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Deal on a gearbox.
- Thread starter svejkovat
- Start date
The 3/8 output shaft probably suggests that this is underrated for a bicycle transmission.
Can anyone point out a source of comparison ( i did a search, but am probably wording it wrong) among gearbox approaches in this range of use (size, weight, and torque requirements)?
I'm wondering about pros/cons of helical gears, worm gears, bevel gears, planetary gears, etc.
It seems like a worm gearbox would be a natural for reducing a motor within a bicycle frame to a useful rpm. It would allow the motor to be mounted along it's narrowest axis (for most motors) that is with the driveshaft front to back, and this style of gearbox is among the most compact for a given reduction. I don't see any setups with this however. Is a wormgear a nonstarter for some mechanical reason?
Can anyone point out a source of comparison ( i did a search, but am probably wording it wrong) among gearbox approaches in this range of use (size, weight, and torque requirements)?
I'm wondering about pros/cons of helical gears, worm gears, bevel gears, planetary gears, etc.
It seems like a worm gearbox would be a natural for reducing a motor within a bicycle frame to a useful rpm. It would allow the motor to be mounted along it's narrowest axis (for most motors) that is with the driveshaft front to back, and this style of gearbox is among the most compact for a given reduction. I don't see any setups with this however. Is a wormgear a nonstarter for some mechanical reason?
boostjuice
10 kW
I think it is very unlikely that gearbox uses worm gear reduction. As both input and output shafts are on the same axis and the reduction is so low that you could easily fit a single or dual reduction via spur or helical gears . Worm gears typically maintain the 90degree offset of the input worm and output wheel, like this inefficient thing.
Spiral bevel gearboxes or hypoids? Any examples of which out there that are affordable and would work into a design?
Or as long as design limitations don't preclude it, is a timing belt as primary drive off of a small low hp motor going to be optimal in terms of noise, weight, and efficiency?
Just seems like a very compact alum bodied hypoid gearbox would be a very nice way to get the reduction I need with the fewest parts in the smalllest space.
I've looked through as many of the surplus industrial sites I can find online. Anyone know of a source for browsing a variety of small gearboxes? Hypoid, planetary, etc?
Or as long as design limitations don't preclude it, is a timing belt as primary drive off of a small low hp motor going to be optimal in terms of noise, weight, and efficiency?
Just seems like a very compact alum bodied hypoid gearbox would be a very nice way to get the reduction I need with the fewest parts in the smalllest space.
I've looked through as many of the surplus industrial sites I can find online. Anyone know of a source for browsing a variety of small gearboxes? Hypoid, planetary, etc?
12p3phPMDC
1 kW
- Joined
- Mar 16, 2009
- Messages
- 462
search for the planetary thread...matex...
you supply the housing and bearings.
you supply the housing and bearings.
John in CR
100 TW
svejkovat,
I looked at the gearbox you linked before, and passed on it due to the size and weight. As a fixed gear reduction, I didn't like it because of the 3 spur gears used to get the same rotational direction for the 2 shafts, which seems like an unnecessary efficiency reduction for a 5:1 ratio. An intriguing idea is to change out the shaft of the central gear, and make it an output shaft as well to create a 2 speed output.
As far as small, tough, cheap gearboxes go, my favorite remains the helical bevel gearbox for an angle grinder. I have a couple, one with a 3.5:1 reduction and a heavier duty one with about a 4.5 reduction. I like the efficient right angle output, but the drawback is that all angle grinders seem to run the same direction, and the helical gears mean left side drive is a must.
John
I looked at the gearbox you linked before, and passed on it due to the size and weight. As a fixed gear reduction, I didn't like it because of the 3 spur gears used to get the same rotational direction for the 2 shafts, which seems like an unnecessary efficiency reduction for a 5:1 ratio. An intriguing idea is to change out the shaft of the central gear, and make it an output shaft as well to create a 2 speed output.
As far as small, tough, cheap gearboxes go, my favorite remains the helical bevel gearbox for an angle grinder. I have a couple, one with a 3.5:1 reduction and a heavier duty one with about a 4.5 reduction. I like the efficient right angle output, but the drawback is that all angle grinders seem to run the same direction, and the helical gears mean left side drive is a must.
