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Leith - Canberra


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leithal_weapon



Joined: 06 Jun 2016
Posts: 35
Location: Canberra


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Leith - Canberra

I'm starting to get the bits to build a small scale prototype for my robot which I want to enter to the Canberra competition in August.

So far the general idea is a mallet/hammer/axe type weapon that swings down and smashes the other robot.

Ive been looking at various mechanical designs of other robots, industrial hammers, medieval hammers etc for ideas.

I think I will start with a cam (or eccentric?) to wind the lever up with the hammer attached, before it lets it drop.

Similar to a Da Vinci design:


I'm also looking at ways to use springs, or maybe even bungy cord to provide more force.

Post Tue Jun 07, 2016 5:47 pm 
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pilleya



Joined: 31 Mar 2016
Posts: 89
Location: Sydney


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The main issue with a cam-style system is that it requires the use of either a sensor such as a limit switch or a shaft encoder. Without this it will be very difficult to make the hammer fall on demand or when you want it to, this might make things a bit more complicated for you.

Post Tue Jun 07, 2016 6:19 pm 
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seanet1310



Joined: 08 Nov 2006
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Location: Adelaide


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Limit switches similar to the setup used by the lifters shouldn't be too hard to fit in with a Cam design.

Or just swing the hammer like a madman
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Post Tue Jun 07, 2016 8:07 pm 
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evil_steve



Joined: 06 Sep 2015
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Or make a featherweight version of this.

Post Tue Jun 07, 2016 9:20 pm 
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leithal_weapon



Joined: 06 Jun 2016
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Location: Canberra


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I think a simple microswitch would work... havent got any ESCs or controller yet but seems like it should be easy to make a small circuit to stop the motor at right position.

Post Wed Jun 08, 2016 12:09 pm 
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leithal_weapon



Joined: 06 Jun 2016
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Location: Canberra


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Evil_steve, that looks like a simple design... maybe i should start with that and see if its strong enough...

I did find the orange hammer robot at the Vivid competition interesting, I think that was just directly driven via motor (with gearing?)

Post Wed Jun 08, 2016 12:11 pm 
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Knightrous
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Joined: 15 Jun 2004
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quote:
Originally posted by leithal_weapon:
I did find the orange hammer robot at the Vivid competition interesting, I think that was just directly driven via motor (with gearing?)


Warboy uses a 350 watt gearmotor (~9:1) which gives it approx 440rpm output on 24v. Mounting the hammer directly to the output was purely due to lack of time / cares. Due to this, it broke the keyways and sprockets twice during the competition.

I highly recommend isolating the weapon from the motor output or at worse, at least supporting the output shaft correctly.

TL;DR: Don't do what I did Wink
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Post Wed Jun 08, 2016 5:12 pm 
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leithal_weapon



Joined: 06 Jun 2016
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Location: Canberra


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Been figuring out RC controllers and ESCs.

Looks like Hobbyking will get me cheap 6 channel TX/RX, LiPo + charger. For ESCs need to wait for either bot bitz, or use hacked Hobbyking ESC if I cant get bot bitz in time. The sooner I get these bits the more time I'll have for playing. Discussion is in http://www.robowars.org/forum/viewforum.php?f=12

I tried assembling first 18V kmart drill, but found M5 grub is too small. Need to grab some calipers or wait for Ondray to figure it out on the weekend. Discussion is in http://www.robowars.org/forum/viewtopic.php?t=2212

Once I get that figured out I'll go raid kmart for 3 more.

Yesterday I also went Bunnings, got some red wheels™, a small compression spring (be useful to stop hammer if it swings too far), bolts, wood for prototyping and a small 2kg bricklayers steel mallet. I got the hardwood handle drilled out with friends drill press so it can swing on a bolt.

Today I visited The Green Shed, only useful stuff I found was two whole boxes of various length springs that I assume are from trampolines. There was also a 24V ozito hammer drill, not sure if useful but only $10.

