[FTC]: Alternative to axles? Does hardening work?

[aklego]

In our problem area we used 3/8" d-shaft and bushings from McMaster Carr:

http://www.mcmaster.com/#rotary-shafts/=sjbxtn
http://www.mcmaster.com/#standard-sl...arings/=sjc10h

We drilled and reamed the Tetrix axle hubs and they worked pretty well.

Another trick (that we picked up on this forum) is to use flat point set screws:

http://www.fastenal.com/web/products/details/0171675

These help quite a bit when the axle-hub joint is subjected to reversing loads.

[RRLedford]

Purchasing D-shaft is not legal, since the flat makes it a custom machined profile, and only round, square and rectangular profile metal bar material is legal.

You have to buy hardened round shaft and grind (Dremel) the needed flats, for at least the lengths where the screws grip, if not the full length.

We design to avoid, as much as possible, applying any torque through the TETRIX shafts, and to always have both ends of shafts supported when bending forces are present. Bolt the gears together for compound gearing, so the shaft isn't transferring the torque.

When we do transfer torque through TETRIX axles, we try to always double hub them, on both sides of gears or sprockets, so that one single set screw loosening cannot kill the mechanism.

You can use long, Grade 8 10-32 SH cap crews for free spinning shafts. On last years bot we did this for our VEX wheeled, chain driven mecanum drive. The smooth zone of bolt was polished to fit the TETRIX sleeve bearings. Worked extremely well, but length is limited.



-Dick Ledford

[aklego]

Originally Posted by RRLedford

Purchasing D-shaft is not legal, since the flat makes it a custom machined profile, and only round, square and rectangular profile metal bar material is legal.

Actually, it was asked and answered on the forum and D-shaft from McMaster-Carr is legal:

http://ftcforum.usfirst.org/showthre...ull=1#post7492

[RRLedford]

Originally Posted by aklego

Actually, it was asked and answered on the forum and D-shaft from McMaster-Carr is legal:

http://ftcforum.usfirst.org/showthre...ull=1#post7492

Well this is a turn around from when first I asked that same question a few years ago after our first FTC season demonstrated how horrible the TETRIX axles are. We ended up belt sanding flats on 3/16" solid round hardened stainless steel shafts -- very tedious but totally worth it.

Unfortunately, the McMaster link does not go down to the 3/16" diameter needed to match up with thr TETRIX hubs and bearings, etc. - but other sources do have the needed 3/16" size D-shaft. The 10-32 Grade8 SH Cap Screws do require a a very slight reaming of the TETRIX hubs to fit them, but this only improves the precision of the fit.

Good news & thanks for the update.

-Dick Ledford

[blockwall2]

Originally Posted by RRLedford

but other sources do have the needed 3/16" size D-shaft.

I have not been able to find any to save my life. There are quite a few places with d-shafts, but all that I have found do not have the 3/16".

I quite like the idea of reaming the axle hubs and buying the 1/4" or 3/8" axles and bushings from McMaster-Carr though.

[aklego]

Originally Posted by RRLedford

Well this is a turn around from when first I asked that same question a few years ago after our first FTC season demonstrated how horrible the TETRIX axles are. We ended up belt sanding flats on 3/16" solid round hardened stainless steel shafts -- very tedious but totally worth it.

Yeah, the rulings on this one have been rather puzzling. The question was actually asked twice last season and the answers conflicted. The upshot was that McMaster-Carr D-shaft is legal but Servo City D-Shaft, due to a chamfered end, is not. That would sort of make sense except that McMaster-Carr shaft is chamfered as well....

[CENTURION]

Originally Posted by aklego

Yeah, the rulings on this one have been rather puzzling. The question was actually asked twice last season and the answers conflicted. The upshot was that McMaster-Carr D-shaft is legal but Servo City D-Shaft, due to a chamfered end, is not. That would sort of make sense except that McMaster-Carr shaft is chamfered as well....

I believe the difference was not just the chamfered end, but that the Servo City ones were cut to specific lengths too. Whereas the McMaster ones were stock length (a couple feet), and you would have to cut the sizes you want yourself.

[aklego]

Originally Posted by CENTURION

I believe the difference was not just the chamfered end, but that the Servo City ones were cut to specific lengths too. Whereas the McMaster ones were stock length (a couple feet), and you would have to cut the sizes you want yourself.

That was indeed part of the rationale. But McMaster Carr also offers a selection of lengths--6" through 4'. (Admittedly, Servo City has a much greater variety)

My hope is that the wording of the raw materials rule will receive some attention this year. Doing so would (hopefully) remove lots of the clutter from the official forums, reduce confusion for teams and make it easier for the forum moderators. But now I'm way off topic....