Basic reduction question.

[drewdiller]

This should be short. Just checking that I understand. The reason for (very well built) multiple-belt-and-gear reduction systems I see in this forum are because:

1) RC engines are way more powerful and light compared to a hub motor, but only if you can get the motor up to the intended very high RPM.
2) To get a usable RPM to the wheel, you have to submit the initial motor RPM to multiple forms of reduction.
3) Using a gearbox for one (or more) stage(s) of RPM reduction is less efficient than a belt drive.

Specifically part 3. Is that a fair statement?

Looking to eventually get a recumpence unit when I can afford to spend moneys on non necessities again, but also weighing my options. After having ridden my first e-bike (250W hub motor), I want:

- 20mph or more (possible on 36V * 20A?)
- Much higher torque for hills and choppy snow
- Less worry about having to watch the CA for running the motor over described wattage
- Less weight, and better distribution of it

 

[TylerDurden]

IMO:

1) RC motors are much lighter & smaller than hubbies of equivalent power
2) RC motors often require reduction: frequently two-stage, but direct friction drive or single belt to large pulley are also seen.
3) RC motors require custom installation, but thereby offer more options.

A gearbox could be as efficient and quieter than a belt reduction, but more costly.

20mph only requires about 300-400w; for how long depends on your battery capacity.

My impression is you want a 500W-1000W system... a geared hubbie is simple; an RC system weighs less, but is not plug-and-play.

 

[reload]

rc motors run at high kv's thus require the reduction. typically you'll see 150-250 kv around here. @36V a 250kv motor runs at 9000 rpm. 20mph is ~260 rpm for a 26in wheel. that'll require a 34 to 1 reduction.

you'd probably want to reduce for about 60mph = 12 to 1 reduction, 800rpm for a 26inch wheel.

you can see why rc'ers go through such great lengths to set up an rc drive.

 

[AussieJester]

you can see why rc'ers go through such great lengths to set up an rc drive.

Can tellz you its highly worth the effort to

TD... i always thought chain and belts were fair bit more efficient than
a gearbox setup. What sort of difference in efficiency between chain/belt setups
is there mate? (i know the chain setup is slightly more efficient than the belts 1-2% IIRC?)
But no idea of the gearbox efficiency in comparisons.

KiM

 

[TylerDurden]

IIRC, belts are about 90%, chains and gears about 98%. Belts heat when you flex em, that energy comes from somewhere.

Gears, on the other hand, need precise alignment and lubrication.

 

[AussieJester]

IIRC, belts are about 90%, chains and gears about 98%. Belts heat when you flex em, that energy comes from somewhere.

Gears, on the other hand, need precise alignment and lubrication.

I think the belts and chain efficiency is lil closer than that I'm sure Miles
posted 2-3% difference? Summoning Auto-Bot Miiiiiles where art thou? Lend your expertise
to the thread LoL

KiM

EDIT: Quote from Jeremy Harris

"A well-designed HTD belt drive can easily rival the efficiency of a chain drive (Gates quote efficiencies of up to 99% for their GT2 belt drives), plus it will stay efficient without lots of maintenance"

And Miles

"I'm all in favour of belt drives, I'd gladly lose 3% efficiency for their advantages."

ref: http://endless-sphere.com/forums/viewtopic.php?f=10&t=8023

I love my belt drive setup quiet and maintenance free fantastic for on road use
would not be so great for offroad in muddy conditions however.

 

[drewdiller]

This is helpful.

I am willing to forego plug and play. I've run into the gamut of problems with my geared hub (I have a Cute motor) and figuring out how to mount the battery in general that I'm building motivation toward learning whatever details I need to solve my issues. I don't like having to have a torque arm, and the general lacking of being able to quick release my wheel (I'd love to just undo a master link of a motor chain and YOINK, in the car you go).

One thing I forgot is abuse tolerance. I ride all year round, and live in MN, which means snow and slush and below zero Fahrenheit.

I should stop posting for tonight, I'm into my second glass, sorry if that didn't make any sense.

 

[TylerDurden]

There are varying opinions out there, I have no problem accepting Miles' and Jeremy's take.