John
There are often "off shelf" solutions that are tempting but when separating the gearbox from the motor it's discovered that the there is no bearing on the input of the gearbox. The motor bearing is required for alignment and any axial load. It's technically difficult to adapt these to other motors and I assumed that would be the case with most angle grinder gearboxes or those removed from power drills. Also, isn't most of this stuff designed for intermittant use?
I noticed quite a few "scooter" gearbox replacement units for reasonable cost. These are dedicated designs and appear to have a female spline input that would be tough to utilize with any but the motor they're designed for. I also noted some gearboxes available for atv's. These kind of look promising, if a little overrated for a bicycle. Sometimes they are incorporated into the suspension with a hollow output shaft on the rear axle. The Hoot and Grubee kit-type gearboxes for bicycles are pretty uninspiring. Many horror stories connected to the Hoot, and the Grubee doesn't look significantly better built.
Just what is the optimum speed reduction for size, weight, torque, noise considerations in motorizing an ultralight bicycle? Right now, it seems a matter (for hobbyists) of trying to make use of what's out there. What, after all, if you were working with a clean sheet, would you be looking toward with those needs in mind? I just started seriously looking a week ago, and am pretty astonished to discover a thread no more than a couple of months old is mining the possibilities of a planetary gearset minus the housing.
When asking this question on a couple of other engineering forums I've been met dismissively, almost with hostility. Existing mopeds are mentioned in the same breath as "why reinvent the wheel". Short sighted, inexplicably mean spirited, and probably not a little bit the stubbornly defensive sentiment within the US automotive industry that has retarded it's progress for a few decades now.
"Existing mopeds", not modern scooters (another species) are generally 30 to 50 year old designs, trotted out again in hopes of cashing in on what is hoped to be a short term energy crisis. I already have a couple of these in my garage. They're fun, but almost entirely uninspiring when I consider what might be accomplished with a modern mountainbike frame and suspension.
I noticed quite a few "scooter" gearbox replacement units for reasonable cost. These are dedicated designs and appear to have a female spline input that would be tough to utilize with any but the motor they're designed for. I also noted some gearboxes available for atv's. These kind of look promising, if a little overrated for a bicycle. Sometimes they are incorporated into the suspension with a hollow output shaft on the rear axle. The Hoot and Grubee kit-type gearboxes for bicycles are pretty uninspiring. Many horror stories connected to the Hoot, and the Grubee doesn't look significantly better built.
Just what is the optimum speed reduction for size, weight, torque, noise considerations in motorizing an ultralight bicycle? Right now, it seems a matter (for hobbyists) of trying to make use of what's out there. What, after all, if you were working with a clean sheet, would you be looking toward with those needs in mind? I just started seriously looking a week ago, and am pretty astonished to discover a thread no more than a couple of months old is mining the possibilities of a planetary gearset minus the housing.
When asking this question on a couple of other engineering forums I've been met dismissively, almost with hostility. Existing mopeds are mentioned in the same breath as "why reinvent the wheel". Short sighted, inexplicably mean spirited, and probably not a little bit the stubbornly defensive sentiment within the US automotive industry that has retarded it's progress for a few decades now.
"Existing mopeds", not modern scooters (another species) are generally 30 to 50 year old designs, trotted out again in hopes of cashing in on what is hoped to be a short term energy crisis. I already have a couple of these in my garage. They're fun, but almost entirely uninspiring when I consider what might be accomplished with a modern mountainbike frame and suspension.
Timma2500
1 kW
I sent rinomechanical the following email...
Subject: Selecting a gearbox for motor assisted mountainbikes.
Hello. I hope you can assist me in selecting a gearbox for the
following application.
Ultra light mountainbike with power assist from small 4cycle motor.
Power assist only. Top speed not to exceed normal bicycle design speed.
Honda GX35 4 cycle gasoline motor.
Net Horse Power Output* 1.0 kW (1.3 HP) at 7,000
Net Torque 1.6 Nm (1.2 lbs ft) at 5,500 rpm
Motor rpm should not exceed 5,500 rpm. Without having a performance
chart/curve
at hand I'd guess that 1.0 HP is a safe max value to work with.
Gearbox will be the middle of three reductions.
