I can definitely sympathize with Tom Miller's frustration with engineers who say, "We tried plastics ten years ago and it didn't work." As a materials engineer, I run into that reaction a lot. My reaction is to ask: how much do you know about why it didn't work ten years ago? Then I ask myself if anything has changed in the past ten years which might help to address that issue.
In any engineering organization, there is a certain amount of tribal knowledge about what works and what doesn't work. This is sometimes based on stories which have been handed down from one person to another, and often some of the key details have been lost. (This is why report writing and proper documentation are so important).
Design engineers should always keep an open mind, and never consider the case completely closed on any topic. Do plastic bearings work in your application? Well, maybe they do and maybe they don't. If you had a bad experience ten years ago, all you can say for sure is that the particular plastic bearing you tried ten years ago didn't work in the particular application you put it in.
That being said, there are also a limited amount of resources, and obviously they need to be focused on the solutions which seem most likely to succeed. This is where engineering judgement comes in. But hopefully, that judgement will be driven by data, and not just by organizational folklore.
Regarding the jetpack, it would be interesting to know more about the propulsion system. Apparently, it generates little heat, but it does generate a corrosive gas. What is the chemical reaction involved?
I'm curious if Mario Böhme's motivation for using the plastic ball bearings on the jetpack was that he's part of the student population therefore open to new ideas and not as beholdent to past conventional wisdeom or because he somehow got involved in this igus awards program. In either case, it's nice to see young engineers actively getting hands-on with old, yet new materials and approaches and trying to break out of the box. Nice work Mario!
Welcome to the world of flight. For the pilot's safety and longevity, a bearing that keeps him secured to his craft is an important component. The aviation authorities probably thinks so as well. This old guy would rather see an established material used with a robust configuration (AKA overkill) on this critical component until the loading parameters are better defined and the plastic bearing can be tested and confirmed to a much higher reliability. Why do you think aircraft cost so much?
They all jumped on one error but missed the part about the bearings not being in the high temperature area. So, although there is a serious error, it is in a different area..
If the bearings are replaced every few flights, it would be very interesting to know why, since I don't do any applications where service that often would be accepted. In fact, A lot more information about the jetpack would be interesting. I don't think that the location of the jets was obvious, in fact, I did not see anything that looked like a jet any place above the wearers cg. and so I would really like to know how it is made to be stable. It does seem to be quite different from the other jetpacks that I have seen. So more information on that part would be good.
I do wonder more than a little about the durability of the IGUS bearings if they must be replaced that often, how about a description of why?
Ceramic bearings may have some of the features of plastic bearings, while being longer lasting -- especially for applications requiring higher bearing loads and elevated temperatures.
My conversion formula says that 600C = 1112F, which is way too high for plastics. 250C = 482F, which is in line with published working temperatures for PEEK.
"Bearings made from PEEK compounds can take thermal conditions up to 600C (482F).Bearings made from PEEK compounds can take thermal conditions up to 600C (482F)."
That something has always been done that way is the worst reason for not changing it ! Congrats to most people for trying new ways, just evaluate the risks, the failures and be careful. Far too many fail and don't put much effort into finding out why.
I'd like to learn about the design as well. However, I like it when young engineers or in this case a student start to think outside the box and look at ideas that may be overlooked by others. It's a good opportunity for us "others" to take a second look at something like plastic ball bearings. I've had a little experience with plastic bearings at lower temps. My experience was positive because of the chemical resistance of the plastic.
Another idea may be to use plastic slides rather than bearings in some instances. In some designs a roller bearing type system may be a little overkill.
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