For simplicity, I'd go hub motor.
For more options, I'd go non-hub.

 

[liveforphysics]

IIRC, belts are about 90%, chains and gears about 98%. Belts heat when you flex em, that energy comes from somewhere.

Gears, on the other hand, need precise alignment and lubrication.

V-belts, which are the highest friction belt setup, often get as bad as 90%. Notched tooth belts seldom drop below 96%, and get as high as 99%. You can get really bad efficiency with a belt when it's oversized for the application, as the wider/thicker the belt, the more heat goes into continously causing a bend in 4 places, which causes internal friction and heating. A belt that handles 5hp may require 200w of power just from flexing the rubber if it's wrapping around a small pulley at high RPMs, where a smaller belt may only require 20w.

Chains are often 97-99%. Love high speeds, love high loads, compact sprocket size, and X-ring or O-ring chains are sealed and require no lube for the lifetime of the chain (not available on the smallest stuff). But they are fairly loud.

Gears depend entirely on the pitch, reduction, and gear type. Worm gears get as low as 60%, bevels around 85%, helicals ~95%, straight cut's with both gears of like size and proper pitch get 98-99%.

 

[Mark_A_W]

Anyone fitted a belt drive to a Nuvinci Hub?

My friend's Giant commuter (grandma) bike has a belt drive to the Nexus 8 hub. First bike I've ridden without a chain. Very nice to ride, except the integral drum brakes are pathetic, especially when you are used to 8" hydros.


I think I could go a series drive dually with a shared belt drive to a Nuvinci, No chains, no derailleurs.

I just spent half an hour cleaning the mud out of my bike tonight, after my daily commute on dirt roads - it RAINED yesterday. I spend a lot of time cleaning chains, and tweaking derailleurs...

The motor would have to be in an enclosure, but it could have forced induction, but shielded so the mud doesn't get in. I don't think a downtube mounted RC motor would last very long if I tried it exposed..

 

[TylerDurden]

Related:
Small article on helicals (interesting, propaganda aside):
http://www.parkermotion.com/engineeringcorner/gearheads.html

 

[Solcar]

My present ebike has a gearbox that uses helical gears. Based on what they looked like after I opened up the aluminum case out of curiosity one day, I guess they are made of acetal material. I have put a few hundred watts through it, and after 10 years it still works well.

http://www.herbach.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=HAR&Product_Code=TM92MEC1999&Category_Code=MEC

 

[liveforphysics]

Interesting article. I read through the whole thing, and they seemed to just totally fail to mention the inherent thrust axis friction forces that happen with helical that don't with spur. In that application for planetary servo boxes, the thrust axis forces stack x2, and require the ring gear to have thrust support as well, which is inherently difficult to do in a method that doesn't cause high friction as speeds increase.

If they were doing herring-bone gears, I could have believed their fancy profile offered efficiency advantages over spur.

The stregnth claims were also failing to mention the much thinner tooth base on a helical...
InIn practice, there is a very good reason that when you can't keep a tranny together, you end up gritting your teeth and taking that huge hit in the wallet to get straight-cut gears, suffer through sounding like a forklift everywhere you drive, but finally no longer spend as many days at the track distributing your transmission parts across the track. Lol

I'm going to have to sum that page up as 90% marketing a product, 10% useful gear info.

 

[TylerDurden]

If drewdiller will forgive the tangent...

Thank you Solcar for the link, that gearbox looks interesting enough to buy, just to take apart.

I also noticed the lack of thrust forces being mentioned in the article. That aside, I think there is merit to the advantages for helicals in applications not subject to extreme shock loads. Simple viewpoint: spur-gear noise indicates wear, heat and loss... but I imagine we are splitting hairs there.

A helical gearbox presents good potential for a solution to some of the issues in non-hub reductions: sound, complexity and vulnerability.

 

[drewdiller]

The more tangents you take, the more perspectives I gain...

 

[Solcar]

You're welcome TylerDurden. It's very efficient, and tougher than I thought it'd be. In the past, I made it output something like 200 in-lbs. of torque.