Timing belt from centrifugal clutch on motor to gearbox input, and
then chain from freewheeel (overrun) sprocket on gearbox output to
sprocket on crankset.
Overall speed reduced to match max rpm at the pedal cranks of approx 80
to 100 rpm.
I'm looking at specs for the planetary boxes. I wonder if planetary is
the right approach for such a
project?
Thank you very much,
This was their response..
Sorry, we do not have gearboxes for your application.
Steve Pullman
Rino Mechanical Components Inc.
216 North Main Street
Freeport NY 11520
www.rinomechanical.com
I get the feeling that there is a reflexive association made between "motorized bicycles" and adolescent boys. Dismissive.
Too bad. Guess ya just have to go it on your own with this stuff.
Subject: Selecting a gearbox for motor assisted mountainbikes.
Hello. I hope you can assist me in selecting a gearbox for the
following application.
Ultra light mountainbike with power assist from small 4cycle motor.
Power assist only. Top speed not to exceed normal bicycle design speed.
Honda GX35 4 cycle gasoline motor.
Net Horse Power Output* 1.0 kW (1.3 HP) at 7,000
Net Torque 1.6 Nm (1.2 lbs ft) at 5,500 rpm
Motor rpm should not exceed 5,500 rpm. Without having a performance
chart/curve
at hand I'd guess that 1.0 HP is a safe max value to work with.
Gearbox will be the middle of three reductions.
Timing belt from centrifugal clutch on motor to gearbox input, and
then chain from freewheeel (overrun) sprocket on gearbox output to
sprocket on crankset.
Overall speed reduced to match max rpm at the pedal cranks of approx 80
to 100 rpm.
I'm looking at specs for the planetary boxes. I wonder if planetary is
the right approach for such a
project?
Thank you very much,
This was their response..
Sorry, we do not have gearboxes for your application.
Steve Pullman
Rino Mechanical Components Inc.
216 North Main Street
Freeport NY 11520
www.rinomechanical.com
I get the feeling that there is a reflexive association made between "motorized bicycles" and adolescent boys. Dismissive.
Too bad. Guess ya just have to go it on your own with this stuff.
boostjuice
10 kW
Look through the Battle robot websites. They tailer to the hobbyist crowd and so are likely much more helpful to the small scale customer. They do custom ratios and sell individual gearbox parts. All at much cheaper prices than industrial power transmission companies like rhinomechanical.
For example, these P80 planetary series gearunits look particularly promising;
-3:1 > 256:1 ratio availability
-Rated to 85 ft-lb (115Nm) of torque in a small 2.5" faced unit.
Using one of these planetary boxes you could build a lightweight BB drive with even greater reduction than Matt's drives all with similar wieght and dimensions. You could start with a first stage belt reduction for noise reduction, followed by an intermediate planetary stage ending with a final chain reduction to a sprocket mounted on freewheel cranks. Thats the plan for my next build anyway.
For example, with an Astroflight 3210 motor (spec pdf) which produces a maximum of (375 in oz of torque @ 2.8hp, 7500rpm) total reduction up to the output shaft of the these gearboxes could be as large as 42:1 before reaching the torque limitations of the gearset.
375 in oz = 2.01 ft-lb
85 ft-lb/2.01 ft-lb = 42.28:1 maximum reduction
anyway, heres the website;
http://banebots.com/c/P80K-nnnn-0005
http://banebots.com/docs/P80A-DATASHEET.pdf
My next build;
There are other battle robot websites out there as well that sell mechanical parts with plenty of adaption potential for ebikes http://www.robotmarketplace.com/products/mechanical_main.html
Boostjuice, that looks like a very promising gearbox. I'm trying to figure out how input can be accomplished with a timing belt. Images of units on that website and pdf files show a keyed hollow shaft for face mounting an electric motor. I didn't read the entire pdf, but at a glance I didn't see any indication that these gearboxes were designed to handle any radial load at the input, which would be necessary even if you simply installed a stub shaft into the hollow shaft in order to mount a timing pulley.
Otherwise the outboard bearing plate that miles linked would be necessary to support a timing pulley on an input stub shaft. Why is there no mention of this on the site? Did I miss something?
Is anyone familiar with these two items from Comet Industries (hoffco-comet)?
