Using Right Angle Reduction Gearboxes

T

theyerb

100 W
Joined
Sep 8, 2008
Messages
122
Location
San Luis Obispo, Ca
I'm getting ready to build my second ebike-- a full suspension, Astro 3210 powered offroad beast-- and I'm trying to figure out how I'll go about gear reduction. Some of the two stage reduction units on ES like Matt's are gorgeous, but I wonder why we can't use commercially available reduction gearboxes. It seems like virtually all of the solutions on here are custom CNC'd units. A compact, right angled reduction gearbox, as long as it maintains high efficiency, seems like the ideal solution. For one, it allows the electric motor to align parallel with the frame of the bike-- a more space efficient design, imo.

Here's one that I'm looking at:

http://www.rinomechanical.com/gearbox_bevel.htm

I don't have an engineering background which is why I'm posting here-- for all I know, I could be overlooking some huge problem.

Is the above gearbox something that could work in an ebike application?
 
Looking at those torque ratings, there's no doubt they'll have one that can handle the job. I looked around locally down here for something similar and the stumbling block for me was the price. With the 5hp+ you're looking pushing through the gearbox, I think the issues will be size, weight, and price. Unless you're able to locate something you can pick up as surplus, I doubt you'll come close to the price of Matt's reduction rigs that are specifically engineered for the job.

John
 
I'm even using a right angle gearbox from a powerchair--one that uses the output shaft as the wheel axle, so it is pretty heavily-built and has nice bearings. :) But it is quite heavy, and it's input method leaves something to be desired. :( Right now I'm using it with the motor it came with, but that might change eventually, and I'll have to work on the output shaft of whatever I use if I do.

I've seen a number of builds around the web using various existing gearboxes of one type or another, including right-angle types--even one from a hefty angle-grinder. :) But one nearly universal thing about them is that they are fairly noisy gearboxes, even the oil-filled ones, and often heavy for ebike applications. Tolerances are often not that precise either, so the gears don't usually mesh perfectly, which can cause noise and can break gears if there are sudden bursts of power that slam teeth into each other across such a gap. The noise might be fixable with helical/curved gearteeth and the right materials, precision, which would all also help the breakage problems. But the only ones I have seen like that have hefty price tags.

Things like Recumpence's drives and Thud's 2-speed are probably much quieter and lighter solutions (though I have not heard or held any of those myself), for the power levels ebikes use.
 
Amberwolf,

Can you direct us to the angle grinder gearbox build? I've got one from a 2.5hp grinder that I've wanted to use. They're probably the best source for a mass produced item (so cheap) with helical gears and built heavy duty for high rpms. They probably don't have the reduction theYerb is looking for with only a 3-4:1 reduction, and they're one direction (definitely left or right side only), but I have one long motor that definitely needs a right and gearbox.
 
Hi,

Matt's unit will be a lot easier to mount and connect to your motor and bike. With a belt 1st stage (if you don't choose a motor too powerful) will probably be quieter.

A Neugart PLE 40-5 single stage ( ratios of 3, 4, 5, or 8 ) might be a good choice. It is rated for 14 Nm, and can handle maximum speeds up to 18,000 RPM:
http://www.neugartusa.com/Produkte/ple.html
  • # low backlash
    # high output torque
    # patented PCS®
    # high efficiency (96%)
    # 22 ratios i=3,...,512
    # low noise
    # high quality (ISO 9001)
    # any mounting position
    # easy motor mounting
    # life time lubrication
    # 30000 hrs design life
It is available in both inline and right angle configurations

I got the following in an email from their sales department (8:1 would be excellent):
As for the noise, there are too many variables that can affect the sound level (load, mounting, etc) but our controlled testing shows 58 dbA @ 3000 RPM no load.  

Pricing for the PLE 40 single stage ( ratio 3, 4, 5, or 8 ) start at around 300.00 in low quantity, depending on the mounting.
Click to expand...
Someone here did a build using a larger model Neugart he purchased on Ebay. I think you can find the thread by searching.
 
I don't have a link to the build; I originally found it some time ago after finding Eric Peltzer's ebike pages, when I was on the quest for a way to convert my original high-speed radiator fan motors to lower speed and higher torque. Problem is the original computer I started all that stuff on had drives die, and there's still a lot of stuff I never recovered. Apparently that includes all that info, since I know I also saved the webpages with pictures and stuff.

All I can remember is that it was a Makita grinder, and that it was a lot larger than the ones I have worked with myself, either 5 or 6" wheel size. I think it was a project started with the actual Makita motor but then replaced with a bigger one later on. The bike was a red 10-speed, if that helps. :(
 
I've spent the last 1.5 hours on a treasure hunt following the links posted here. Thanks! It looks like I'm not being very innovative with my inline right-angle reduction gearing ideas-- there is a lot of thought and experimentation in the area.

