2 speed reverse-select geared bike

B

bobc

10 kW
Joined
Jan 20, 2011
Messages
993
Location
Knutsford England
A few things have come together in my mind regarding the ebike. I made one for my nephew with a big turnigy outrunner driving a jackshaft. This does it's job well, it's able to drag him up pendle hill at barely legal speeds. But on the flat it screams away at full revs not achieving very much. Because of the speed and power limit rules in UK this is OK, but for other regions it must be frustrating. What is actually needed is a less powerful motor, geared down to climb hills and geared up to cruise on the flat. Hence to the "queerbox" - a 2 speed gearing system I made for our greenpower car using ratchets and reversing the motor direction to select high/low ratio.
OK motor to jackshaft drive is taken by spur gears for low range and a chain/belt for high range. On the jackshaft, the gear and pulley/sprocket are both in sprag clutches so they will only drive the bike forwards. The final drive from the jackshaft to the wheel is same as the other bike - could be a chain or a belt.
The motor is on a RC ESC (sensorless) so to reverse it you need a changeover switch on 2 leads. Note you can't switch this under power, so position the controls so you have to take your hand off the throttle to switch the switch - easy natural interlock. Sensored drives usually have a reverse switch already so they're rather less of a worry.
50A changeover swtches are readily available - and of course this only switches when the motor is off. The only extra hardware is 2 sprag clutches (£15 each) and a pair of spur gears (which are usually idling except when in low range).
The only question mark I see with the system is the longevity of the sprag clutches - comments?
I'll put a drawing up when I get home....
 
If you search the forum you will find a couple of threads on designs for this type of "reversing shift" gearbox.
this is one of them...
http://endless-sphere.com/forums/viewtopic.php?f=28&t=21450&hilit=2+speed+reversing+gearbox
 
Lotsa 2-speed tranny chatter here:
http://endless-sphere.com/forums/viewtopic.php?f=28&t=8644
 
Forgive the noobie - I have to learn what things are called on here before I can search for them....
And there's nothing new is there ;^)
I think I might give this a go, it looks as though it ticks a lot of boxes. While it IS possible to simply throw a massive motor at the problem, I reckon a geared system is a bit more elegant...
Oh yeah - with the reversing to change gear method - it means the bike can NOT be pushed backwards..... shouldn't be much of an issue I would have thought..?
 
bobc said:
Forgive the noobie - I have to learn what things are called on here before I can search for them....
And there's nothing new is there ;^)
I think I might give this a go, it looks as though it ticks a lot of boxes. While it IS possible to simply throw a massive motor at the problem, I reckon a geared system is a bit more elegant...
Oh yeah - with the reversing to change gear method - it means the bike can NOT be pushed backwards..... shouldn't be much of an issue I would have thought..?
Click to expand...

Hi bobc,
The 2 speed is defo the way to go. I know I have not done much testing with my gearbox http://endless-sphere.com/forums/viewtopic.php?f=28&t=21450&hilit=2+speed+reversing+gearbox in the real world yet but I done enough to know it would be a big advantage to have such a system. My main concern, for my needs is that I need to be able to roll the bike backwards but im hopeing I may have a solution for this when I come to remaking my GB. As regards finding a sensorless RC esc with reverse.. they do exist..
 
This has sort of made my mind up to do another skip rescue mountain bike conversion.... this time for me.
I'll get 2 5Ah3s lipolys from hobbyking, and they have a 2kw outrunner at $30..
12mm sprag clutches with keyways are £15 each at simplybearings.
Various other bearings and sprockets will be £50 or so from HPC,
I'll need new hubs & spokes (I'll need to convert to disc brakes on the front), + a freewheel from the bike suppliers - say £50
I reckon that's a little over £200 (say $300) + some time. Ebike kits on ebay can be cheaper but are nowhere near as good -
this would give me a hill climbing stealth bike with a reasonable turn of speed... I checked out my daughter's old bike - I think it will do just fine - maybe I'll put suspension forks on it.
My nephew is very happy with his bike; apparently his latest game is striking up conversations with road bikers on racers struggling up long hills.... He's been using it for a couple of weeks now; I need to wire in the celllog8 to shut off the controller on low volts...
 
yeah- I also need a big reversing switch - digikey have a 50A HKK one which I hope will suffice, for $38; 50A is a bit light but I figure I will never switch it while the amps and volts are there.... (it's a 65A motor - bit will see much less amps than this most of the time...)
Gearing plans: - if I do 10:1 from the jackshaft to the wheel, I'll need 3.3:1 on the gears and 1.6:1 on the belt/chain between motor and jackshaft - with a 7000rpm motor that gives me ~15mph or ~32mph. I'll probably alterthe ratios a bit but this first stab show's it's all doable with reasonable size sprockets (e.g. they go round the sprags where necessary...) - bring it on, I think I'll start spending money tonight ;^)
 
Interesting thought - and it is an alternative way forward; but I think I'll stick with the big switch - it means I can use a cheaper plane ESC and when I let go the twist grip the bike will stop (rather than going at full speed in a different gear....).
An ESC with a separate reversing switch input would be interesting.....
 
