Mid drive motor with spur gear instead of chain

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avandalen   10 W

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Mid drive motor with spur gear instead of chain

Post by avandalen » Feb 15 2015 7:05am

For my Maxun One solar bike, I want to develop a 350W high efficient and light weight mid drive motor, see here: http://www.avdweb.nl/solar-bike/hub-motor/cyclone.html.

Image

Instead of a chain drive and I want to use a spur gear. And using a protecting by housing to avoid dust.

If I’m not wrong, a 8620 case hardened 12t/90t spur gear, 16 DP, pressure Angle 20, thickness 0.3” should handle 350W easily, I have used this site for strength calculation:
http://www.rushgears.com/Tech_Tools/Hor ... epower.php

Here is a drawing which was created automatically by Inkscape, you can print it 1:1, take the DP16:

Image

Spur gears are standardized according this formula:
Diametral Pitch [DP] = tooth number / pitch diameter [inch]
Spur gear theory:
http://www.bostongear.com/pdf/gear_theory.pdf

Who has experience in this field and can give me help and advice?
Last edited by avandalen on Mar 24 2015 3:22pm, edited 4 times in total.

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Re: Mid drive motor with spur gear instead of chain

Post by MitchJi » Feb 15 2015 10:39am

Hi,

A belt drive will be quieter.
Best Wishes!

Mitch


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Re: Mid drive motor with spur gear instead of chain

Post by avandalen » Feb 18 2015 9:58am

MitchJi wrote:Hi,

A belt drive will be quieter.
Yes but is has to high losses. The efficiency should be > 90%.

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Re: Mid drive motor with spur gear instead of chain

Post by MitchJi » Feb 18 2015 10:40am

avandalen wrote:
MitchJi wrote:Hi,

A belt drive will be quieter.
Yes but is has to high losses. The efficiency should be > 90%.
I believe that is incorrect:
http://en.m.wikipedia.org/wiki/Belt_%28mechanical%29
Belt drive is simple, inexpensive, and does not require axially aligned shafts. It helps protect the machinery from overload and jam, and damps and isolates noise and vibration. Load fluctuations are shock-absorbed (cushioned). They need no lubrication and minimal maintenance. They have high efficiency (90-98%, usually 95%), high tolerance for misalignment, and are of relatively low cost if the shafts are far apart. Clutch action is activated by releasing belt tension. Different speeds can be obtained by stepped or tapered pulleys...

Timing belts, (also known as toothed, notch, cog, or synchronous belts) are a positive transfer belt and can track relative movement. These belts have teeth that fit into a matching toothed pulley. When correctly tensioned, they have no slippage, run at constant speed, and are often used to transfer direct motion for indexing or timing purposes (hence their name). They are often used in lieu of chains or gears, so there is less noise and a lubrication bath is not necessary...

Timing belts need the least tension of all belts, and are among the most efficient.
http://ww2.gates.com/facts/documents/Gf000284.pdf
Synchronous belts do not slip, need retensioning or require lubrication. Offering 98% constant efficiency, these belts are now being used on all types of plant equipment and machinery. This report tells how they stack up against chains, gears and traditional V-belts.
Best Wishes!

Mitch


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Re: Mid drive motor with spur gear instead of chain

Post by Thud » Feb 18 2015 11:53am

Hi avandalen,

Do you have an engineering background?
You will need to calculate any shock forces that the gear train will be subject to & size according to that parameter.

Best practice will have a shock absorption system & maximum torque limiting (slipper clutch) mechanism to protect the gear teeth.

look at your 16t drive sprocket, & study under cutting of low tooth count spur gears...in my glance over, I see a little undercutting....may or may not be an issue.

you are correct that toothed drive belts eat a LOT of power in high-reduction applications, they perform best in more linear power transfer applications.

I can only assume you will have the gear train enclosed & lubricated properly for the application.

if you build it, please share your progress.
T
get some......

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Re: Mid drive motor with spur gear instead of chain

Post by avandalen » Feb 20 2015 9:07am

Thud wrote:Hi avandalen,

Do you have an engineering background?
You will need to calculate any shock forces that the gear train will be subject to & size according to that parameter.

Best practice will have a shock absorption system & maximum torque limiting (slipper clutch) mechanism to protect the gear teeth.

look at your 16t drive sprocket, & study under cutting of low tooth count spur gears...in my glance over, I see a little undercutting....may or may not be an issue.

you are correct that toothed drive belts eat a LOT of power in high-reduction applications, they perform best in more linear power transfer applications.

I can only assume you will have the gear train enclosed & lubricated properly for the application.

if you build it, please share your progress.
T
Hi Thud,
>>> Do you have an engineering background?
Electronic engineering, no mechanical engineering

>> maximum torque limiting
The motor has a torque limit because the motor current is limited.

