire** · 22nd August 2010, 15:01

got some images of the robot so far.

will post a video of the new axe when i upload it.

also their is a problem with the chain, for some reason the sprocket isnt straight, this is causing the chain to jam and be looser when the axe is back.
the chain has only came of once, but i think thats because its hitting the motor mount and knocking the chain off. the drive sprocket also came off so had to refix it.
also the motor doesnt seem to be able to lift enough to flip my robot if its flipped. so il eventually buy a new motor and axe (think the handles causing the problem). il also be able to get a motor with the sprocket on it, i think that may be causing a few problems.