Next I need to figure out some low torque drive system to either run a cam or even eccentric type drive for the hammer.

Looks like two main options are geared scooter motors from Motion Dynamics, or ebay winch motors.

Which would be the better choice? Im hoping for something simple to work with. Seems scooter motors need a chain (though I heard of some belt driven motor at the Vivid festival?), winch might be able to used more directly?

Post Thu Jun 09, 2016 3:22 am 
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leithal_weapon



Joined: 06 Jun 2016
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Location: Canberra


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evil_steve, looked at that video and couldnt figure out the motion, but then I found

http://www.robotwars101.org/forum/viewtopic.php?f=1&t=1754&start=210


I have no idea how one could make/find? something like that. Cool nonetheless.

Post Thu Jun 09, 2016 4:20 am 
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leithal_weapon



Joined: 06 Jun 2016
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Location: Canberra


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Very rough idea of possible mechanics:

Post Thu Jun 09, 2016 4:44 am 
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leithal_weapon



Joined: 06 Jun 2016
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Location: Canberra


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What has successfully been used to detect when to stop a cam? I can think of a few paths, using switches, a sprung piece of metal that touches something, using a hole with photodiode and LED, etc. You can even get proper rotary encoders cheap if you have small microcontroller to interpret them.

Post Thu Jun 09, 2016 8:01 pm 
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seanet1310



Joined: 08 Nov 2006
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Location: Adelaide


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the basic way would be a miroswitch setup. People have had surprisingly robust designs with a variety of weapons, can also be done with minimum electronics for the mechanically minded .

Photodiode and little micro idea has merit although not sure if anyone has done it in Australia at least. May need to consider the frame contorting and the resultant potential misalignment of the hole.

A simple hall effect is also easy to do with a magnet or two, chip and small micro.May be a with a largish magnet you may be able to make it a little more tolerant to misalignment than a photodiode.

You don't need the fine control a rotary controller would provide but doable with a little micro (

Reed switches wouldn't work due to all the vibration.
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Post Thu Jun 09, 2016 8:26 pm 
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leithal_weapon



Joined: 06 Jun 2016
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Location: Canberra


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I'm also looking at various options for motors.

It occurred to me that worm motors from cars/trucks such as the wipers, electric window, or even minivan door motors, might be handy to drive the cam since they are compact and would be easier to mount then winch motor. Also I should be able to get them easily around here for hopefully not too much $$$, so im not so worried if I break a few.

Has anyone used them for weapon drives?

I guess using a chain or belt I could increase the torque from them even more.

Post Thu Jun 09, 2016 9:13 pm 
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Ondray



Joined: 06 Jul 2015
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Location: Newcastle


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Haha! I am using a pair of electric window motors from my old Vovlo in Hellamax. They worked great! I used a chain to transfer power to the separate weapon shaft - mostly to isolate the motor shafts from getting damaged but also gave me the option of gear reductions.

I did have a nightmare getting the chain sprockets to drive from the motors, but they are durable, have a nice gear reduction, run at around 12V and are the right size/weight for featherweights. I'm guessing you could get a pair from an auto wreckers pretty easy.

They aren't the most powerful motor and the ones I used had a locking mechanism when they weren't being operated (I presume to stop the window sliding down when the motor wasn't operating)

Post Thu Jun 09, 2016 11:15 pm 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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Wiper motors used to be the go-to item for bot propulsion back in the day; they are relatively cheap and powerful. The main problem with most motors salvaged from cars is that the shafts are usually very short and have splines that make it difficult to attach anything to the shaft. Sometimes you can get lucky or it can be possible to replace the shaft on some motors (requires machining).

You can buy similar motors with very handy long shafts from the Robot Marketplace and possibly China.



http://www.robotcombat.com/products/AME-218-2003.html

The gears in these motors are not strong enough to take repeated shock loads but the snail cam idea should be fine.
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Post Fri Jun 10, 2016 8:43 am 
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