And I've begun...
digikey reversing switch £26
HK RC stuff - outrunner, ESC, celllog and Lipolys £86
hall throttle twistgrip £6
Bike stuff next - but I need to count the spokes first ;^)
front & rear hubs + LH freewheel + 7 speed cassette £62
 
bobc said:
- it means I can use a cheaper plane ESC .....
Click to expand...

Bob,.. you may wish to read some of the many threads on using cheaper ESC's with RC motors on Ebikes.
There is a LOT of experience on this, mostly resulting in expensive smoke and frustrating failure followed by an order for a Castle ESC. :roll:
 
Thanks HH,
I appreciate what you say - I see it as a shot to nothing, if it works I'm over a hundred dollars better off, if it doesn't I've lost about 20. I've tried 2 cheap plane ESCs on bikes now & neither let the magic smoke out (one has been caned for a couple of weeks....) so - fingers crossed ;^).
I must be careful to stop with these $20 "shots to nothing" before I get up to 8 of them.......
 
Bike parts arrived today, so I've turned back the disc brake mounting for the rear and put the left hand thread on for the extra freewheel mounting. I also got the 12mm sprag clutch/bearings. I think I'll go for 1/2" chain for the final drive - puts more sort of "standard" stuff on the bike. I'll use 6mm chain and 1.0module steel gears for the primary drive & see just how much of a racket they make... the gears are for hill climbing only so they won't often be loaded but they'll always be turning... I'll engineer a box round the primary drive to try to keep the noise/grease in and fingers/grit out.
The spoke calculator said 258mm so I bought a set (£10) and a couple of pillow block bearings (£16)
That's got the running total up to £206; now UPS want an extra tenner for importing the damn switch from US - that is ridiculous - £216
Gears/sprockets and chain to sort out now!
£91 bought me spur gears, sprocket, 6mm chain & split link - running total £307
 
So the LH thread has replaced the disc mount on the hub, & I've made some housings for the sprags. I'll build up the back wheel over the weekend & draw up the remaining sprockets. I think I'll go for 8mm chain again; I just need too much gear ratio in the final drive to use 1/2" - I'm going for 12:100 teeth.
hubandsprags.jpg
 
Hi bobc,
I see you are making good progress , Just thought I would mention thou.. I have now fitted my GB to a bike and I was not that concerned at first the fact that the GB can not be back driven, But within 10mins I found it to be a right pain in the A#! . Have you come up with any ideas how this can be got around that you would be willing to share.
 
Actually no, like you I guess I reckoned it wouldn't be an issue....
Off the top of my head - I could put some kind of dog clutch on the output sprocket on the jackshaft - you can use ball bearings to engage the drive, have a spring loaded plunger force the balls out to engage the inside of the sprocket & push it in when you want to go back - I'm assuming the problems are when you're on the bike & want to just push back a couple of feet; when you're off the bike you'd just lift it...?
Maybe I should draw a picture....
Or some kind of clutch - a centrifugal clutch driving the sprocket would do the job, or an electrically operated clutch (I don't know where to get either of these items). Anyone seen anything vaguely suitable? - it has to be compact & on a 12mm shaft & cope with 10 to 20Nm torque and go up to 3500rpm.....??
quick check - loads of minimoto centrifugal clutches on fleabay - and no information about their specs.....
 
I can see it might be a pain - I guess I'll have to try it & find out the hard way - I do think the centrifugal clutch offers a way out though ;^)
trouble is they're all engineered for progressive takeoff with a twist & squirt little bike, not what I want which is no torque at 0rpm & lots at 100rpm+.
I could always make my own I suppose.......
 
Like you say, its not to much of a problem when your not on the bike as it can be lifted but it is surprising how often you need to just roll back even the smallest amount without even thinking about it. I was thinking along the lines of like you have already said a sort of a plate that is normally engaged onto the output sprocket but can be push out of engagement via a lever. I do think you may be able to get used to it for normal road riding but for any sort of technical riding situations a solution may need to be found. Its a shame because its such a simple 2 speed concept but if disconnecting the output sprocket is a must then this makes it not so simple :evil:
 
I agree. Centrifugal clutch seems the best option.

Looking at gwhy's avatar, I can quite understand why he needs this. I don't see it as being much of a problem for most people.
 
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