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#25 vs. #35 chain


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Phyrexian Robotics



Joined: 31 Aug 2012
Posts: 7
Location: Athens, Georgia USA


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#25 vs. #35 chain

I'm using 2 EV warrior motors (essentially huge-ass scooter motors) in the drive of a featherweight. The end product should be a fast drivetrain-centered pushbot with large (~20cm) wheels something like vendetta.

Using the team tentacle torque/AH calculator, I determined I needed somewhere around a 7 or 8:1 reduction to get the speed, torque, and current draw I want. I was originally going to use #35 chain for the reduction, but due to the size of the wheels and sprockets I could feasibly use, I would not be able to achieve the reduction I needed in a single stage.

I can't decide whether I should use #35 chain and a 2 stage reduction or #25 chain and a single-stage reduction.

#35 chain is stronger and less likely to skip, but a second reduction stage adds a second potential failure point to the drivetrain and takes up weight and space. #25 chain would be weaker, but it would be lighter, simpler, and more compact.

I have seen both #25 chain and #35 used in featherweights, but since the drive I am using is more typical of lightweights than featherweights, I was wondering if #25 chain might be marginal and using #35 chain would be worth the added weight and complexity.

Post Tue Sep 25, 2012 10:02 am 
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Nick
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Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW


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You can use #25 chain for the first stage as the torque will be lower there. I don't like large single reductions with chain; the extreme difference in sprocket sizes means the motor sprocket only has a few teeth engaged, increasing stress and the chance of losing the chain. If you go single stage, add an idler sprocket to increase the chain wrap around the smaller sprocket.

Post Tue Sep 25, 2012 10:39 am 
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Daniel
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Joined: 30 Aug 2005
Posts: 2729
Location: Gold Coast


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I would use #35 and two stage reduction. Vendetta and Avenger always have problems with the large reduction #25 chain setups. Most of the problems is at the large sproket side and I've spent a lot of time trying to keep the chain from derailing at that end. However even when the chain stretches I've never had a problem with skipping, my chains seem to hug the sprockets. They'll derail rather then skip. Larger size chain with low reduction sprockets is the way to go. Vendetta has been redesigned with gears rather then sprocket, but I can't afford the rebuild for a year

Post Tue Sep 25, 2012 11:45 am 
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Phyrexian Robotics



Joined: 31 Aug 2012
Posts: 7
Location: Athens, Georgia USA


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Thanks for the info. #35 2 stage reduction it is then.

Post Tue Sep 25, 2012 12:05 pm 
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Phyrexian Robotics



Joined: 31 Aug 2012
Posts: 7
Location: Athens, Georgia USA


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Also, do you know roughly what the top speed of Vendetta is? Since I've only build ants and beetles before, I don't have a baseline for how fast a "fast, pushy wedge" should be in a featherweight. I was originally planning a top speed of about 25kph. For most events I would prefer faster, but the "arena" at the closest event that runs featherweights (Robot Battles in Atlanta) is an unenclosed raised platform, making all sides a pushout, so I would need more precise control than raw speed in that environment. Needless to say the local venue is not full combat! Laughing

Post Tue Sep 25, 2012 12:20 pm 
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Daniel
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Joined: 30 Aug 2005
Posts: 2729
Location: Gold Coast


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I have no idea. Confused Our arena is 4.8m square and I guess it can get from one side to the other is 1.5 seconds, so maybe 12km/h. Maybe it can do it in 1 second, but I'm not confident to say that. But the current version is a very crappy pushy bot. Its more of an annoying, boring brick and truthfully I hate it.

Post Tue Sep 25, 2012 12:34 pm 
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