We are dealing with mounting encoders & realize that we need to swap out our axles. Is there a problem if the end of our axle comes through the bearing by 1/2", but stays inside the perimeter of the frame?
If the axle stays inside the frame perimeter, thereās no problem legally. If it sticks out though, that would then define the new frame perimeter and since itās articulated it would be illegal.
1 Like
When I read your question, I cant help but think you are asking for engineering advice and not about rules legality. Is this the case?
Heās asking if the axles sticking out from the outer frame, but within the perimeter are legal.
If heās asking what you think heās asking, then I think we need pictures. What youāre describing may end up defining the Frame Perimeter, which would be illegal.
Minor Protrusions that exceed the frame perimeter are allowed if they are less than 1/4 inch.
I believe that shafts qualify as āminor protrusionsā as the year that minor protrusions were not legal (2015?) I seem to remember the kit bot was illegal without modification due to the shafts slightly sticking out of the frame perimeter.
Yeah, thatās totally fine. Iām guessing what happened is that the inside rail was installed one hole too far out from the end. No bigs.
But just to be sure, when you look straight down from the top can you see the axle sticking out?
https://andymark-weblinc.netdna-ssl.com/product_images/am14u4-kit-of-parts-chassis/5c2fa4e661a10d20e10dd2b1/zoom.jpg?c=1546626278
Are your outer plates turned inward like that?
If they are, then youāre OK rules-wise (as long as you donāt put the axle too far out).
Thereās no particular engineering or design requirement for how far axles extend beyond bearings.
I would be concerned if a moving part (I assume your axles are going to move) are going to be deemed a āminor protrusionā. Also the rule is 1/4" not 1/2". As long as they are inside the FP they are not an issue. I would want clarification before I build something with them being part of defining the FP. In previous years (insert required statement about the past meaning nothing, nothing I say) mechanism bits other than fasteners typically were not allowed as āminor protrusionsā.
I would not list the ends of drive shafts as similar to ābolt heads, fastener ends, weld beads, and rivetsā. All of those are rigid, non-moving, fasteners connecting two or more structural elements, which is not the case for a drive axle. To be safe this would be a good question for the Q&A.
I would contest the following statement with a response to this thread back in 2014 by Al Skierkiewicz (Head LRI for FIRST).
In previous years (insert required statement about the past meaning nothing, nothing I say) mechanism bits other than fasteners typically were not allowed as āminor protrusionsā.
But yeah the Q&A would be the best call if this is the situation that the OP is asking about.
Also, another thread from 2014 about the same issue, with a similar tone to the responses:
Could you cut the axles a little ways off to the correct length so they only sit within the bearing or does that mess up something with the drive?
Sorry I am not understanding the point you are making. The quote attributed to Al states that bearing are pushing that definition. A reasonable conclusion from that statement is that axles protruding āpastā the bearing would be pushing it even more. Ie they would not be considered as minor protrusions. I really struggle to fit a bearing or axle into the language of R1 which states:
āfixed, non-articulated structural elements of the ROBOTā
At a minimum I would Q&A it and plan on showing up for tech inspection with a printout of the answer rather than hanging the legality of your design on a 6 year old forum post (which has even less weight than a Q&A answer)
Note: this is in no way disparaging Al, it is pointing out that Chief Delphi posts even by FRC heavyweights, do not have official standing at tech inspection. Q&A answers also can be overruled, but they at least carry āwe intentā, or āour interpretation isā weight.
Also, they have been fairly consistent with applying the everything inside the FP in starting config (R2) to apply to everything except āminor protrusionsā. Both at events and in Q&A answers they have been pretty restrictive as to what gets exempted as a minor protrusion, and I would bet a shaft sticking 1/2" past your FP is not going to get exempted.
OK,
I hope that a few statements here will help in the understandingā¦
- When any part protrudes from the frame, it is evaluated for FRAME PERIMETER or minor protrusion. If it is obvious structure (axles would be included in this illustration in most cases, then the perimeter still needs to be under 120".
- Bumpers need to be mounted on the FRAME PERIMETER. As such, to cover these āmajorā protrusions, additional material may be needed to satisfy bumper mounting rules.
- One of the biggest concerns to vendors and inspectors is that team sometimes do not read the assembly instructions fully. As shown in the drawing above, the assembly of the kit frame would allow for the bearing and about 3/8" of shaft to protrude from the inner surface of the C channel. However, the FRAME PERIMETER is defined by the outer edge of the C channel and therefore even the shafts are likely to rest behind the perimeter.
- The definition of minor protrusions has not changed in many years. The words āsuch as bolt heads, fastener ends, rivets, cable ties, etcā does not include structural parts or axles. The 1/4" specification is used with this definition to allow teams to weld their frame, mount mechanical devices without the need of specialized hardware and to use kit bot chassis kits where the heads of all the bolts supplied are 1/4" or less in height (when inserted with the bolt head on the outside of the frame).
It is impractical to ship sizing boxes to all events so they were eliminated long ago. To visualize this, think about your design and evaluate if your robot could slide into a sizing box without contacting axles or other structural parts.
2 Likes
Thanks Al. Appreciate the response.
With the readers digest version being: axles extending past frame may redefine the FRAME PERIMETER (R1) and may cause you grief with the bumper rules (R24a and R26)ā¦
Even shorter version: Its a bad plan, donāt do it.
Trying to attach a photo. Not sure why this would be an issue as it is inside the frame perimeter. Please advise.
Thatās fine.
Yeah that is fine.