pic: Off-Season Drive Project

[Ty Tremblay]

[cdm-description=photo]40740[/cdm-description]

[Andrew Lawrence]

It seems like with the octagonal frame, you have room for 2" wide - if not wider - wheels. With the 4" Colsons coming in a 2" wide variety, is there any reason you opted to choose the 1.5" wide wheels?

[Ty Tremblay]

It seems like with the octagonal frame, you have room for 2" wide - if not wider - wheels. With the 4" Colsons coming in a 2" wide variety, is there any reason you opted to choose the 1.5" wide wheels?

Good catch. I had originally designed the drivetrain without the octagonal frame up top. Now that I've added it, I have room for the 2" wide wheels. The only qualm I have is that I won't be able to use an e-clip to hold the wheels on the shaft because the WCP hubs are 1.5" thick. I suppose a screw, a washer, and some loc-tite would suffice. Thoughts?

[Deke]

Good catch. I had originally designed the drivetrain without the octagonal frame up top. Now that I've added it, I have room for the 2" wide wheels. The only qualm I have is that I won't be able to use an e-clip to hold the wheels on the shaft because the WCP hubs are 1.5" thick. I suppose a screw, a washer, and some loc-tite would suffice. Thoughts?

We have used bolts and washers to hold wheels on the past few years with cantilevered axles, it works great and eliminates any 'slop' in the assembly.

[Andrew Lawrence]

Good catch. I had originally designed the drivetrain without the octagonal frame up top. Now that I've added it, I have room for the 2" wide wheels. The only qualm I have is that I won't be able to use an e-clip to hold the wheels on the shaft because the WCP hubs are 1.5" thick. I suppose a screw, a washer, and some loc-tite would suffice. Thoughts?

It will be a bit more tedious than normal, but using a 1/2" snap ring would definitely be possible since you can fit a snap ring tool inside the small amount of space the Colson bore opens up. Alternatively, as you mentioned, a tapped hole with a screw, washer, and loctite will also be an effective method.

Another question - is your bellypan just not lightened yet, or are you using a solid piece of aluminum? If you don't have the resources to waterjet a diamond-bellypan, I highly suggest using a solid piece of 6mm or 1/4" thick plywood as a bellypan. It's much lighter than a solid aluminum plate, and will serve well as an electronics pan as well as providing the torsional stiffness the diagonals that a diamond bellypan provide.

[EricDrost]

I suppose a screw, a washer, and some loc-tite would suffice. Thoughts?

This works well. I'd use a hex cap screw (which you can tighten with a wrench, not a screw driver/hex key) so you can get some extra torque on it.

[Andrew Lawrence]

This works well. I'd use a cap screw (which you can tighten with a wrench, not a screw driver/hex key) so you can get some extra torque on it.

EDIT: I was unaware you were referring to a socket wrench, not a regular wrench


In this particular scenario where there is a small, confined space for a tool to fit into, I'm not sure if you will be able to position a wrench in a way that allows you to get a significant torque advantage. A standard socket head should be sufficient to get the required torque, and the loctite will help in keeping things in.

[EricDrost]

In this particular scenario where there is a small, confined space for a tool to fit into, I'm not sure if you will be able to position a wrench in a way that allows you to get a significant torque advantage. A standard socket head should be sufficient to get the required torque, and the loctite will help in keeping things in.

MORT ran 2" wide colsons with this retaining method this year. We had issues on our practice bot with socket head screws and loctite not being enough to retain the wheel. YMMV, but I would recommend a hex cap screw.

[Andrew Lawrence]

MORT ran 2" wide colsons with this retaining method this year. We had issues on our practice bot with socket head screws and loctite not being enough to retain the wheel. YMMV, but I would recommend a hex cap screw.

Maybe I'm misunderstanding you, but I'm not understanding how you could fit a wrench (http://upload.wikimedia.org/wikipedia/en/9/98/Chrome_Vanadium_Adjustable_Wrench.jpg) inside the 1 3/16" bore of the wheel (http://i.imgur.com/NoICVRq.png) and hold it perpendicularly to the axis of rotation so that you can get the mechanical advantage to gain the extra torque.

[Akash Rastogi]

Maybe I'm misunderstanding you, but I'm not understanding how you could fit a wrench (http://upload.wikimedia.org/wikipedia/en/9/98/Chrome_Vanadium_Adjustable_Wrench.jpg) inside the 1 3/16" bore of the wheel (http://i.imgur.com/NoICVRq.png) and hold it perpendicularly to the axis of rotation so that you can get the mechanical advantage to gain the extra torque.

Socket (http://i.imgur.com/W99yVWC.jpg)...not adjustable...

[EricDrost]

snip.

https://i.imgur.com/V3OJwM7l.jpg

This is our drivetrain with incorrect screws retaining the wheels.

We used large washers for cosmetic reasons, we did some machining on the face of the wheel and wanted to keep it covered.

Edit: Or as Akash pointed out, socket wrenches work in the set up you have CADed.

[Andrew Lawrence]

Socket (http://i.imgur.com/W99yVWC.jpg)...not adjustable...

That makes more sense than a regular wrench - my apologies.

I revise my previous statement to say that, thanks to Eric's example, a hex cap screw works equally as well any method of retaining.

[Ty Tremblay]

Another question - is your bellypan just not lightened yet, or are you using a solid piece of aluminum? If you don't have the resources to waterjet a diamond-bellypan, I highly suggest using a solid piece of 6mm or 1/4" thick plywood as a bellypan. It's much lighter than a solid aluminum plate, and will serve well as an electronics pan as well as providing the torsional stiffness the diagonals that a diamond bellypan provide.

