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Unread 16-01-2017, 15:15
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Re: FRC Bearing Load Ratings (Climber Winch)

The idea of using 1/2" shaft to support a winch drum to lift over 100 lbs, sounds a bit crazy to me.
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Unread 16-01-2017, 15:28
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Re: FRC Bearing Load Ratings (Climber Winch)

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Originally Posted by MrForbes View Post
The idea of using 1/2" shaft to support a winch drum to lift over 100 lbs, sounds a bit crazy to me.
It's not that it's the optimal design, but it's a widely accessible design; some teams and some winch designs may not really work through a stronger method.
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Unread 16-01-2017, 15:29
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Re: FRC Bearing Load Ratings (Climber Winch)

I totally understand....many folks seem to be rather focused in their conceptions of how robots are built.
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Unread 16-01-2017, 15:35
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Re: FRC Bearing Load Ratings (Climber Winch)

Depending on which concept we opt for, we may well go with a larger diameter tube based design. One of our concepts calls for elements protruding multiple inches from the surface of the winch drum, so a smaller diameter helps reduce packaging concerns. Thus the desire to use a 1/2" hex shaft.
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Unread 16-01-2017, 15:51
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Re: FRC Bearing Load Ratings (Climber Winch)

Slightly off-topic but does anyone have experience using 3D printed bushings? We want to 3D print a 5mm hex bushing to interface with REV Robotics' 5mm hex shaft[1], but we want to make sure the 3D printed bushing won't crack under load[3]. We are planning on printing a few and testing them by hand, but if anyone has any info on this, I would appreciate it.[4]



[1]http://www.revrobotics.com/rev-41-1349/[2]
[2]I know they sell bushings for that purpose, but we don't want to have to wait for them to ship overseas.
[3]To be clear, this is not the load of the climber. This is a small flap we are actuating with a REV Smart Robot Servo. The flap is only taking a few pounds of force total.
[4]Both empirical and anecdotal information is welcome. If anyone has any ideas on how to lathe and mill that small of a hex bushing that would be welcome too.
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Unread 16-01-2017, 16:32
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Re: FRC Bearing Load Ratings (Climber Winch)

For a hole that size, I would just use a file to make a hex shaped hole in an aluminum bushing.

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Unread 16-01-2017, 16:42
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Re: FRC Bearing Load Ratings (Climber Winch)

If you use 5mm hex stuff a lot it may be worth investing in a 5mm hex broach (McMaster has them). Some teams have ground their own broaches from old machine tooling for a lower-cost option. (Not that I have anything against filing, if you making just a few it's a great option)

To directly answer your question, I recall seeing a team last year with 3D-printed wheel hubs, so printed parts can be used in high-stress situations. Your success will depend on the printer, materials, and printing pattern, not simply that its 3D printed. You can also do fun things like soaking the part in epoxy to make it ~100% dense and thus stronger.
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Unread 16-01-2017, 17:25
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Re: FRC Bearing Load Ratings (Climber Winch)

Quote:
Originally Posted by MrForbes View Post
The idea of using 1/2" shaft to support a winch drum to lift over 100 lbs, sounds a bit crazy to me.
We did it last year. 1/2" aluminum hex shaft (not sure what alloy, just whatever was laying around), connected to the frame by 4 bearings in VEX brackets (two on each side of the robot). Granted, the winch spools (one on each side of the robot) holding the load were sandwiched pretty closely between the bearings so they were well-supported.

We did bend a shaft during prototyping when we tried lifting using one spool in the center of the base we were using (which was probably about 28" wide) with the shaft only being supported on the ends by bearings. Still no damage to the bearings, but the shaft was definitely shot.
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Unread 16-01-2017, 17:29
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Re: FRC Bearing Load Ratings (Climber Winch)

Quote:
Originally Posted by JamesCH95 View Post
If you use 5mm hex stuff a lot it may be worth investing in a 5mm hex broach (McMaster has them). Some teams have ground their own broaches from old machine tooling for a lower-cost option. (Not that I have anything against filing, if you making just a few it's a great option)