"Cone Clutch Drive System Component"
"Speed Variator Drive System"
Here's the webpage...
http://www.hoffcocomet.com/comet/oem-drive-systems.asp
Otherwise the outboard bearing plate that miles linked would be necessary to support a timing pulley on an input stub shaft. Why is there no mention of this on the site? Did I miss something?
Is anyone familiar with these two items from Comet Industries (hoffco-comet)?
"Cone Clutch Drive System Component"
"Speed Variator Drive System"
Here's the webpage...
http://www.hoffcocomet.com/comet/oem-drive-systems.asp
Banebots returned a phonecall and confirmed what I thought. In the photo of the gearbox is a pinion gear. This is the input "sun" gear for the first gear reduction in the box. When this gear is pushed into the input side of the box, it now presents a hollow for the shaft of the electric motor. In order to drive this pinion with a timing pulley, you'd need to insert an 8mm stub shaft and support it with an outbound bearing block. You'll have to make your own, since the bearing blocks available from banebots are not made for the input side of the gearbox. In addition to this, that pinion gear is not intended to provide axial support for a pulley. You'd need to either add another bearing block so that you have support on both sides of the pulley, or you would have to machine a bearing into the input side faceplate of the gearbox.
If the motor it is designed for is inexpensive enough you might save a little work by simply tossing out the guts of the rotor windings and shaft, and using the motor end plates and bearings to support a shaft with timing pulley. Seems like a lot of effort just to work around the full length of motor and gearbox combo as designed, especially since in the end you're only shaving off an inch or two.
All that said, I looked through some more sources of planetary gearboxes and did not see anything in the sizes we're after with a bare shaft input and output. Any other sources that you know about?
Forgive me miles if all of this was what you were implying anyway in your last post.
If the motor it is designed for is inexpensive enough you might save a little work by simply tossing out the guts of the rotor windings and shaft, and using the motor end plates and bearings to support a shaft with timing pulley. Seems like a lot of effort just to work around the full length of motor and gearbox combo as designed, especially since in the end you're only shaving off an inch or two.
All that said, I looked through some more sources of planetary gearboxes and did not see anything in the sizes we're after with a bare shaft input and output. Any other sources that you know about?
Forgive me miles if all of this was what you were implying anyway in your last post.
boostjuice
10 kW
Yes bearing support is an issue. It's not drawn in the diagram, but I did intend to place a 1/2" wide bearing within the wall of the plate that the planetary box bolts onto. That way it would not be any wider than the dimensions shown, but yes you would probably need another bearing block on the left side of the pulley to share the radial force imposed on the stub shaft. I had assumed the input pinion of the planetary box had bearing support, but couldnt be positive as the spec sheet doesn't show this area well. I have access to a machine shop so making an 8mm > 1/2" keyed shaft to adapt the 50T pulley to the planetary input hollow is no issue for me, but it would suck to have to add more width to the drive through outboard bearing support, as you are approaching the direct motor/gearbox coupling width, which is too wide for pedal stroke/leg clearance.
Unfortunately for many, i think when attempting this sort of project it is a neccessity to have access to at least a metal lathe and assorted hand tools.
Unfortunately for many, i think when attempting this sort of project it is a neccessity to have access to at least a metal lathe and assorted hand tools.
...unless you could source another gearbox. Unfortunately, as you mentioned, the industrial suppliers usually ask many hundreds of dollars for their versions.
There probably is some radial support of the pinion gear, it's probably a pin in the center of the plantary gear carrier plate. Whether, when combined with the bearing in your framepiece it will support the side loads of a timing belt is a question best answered by an honest to goodness engineer. I"m guessing you'd be OK with it, but when you think about the role of the planetgear carrier plate, it's really not designed to manage side loads. It's supposed to "float" around that pinion gear and deliver torque in a straight line. Constantly relying on it to support the sideways loading of a timing belt may just lead to failure very quickly.
There's a chance, I suppose, that the designer left out the center pin on the carrier and intended only the shaft of the bolted on motor to keep the pinion gear aligned. I've never taken apart a larger planetary box like this, but this is often the case on c-face gearboxes I have used before. In this case you'd have no choice but two bearing support for the timing pulley.
