2 speed reverse-select geared bike

[bobc]

OK, I've been running this today; no disasters or burnt fingers; it's good but too slow.... originally designed for a much smaller motor (which therefore revved a lot faster) it maxxes out at just 17mph in the high gear, so almost legal ;^)
So I need to go for a rather smaller rear sprocket (that one's 100 teeth...)
OK the interesting bit: the reversing gearbox... What can I say - it seems to work exactly as expected, and, also as expected, it's a bit on the noisy side. The steel gears are in mesh all the time (even when drive is via the belt). Once you're up at 17mph there is enough wind and other noise to make the motor/gear noise seem not too bad.
The little (3mm pitch,9mm wide) belt skips a bit when full throttle is applied - I don't think it's going to last long: I'll start making the 5mm pitch components.
What this really means is that I am going to have to finish off the lipo charger/equaliser I was making.... ;^)

 

[bobc]

Ran this again today (charging the batteries now....). I must say, the motor and ESC work very well. In 1st gear the bike wheelies up to 10mph from crawling speeds and in top cruises happily at 19 or so (though the belt is now slipping too much for top gear to be practical). The ESC is a "hobbyking 50/60" - dirt cheap & I'm running on 6s 5Ah LiPo. Next week I'll get a 5mm pitch belt replacement and get an 80 tooth rear sprocket cut. Once the toothed belt is working right and the gearing is sorted, I have every confidence this is going to be a really simple, practical and usable system. Having the 2 gears means you don't need ridiculous power levels to maintain a reasonable speed on the flat and still be able to get up steep hills. As has been pointed out above, this is a really simple solution, with very few parts, all easy to make! Not being able to push the bike backwards has not (yet) been any sort of issue. Looking forward to seeing what mileage I can get from the 2 small batteries .... ;^)

 

[gwhy!]

Im glad its working out, the whole pushing the bike backwards was a major body blow for me ( Im still working on a solution ) but im sure for normal riding and may be some light off road it would not be a problem for 99% of people, well done for getting this up and running. How quick do it shift gear, what I mean is it seamless ( smooth ).

 

[Miles]

We need to get "instant reverse" incorporated into all the controllers that are being developed for ebikes.....

 

[bobc]

Haha - the gear change is anything but seamless - but it had to be that way for me, using a standard RC ESC & physically switching 2 motor leads. I needed to be sure the ESC was off before switching the motor leads & did this by positioning the reverse switch so that it (1) had to use the throttle hand and (2) was some distance from the throttle.... I figure that in reality the lower gear will only be used in fairly exceptional offroad/steep hill stuation.
Yes, if the ESC was doing the reversing I agree that it could be made pretty seamless! The motor's interia is so low the gearchange could actually be instant.

 

[bobc]

Finally got he whole bike working today, gears, belt drive, everything. Was fine for about 10 minutes then I went up the hill & the sprag clutch on the spur gears failed & I lost the low ratio. I'll look into how & why it failed & report back. That apart - brilliant; the belt drive in particular seems very strong. I'll post a photo tomorrow - the system is looking compact & effective. Perhaps my mistake was using the cheap sprags....

 

[Miles]

Perhaps my mistake was using the cheap sprags....

This is what we need to find out..... The Chinese usually give a nominal torque rating of 7.5Nm for the CSK12 (with a max. torque factor of 2.5x nominal).

Did you see this thread, Bob?
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=28935

 

[nonlineartom]

How many Ah do you burn going up Pendle Hill? I've been thinking about tackling that one myself as the views are stunning.

 

[bobc]

Dammit Miles- I'd looked everywhere for that snippet.... Suddenly everything is clear....
8krpm motor is 840rad/s - 2kW @ that speed is 2.4Nm. put it thru 6:1 gears & that's 14.4Nm. That's 2x the sprag rating on the low gear (only 1x on the high gear/belt).
So I'll have to stop diong the wheelies........ ;^)
Now you pointed it out I had a look at the other thread ;^) - to be honest I still haven't had any reliability issues with the RC stuff: I suspect it's the people who are not quite geared right & let the ESC bog down who blow 'em up - I think if you give them full throttle with low output volts (PWMing) they only last a few tens of seconds. After all, they're designed for running a prop.
Have you seen any sprags with a marginally better spec, the same physical size? I do note that there seem to be 2 sorts; a £15 sort which I bought and an £80 sort which I didn't....
Tom, it's my nephew who's commuting over pendle - Clitheroe over to Sabden, then up again over to Simonstone - He STILL hasn't used the ebike - he seems to just use it after work to wind up the lycra wearers... (his dad was out training on his racer the other evening, toiling up some hill when he heard a tell- tale whine coming up behind.....;^)

