Helical Gearbox Discussion

[etard]

I like Thud's relatively simple 2 speed transmission, but I would like to use gears instead of chains or belts to keep the thing small. I also like things as silent as possible so I can keep my earphones at a sane level, unlike on my 2 stroke. Helical gears seem to be the answer. While looking at explanations of how helical gears work, I came across this quote:

"One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees."

found here: http://www.howstuffworks.com/gear3.htm

On this page they show a very small helical gear meshing with a large helical gear. Is this any more efficient than the power sucking worm drive? Or is the worm drive a helical gear?

Since all automobile transmissions use helical gears now, why hasn't anybody tried to pick some up for cheap and implemented them for use on ebikes?

This has probably been discussed in one of the transmission threads already in great depth, so apology in advance for repetition.

 

[enoob]

no expert on this but i may have some helpfull info for ya.

helical gears only advantage is the noise level. straight cut gears are stronger , helical gears give up efficiency for decibels in the way they mesh, more time spent rubbing eachother. i suspect chains and sprockets are more efficient than any helical gear.

so it comes down to what your priority's are - noise level ? or efficiency ?

check out the gear system on the setup in the link below pretty sure its a worm driven setup but made to work with a power drill most drills are in the 2000 rpm range.

http://endless-sphere.com/forums/viewtopic.php?f=28&t=14061

 

[boostjuice]

This is the gearunit im using minus the AC motor pictured - I use a custom adapted Cyclone "1000/1500W". They are a 2 stage bevel-helical gearunit. The A05 sized casing i use is only 100mm wide so it easily fits between the cranks even with a freewheel and overhung support bearing on one side.

The manufacturer quotes 3% loss per stage, so 94% efficiency overall. Once the gears bed in they are damn quiet - hub motor quiet.

Helical gears are quieter than straight cut, but must be a bit larger to transfer the same torque -however not a whole lot larger. This is due to a lower surface area of contact in the gear meshing. Shaft bearings must also support thrust loads and axial loads. Straight cut only need to support radial loads. Mechanically, they are are a great option for high torque speed reduction when lubricated via oil bath. Unfortunately this complication and the fact that cutting helical gears is extremely expensive means they will never be economical for most e-bikes. My gear unit cost me a bit over $1000AUD.
http://www.bonfiglioli.com/apres_uk.html

I looked long and hard for small sized high reduction gearunits of similar dimensions/design and at low cost. I checked surplus stores and considered adapting automotive parts. All were too bulky, had bad dimensions for bicycle adaption, or just didnt have the reduction required. I reluctantly settled on buying an industrial gearunit new as i couldn't find a suitable alternative.

Oh, and worm gears are different to helical and are very innefficient at most reductions and loadings. However worm gears are smaller/lighter/more compact for a given output torque than the abovementioned setup. They also are great in that they always have perpendicular input/output shafts.

Will post pictures of my build in short time. Have had to redesign and reconstruct the mounting due to the torque ripping the thing of the frame.

 

[Miles]

It weighs 5 kg, boostjuice?

 

[boostjuice]

4.8kg by my scales. Total weight with the cyclone motor and flange adapter ring is 10.6kg. However low and central mounting on the frame makes the weight more than acceptable.

It might sound heavy, but then how much does an unlaced Crystalyte 5000 series hub motor weigh.....? 10kg ....and its unsprung centrifugal weight (on a soft-tail), and it cant utilize gears.

 

[Thud]

etard says:
, why hasn't anybody tried to pick some up for cheap and implemented them for use on ebikes?

The problem of modding gears is they are TOUGH to work on after the heat treatments.
I am all for gears in a transmision,
I speculate I could reduce the size of my 2-speed by 50%+ using gears.

