What those? Those are only the small test springs.
I looked at snail cams during initial design but came to the conclusion there would be too much friction for the sorts of opponent-into-the-roof forces I had in mind. The forces involved require ball bearings to tension and release and i didn't find a nice way to do it with snail cams where the bearing rides the cam and provides constant force during the tensioning stroke. I've already shown that my leadscrew system can do the tensioning, so the last question mark is the quick release.
Mon Mar 13, 2017 7:37 am
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
Can't wait for the first spring VS CO2 flipper match . _________________ Australian 2015 Featherweight champion
UK 2016 Gladiator champion
Mon Mar 13, 2017 7:47 am
chunkulator
Joined: 27 Jul 2016
Posts: 219
Indeed. If I can get it all to work reliably it should be lots of fun.
Mon Mar 13, 2017 7:53 am
Knightrous Site Admin
Joined: 15 Jun 2004
Posts: 8511
Location: NSW
You can mitigate the majority of the friction using a roller bearing on the follower.
For this kind of design, I always look at the snail cam design because you can make it compact, changing gear ratios and springs can give you variable force and reload times and you can use a powerful brushless motor that only needs single direction control to both reload and trigger. _________________ https://www.halfdonethings.com/
Mon Mar 13, 2017 8:28 am
chunkulator
Joined: 27 Jul 2016
Posts: 219
All good points. I suspect the chassis I have built is fundamentally the wrong shape for a snail cam, so I don't think I can easily try it out. I optimised the hinge geometry fairly hard for the leadscrew. However for V2 it's probably worth serious consideration. I suspect a different shaped bot entirely would be the way to go with a hinge point in front of the snail cam or a 4 bar arrangement.
Mon Mar 13, 2017 5:28 pm
Cpnwolfe
Joined: 29 May 2012
Posts: 454
Location: Rockhampton/qld
I am working on a snail cam bot we can compare in june _________________ Creative Instigation - Build Something Awesome!
Seems there will be quite a few flippers at vivid. Maybe I should also get my shaker bot Mr Tickles together to give them all a run for their money.
Mon Mar 13, 2017 7:52 pm
chunkulator
Joined: 27 Jul 2016
Posts: 219
Successful test fire of the quick release mechanism today. Possibly a little underwhelming on a housebrick and a half (around 6 kilos). At least the dog was scared of it.
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
Was that using the larger springs? _________________ Australian 2015 Featherweight champion
UK 2016 Gladiator champion
Sun Mar 26, 2017 7:18 pm
chunkulator
Joined: 27 Jul 2016
Posts: 219
Unfortunately yes. Maybe I need to stretch them more to make them really sing.
Sun Mar 26, 2017 7:29 pm
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
Yeah - I was just thinking pre-tensioning might help _________________ Australian 2015 Featherweight champion
UK 2016 Gladiator champion
Sun Mar 26, 2017 7:39 pm
chunkulator
Joined: 27 Jul 2016
Posts: 219
I bought some bigger springs off Ebay and test fired 6 kg of housebricks about 1.5m into the air. Ok, so it's no Citizen Flips but this is starting to look like a somewhat dangerous bot.
I now have a big brushless motor mounted on a homemade gearbox to tension the springs. I'm pretty proud of this gearbox given that it's built by hand out of 3mm steel only using a jigsaw, angle grinder, drill press and crappy gasless MIG welder:
Next I need to cut some holes in the sides of the SHS for the leadscrew lugs and fine tune some of the gear meshing. Then I'll be ready to test tensioning the big springs in situ in the bot.
I tried tensioning up it with one spring in it but it got jammed because the frame got pulled out of shape. I'm going to need to spend some time making the frame more rigid before I can reliably flip I think.
Sun Apr 09, 2017 7:29 pm
chunkulator
Joined: 27 Jul 2016
Posts: 219
I welded cross members in place on the frame and it's nice and rigid now. Once I stripped down, realigned, and thoroughly greased the mechanism I got it reliably tensioning the big springs:
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