Mcmaster half links vs Vex half links

When designing our (no longer) offseason chain in tube drivetrain, I made the mistake of requiring an odd number of chain links. The design required fixed center to center distance (i. e. no tensioner), so we needed to use half links to get the appropriate length of chain. We first tried vex half links, but these had long pins that jammed in our 17t Andymark double sprockets. Mcmaster half links worked much better as they are the same width as regular 25 chain links (no cotter pin).

More importantly, make sure that you use center to center distances with even numbers of links, because half links reduce load capacity by up to 30%. It’s worth noting that master links also reduce load capacity by up to 30%, so replacing a master link with a half link isn’t a big deal (Source: https://www.diamondchain.com/wp-content/uploads/2017/03/TechnicalEngineering.pdf).

I suspect you won’t be happy with any half link in this application, but if you can find a way to make 16T sprockets work (regular sprockets with spacers for the wheels that just need a single sprocket, and fabbing some double sprockets for others) that will get you back to an even number of links.

Another option would be to run 1 link long, and cut access windows in the side rail to allow some sort of tensioner.

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The 16t sprocket is very clever but I don’t think we could manufacture the double sprockets and the ones that vex sell are too thick to fit in box tube. With some recutting we could add versablocks for tensioning, but we’re trying to avoid doing that if possible (gussets, belly pan, and drive rails are already cut and shop time is limited).
Thankfully this is just a prototyping / outreach drivetrain so it’s not going to be playing defense and won’t weigh more than 45 lbs, so I think we might get away with this.

Turns out Vex already makes what you need.

Electric Scooter Parts sells some 25 chain Link and a Half segments. One solid segment of links - no cotter pins or sub-parts to breakdown.

Item # CHN-25LHL

Use with the Rev or Vexpro tool chain to assemble it without masterlinks. These saved us in 2019 when a few numbers weren’t entered properly in our models and we needed to use some half links on parts we couldn’t get remade given time/sponsor ability.

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AndyMark also sells 1.5 links that you can use in lieu of half links.

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Sweet. Missed the memo they added that part in the last year or so.

Glad to see these are more commonly available at an FRC distributor.

While it spares you the hassle (and potential failure point) of dealing with the cotter pin, these links are still notably weaker than standard links and may also elongate/deform at an accelerated rate compared to normal links. Ideally they should be avoided whenever possible.

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Just noting that you can also buy them from Andymark