Grinder gearbox to handle 90° bend on bike drive

[John in CR]

I have a couple of motors that I'd like to try but they are somewhat long, so I'd like to place them in line with the bike axis instead of sideways. To do so requires a 90° bend in the rotation, and I'm trying to figure out something off the shelf. The best I've come up with is the 90° gearbox on a portable grinder. They seem to handle plenty of rpms and must be strong and durable. I don't know if it's a simple miter gear with a 1:1, or even better for my purposes, a beveled gear with a non-direct gear ratio. Any thoughts regarding something better or cheaper that would also work. Anything wrong with the idea?

John

 

[docnjoj]

Sounds like a plan, John! Harbor Freight, 20 bucks!
otherDoc

 

[John in CR]

$20 + shipping to Miami + $40 or so forwarding to Costa Rica + import duties and taxes = better to just get one here or cannibalize the one I have. A used heavy duty one locally would be ideal.

I assume that I should retain the same direction of rotation, since the gears may be designed to take the stress and load in one direction. This idea seems cheaper, more compact, and lighter than trying to track down something like a small differential for a small ATV or riding lawnmower. Being simpler it should have less loss in the gearing too. My main concern is whether it's likely to hold up for a reasonable time.

Maybe I'll keep the Comet CVT between the output shaft and chain, which would lessen the stress and make hill climbing a breeze. I just want to get the inadequate motor off of my 450lb e-moto with the performance of an ice wagon, and on to a 100lb e-bike which should be fun even with 100lbs of kids and groceries.

John

 

[John in CR]

It just seems to get better. My grinder has a 3:1 reduction and a 1/2 output shaft. That's 30krpm input and 1kw, built for very harsh environment, and these things take significant shocks to that drive chain, as anyone who's used a grinder can attest. Unless I'm missing something, it should handle a bike no problem. That 90° bend will make for some real flexibility in motors and motor placement too. With a gear reduction and high rpm no problem, it may be prove useful for an RC motor install too.

John

 

[johnrobholmes]

I only see it as being a great idea! My only concern would be efficiency and maintenance. Does it require relubing every 5 hours of use?

 

[John in CR]

I only see it as being a great idea! My only concern would be efficiency and maintenance. Does it require relubing every 5 hours of use?

I hope not. I've never lubed one and I don't even see a place to lube mine. I did a summer in college at a meat and potatoes machine shop, and I'm sure I logged at least 100 hours of use on what was already a well used machine, and no maintenance whatsoever, just change the disk. They are such dangerous and abused machines, I think it's something that really has to be overbuilt.

John

 

[drewjet]

Now put that together with the 3 speed Dewalt gearbaox a large RC motor and HOLY COW!!! we are talking one badass drive system

 

[John in CR]

I opened it up today, and the gears are spiral beveled gears, so definitely one way operation, and for mine it means left side drive. Based on the size and shape of these gears and the nature of their designed use, I'm sure these will prove even more durable than those drill hammer gearboxes that the robot guys swear by. There was some grease in there, but the gears themselves were pretty dry. If it's advisable, I'd like to plug the 3 holes in the housing and put some gear oil in there to make it more quiet and virtually assure long life. The minimum diameter of the input shaft is 11mm, and output shaft minimum is 12mm. Plus the output shaft has useful items like 12mm flats and a large self-tightening nut. The 2 threaded holes in the aluminumhousing for mounting the handle on either side would also prove useful for mounting it to the bike. Just make a plug to replace the button used to lock the shaft while changing disks, and use that hole for adding gear oil just like a differential on a car. For someone looking to mount a motor in line with the bike frame, it seems to be an almost ideal solution, and might even open up the possibility of a simple DIY shaft drive.

John

 

[docnjoj]

Sounds clever, John! Maybe use the holes for Zerk grease fittings and leave one with a small screw for outpressure. Not my original idea, I think Reid did it to MY1018.
otherDoc

 

[PaulM]

One caution on converting to gear oil is whether the shaft seals will prevent leaks. Also, most oil filled gearboxes have some kind of vent on them to handle expansion from heat to prevent blowing the seals out.

 

[Miles]

Are you two twins, or what?

