Bikeguide.org - Bike maintenance for BMX'ers
The Street => The Bike Shop => Topic started by: Eggit2 on October 24, 2016, 11:06:38 PM
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Short story is my that my Dad and I are building an ultra-light airplane. The plans call for 20" bicycle wheels, but some of the other people that have built them have ran into bent axles and rims or blown out bearings. Most guys are just using some shitty cargo bike wheels and I told him I can do way better.
I'd just an anti-gram or something, but we want to go with disc brake. We have lathe and mill access and will most likely be making a custom axle for whatever we go with. I'd kinda like to stick with something similar to the g-sport style axle design just for the ease of modifying it, and the strength. I can't seem to find any beefy street oriented hubs with disc mounts.
I've looked at 20mm thru axle hubs, and figure we could make an axle for them no problem, but a lot of the ones I see have rather small bearings. We have also considered replacing the bearings with a bushing if they become a problem, not like the wheels need to roll all that well on a plane. Again though, not much room to be fitting a bushing in.
Another option I have looked at is using a lefty hub. This makes sense as the wheels are only going to be mounted on one side anyways. Making an axle is a little more complicated, but within reason. They are also kind of pricey though.
A final consideration is that the more off the shelf it is the better. If an axle (or female bolt) were to break on a flight, it would be nice to be able to hit a local store and make a repair.
Just curious if anyone has any ideas?
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I doubt you are going to find massive bearings on a disc 20mm front hub, they can only go so big due to the mounting of the disk. Are you sure those bearings are really going to be too small though?
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Unless you're planning on landing harder than this sort of behaviour, then I reckon bearings won't be a concern....
(http://ep1.pinkbike.org/p5pb11472302/p5pb11472302.jpg)
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Yea, A basic 20mm thru is probably going to be good enough, the bearings are certainly stronger than what most guys are using. I was just curious if there was something out there I was missing.
Those guys have suspension, are landing on slopes, have axles mounted on both sides and don't weigh 800 lbs loaded. I ain't no engineer, but its very different circumstances.
The junk these guys are using is good for normal landings though, and even the ones that have snapped axles on landing haven't resulted in a major incident. The landing speeds on these things are pretty slow. Just trying to beef it up and improve the common point of failure.
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You not thought about machining a hub up? Maybe look for a good set of bearings first and work around them.
What discs are you planning on using? Surely any off the shelf pads will get destroyed stopping an 800lb plane. I'm guessing there's specific plane calipers / rotors.
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I would just go for a downhill hub and lace it to a bmx rim. Not sure if you can find a 48h if you need that though.
http://www.chainreactioncycles.com/se/en/hope-pro-4-mtb-front-hub-20mm-axle/rp-prod145293 (http://www.chainreactioncycles.com/se/en/hope-pro-4-mtb-front-hub-20mm-axle/rp-prod145293)
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Like stated above you will not find large bearings in a 20mm hub, but if you are looking for strength I would probably say Shimano Saint or ZEE hubs will be the strongest as they are forged rather than CNCd so the material properties should be advantageous. The centerlock disc mating system will give you great options for small strong heat resistant rotors aswell.
http://www.chainreactioncycles.com/us/en/shimano-saint-hub-front-m820/rp-prod82556 (http://www.chainreactioncycles.com/us/en/shimano-saint-hub-front-m820/rp-prod82556)
http://www.chainreactioncycles.com/us/en/shimano-zee-front-mtb-hub-m640/rp-prod82444 (http://www.chainreactioncycles.com/us/en/shimano-zee-front-mtb-hub-m640/rp-prod82444)
If you dont want shimano I would look at Hope would be the next stong cheap option.
http://www.chainreactioncycles.com/us/en/hope-pro-4-mtb-front-hub-20mm-axle/rp-prod145293 (http://www.chainreactioncycles.com/us/en/hope-pro-4-mtb-front-hub-20mm-axle/rp-prod145293)
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I doubt you'll find anything 36h if you're lacing to a 20" rim
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They're dirt cheap over here, though may not be in the land of the free, but the old hope big'un hubs were a cool design, used bigger bearings , took a 20mm axle, came in 36 hole and build strong. They use a bespoke 5 bolt mount, but you can still get the rotors from hope, or just laser cut your own (bigger?) ones.
http://www.retrobike.co.uk/forum/download/file.php?id=62002
Im no expert, but id guess most of the braking comes from the wind resistance, dragging the tail skid, etc? I would have thought 2x 200mm rotors with decent brakes and metal pads would be fine, the pads will get hot, but they wont be working for long enough for the heat to transfer into the caliper and oil.
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Yea I'm not really worried about braking. The prop does a lot of the work. Some of the guys using dirt runways don't even run any brakes. One of the main reasons they are there is for steering while taxiing. Eve on landing, they are on for such a short period that heat shouldn't be an issue, and I don't foresee pad wear being one either.
Thanks for the suggestions. I'll take a look at some of these. I might be able to get by with 32h and a BMX race rim, still probably stronger than what a lot of guys are using. Making a hub is a little out of the question as we only have a small 2 axis lathe. I could possibly try to do it at work, but thats a big project to try and hide from the bosses.
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Defcon4 could probably make you a hub to the specs you want...