 

[Miles]

Dammit Miles- I'd looked everywhere for that snippet.... Suddenly everything is clear....
8krpm motor is 840rad/s - 2kW @ that speed is 2.4Nm. put it thru 6:1 gears & that's 14.4Nm. That's 2x the sprag rating on the low gear (only 1x on the high gear/belt).
So I'll have to stop diong the wheelies........ ;^)

Steiber/Formsprag give a nominal torque rating of 9.3Nm for CSK12 but, with a max. torque multiplier of only 2x nominal.

I noticed Simply Bearings just copy the Steiber data over for the cheapies, too...

We need to do some testing, I think..... You've made a start 8)

There's not a lot of difference in price as you scale up. As you noticed, there's a huge difference in price between the Chinese and Steiber/Formsprag.
It makes sense to work out how much we need to de-rate the Chinese ones to make them reliable.

 

[bobc]

Here's a picture of the finished installation

I'll rebuild with a cheap sprag & be gentle with it, see how it goes. Certainly it's interesting how it failed pretty much exactly where the spec predicted.

 

[bobc]

OK, having looked around it seems as though the 15mm bearings have twice the torque capability of the 12s & are not a great deal bigger, so I'll try to shoehorn one of them into the gear.... It feels like the right thing to do (with the lower gear having twice the torque ;^). Hopefully I can make it all fit OK......

 

[bobc]

OK - been running the bike today (about 5 miles). So far so good - nice to control, plenty of poke - the odd small mechanical issue which I hope I'll be able to fix (couple of screws come loose I think).
It does 8 / 16 mph in the 2 gears, and it's not too noisy. I'm getting a smaller sprocket for the wheel over the next few days & maybe a bigger one for the jackshaft - I want to get max speed in top nearer 20 or 25....
The MTB is so much nicer than the folder at speed with its bigger wheels & tyres: I also have to ditch the knobblies & get some road tyres on there & start thinking about longer journeys.
Maybe I'll post a vid for miles - I'll have to tape my video to my helmet....
I didn't say above, I've fit a 15mm sprag to the lower gear now. tonight I loctited some of the screws &replaced the 8mm screw in the photo above with a good old hex head bolt - I hope that will solve the "screw loose" issues ;^) I should get the 80 tooth wheel sprocket tomorrow, when that's on I'll do a range check at 20mph. I'm hoping for 6 miles or so (on 6s 5Ah lipo) so a doubling of battery capacity will get me to work.... (and some nice weather....)

 

[bobc]

80 tooth wheel sprocket now made & fitted. Bike now does 10/20 in the 2 gears (quelle surprise....)

Actually the bike seems real good for now - fairly quiet & powerful - once I've replaced the knobblies I'll do a range test.

 

[Whiplash]

Do you have a complete pic of the whole bike? Nice build!

 

[bobc]

bit of a vid of riding the bike. I set off in low gear unnecessarily - just to demo the gear change. Unfortunately the vid cam on my helmet has a rather narrow field of view so all you tend to see is road - I'll probably fix it to the bike next time
[youtube]2apscqKTWYk[/youtube]
Monday night - did a range check. 5Ah@ 23V is 115Wh, it went 4.4 miles at 20mph (pretty much all electric)
Considering how hard it is to pedal the thing, I'll do another check when I get more suitable road tyres on it;- 25+Wh/m seems rather high.... but I suppose I am a big fat git. Comparing the MTB with my road bike, when you freewheel it feels like the brakes are on. I'd like to get it down to <18Wh/mile, then 10Ah lipo would get me to work....

 

[bobc]

Another range check, this time with michelin city slickers on, result 4.8 miles, 10% range improvement by getting rid of the knobbly tyres.
Noticably easier to pedal too - yes thanks I'll have that. And a mate wants my old tyres - result ;^)

 

[bobc]

Here's a picture of the whole bike
Ready for a quick journey to the pub....
love these long summer evenings ;^) (the electrics mean you arrive quick and non - stinky...)