 

[docnjoj]

Just great minds thinking alike, Miles!
otherDoc

 

[John in CR]

Thanks guys, that's why I asked, to get the "things to look out for". I doubt the bearings provide a seal good enough to hold back pressure, so some research is required. My thought was to partially fill with oil, enough that the bottom edge of the larger driven gear dips in, but keep it below shaft level to avoid leakage. ie just enough to keep it lubed, but probably not enough to dampen the sound very much. I wonder if the grease in there already accomplishes a similar result by liquefying when the gearbox gets warm.

John

 

[PaulM]

Even if the oil is below the shaft at rest, it will still leak with no seal when running as the oil will fling around everywhere. I would be inclined to just leave lots of grease in it, and possibly add a grease fitting as was mentioned above. Lots of grinders see a lot of abuse everyday and seem to hold up just fine.

 

[Ypedal]

http://www.powertoolandsawservice.com/media/ag002.html

Aparently not a good idea to put too much grease in them, might not be the same story with the motor section removed tho.

 

[John in CR]

http://www.powertoolandsawservice.com/media/ag002.html

Aparently not a good idea to put too much grease in them, might not be the same story with the motor section removed tho.

It makes sense to me that too much grease in there would "gunk up" the gears, preventing them from spinning and meshing together freely, kinda like trying to swim through mud.

I think I'll just leave well enough alone. If I open it up again, just redistribute the grease already in there to get a fresh coating on the gears and that's it. I'm not a very good welder, so my grinder gets quite a workout, I'm sure approaching what would be continuous use in a bike drive train. The cast AL housing on the gearbox has only gotten notably warm during continuous use for 20-30min while grinding, but never hot to the touch, so I'm not going to worry about it.

My first implementation with it will be output to the heavier duty version of bike chain, and I'm sure the chain and/or sprockets will fail before these gears do.

John

 

[TylerDurden]

Others here:

http://www.endless-sphere.com/forums/viewtopic.php?f=12&t=2973&p=60850&#p60850

 

[John in CR]

TD,

From what I can tell, I have the identical gearbox, but the 2 motors I have are significantly more powerful. One is rated at 3kw continuous at 3000rpm. The other is a powerpack motor that loaded does 4.5hp at 17krpm. The 3kw motor is bigger and almost 10lbs heavier, but has nice heat sink fins at the brush end and is well sealed from the environment. After the 3.5:1 step down of the gearbox, the required sprockets will be easy to source and size. The powerpack motor has an impressive sound and is probably a better match to the gearbox in terms of torque and rpms going thru it, but I'll still need another stepdown of 6 or 8:1. It might be fun, but I question the durability. Any thoughts?

John

 

[MitchJi]

Any thoughts regarding something better or cheaper that would also work.

John

Hi John,

Probably a lot more expensive but might be better quality or easier to use:
http://www.stober.com/
http://www.stober.com/motion/raplanetary_highfeature.htm
http://www.stober.com/motion/raplanetary_gearfeature.htm

 

[TylerDurden]

From what I can tell, I have the identical gearbox, but the 2 motors I have are significantly more powerful. One is rated at 3kw continuous at 3000rpm. The other is a powerpack motor that loaded does 4.5hp at 17krpm. The 3kw motor is bigger and almost 10lbs heavier, but has nice heat sink fins at the brush end and is well sealed from the environment. After the 3.5:1 step down of the gearbox, the required sprockets will be easy to source and size. The powerpack motor has an impressive sound and is probably a better match to the gearbox in terms of torque and rpms going thru it, but I'll still need another stepdown of 6 or 8:1. It might be fun, but I question the durability. Any thoughts?

Craig's comments in the other thread give me the impression that keeping the motor from lugging and a good mesh (if custom pinion gear) are the primary issues.

Generally, I like the 90* idea... easier to hide can-shaped motors.

 

[MidniteTweeker]

If you can, you might try to find out a little more about the specific grease that was originally used. I used to think grease was grease and oil was oil, until I discovered that certain kinds of greases and oils cause certain O-ring seals to deteriorate. It would be a shame to inadvertently use something that caused an otherwise perfect gearhbox to start oozing schmutz.

MT