To directly answer your question, I recall seeing a team last year with 3D-printed wheel hubs, so printed parts can be used in high-stress situations. Your success will depend on the printer, materials, and printing pattern, not simply that its 3D printed. You can also do fun things like soaking the part in epoxy to make it ~100% dense and thus stronger.
Yeah, as a team who used (or at least attempted to use) 3d printed wheel hubs I'd recommend steering clear of 3d printing for high stress applications. It went pretty terribly for us, and we had to switch out everything last minute. The type of hubs we used were just the VEX Versa hubs. I think the material was ABS but I can't be sure.
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Unread 16-01-2017, 17:40
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Re: FRC Bearing Load Ratings (Climber Winch)

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Originally Posted by Cog View Post
Yeah, as a team who used (or at least attempted to use) 3d printed wheel hubs I'd recommend steering clear of 3d printing for high stress applications. It went pretty terribly for us, and we had to switch out everything last minute. The type of hubs we used were just the VEX Versa hubs. I think the material was ABS but I can't be sure.
As a counterpoint, last year 2667 used 3D printed wheel hubs (with 8" wheels and the stock 42t AM HTD pulleys), made out of PLA and had precisely zero failures. If you're only running one regional, it MAY be fine, depending on the design of the part and the loading.

This is coming from the person who was EXTREMELY skeptical and made sure we printed half a dozen extras. Like with a lot of things, YMMV.

On the topic of climbers, this year 'Snow Problem designed one that used 4 1/2" hex bearings and a ~29" run of 1/2" 1018 steel hex shaft, with a bolt attached to a shaft collar serving as the "hook" for a loop. So far it has failed twice: once was the rope (turns out a random cord from a surplus store is NOT what you should be making your rope out of), and once from shearing the bolt, which was 1 1/2 or 2", 8-32 SHCS, alloy steel, and costs us about 10 cents and 10 minutes (if that) to replace.
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Unread 16-01-2017, 18:19
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Re: FRC Bearing Load Ratings (Climber Winch)

Quote:
Originally Posted by Ari423 View Post
Slightly off-topic but does anyone have experience using 3D printed bushings? We want to 3D print a 5mm hex bushing to interface with REV Robotics' 5mm hex shaft[1], but we want to make sure the 3D printed bushing won't crack under load[3]. We are planning on printing a few and testing them by hand, but if anyone has any info on this, I would appreciate it.[4]



[1]http://www.revrobotics.com/rev-41-1349/[2]
[2]I know they sell bushings for that purpose, but we don't want to have to wait for them to ship overseas.
[3]To be clear, this is not the load of the climber. This is a small flap we are actuating with a REV Smart Robot Servo. The flap is only taking a few pounds of force total.
[4]Both empirical and anecdotal information is welcome. If anyone has any ideas on how to lathe and mill that small of a hex bushing that would be welcome too.
While 3D printed bushings with a hex bore are viable, I'm not sure if I'd go this route. That would mean the bushing would be rotating with the hex shaft, making the OD of the bushing the bearing material. Regardless of the bearing material, this is typically not the best idea. I'd either turn down or file down the corners of the hex shaft to round so you can just use normal sleeve bearings, or I'd make a plug at some sort that has a hex bore and just converts it to a larger round diameter and use a proper bearing. But if you have to use a hex bore 3D printed bearing, there are definitely some extra things you can do to reduce friction and make it more wear resistant.



Quote:
Originally Posted by JamesCH95 View Post
To directly answer your question, I recall seeing a team last year with 3D-printed wheel hubs, so printed parts can be used in high-stress situations. Your success will depend on the printer, materials, and printing pattern, not simply that its 3D printed. You can also do fun things like soaking the part in epoxy to make it ~100% dense and thus stronger.
I would not recommend using epoxy infiltration on 3D printed parts to increase the structural integrity. Epoxy infiltration is intended to increase the sealing capacity and fluid pressure capacity of printed parts. Also, it's extremely difficult to achieve 100% penetration and even more difficult to confirm the penetration of the epoxy for an average FRC team. There are plenty of ways to make 3D printed parts more successful that are far easier than epoxy infiltration.

Quote:
Originally Posted by Cog View Post
Yeah, as a team who used (or at least attempted to use) 3d printed wheel hubs I'd recommend steering clear of 3d printing for high stress applications. It went pretty terribly for us, and we had to switch out everything last minute. The type of hubs we used were just the VEX Versa hubs. I think the material was ABS but I can't be sure.
Without giving more information on what specifically went wrong, I'm not sure if it's wise to just advise people to steer clear of additive manufactured parts for structural parts. There are plenty of teams that use additive manufacturing with success in all sorts of applications.
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