Noise:
I just re-watched recumpences video's trying to compair my tranny sounds to his reduction units, they are equill as far as I can tell. Anyone can tell something is happening when you pass by them. Not really stealth under power.
A "proper" fully enclosed gear box will be quieter but again, I have heard some old willy's Jeeps (straight cut tranny gears) that just howl.
I have been looking for some fiber re-enforced gears, But have found nothing off the shelf.
Proto-typing one offs & the low volume would require some serious investment.
Is there much interest in a 2-speed unit?
Is it time to re-open the 2 speed thread & delve into the "ultimate" unit?
Any thing can be made.
I would be suprised if Matt isn't finishing a design right now

motor noise:
Are the Astro inrunners quieter than a = outrunner? (I assume so)
My 2 cents:
I think the 1st solution is a more "Bike" friendly motor design. (although my 80-100 turnigy showed up this week )That = less reduction & noise associated with high The rpm stuff & may simplify the 2 speed unit design.

(Thuds new years resolution #1-get post replys to 5 lines or less )

 

[etard]

Boost,
That answers a lot of questions, thanks. So at a right angle the gears experience the same loads as if perpendicular, is that correct? (Axial and Thrust) So along with expensive hardened gears, it requires expensive robust bearings, inside of a stout case to hold all the forces? I am beginning to see why very few have gone down this route. Have you opened yours up to peek inside? Or is it sealed?


I enjoy long-winded responses Thud, thanks for that. I am thinking of finding a motorcycle gearbox and stripping some gears out for experimentation, would you be interested in me sending you a few? What should I look for? I wonder if a transmission shop would have some laying about... The way I see it, the answer to most problems is around us, we just dont have X-Ray vision. :wink:

Oh yeah, as far as Recumpence, things have been awfully quiet in Illinois lately (besides the constant weeping of Bears fans :wink: ) I wonder what he has in store for us this winter.... Should I be saving my coin?

 

[Miles]

I think bj meant that helical gears generate axial as well as radial forces, etard. Straight cut gears only generate radial forces.

 

[Thud]

etard,
thanks for the offer, but.....
I have no less than 13 motorcyles assembled right now & 6+parts engines/transmisions. Motorcycle parts I got in abundance.
would you like ME to send you something to look at? :lol:
adaptation is the real bi_ch.
To modify the shafts & gears you need to grind the hardend parts to size.(a dirty, time consuming task) another little know fact is the designers take nesisary liberties with diametral pitch to make the ratio's of the different speeds all fit the shaft centers & mesh correctly. So there are very wierd 1/2 #s in many transmisions. That means you need to keep the gears in pairs as they were in the original.
On a side note the gears in motorcycle transmisions are all straight cut. (kind of off topic )The primary reductions are often helical cut. (my old Hondas are all straight cut on the primarys)
I have been eyeing a suzuki motor lately, contemplating the manufacture of a custom shifting cam to get the 3 speeds I want. built into a fabbed compact gearbox, adquitly sealed & lubed. But I really think the amount of work to adapt the "parts" is more than adapting a whole unit a'lla FrankG.
None of this is ment to dampen the discusion, given the topic of the thread I say design away & do the math on what you think ya need, I am certain we can get it built. (justifying costs is another topic! )

 

[amberwolf]

The wheelchair motor's gearbox I am using now has some helical gearing in it, but some is plain (radial); I'm not sure why. It's from Invacare, made in China for them. Weighs about as much as the motor itself, but it is also designed to directly support one of the main wheels of the chair (it's output shaft *is* the axle).

It is pretty quiet, but not silent by any means. It kind of sounds like a servo motor in a robot sound effect from sci-fi movies. It's still quieter than some of the other noises on my bike, like the temporary pedal chain tensioner.

If I remember, I'll take pics of the inside when I next take it off the bike for drivetrain modifications. (probably not soon)

FWIW, in converting the motors 4500+ RPM to ~200RPM it outputs enough torque that it destroyed one of my triple's chainrings at the front of the last drivetrain section--bent it like a taco (almost), when I was in highest gear and had to stop suddenly for a right-cross attempt by a truck, and forgot to shift back down and accelerate very slowly until it shifted down.