You'll have to ask banebots about this specifically.
Got to be more straightforward solutions out there.
There probably is some radial support of the pinion gear, it's probably a pin in the center of the plantary gear carrier plate. Whether, when combined with the bearing in your framepiece it will support the side loads of a timing belt is a question best answered by an honest to goodness engineer. I"m guessing you'd be OK with it, but when you think about the role of the planetgear carrier plate, it's really not designed to manage side loads. It's supposed to "float" around that pinion gear and deliver torque in a straight line. Constantly relying on it to support the sideways loading of a timing belt may just lead to failure very quickly.
There's a chance, I suppose, that the designer left out the center pin on the carrier and intended only the shaft of the bolted on motor to keep the pinion gear aligned. I've never taken apart a larger planetary box like this, but this is often the case on c-face gearboxes I have used before. In this case you'd have no choice but two bearing support for the timing pulley.
You'll have to ask banebots about this specifically.
Got to be more straightforward solutions out there.
boostjuice
10 kW
It would be interesting to build this configuration. It would be noisy as hell, but probably as compact and interference free as you could get for the amount of reduction. Unfortunately i cannot find any 1:1 mitre gearboxes that utilise the bearing arrangement shown to minimise width. All the ones i found with just enough torque rating to keep the size small had awkward shaped housings that would require offset mounting and interfere with the pedal stroke. So one would have to build the mitre/bevel stage themselves, or get one custom built.
To make the mitre stage long lasting you would really need an oil filled case, and to do this you would have to incorporate gaskets and add oil containing bearing seals, which is really more trouble than it's worth.
To make the mitre stage long lasting you would really need an oil filled case, and to do this you would have to incorporate gaskets and add oil containing bearing seals, which is really more trouble than it's worth.
I guess spiral bevel and hypoid gearboxes (a special type of spiral bevel) for right angles are much quieter than beveled spur gears. They also have higher torque ratings for a given size/weight since there is more gear face in mesh. The hypoid drive has the advantage as well of having its input off the center of the other gear so that you could have a little more flexibility in your design for getting the motor out of the way. All this from what I've read in the last week anyway. I'm a 'holiday inn express' kind of engineer. These reductions are much more expensive to manufacture, but the trick is finding one that is already in mass production on some other consumer item. Something like a hypoid circular saw, but a bit bigger, and as was noted earlier, able to be separated from it's motor for use with another. I've looked all over the net. Nothing comes up. No doubt at all that it's out there, but unless it's already in mass production for some other application, it's waaaaay out of the budget for a motorized bike.
boostjuice
10 kW
Yes i agree that hypoid or bevel-helical would have a strength and noise advantage over straight spur mitre gears, but i think in this application mitre gears would be strong enough and themselves quiet after the majority reduction of the planetary box. However from a noise perspective, the planetary box would be the main noise contributer. To think, the single stage cyclone planetary boxes whine like a strangled cat and those motors are only spinning at 2500rpm, not 7500rpm like the Astro motors.
If making your own gearbox Mitre gears are much cheaper to buy than hypoid and bevel-helical gearsets because machining them is much more straightforward. However i agree an off the shelf consumer item with a usable gearset in it would be heaven. As you say im sure they are out their but finding them.......
If making your own gearbox Mitre gears are much cheaper to buy than hypoid and bevel-helical gearsets because machining them is much more straightforward. However i agree an off the shelf consumer item with a usable gearset in it would be heaven. As you say im sure they are out their but finding them.......
Lucky_Hoodlum
10 W
- Joined
- Apr 11, 2009
- Messages
- 66
http://www.teamwhyachi.com/gear.htm
Now that I think of it, yamaha used to make a shaft drive moped called the QT50 that most likely used a spiral bevel shaft drive at the rear wheel. It was a tiny little lightweight bike. That would probably be just about an ideal drive for use somewhere in an ebike transmission if you were looking for an angle drive. It's probably pretty bulletproof and might be very cheap off of an otherwise trashed QT50 if you could locate one.
