Re: Rhino track failier?
 

Just want to highlight this level of Customer Service in any industry is unparalleled. The insight and full honesty into what is going on makes AndyMark the company that it is.

Andy- sounds like the addition of ribs is a solid solution path. For whatever my two cents is worth, I agree with the solution.

-Brando

Re: Rhino track failier?
 

We have yet to test our VexRhino (custom drive using AM pulleys and belts).

We will let you know if we have any failures.

Re: Rhino track failier?
 

To echo Brandon's feelings. This could well serve as a prime example of a customer service goal for a business in any industry to emulate.

I just sent a link to Andy's post to our other mentors on our team telling them that this is one of the main reasons I like volunteering with, working with and associating with the people that make FIRST what it is.

Thank you Mr. Baker

Re: Rhino track failier?
 

Andy, I think Rhino customers really appreciate the open approach AM is taking to address this. I agree that a mold improvement is likely to solve the problem.
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Another approach, more in the quick-fix direction, might be to distribute the tension and shock loads on the pulley over a larger area. This might be accomplished by inserting a tight fitting sleeve (maybe aluminum tube) through the pulley bore (0.96 inch), and then sleeve type bearings (maybe oil-lite bronze) into the ends of the sleeve to accept the 3/8 inch bolt spindle.

I have ordered some pulleys to try this, along with aluminum tube and bronze bearings. Tube and bearing part numbers from McMaster-Carr are 9056K28 and 6338K465, respectively. I plan to turn the tube O.D. for a tight fit to the pulley bore, then bore (drill) it to a tight fit for the 5/8" bearing O.D., and face to 2.175" long. After a light press to fit the tube into the pulley, the bearings can be inserted and then the assembly should replace a damaged one. I don't know how much extra friction the sleeve bearings will add, relative to the 1416ZZ ball bearings -- current draw will tell that tale. If this approach works it might be used to repair damaged pulleys.

I am just an electrical engineer fiddling with mechanical things based on FRC experience. I would appreciate critique of this idea, especially from those with stronger Mechanical Engineering background and/or more FRC design experience.

Re: Rhino track failier?
 

Agreed. Always impressed by AM customer service. And great job sourcing locally, 1 week is a pretty impressive lead time for a mold change.

Re: Rhino track failier?
 

Thank you all for your understanding, support, and patience.

Richard, this is brilliant! Thank you for posting the idea. We may try something similar here in our tests. You're an ME in disguise!

Regarding the mold changes, we are implementing 4 changes to the pulley.



Due to the speed of things happening, if folks want to post input here on what else to do to this Rev4, it may or may not get implemented.

Andy B.

Re: Rhino track failier?
 

The only issue that I see, looking at the drawing for the pulleys is that the center bore is relatively loosely held at .95-.97. You may want to open the pulley bore slightly to prevent the need for matched sets of tubes and pulleys to get the desired light press fit.

Re: Rhino track failier?
 

Andy the revision looks pretty good. Are there going to be longer bolts included in the upgrade or do you feel the current bolts will be long enough even with the bolt recess change?

Re: Rhino track failier?
 

Good question, Cliff.

We also discussed this issue. The distance of thread engagement was 0.485 with the current version. With the new version (Rev4), the engagement will be lessened by 0.125, resulting in 0.36. Since there is a taper on the end of the screw, the last 0.15" (approximately) can't be relied on with regard to screw thread engagement. So, we now have about 0.21" of engagement. Since it's a 10-24 screw (with 24 threads per inch), that means we now have 5 threads of engagement at each screw. With 6 screws all having this same engagement, we believe that this will be enough. However, we will make a test and report back if this is good or not.

Andy B.

Re: Rhino track failier?
 

Thank you for the kind words, Andy! I will post results of our attempt at this quick-fix.

Agreed. We will run a 61/64 31/32 inch ream through the plastic parts before pressing.

Re: Rhino track failier?
 

Would filling the hollow spaces in the pulleys with something like epoxy work to mitigate this?

Re: Rhino track failier?
 

Do the failures seem to be coming from the weakest area as shown by the arrow? It seems that way, but we haven't busted any because we haven't driven any... Busy work on more important things. :D

Re: Rhino track failier?
 

Yes, that would help also. Good idea!

Yes, you are correct, Brad. That is where the failure is happening.

Andy B.

Re: Rhino track failier?
 

If that's the case I think it would be better to change the screw so it has a smaller diameter and can be tightened without a socket such as a hex head, but I doubt you can source that in self threading style.

I just seems that's the area that needs to be modified to make the most strength in addition to the ribs.

Any thoughts on a material change such as Nylon?

Re: Rhino track failier?
 

It seems like the fact that there's an edge rather than a chamfer/fillet where the well for the screwhead begins (radially out from the center) might be a point of failure. All of the fractures pictured are at the depth of the well, so I think having an edge there to bend around is contributing somewhat. Just a guess though.