A heavy duty angle grinder shows a lot of promise. If it were paired with a low rpm motor, you might not even need further gear reduction.
 
Just make sure whatever gearbox you get has no or at least very minimal lash, meaning that the gears mesh as perfectly as possible, and there is no "wiggle" on the output shaft if the input is held motionless.

Otherwise you risk easily damaging the gears or even shearing off the teeth eventually (as can happen to Sturmey Archer 3speed hubs) under high torque loads, especially if the gear teeth were already separated (from rolling in reverse a bit) then are thrust suddenly forward into the other gear's teeth by motor input.

So cheap grinders probably will not last long; higher quality ones should be better. But even with the cheaper ones, as long as you are careful not to slam thrust thru it suddenly, they'll probably last longer.
 
After some thought and playing around with an angle grinder, I think it's probably not the best candidate for ebikes-- they aren't designed for the high output loads that we seek.

Then it came to me: what better tool than a right angle drill or hole hawg :shock: They are geared at a much higher ratio and designed to output far more torque and power than an angle grinder. Their outputs range from around 500-1800 RPM at 120 volts-- about 1/10 the RPM that a lot of angle grinders reach.

Used in an ebike application, an output of around 500 RPM be a nice sweet spot-- something well within reach once the voltage is chopped by 2/3 and matched with the right motor.

Now it's just a matter of finding one with a burnt out motor on ebay.

milwaukee_1680-21_01.jpg
 
I got a few of the Hole Hawg drills that I may try at some point. There are 4 main problems with using them:

1. man, are they heavy
2. the motor would have to be bodged on somehow to drive the existing motor (it has a gear milled on the end of the rotor shaft)
3. the inefficiency of the drivetrain is probably considerable
4. hard to remove the chuck, I couldn't do it without ordering the special shims from Jacobs, and I gave up.

If you want one to experiment with, you can most likely get one for free like I did. Find a place that sells reconditioned tools, a place that repairs them, Factory Authorised Repair place etc, etc, and then ask politely. I think I actually got three. The gears were stripped, that's what could not be fixed. When one gear goes bouncing around inside the gearbox, things get messy. I figure that from 3 or so, I should be able to get one geartrain working.

But it's awfully hard to get away from those concerns at the top. They're showstoppers. After I hit #4, I decided that there may be easier ways to build ebikes. Who knows, I might get one working just for kicks somewhere down the line.

Katou
 
Oh, the reason I never went beyond theory with angle grinders as a transmission is that the reduction ratio is too small to be useful.

Here's my reasoning:

1. typical angle grinders run at around 10,000 rpm output (the grinding wheel goes 10,000 rpm)
2. typical universal motors (small, used for most portable power tools, generally loud, ALWAYS has brushes) run at 10,000 rpm up to 30,000 rpm

Do the division, and most likely the reduction is 2:1 or so. Typically, people need far more than that, more like 8:1 or greater. I'm designing for around 10:1 with my bike.

Add to that, the grinder motor output shaft has the pinion gear milled into it - it's not separate. That means that if you take out the motor, you also get rid of that pinion gear. The only way to use it, is to leave the motor in place, and run a belt to turn the motor with your motor of choice.

That being said, universal motors will run on DC directly in theory, I've never done it, you just have to get the voltage up to 100v or so. I have seen a video on youtube - search on "power hawg" and you will find it - a guy is using an inverter to run a drill on AC from his DC battery pack.

Inefficiency and increased mechanical and electrical complexity for little gain? No thanks. That's my story and I'm sticking to it.

Katou
 
The angle grinder is pretty much out of the question for the reasons you described: they have a low gear reduction and spin at around 10,000rpm. The angle drills, otoh, spin at below 2000rpm and have a reduction of around 10:1. Stick a low RPM motor in their and chop the voltage to 36 volts and that motor would be right in the sweet spot.

The biggest hurdle is that when original motor is taken out, it takes out a pinion gear with it. Need to figure out how to attach that small pinion gear to a larger output shaft.
 
Try a right angle adapter for a 1/2 drill. That would be a lot cheaper unless you can find a broken drill.

Unlike you guys I have much more faith in the larger diameter helical beveled gears of a large angle grinder holding up under ebike use than I the beveled gears of right angle drills. I guess it's the summer I spent latched on the end of a big angle grinder, and seeing firsthand the shock loads and more continuous use for which they are designed to withstand. If you can find one for a hammerdrill, then you might change my mind. I have a couple of angle grinder gearboxes, so some day I'll find out for myself, though I will modify the gearbox slightly to seal it up for an oil bath.
 