 

[boostjuice]

Boost,
So at a right angle the gears experience the same loads as if perpendicular, is that correct? (Axial and Thrust) So along with expensive hardened gears, it requires expensive robust bearings, inside of a stout case to hold all the forces? I am beginning to see why very few have gone down this route. Have you opened yours up to peek inside? Or is it sealed?

lateral/radial (not axial - my mistake) loads are just three different words for the same thing. Force applied perpendicularly - at a 90degree right angle to a shaft. Because helical gears have a helix tooth angle, they generate thrust loads as well as axial loads due to the gears trying to push away from each other in two directions or axis during meshing. (Thrust load = force applied length-ways through a shaft, think sticking a javelin into someone :lol: )

Gear units will always be expensive due to their complexities. The reason chain/belt based drives are cheaper and more forgiving to setup is because the power transfer medium is flexible enough to accommodate imperfect setup. The result being that shaft to shaft distances and the axial alignment of sprockets/pulleys are not super critical. The small amount of sideways flexibility inherent to chain/belts together with the use of idlers/tensioners allows a much more care-free/flexible placement of relative jackshafts/transaxles.
Machining costs increase exponentially with accuracy/precision requirements, and that doesn't favour gears from a $$$ point of view.

the main issues with Gearboxes/Gearunits;
- Multiple bearings supporting a common shaft must have their bearing reliefs machined perfectly concentric in relation to each other to avoid angular misalignment/eccentricity of shafts. The relative location of gear-coupled shafts must also be highly accurate.

-Proper gear meshing requires accurate location of pinion and gear so as to avoid premature wear on the teeth, and keep force away from ends of the teeth which can prematurely fatigue/wear/break them. Oil bath lubrication requires low tolerance seals to keep oil in where shafts enter/exit the casing. Removable plates needed for the installation of gears and shafts must also have gaskets to avoid leakages.

-As you suspected, a strong rigid single piece frame/casing is preferable. Manufacturers usually cast these into a basic form before machining faces and bearing retainers into them and adding plates after the internals are installed.


As thud mentioned, they are not something that you want to be manufacturing on a small scale. The economics just don’t add up.
I haven’t opened up my gearunit up to have a look. My curiosity was quenched by the internal cutaway drawing shown a few posts back. However I did replace the gear oil after the initial run-in period. Although the manufacturer specifies maintenance free operation/lubed for life, the engineering firm i purchased it from explained that the small amounts of filings that accumulate during run-in will increase the wear rate of the gears. Best to change it once.

 

[boostjuice]

The wheelchair motor's gearbox I am using now has some helical gearing in it, but some is plain (radial); I'm not sure why.

It is pretty quiet, but not silent by any means. It kind of sounds like a servo motor in a robot sound effect from sci-fi movies. It's still quieter than some of the other noises on my bike, like the temporary pedal chain tensioner.
(

There are bevel/mitre gears with teeth of straight cut but perpendicular orientation, and then there are bevel - helical/spiral gears that feature angled/curved teeth that 'pad' the contact of meshing teeth through the angled approach. Both provide a 90degree rotational orientation change between input and output shafts (handy for mounting motors/gearunits of long length on a bicycle), but there is a large difference in noise production, and due to the extra complexity of machining gears of even less linear shape - cost as well.

If your gearunit is that noisy, it may be that your gearunit uses straight cut bevel/mitre gears.

 

[Miles]

Axial/lateral/radial loads are just three different words for the same thing. Force applied perpendicularly - at a 90degree right angle to a shaft. Because helical gears have a helix tooth angle, they generate thrust loads as well as axial loads due to the gears trying to push away from each other in two directions or axis during meshing. (Thrust load = force applied length-ways through a shaft, think sticking a javelin into someone :lol: )

I've always understood an axial load as being one along the direction of the axis of the shaft.

http://en.wikipedia.org/wiki/Ball_bearing

 

[amberwolf]

If your gearunit is that noisy, it may be that your gearunit uses straight cut bevel/mitre gears.

You're probably right--I misunderstood which kind of gear was being talked about.

 

[boostjuice]

Axial/lateral/radial loads are just three different words for the same thing. Force applied perpendicularly - at a 90degree right angle to a shaft. Because helical gears have a helix tooth angle, they generate thrust loads as well as axial loads due to the gears trying to push away from each other in two directions or axis during meshing. (Thrust load = force applied length-ways through a shaft, think sticking a javelin into someone :lol: )

I've always understood an axial load as being one along the direction of the axis of the shaft.

http://en.wikipedia.org/wiki/Ball_bearing

Yes my mistake. Ye be right as usual