RC downhill bike design -

HAL9000v2.0

HAL9000v2.0

10 kW
Joined
Apr 14, 2008
Messages
977
Location
Zagreb, Croatia
I started to think about my next bike. It will be downhill based bike with rc motor. First here is sketch of gearing , as I see it. First reduction is with belt drive, then little chain to first cluster of sprockets which is located on pedal axis. second cluster is turned around and it is located on axis of rear swingarm. This is only sketch aand ratios are not correct. Shifting will be done with two aluminum plate which is guided with two arms that make parallelogram and the movement is parallel with plane that lays on top of each sprocket in one cluster. between these plates on front side of the bike will be simple chain guide and on back side chain tensioner similar to rear deluieuer ??!?.
Fell free to comment. I want to hear bad sides...

skica%20pogona.JPG
 
Did you design this around a certain frame? Or are you going to build the frame around the drivetrain? It just looks a little hard to package, that's all. Also, I don't see much advantage to removing the sprocket cluster from the rear wheel, aside from not having the derailleur hanging down. If you want to keep both of the 8 sprocket (maybe 9?) clusters with the parallel shifting idea, I would put the one on the back wheel, eliminating one chain and one jackshaft. This would still use the shifting mechanism you are proposing and the derailleur could likely be made much smaller is there is much less "change" in chain length to accommodate. Might not make for very good pedaling ratios however.

Nice drawing BTW, I only know how to use AutoCAD, and while I can do 3D reasonably well, it would take me forever to do what you've done!
 
I did not explain all... sorry.
1. I plan to build a carbon frame around this.
2. I want that chain is going through swingarm so no shifting there
3. I want all to be closed with frame only pedals sticking out.
 
I like it :D I have said this in a few threads on this forum about a variation on a CVT and what you have show is along the lines that I have thinking about, but instead of 2 gear clusters using 2 variable size pulleys ( as in a variator system on a auto scooter ) the rear pulley will be sprung to always try and make the pulley diameter as big as possible and also maintaining contact with the v-belt. The front pulley could be either dynamically adjusted with weights using centralfugal force ( variator ) or with a some sort of manual lever thrust system that can push the front pulley together to increase the diameter this in turn will cause the belt to be pulled into the rear pulley changing the gear ratio, when the thrust is released bit by bit from the front pulley the rear pulley will automatically move its way back to the large diameter . It works a treat on motor scooters and I think it would make a lighter and less clunky gear shift rather than using gear clusters and a lot less maintenance to.
 
Know what you mean. :wink: Just trying to figure it out. See attachment.

gwhy!: That was the first idea. but Cvt drives is more for high rpm low torque and here is vice versa situation. I think that scooter cvt will have very low efficiency used like this also it will be at least two times heavier.
 

Attachments

  • gearing.xls
    67.5 KB · Views: 221
You may well be right about the efficiency at lower RPM, just a thought :D , But your configuration is good just not sure how smooth the gear shifts would be :? .
 
How about #219 chain for the second motor reduction? Bit of a nuisance, but it would enable you to increase the ratio there...

How much power do you want to get out of that motor? 2600rpm is quite slow... and 12t pulley is quite small....
 
I think of it as a climbing assistant so as much as possible is nice but ill be real and say 1-2kw. I am considering dual or even triple chain for the first one so I can go to smaller chain with biger ratio. But some how it seams that 1:7 is the biggest i will be able to fit in. Or add another axle with additional reduction belt.
 
very nice cad. interesting use of sprockets. flex under heavy pedalling may cause some unanticipated problems. i see a shock--is this a softtail? if so, is there enough room for the tensioner on the first chain segment to allow full suspension travel? also, what if you want to swap out sprockets to experiment with gearing?
 
No. It can be plettenberg also... :D just kidding... what do you think ..smaller? bigger?
You right about the pulley. It's not have to be 12t this I entered into sheet just to see complete ratio that I need.
It seams to me that additional axle in must.
 
HAL9000v2.0 said:
No. It can be plettenberg also... :D just kidding... what do you think ..smaller? bigger?
Click to expand...

I was thinking, more efficient..... It's running slowly in an enclosed space... Granted, you have lots of gears to maintain the rpm...

How about getting someone to custom wind a Scorpion kit (one of the new big ones)?

The motor that David B is developing should be ideal.
 
Actually, empirical test (with hub motor) show that I need only two gears first and last. First when something is wrong and last when all works well.

For a fewer speed cassette I am not sure how good will the shifting be.

Retrodirect will be ideal for this system with two gears but where to put cranks?
 
3 speed epicyclic as shared gearbox on the suspension pivot axle? Two separate inputs to it.

3 speed hub gear in the rear wheel? They only weigh 1 kg and subtract the standard hub weight from that.
 
Nice drawing!

It looks like it might have trouble shifting gears. The shifting mechanism is not shown, so I don't know what you had in mind. The spacing between the two cassettes is close and the chain might not like the angles involved. When you shift one cassette, I'm not sure if the other one will shift correspondingly at the same time unless you have two derailleurs. It would be nice to see if someone else has done something like this already.

One way around that would be to use an internally geared bike hub(s), like a Rollhoff or Shimano.
 
Miles said:
3 speed epicyclic as shared gearbox on the suspension pivot axle? Two separate inputs to it.

3 speed hub gear in the rear wheel? They only weigh 1 kg and subtract the standard hub weight from that.
Click to expand...

Nice. 2x 3 speed hub gear, one in wheel one on the suspension pivot axle. input from pedals via freewheel and direct input from motor.
it is only 350% ratio difference. I need at least 600%, so 3 speed hub in wheel an 9 speed shimano on the swingarm axle is 630% what is ok (Two cassettes is 650% 11-28 and 840% with 11-32 ).
I have regen but I will turn motor with pedals when it is off...
Now I am missing only "electro-controlled-freewheel-clutch"...
...or to use centrifugal clutch that will turn on motor, let say, above 25kmh...
...

yes, fecher it will be nice to see that is working somewhere...
There is no derailleurs at all ...imagine something like downhill front chain guard moving parallel on both cassettes. And one have chain tensioner with two small sprockets in it.
 
If you had 1500 Watts output - that would get you up a 22% gradient at around 25 kph. Ok, lets say 20 kph - that's still within 350%...

Couldn't you buy a Rohloff hub with the profit from your production line? :) That would get you 526% on the suspension axle. Even if you ran out of juice, you'd still be ok....
 
Awesome CAD drawing, how can I get that program for free? :wink: I have to agree with Miles, an internal hub would clean up all that cassette mess you have. And Fechter has a good point to, in that the chain is not going to like the angles with the cassettes so close. Maybe the Shimano Alfine would get you the desired reductions in one simple package. Then you could use a bmx chain and sprockets for a more stout driveline. If you go with the Alfine, you could probably get away with all belt drive too. Gary has a 3 speed internal and he says the motor goes through the gears about as fast as he can shift, so if you have too many gears you might spend more time trying to shift than pedal. Maybe you could put hall sensors on one of the pulleys that would send a signal to a servo to shift gears at a certain rpm, and have automatic electronic shifting! :twisted: That would make even the DH guys jealous.

Love the idea of building your own frame, :twisted: it seems there are a few of us here that are not happy with current frame specs, and custom is the only way to go. Have you priced the cost of such an undertaking? :shock:

Great ideas though, I can't wait to see your Optibike eater! 8)
 
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