John, angle grinder or angle drill, how would you go about replacing the motor? After looking at exploded part diagrams, it looks like the pinion gears on a lot of these things are attached straight to the stock motors. I would love to hear how you would select your motor and rig it into the angle grinder-- I currently have rough ideas but everything is speculation.
 
Well, you might do it the same way I pondered using one of my right-angle powerchair gearboxes that also uses a gear made as part of the motor shaft:

I had planned to cut the shaft off some distance from the drive-end (DE) bearing. From there, two possibilities came up:

1: Use a sleeve coupler to the replacement motor's output shaft. The rep. motor would be affixed to an adapter bracket made from whatever was available to securely mount it to the gearbox's input side, in such a way as to allow me to reach the coupler to tighten down any set screws/etc. and verify it's balance. The bracket would be made so that if I needed to I could recenter the motor in it vertically so the gears could mesh properly inside the gearbox, as I didn't expect my machining skills to allow enough precision to do it close enough without adjustment.

2: If #1 was impractical for any reason, I thought I would mount the motor parallel to the gearbox, instead of inline with it, and affix pulleys or sprockets to the output shaft of the motor and the stub of the gear/shaft, connecting with chain or belt as worked out with whatever materials I had on hand of the right lengths/sizes/etc. The mounting of the motor would be made in such a way as to allow tensioning of the connecting belt or chain, so that the gear and shaft are kept parallel to the gearbox gears for proper meshing (as there is only one bearing on that shaft, so nothing else to hold it parallel, unless a second one is added).

The advantage to #2 is that it also allows for correcting some of the gearbox reduction ratio if it was incorrect for my application, by changing the pulley or sprocket ratios. The disadvantage is that it is no longer a long thin package as it would if the motor were inline with the gearbox.
 
theyerb said:
John, angle grinder or angle drill, how would you go about replacing the motor? After looking at exploded part diagrams, it looks like the pinion gears on a lot of these things are attached straight to the stock motors. I would love to hear how you would select your motor and rig it into the angle grinder-- I currently have rough ideas but everything is speculation.
Click to expand...

I couldn't put my hands on the mounting plate I made, but here's a small angle grinder gearbox ready to go for a Kollmorgen 400w motor. I had to cut the grinder motor rotor shaft and make a sleeve to connect the new motor. The motor and gearbox housing mount to a common plate.
Angle grinder gearbox 1.JPG

To me the issue of a grinder gearbox is that they are one direction only, so no regen. The one above can only go on a left side drive. It has a gearing reduction of 4.25:1, which is perfect for the Kollmorgen leaving me probably 2:1 to 3:1 chain reduction to the wheel. Where one could really shine is if you had a long extremely high rpm motor. Then you can orient the motor in line with the bike's axis, and get some gearing reduction too. Note that this gearbox with just some grease inside, was designed for 25krpm input from a 2 hp motor, to be used under harsh high shock conditions.

John
 
Dude, way to go!

This unit looks like it supports the shaft on bearings located inside the head. That is the major hurdle. Perhaps this is standard, I've only taken one grinder apart. The one I took apart used the bearing of the motor to hold the output gear in the right-angle assembly. In that case, if you took away the motor, the part going into the right angle head would not be supported and would wobble all over.

Do you think that this is normal? If this is the standard way to do it, then that makes it all possible. The ratio that you found is quite respectable as well. Now, if we could just figure the frictional losses.

I'm quite impressed.

Katou
 
Just as a warning, the HF grinders (at least the cheap ones) have a lot of lash, and have very poor output shaft bearings (if any; some seem to just have sleeves!), so they will wear quickly and possibly even break teeth off. You'd want to check out the insides of it before putting in the effort of using it for that. ;)

Mine died that way just being used as a grinder, and with not all that much actual use on it. The motor works great, but it doesn't spin the output anymore due to the damaged gears in the angle box. :( Fortunately I have a better one (Makita) now, thanks to JEB, but it showed me that I would want to be careful about picking gearboxes in the future. Before that it was not really something I'd thought that much about.
 
The one pictured above has bearings on both input and output shafts. It's from a McCullough. My working grinder, a Black & Decker is definitely of lower quality just judging by the noise and how much hotter the gearbox gets. I haven't opened the B&D, but I have no doubt the McCullough gears are better. Both were only about $25, but the quality difference is obvious and is something you can get a feel for before buying.

The one I really want to put to good use is one from an old pro large grinder, maybe a decade old, whose motor burned out with the gearbox still in good shape. Check your local machine or welding shops for something used, but with a good gearbox. Then maybe you can pick up something high quality like Makita or Bosch for cheap or free.

John
 
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