I e-mailed George at G-Sport, for those who have no idea who G-sport are, they make top notch BMX parts. Seeing as I have heard of a freecoaster in the works on a few occasions, I figured why not ask them. Anyway, he had a look at this thread, and had this to say on the matter.
''I can pretty much follow your idea from that I think.
Feel free to post any of this on that thread if you want.
The biggest issue (though not insurmountable) is how you provide “resistance” for the clutch element(s). On ANY freecoaster, you need to provide a way for the hub to “know” when you are pedaling. With an ordinary freecoaster the clutch element is loosely held by a spring relative to the axle, so when the driver advances RELATIVE to the (stationary) axle, and the clutch element is being loosely held to the axle, the two can screw together and engage drive. Without this element the cranks can just spin and take the clutch with them at it’s un-engaged spacing. You can get over this by running some sort of stationary element in from the side, but this will obviously conflict with the existing large bearing which I imagine you had intended to use as your main hub bearing…
Assembly. As I think you realise, the clutch element is larger than the hole in the drive side of the hub shell and has to come in from the other side, so fixing two half shells together will leave no way to insert the clutch elements, you seem to be aiming to get round this by having the hub bolted together, which will work, but means disassembling the entire wheel (spokes and all) to do anything inside the hub.
Bearings. If you have to remove the driver to shell bearings to get a friction element through to the clutch elements, then you need to put the main hub bearings inside/between the two clutches and there isnt much space left there.
The stresses are actually HIGHER due to the 1:1 drive ratio than they would be on a geared up BMX, combine this with the “crash” engagement that you are likely to get using the unit to slow down and the loads will be pretty big (though it probably could be designed to work).
If you use current parts, then you will be restricted to a main crank axle diameter of about 15mm which is simply not strong enough IMO… And those threaded parts are not straightforward to make if you “simply” want to make them in a larger size…’’
This is the biggest issue with this idea, to go with this particular idea, the lack of resistance for the clutch mechanism to act upon poses a big problem. One solution would to be to have one side of the hub driven, and the other side the frame would clamp on to a static axle. I had realised this, and I am trying to think of a solution allowing me to use my initial idea.
This is a fair point, however, the drawings I am working on show a single piece hub shell, my idea being that the ring that the clutch engages with is to be ‘‘top hat’’ shaped with allen bolts to secure it, rather than ring being threaded and a pain to remove.
This is dependant on on whether I can figure out a solution to problem 1 which allows me to use the initial idea. If I can’t use the initial idea, then i have to work with this.
Not sure what so say regarding the loads being greater. As for the slowing of the unit, brake pads could be the way to go.
I had planned on using parts that are avaliable now. One thing to do would be to test some with parts that are avaliable now, and try some with custom parts.
Searching these forums, I found the following thread:
Containing the following link:
I have mailed Kevin Jones, the guy who created and is riding the unibike in the vid, though he hasn’t been on myspace for a bit. I also mailed the person who posted the vid, asking if the hub was able to drive the bike in either direction and coast in either direction, and I am told that it does.
If Kevin’s attention could be brought to the matter of the hub being used in unicycling, we could potentially have access to a freecoasting unicycle hub that has already been designed and ridden. If not, then It may be a bit longer, but I’m still plodding away at it.
Currently, I am trying to figure out how to get a static element in the hub, to create resistance for the clutch mechanism. I have drawn an idea on how to have the clutch mechanism operate in both directions off of one driver, which will take up less space and weigh less than the having the mechanism operating on two drivers. Though, at the moment, getting a static element in the hub from the side of the hub that the clutch will not be, while keeping the cranks aligned, escapes me at the moment.
The main part of the axle will be 20mm. The part of the axle on the right of the drawing, that I have drawn as seperate, I am wondering if i should have that as part of the axle, or as a seperate piece held on with a nut. This larger piece will be the driver of the freecoaster.
The driver, will be threaded at the point on the drawing where it sits inside the clutch lump, and the clutch lump will be threaded on the half that sits on the driver. The clutch lump will engage with the clutch plates, the left most if the axle is driven forwards, and the right most if the axle is driven backwards.
The static axle will be clamped in the bearing clamps, with two different size needle bearing units inside for the normal axle to run on, and one cartridge bearing unit on the outside for the hub shell to run on. The clutch springs will sit on the static ‘‘axle’’, and will push against the inside of the clutch lump to creat the resistance needed for the freecoaster to work.
I recon that I could get the internals working, including the hub body bearings, in a space of 75mm. The hub will have the typical 100mm bearing spacing.
Anyway, that’s the basics of it, now I want your thoughts on it, so be cruel.
with the new sym cranks, this hub could take flatland to new levels. Since with coasting you probably won’t be doing too many crank rolls, the sym cranks would be the ideal cranks to have when coasting and standing on the cranks for flatland.
definitely going to get one of these (36 or 48 hole) when/if they start getting somewhat reliably produced.
Yeah, sound’s a plan. I was thinking of the Sym cranks for ramp, I think they’d work well.