The plan is to use either .0625" polycarbonate or garolite to allow us to leave it solid, maintain the weight advantage, and to easily mount and insulate electronics.

http://i.imgur.com/W7jAg3A.jpg

We're partnering with another team to help with the waterjetting.

[AustinSchuh]

The plan is to use either .0625" polycarbonate or garolite to allow us to leave it solid, maintain the weight advantage, and to easily mount and insulate electronics.


I'd seriously question that decision... Polycarbonate will be very floppy.

[sanddrag]

https://i.imgur.com/V3OJwM7l.jpg
This is our drivetrain with incorrect screws retaining the wheels. That is a thing of beauty. I can't believe I haven't seen it before. What's the part number on those wheels, and do you have a link to any more pictures?

[Akash Rastogi]

That is a thing of beauty. I can't believe I haven't seen it before. What's the part number on those wheels, and do you have a link to any more pictures?

I don't think there are build season photos on the team website yet, but you can find some random pictures of the drive on the team facebook page.

Here's one, and there should be more if you keep clicking next https://www.facebook.com/photo.php?fbid=732489503436161&set=pb.153139828037801.-2207520000.1404626577.&type=3&theater

If there's anything in particular you want to see, just ask!

[AdamHeard]

Using a bolt to retain the wheels and take up all slop is a bad idea as it will preload the bearings. It's also more likely to loosen the fastener.

[Chris is me]

Using a bolt to retain the wheels and take up all slop is a bad idea as it will preload the bearings. It's also more likely to loosen the fastener.

Compared to two snap rings, etc. it's definitely sub-optimal, but with regular maintenance (check the bolts before a match) and some Loctite, it's a decent enough solution that will retain wheels and account for manufacturing tolerances. Just don't over-tighten the bolts as the tighter they are, the more preloaded your bearings are, and hex bearings seem to be particularly temperamental in FRC.

By the way, the wheels in 11's photo are 2" wide black Colsons.

I'll third the notion of not using thin polycarbonate as a structural belly pan. Polycarbonate is great for some applications but in this one the thickness you need for polycarbonate to be sufficiently rigid makes it a poor choice compared to thinner sections of other materials, such as garolite. We still use an un-lightened 1/16th aluminium belly pan though this is suboptimal.

[Andrew Remmers]

Kind of reminds me of an old 179 drive.

http://www.chiefdelphi.com/media/img/279/279c65c661d60468aafc145367e7a6da_l.jpg

http://www.chiefdelphi.com/media/img/30d/30ddead1f188b840980e763287d7b504_l.jpg

[IndySam]

Using a bolt to retain the wheels and take up all slop is a bad idea as it will preload the bearings. It's also more likely to loosen the fastener.

We have used a bolt to retain wheels for three years and have never had a single problem. We do not take up slop with them, we always leave a little slop just like you would with a retaining clip.

[AdamHeard]

We have used a bolt to retain wheels for three years and have never had a single problem. We do not take up slop with them, we always leave a little slop just like you would with a retaining clip.

That is what I was recommending. As opposed to clamping the bearings.

I still prefer snap rings for reliability, fabrication time and swap out speed. They're easier to do than people think.

[Brandon_L]

https://i.imgur.com/V3OJwM7l.jpg


Is there a reason that thread locking screws (http://www.mcmaster.com/#92360A248) aren't used in that situation more commonly? We ran them this year on our wheel axles, with e-clips on the inside and we've never had to adjust them and never had any issues. We use them pretty frequently on other assemblies as well and I love them.

[Aren Siekmeier]

Is there a reason that thread locking screws (http://www.mcmaster.com/#92360A248) aren't used in that situation more commonly? We ran them this year on our wheel axles, with e-clips on the inside and we've never had to adjust them and never had any issues. We use them pretty frequently on other assemblies as well and I love them.

How many uses is the nylon good for? We remove wheels all the time, not just for wheel maintenance, but also for shaft maintenance and if they got in the way of something else because our design was too constrained... :( We've used bolts, washers, and loctite in the past because drilling and tapping the hole seemed like the easier way to go, rather than machining a groove, but in the interest of maintenance, we'll definitely check out snap rings for the future. If you bother to machine the grooves and have the right tools, it seems far more convenient.

[AdamHeard]

How many uses is the nylon good for? We remove wheels all the time, not just for wheel maintenance, but also for shaft maintenance and if they got in the way of something else because our design was too constrained... :( We've used bolts, washers, and loctite in the past because drilling and tapping the hole seemed like the easier way to go, rather than machining a groove, but in the interest of maintenance, we'll definitely check out snap rings for the future. If you bother to machine the grooves and have the right tools, it seems far more convenient.

If you have people with basic lathe skills, the snap ring groove is actually a faster operation than drilling + tapping.

If the shaft was predilled (already had a hole in it), it'd become comparable but I still think the groove is a tad less tedious to machine than tapping once the skillset is obtained.

Also, the tolerances for the groove width and depth are are like +.003/-0.0 and +/-.002 but we've been fine in situations where we've botched that by quite a bit. So it isn't as daunting as that makes it seem. The width tolerance is set by your insert too, so you don't even deal with that.

[Aren Siekmeier]

If you have people with basic lathe skills, the snap ring groove is actually a faster operation than drilling + tapping.

If the shaft was predilled (already had a hole in it), it'd become comparable but I still think the groove is a tad less tedious to machine than tapping once the skillset is obtained.

Also, the tolerances for the groove width and depth are are like +.003/-0.0 and +/-.002 but we've been fine in situations where we've botched that by quite a bit. So it isn't as daunting as that makes it seem. The width tolerance is set by your insert too, so you don't even deal with that.

So there's another point for snap rings and against bolts :)

Lathe and mill work is relatively new on our team, so we are still figuring out the do's and don't's and can's and cannot's on our machines. Good to hear how it can really be a "snap" :P