#25 double idler sprocket for 1/2" hex shaft?

I’m currently working on an FTC robot, and one of the “hey, I wish we had a…” items was a Double Idler Sprocket for #25 chain that had a 1/2" hex bearing (or 5mm hex, but I’m not holding my breath on that one). Does anyone have any idea if such a thing exists?

The purpose is to have a double-articulated arm with a roller at the end, but have all of the motors mounted on the base of the arm (so the arm isn’t supporting the weight of any of the motors). A common shaft would provide articulation for the “elbow” of the arm (using a sprocket fixed to the shaft), and the double idler sprocket would transmit power around the shaft and up to the end of the arm to spin the roller.

Does anyone know where I might be able to source said idler sprocket with two sprockets connected (double idler sprocket) that is for #25 chain that has 1/2" hex or 5mm hex bearings? Or is there a simpler way to do this that I’m not thinking of?


Could you attach two 1.125" bore sprockets together with screws and standoffs? These fit the 1/2 hex bearings. The smallest I’ve seen is 32 tooth, Andymark am-0233 and Vex P/N 217-2690.

2x plate sprockets with bearing bores (e.g. VexPro 217-2690) + hex bearings + standoffs to attach the sprockets together?

Andrew and Carlos - Brilliant! I’ve never used bearing-bore sprockets, but that makes so much sense. Thanks a lot!


Two plastic Rev Sprockets with bolts. Sand down the inside stubs and they are almost perfect. No standoffs needed.

I’m not so sure that sounds stable at continuous speeds. That seems like it would heat up and have problems. I think I’m more comfortable with the hex bearings and bearing plate sprockets.

Thanks tho!

If you are using the VEX sprockets, you can use versahubs between them instead of standoffs.

Yup, 217-2591 (1/2") or 217-3234 (1/4") work perfectly for this application. If you do choose to use the 1/4" VersaHub spacer, make sure you’re careful with how you position your master links.

Documentation for this seems a bit light. Can someone review this parts list?

1x VexPro 217-3234 VersaHub
2x VexPro 217-2690 Sprockets (or AM part am-0233)
1x VexPro 217-3875 Flanged 1/2" Hex Bearing (or AM part FR8ZZ-HexHD)

Does this seem reasonable, or do I need more?


I think you’d want 2 bearings, one for each sprocket, plus screws etc. to assemble it. That chain spacing with the 1/4" hub seems awfully close to me, but as the students on my team always say, “clearance is clearance.”

Since the two sprockets are mated together with the VersaHub, I wondered if one bearing would do the trick (this is going to be a low-load system anyway). It may be more stable with two, but only slightly. I figure two 1/4" hubs would do the trick, they’re really cheap anyway, if one is too tight I can mount them back-to-back to increase the separation (VersaHub win).


One bearing may work if you put it in the versahub(s) between the sprockets.

Just FYI, it worked beautifully. Thanks so much Carlos, Allen, and Karthik!

What I eventually used:

1x VexPro 217-3234 VersaHub
2x VexPro 217-2690 Sprockets
2x AndyMark FR8ZZ-HexHD Flanged 1/2" Hex Bearing
2x VexPro 217-2737 1/2" Hex Clamping Shaft Collar
1x REV REV-41-1450 UltraHex Shaft (1/2" Hex to 5mm Hex)
2x REV REV-41-1327 5mm Hex Shaft Collar