(edit)
Hey, look what 5 mins search on ebay scared up...
http://cgi.ebay.com/ebaymotors/Yamaha-QT50-Driveshaft-Assembly_W0QQitemZ160336560121QQcmdZViewItemQQptZMotorcycles_Parts_Accessories?hash=item2554cdbff9&_trksid=p4506.c0.m245&_trkparms=72%3A1171%7C65%3A12%7C39%3A1%7C240%3A1318
(edit)
Hey, look what 5 mins search on ebay scared up...
http://cgi.ebay.com/ebaymotors/Yamaha-QT50-Driveshaft-Assembly_W0QQitemZ160336560121QQcmdZViewItemQQptZMotorcycles_Parts_Accessories?hash=item2554cdbff9&_trksid=p4506.c0.m245&_trkparms=72%3A1171%7C65%3A12%7C39%3A1%7C240%3A1318
What? Someone said "i don't care... money is no obstacle"?
http://www.nasatech.com/Spinoff/spinoff2001/t2.html
10hp rotary engine fits in the palm of your hand.
But then again, the "engine of the future is now!" claims made by various parties connected to the rotary engine have been no more reliable over time than the "great disappointments" realized by every new sect of the Adventist church since it first appeared in our midst. So what will YOU be driving when the rapture is upon us?
http://www.nasatech.com/Spinoff/spinoff2001/t2.html
10hp rotary engine fits in the palm of your hand.
But then again, the "engine of the future is now!" claims made by various parties connected to the rotary engine have been no more reliable over time than the "great disappointments" realized by every new sect of the Adventist church since it first appeared in our midst. So what will YOU be driving when the rapture is upon us?
12p3phPMDC
1 kW
- Joined
- Mar 16, 2009
- Messages
- 462
A friend of mine at work gave me two wheels from a
1980 yamaha 850 shaft drive motorcycle. They are very flexible
in terms of drive mounting options for a high powered wheel
because there are dual disc brakes up front and a rear disc on the
right and the drive side on the left.
The shaft drive interface plate to the wheel is a 6 bolt
star pattern. There are bonded rubber isolators in each mounting hole
to absorb shock. The input to the 6 bolt plate is a splined cylinder.
Really nice assembly actually. It would be easy to convert to chain drive too.
Anyway it's pretty similar to the Yamaha moped or scooter.
It's a nice little scooter. Super simple and highly integrated...
It looks like the shaft drive is also the entire swing arm...or at
least half of it.
It would make a great conversion or chop it up and turn it into a low racer
with a streamliner fairing. you could do a parallel drive with it...
Put another dc motor shaft drive assembly on the right ...now you've got a hybrid.
Probably pretty heavy though.
1980 yamaha 850 shaft drive motorcycle. They are very flexible
in terms of drive mounting options for a high powered wheel
because there are dual disc brakes up front and a rear disc on the
right and the drive side on the left.
The shaft drive interface plate to the wheel is a 6 bolt
star pattern. There are bonded rubber isolators in each mounting hole
to absorb shock. The input to the 6 bolt plate is a splined cylinder.
Really nice assembly actually. It would be easy to convert to chain drive too.
Anyway it's pretty similar to the Yamaha moped or scooter.
It's a nice little scooter. Super simple and highly integrated...
It looks like the shaft drive is also the entire swing arm...or at
least half of it.
It would make a great conversion or chop it up and turn it into a low racer
with a streamliner fairing. you could do a parallel drive with it...
Put another dc motor shaft drive assembly on the right ...now you've got a hybrid.
Probably pretty heavy though.
Actually it appears as if the entire motor is included in the swingarm. Don't even have to mess with a universal joint on a floating spline like my BMW that way. Motor weight is so far forward that it barely contributes to unsprung weight at the axle. Pretty cool minimalism. At this weight and under 35mph there are all sorts of design flexibilities that you'd never get away with on a 435lb 180mph motorcycle.
What fun. If I had a motorcycle/moped/bicycle graveyard next door I'd probably go crazy in it. Unfortunately, the automotive part-out (junk) yards around here don't take them. Not worth their trouble. All this stuff gets channeled straight into the scrap recyclers. Damn shame.
What fun. If I had a motorcycle/moped/bicycle graveyard next door I'd probably go crazy in it. Unfortunately, the automotive part-out (junk) yards around here don't take them. Not worth their trouble. All this stuff gets channeled straight into the scrap recyclers. Damn shame.