Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
* V belts are the most tolerant if you can find or make the pulleys. An A sized pulley is the most common for featherweights, get an AX type as the yare more flexible and slip less. V belts still don't liked to be misaligned though...
* Timing belts break unless you oversize them compared to most bots. They strip if under tensioned and large timing pulleys can be pricey. UK builders sometimes use them with an un-toothed pulley to allow some slip - seems like it is very sensitive to tension. I like the ones with metal reinforcing chords.
*Multi-V belts are probably the best solution but you have to make your own pulleys (or get Aaron to make them ) _________________ Australian 2015 Featherweight champion
UK 2016 Gladiator champion
Well I have the tools and material. Just not the skills.
Thanks nick.
What about sources of belts. Better of with sized belt and movable mounts or custom sized belt to suit? _________________ Steven Martin
Twisted Constructions
http://www.botbitz.com
Fri Jun 19, 2015 5:06 pm
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
Its hard to find custom sized belts - those orange urethane ones I use are good but the material is hard to get. You can also get these 'powertwist' belts:
They are very tough and non-slip but expensive and very stiff - they don't like to go around the sized pulleys we like to use. It is probably easier to mount the motor on slots so you can tension the belt. Timing and multi-V belts can have an adjustable idler pulley to do the tensioning; much easier than moving the motor.
Ebay is a good source of all types of belts or most local engineering shops will stock V belts and maybe timing belts. Aaron has a good supplier for the multi-V belts.
Making a V pulley is surprisingly easy. Glen or I can supply the dimensions and all you need is a parting-off cutter to make the V. _________________ Australian 2015 Featherweight champion
UK 2016 Gladiator champion
Fri Jun 19, 2015 5:23 pm
Glen Experienced Roboteer
Joined: 16 Jun 2004
Posts: 9481
Location: Where you least expect
Lots of the UK guys and US it seems go with a timing belt on the motor then a plain flat belt style pulley on the weapon, seems to work, but needs tension to work, any tweaking of the frame and it would struggle to spin. I'm not a fan personally
Two timing belts - i had really good success with that in old demon, but you have zero slip which sometimes the brushless doesn't like.
Multi ribs - Based on aarons drive pulleys they work really well, even with next to no tension. downside is they are a little wide compared to a V belt but the trade off is the pulleys can be smaller diameter as they aren't very deep. Would use them for sure.
V belts - my fave. Easy to make the pulleys, they have mega grip if you want them to (decimators weapon has zero slip basically), tension themselves to a large degree and are very cheap.
I can't recall the size i use in demon and decimator but its smaller than an A section belt. 10x5.5 i think, have never broken one (ignoring the last nats when it got cut in half by the blade hehe) or worn any out. They cost about $5 from small parts. _________________ www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz
Fri Jun 19, 2015 5:26 pm
Ellis
Joined: 21 Jul 2012
Posts: 129
Location: Shopshire, England
Almost all builders here use the timing belt approach. Toothed motor pulley, smooth weapon pulley. In my experience tension isn't actually all that critical, no more or less important than with other belts. Teeth on the motor end guarantees it's always being driven and smooth pulley on the weapon ensures slippage - works very well.
Importantly though most of us are using HTD belting, usually 15mm (standard cut) wide HTD5. The things are incredibly robust and outperform other options. HTD stands for High Torque Drive. Dual 9mm (standard cut also) wide belts might be an option. _________________ Online store - www.ranglebox.com
Pulsar and friends.
Fri Jun 19, 2015 8:39 pm
maddox
Joined: 21 Dec 2006
Posts: 786
Location: Belgium
The timing belt/smooth weapon pulley setup works fine for us. Nebelwerfer uses a T05 10mm , and Valkiri a T05 25mm. Steel core.
A sleightly more expensive variant has kevlar core.
But yes, you need to take a wide one to do the job.
Main advantage of the timing belt is the same as for the poly Vbelt, they can take small pulleys.
Tension. Not as critical as most people think. Due the high speed of the brushless motors the belt tensions itself.
Unfortunatly, with a smooth ali pulley, some extra is needed, in our case, it's Belt Spray.
Sticky stuff on that pulley gives a huge increase in grip, but not enough to eliminate any slip.
Fri Jun 19, 2015 9:55 pm
Glen Experienced Roboteer
Joined: 16 Jun 2004
Posts: 9481
Location: Where you least expect
Interesting about the self tensioning of the flat belts, would not have thought that would be the case at all _________________ www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz
Fri Jun 19, 2015 10:23 pm
miles&Jules Experienced Roboteer
Joined: 19 May 2010
Posts: 3973
Location: ipswich QLD
Is it true that sorter belts are less likely to slip because of stretch?
In the ali version of judge mental it had a long 60cm timing belt….that seemed to get looser more often, but maybe had more power….with the steel version of judge its belt was only 20cm long and didn't seem to slip but also didn't seem to have as much power…think it was the same ratio to…maybe thinner belt though. _________________ Miles Blow - Julie Pitts
www.mulesfilm.com.au www.wombokforest.com.au
-Pickasso- Vivid Sportsman champion 2015
Sat Jun 20, 2015 10:20 am
Ellis
Joined: 21 Jul 2012
Posts: 129
Location: Shopshire, England
A shorter belt will stretch less overall
relative
to a longer belt of the same spec, yes, though a section of belt will stretch the same amount regardless of if it came from a long or short belt. If you imagine a 1cm segment of rubber band can stretch to 2cm long, a 5cm segment will stretch to 10cm long. Whilst longer appears stretchier it isn't, the elongation % is the same for both. Same for belts, it's additive.
Since in our case we're generally using the same pulleys for short or long belts it's good to keep them on the shorter side, so potential slackness is kept to a minimum.
In the case of HTD and other cored timing belts the stretch in the lengths we use is so minimal it's not worth worrying about.
Also yeah the way flat belts work here is that the yank from a brushless is so fierce it pulls the belt hard to tension it, as long as it isn't way too loose it works great. _________________ Online store - www.ranglebox.com
Pulsar and friends.
Sat Jun 20, 2015 8:47 pm
Jaemus Experienced Roboteer
Joined: 01 Apr 2009
Posts: 2674
Location: NSW
Urethane V-belt in Catastrophe per Glen's rework of the weapon drive, it's been faultless and not too sensitive to getting the tension exactly right, and you can allow that little bit of slip to save your burshless. _________________ <Patrician|Away> what does your robot do, sam
<bovril> it collects data about the surrounding environment, then discards it and drives into walls
Tue Jun 23, 2015 11:45 am
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