 

[Whiplash]

Very nice indeed!

 

[bobc]

Thanks whip,
It has been quite a successful project & I find the bike very usable & low maintenance. It's a compellingly simple way to get a geared ebike, also leaving you with the original bike transmission unchanged (with no extra drag from the electric parts). It's done 30 or 40 miles now; there's still one issue with it, but that's liveable with.
Parts needed:
rear wheel - shimano deore disc brake hub : turn off the disc brake mount & thread for left hand thread freewheel.
ACS southpaw freewheel
sprocket, 8mm pitch x 80 tooth, laser cut & bolted to freewheel
Motor: turnigy outrunner with 8mm shaft. 20 tooth 1 module spur gear & 20 tooth 5mm pitch HTD pulley, both mounted on a single tapered insert.
Motor bracket: 3mm angle steel (actually hacksawed out from a big piece of ERW RHS box)
Layshaft: 12mm running on 2 12mm pressed steel plummer blocks.
Output sprocket 8mm pitch 16 tooth, fit to taper on shaft
120 tooth 1 module spur gear, on a 15mm ID sprag clutch
60 tooth 5mm pitch HTD pulley on a 12mm ID sprag clutch
belt tensioner - turned from some 30mm ally, on 2 flanged 8mm ball bearings. Bracket is small bits of 5mm steel.
2 mounting/clamping plates made from 10mm Al plate, all held together with the 4 plummer block mounting bolts. These plates have a 32mm diam. groove in so that the seat stay doesn't get squashed, & to help align the layshaft.
Speed controller: towerpro 50A (for model plane)
throttle: hall effect twist grip + my own interface to ESC
reversing switch: 50A DPDT from Digikey
Isolator switch: FIA switch for cars
Battery: 6s 5Ah turnigy LiPo

The issue I still have with it is that I can't find a 71 tooth 5mm HTD belt. So I've had to put a synchroflex belt on & that won't take full beans....
As you can see the build is pretty simple, I think it's a good way to go for anyone...
( who has a lathe & can drive it...)

 

[gwhy!1]

Hi bobc,
I am very pleased its holding up for you. I guess your only put low power through this system, how is the sprag clucthes holding up? . I am still thinking about this ( and my problem not being able to roll backwards ) and looking at your setup have given me a idea. Some sort of movable plate that is always engaged with one of the gears ( so for normal use it will never get used but if you need to roll backwards you can disengage one of the gears ). I think I need to draw this out and make sure my logic is right. If my thinking is right I don't think it would be to difficult to implicate. What do you think ?.

 

[bobc]

Hi gwhy,
I broke the first sprag on low gear straightaway and replaced the 12mm one witha 15mm one (twice the torque capability). So far so good, but not many miles on it yet & I'm very conscious of the unused gear whistling around backwards. I'll see how it goes - if I get a few hundred miles out of a sprag I'll be reasonably happy, it's not a big job to change one anyway.
Bob
PS I'd be tempted to try a centrifugal clutch if the rolling backwards thing was an issue - they're ten a penny & easy to put in place. One of those spring clutch things should work (even better) but might be tricky to source. Any dog clutch type arrangement will be tricky to make "good"....

 

[bobc]

Update;
the bike now has 3 off 6s 5Ah Lipolys and typically 15 miles range at 21mph. The sprag clutch on the higher gear was showing signs of distress (I've had to open the throttle gingerly for a few weeks so I've replaced it but I'm pretty sure I'll have to put a 15mm one on there as well eventually) So I conclude that the cheap 12mm sprags simply can't take the torque from a 6374 turnigy outrunner with a 50A controller, even in the higher gear!Otherwise, going well, I'll try the 14mile commute to work next week - should be an adventure!

 

[bobc]

Just motored to work for the first time. There was JUST enough electricity - low volts lockout dropped in at the top of the hill letting me freewheel the last couple of hundred yards to work. So: with (yet) another battery (up to 20Ah 6s) it'll be perfect (spare capacity to cope with headwinds & reducing depth of discharge). Very pleasant ride - with that all important frisson of range anxiety! On charge now, full amps out of a bench power supply, I'm knocking off at lunchtime.
ciaou
Bob
PS and home again - bags of juice left in this direction, just down to 3,77V per cell. I can't tell you how nice it was to cruise through cheshire on a warm late summer afternoon. But I'll order ghe extra battery now....