www.robowars.org

RoboWars Australia Forum Index -> Technical Chat

Sand casting a robot chassis
Goto page Previous  1, 2, 3, 4, 5, 6  Next

Post new topic   Reply to topic
  Author    Thread
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11729
Location: Sydney, NSW


 Reply with quote  

The shafts of outrunners are usually easily removed, So you could machine the sprocket's hub much shorter and get it TIG welded to the shaft to save space and make sure it never shifts. Set screws are always a bit dodgy - they come undone at the worst time.

After looking at your CAD, is there any reason why you couldn't save space by cutting a hole or a pocket in the top plate, just above the sprocket hubs? It looks like you already did that under the back of the motor - is the front of the motor in a pocket in the middle plate?
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Wed Jan 18, 2017 6:41 am 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 210


 Reply with quote  

If I don't shorten the sprockets, the "pocket" would need to go all the way through the top plate exposing the shaft at the top (which may not be the end of the world). But, yes, if I can shorten the sprockets then a pocket could ease the pinch by a few mm.

I also tried the Scorpion motor in CAD on my way to work this morning and it makes the whole thing much easier. I can fit everything without messing with the sprockets but it costs me an extra $100. I'll post some updates CAD screenshots later.

I was hoping to keep the sprockets interchangeable until I find the optimal gear ratio. But once I know that I could totally weld the (hubless) sprockets on.

Post Wed Jan 18, 2017 12:10 pm 
 View user's profile Send private message
maddox



Joined: 21 Dec 2006
Posts: 753
Location: Belgium


 Reply with quote  

Or have the shaft and gear machined from a solid piece of steel.

Post Wed Jan 18, 2017 12:37 pm 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11729
Location: Sydney, NSW


 Reply with quote  

Its definitely not the end of the world to have a couple of small(ish) holes in the top. Only axe and crusher bots have easy access to the top of other bots and we don't have many (or any!) of those active at the moment.

With that scorpion and similar sized motors, the internal shaft is often 8mm and steps down to 6mm to fit a propeller hub. Its handy to buy a short length of 8mm silver steel to replace the original shaft and that will make welding the sprocket easier & stronger.
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Wed Jan 18, 2017 12:40 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 210


 Reply with quote  

Good to know. That means I can use the 8mm ID sprockets i already have instead of ordering new 6mm ones too.

Does it matter if I use ground 4140 instead of silver steel for the shaft? I already have a bunch of that.

4140 requires special treatment when welding I've heard, but I'm not sure about silver steel.

Post Wed Jan 18, 2017 4:51 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 210


 Reply with quote  

Also a good suggestion Maddox. I suspect i may be able to cut a sprocket on the end of some 30mm round bar with my CNC machine if I can find the centre and then turn down the shaft. The welding route sounds more achievable with garage technology though.

Post Wed Jan 18, 2017 4:54 pm 
 View user's profile Send private message
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11729
Location: Sydney, NSW


 Reply with quote  

4140 should be fine - I only suggested silver steel as it is easy to get precision ground 8mm rods. 4140 is probably easier to weld to a sprocket too.
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Wed Jan 18, 2017 5:00 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 210


 Reply with quote  

Of course, the other solution would be a mount a tyre directly on the outside of the motor can if it had good bearings, which it probably doesn't ...

Post Wed Jan 18, 2017 5:18 pm 
 View user's profile Send private message
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11729
Location: Sydney, NSW


 Reply with quote  

Direct drive is a sure way to kill the motor! Even if the small bearings don't crap out, the motor can tear out the mounting screws or separate the magnet ring from the endbell
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Wed Jan 18, 2017 5:31 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 210


 Reply with quote  

Well that's clearly a bad idea then.

Post Wed Jan 18, 2017 5:43 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 210


 Reply with quote  

Turns out the Turnigy T600 motor is 6mm all the way through. I just pulled one apart. I can confirm that the shaft is removable though.

Oh well, I guess I can weld a 6mm sprocket to it.

Post Wed Jan 18, 2017 7:08 pm 
 View user's profile Send private message
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11729
Location: Sydney, NSW


 Reply with quote  

Luck of the draw Rolling Eyes Not that I am a Scorpion motor salesman, but on some motors you can see a taper on the shaft right at the front of the motor. If the specs say its a 6mm shaft and you see a taper, its a good bet that the shaft inside the motor is at least 8mm.
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Wed Jan 18, 2017 7:19 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 210


 Reply with quote  

Anyone got a good source for 15mm ID disc springs? Blackwoods, Konnect/Coventry, element14, eBay and even McMaster Carr seem to be no help. Some of them stock 16mm Bellevilles, which are much thicker than disc springs and don't seem to offer any give unless you're talking tonnes of earthmover or something. The only 16mm ones stocked at Blackwoods are made from 3mm thick steel and have no give whatsoever, for example.

I have a request in with http://www.erwengineering.com who seem to make them locally, but any other suggestions?

Post Sun Jan 22, 2017 7:41 pm 
 View user's profile Send private message
Glen
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 9465
Location: Where you least expect


 Reply with quote  

Yo, I've always heard them referred to as wave or crinkle washers.

http://www.smallparts.com.au/store/item/w0150t017016w3s400/washersspring3wavetype400gradestainless/

https://www.bolt.com.au/516-crinkle-wave-washers-steel-p-22796.html
_________________
www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

Post Sun Jan 22, 2017 7:57 pm 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11729
Location: Sydney, NSW


 Reply with quote  

I got some similar disc springs from MSC Industrial: http://tinyurl.com/jmw2c3t . If you can't find what you need, try using different search words: 'pre-load' might turn up something useful.
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Sun Jan 22, 2017 8:03 pm 
 View user's profile Send private message
  Display posts from previous:      

Forum Jump:
Jump to:  

Post new topic   Reply to topic
Page 4 of 6

Goto page Previous  1, 2, 3, 4, 5, 6  Next

Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

 

Last Thread | Next Thread  >
Powered by phpBB: © 2001 phpBB Group
millenniumFalcon Template By Vereor.