I have re-drawn the hub, well everything but the axle, as I’m still deciding whether to go one piece or two piece. It will be one piece connecting the cranks, at around 20mm straight through, but I can’t decide whether to have the driver as part of the axle, or to have it as a second piece. I have all the bearing sizes, so the bearings are in the drawings. I have a couple of people I want to look over the idea and drawings, then I’m going to shop about for quotes for one, and for five complete hubs soon, and obviously go to the place that offers me the best deal.
I’ll post up any progress as and when it happens, could be over any ammount of time really.
Whatever happened to this idea? Any developments or prototyping?
I was thinking about this kind of thing in general while watching some BMX flatland videos. I’ve thought of something that would both simplify the design (I’d think) and increase functionality. It’s quite simple actually.
I’d say, completely scrap the idea of requiring a ‘dead zone’, or specific crank orientation to engage freewheeling. Especially if you’d implement this at a horizontal position, this would significantly limit stuff like hopping, upspins, etc. The solution: use an independant toggle switch/lever/button to engage and disengage the cranks.
What I’m suggesting is basically a button, placed somewhere like under the seat, which engages and disengages the cranks. Get rid of all play. When you’re engaged, you’re completely engaged in every position and direction. When you disengage, you’re completely disengaged in every position and direction.
I’d have to find some schematics for the types of systems that are currently used (for freewheel hubs) to know if there could be a simple modification and implementation of a toggle. I’d expect that a lot of the mechanisms in the hub have to do with the dead zone and engagement/disengagement which relates to the crank position. A new design might be needed for such a thing.
A simplified version of this idea, for example, could work like the brakes on your car. Have an internal axel attached to the cranks. The wheel is attached to the external axel, which is attached to the internal axel with bearings so that it can freely spin. Like your drum brakes, the internal axel has 2 (or more) pads which move inwards and outwards. When in the outwards position, they touch the outer axel, engaging the inner axel to the outer one. They would naturally require a lot of radial force to stay engaged without slipping. The force exerted on the wheel tangentally would be taken by the ‘brake pads’, while the radial force (the force from the ground to the wheel) would be taken by the hub bearings.
Anywho, I’m interested to see if you’ve gone farther with this, and what you and others think of the idea of using a switch to engage and disengage the wheel rather than a specific crank position.
At the moment, it’s lack of money that is stopping any work on the idea.
As for the button to engage / disengage the wheel, it would be good in that the unicycle would feel like a normal unicycle, then it would coast at the touch of a button.
I can’t see the idea being any simpler. How would the button engage the wheel, what kind of system? I mean a button mounted away from the hub says complications to me. I had thought along the lines of your idea of a button to engage drive, the answer could, in the basic form, be a geared hub with a gear removed. However, I think a button at the cranks to engage drive on a coasting hub could be proned to accidental engagement, when doing tricks for example.
When drawing up the hub, I have allowed for a set of brake pads, like those in a coaster hub, which would help with the problem of instant engagement, and give more controll of the hub. As with a normal freecoaster hub, any play in the hub can be removed by putting spacers into the hub.
It’s not a specific crank position that would engage the drive, the hub would engage wherever the rider wanted. When riding a bike, and you aren’t pedaling, are your feet in the same position then as the previous time spent not pedaling, and the next time? The crank positioning is down to the rider. Freecoaster hubs are the same, whatever position the rider feels the cranks are comfortable, will be the home position.
One possibility that you might consider is introducing a magnetic clutch. They used to use these on some of the big old continuous sheet feeding computer printers to step the paper movement a line at a time. They worked by passing current through magnetic dust, which then “seized up” the input shaft to the output shaft.
I don’t know how much current they took, but they were very efficient at what they did. So, on the unicycle you would have a button to cut in the freewheel. You would need to figure out a different system to feed in the power of course.
See this for examples of modern magnetic clutches.
What I was suggesting was a button mounted somewhere like under the seat. It would be attached by a cable to the hub, effectively, where it would engage and disengage the mechanisms.
I like the idea of being able to choose when to disengage and engage the cranks independently of crank position and movement because it opens up more things that are otherwise limited. I like the idea of being able to coast while spinning the cranks in any direction with it having no influence on your wheel. Hell, another nice addition would be to have a brake that stops the cranks in place. My ideal system would give you complete control over crank engagement, crank position and freedom, etc.
I don’t know how freecoasting hubs work right now. I’ll look into it after class tonight. My idea probably has little to do with the mechanisms of traditional hubs of this sort. It’s not complicated at all though. It’s basically an internal brake, or clutch, that engages an outer drum to an inner drum. My example was like a drum brake on your car. Another example of the kind of system I’m suggesting is a clutch.
A magnetic clutch would be sweet too - it would just act in a concentric fashion rather than how it works in cars (engaging 2 parallel discs).
It makes sense to me to have a button on the axle, just like the Schlumpfs 2 speeds. It would probably just take practice to be able to switch into and out of coasting mode and do tricks without accidentally hitting the button. (I never thought that people would be able to shift on the fly with the 2 speeds, but they manage it just fine)
You may be able to make one of these coasting unicycles (relatively) easily by modifying a schlumpf so that the 1.5 gear is just disengaged. Then you could shift between normal 1:1 riding and coasting. I’m not sure how plausible this is though, since I don’t know how the insides of the schlumpf work.