I know that chains are used normally:


Do you think a chain is better than a spur gear in respect to efficiency, noise and wear?

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Re: Mid drive motor with spur gear instead of chain

Post by izeman » Feb 20 2015 3:19pm

avoid spured gears if you want it to be silent. they make a high pitched noise.

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Thud   100 MW

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Re: Mid drive motor with spur gear instead of chain

Post by Thud » Feb 20 2015 6:13pm

Do you think a chain is better than a spur gear in respect to efficiency, noise and wear?
Efficiency: Properly designed to handle the power levels your looking for, they will be about = .
In theory, gears will have a slight advantage.(maybe 3 or4% under load)

Noise: Nothing is silent. Pick your poison

Wear: Dificult question. I usualy have an idea of service life I'd like to achive. That said...there are many compromises that need to be factored...& any mechanical device is going to wear out eventually. If pressed, I would give the advantage to a properly designed gearbox, fully sealed w/correct shock absorbtion implimented.


I favor chains.
They are far more tollerent of dirty environments = more fogiving of a non seald box to run in.
In my experiance, more cost effective for single unit manufacture. You can buy a lot of chain & sprocket for the price of a single gear.
Huge assortment of stock sizes available in almost any pitch.

And mostly because I do my own machine work.They are easy to design with & easy to manufacture too (IE-forgiving in center to center measurement)

Simple jack shaft chain & sprocket reduction is "chain saw" easy compared to "Swiss watch making" of correct gear box construction.

I say "correct" a lot...if your going to the trouble of designing with spur gears, cutting corners will create huge disapointments regarding durability & life span.


Thats enough for one post.
get some......

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Re: Mid drive motor with spur gear instead of chain

Post by r3volved » Feb 20 2015 7:01pm

I've had the same thought on using enclosed lubed gears. Thanks for dropping your insight Thud.

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Re: Mid drive motor with spur gear instead of chain

Post by recumpence » Feb 20 2015 8:11pm

The statement that toothed belts use alot of power is not generally true. The issue would be high rpm. Below 15,000 rpm a toothed belt is efficient, quiet, and very long lasting. Chains are extremely noisy and inefficient at rpm above 2,000 in my experience. They are definitely cheap to work with, though.

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Re: Mid drive motor with spur gear instead of chain

Post by mfj197 » Feb 21 2015 2:37am

You probably already know this but most commercial crank drive are geared. Have a look at the BBS01 / 02 motors which might help your ideas. They use helical gears and one nylon gear all to reduce noise.

Michael

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Re: Mid drive motor with spur gear instead of chain

Post by avandalen » Feb 26 2015 4:30am

recumpence wrote:The statement that toothed belts use alot of power is not generally true. The issue would be high rpm. Below 15,000 rpm a toothed belt is efficient, quiet, and very long lasting. Chains are extremely noisy and inefficient at rpm above 2,000 in my experience. They are definitely cheap to work with, though.

Matt
A timing belt would be nice. However there is not much space on the crank spindle, so what should be the width of a timing belt here?
Also, I think it is a problem for a timing belt that a very small sprocket for the motor is required.
Regarding the efficiency of a timing belt. The loss of, for instance, the Gates Carbon Drive Belt System is in contrast to what is certainly not small.
Last edited by avandalen on Feb 27 2015 4:45am, edited 2 times in total.

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Re: Mid drive motor with spur gear instead of chain

Post by avandalen » Feb 26 2015 4:34am

mfj197 wrote:You probably already know this but most commercial crank drive are geared. Have a look at the BBS01 / 02 motors which might help your ideas. They use helical gears and one nylon gear all to reduce noise.

Michael
Yes I know, that was actually my motivation to use a spur / helical gear.
Last edited by avandalen on Feb 26 2015 5:39am, edited 1 time in total.

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Re: Mid drive motor with spur gear instead of chain

Post by izeman » Feb 26 2015 5:01am

izeman wrote:avoid spured gears if you want it to be silent. they make a high pitched noise.
i quote myself. by "spured gear" i was referring to STRAIGHT spured gears. as you already mentioned you should use skew or helical gears. this of course needs different bearings as you then have not only tangential forces but forces perpendicular to them trying to move the axle out of the bearing.

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Re: Mid drive motor with spur gear instead of chain

Post by avandalen » Feb 26 2015 5:30am

izeman wrote:
izeman wrote:avoid spured gears if you want it to be silent. they make a high pitched noise.
i quote myself. by "spured gear" i was referring to STRAIGHT spured gears. as you already mentioned you should use skew or helical gears. this of course needs different bearings as you then have not only tangential forces but forces perpendicular to them trying to move the axle out of the bearing.
A double helical gear would be preferable here. Is this expensive?
Image
Last edited by avandalen on Feb 26 2015 5:41am, edited 2 times in total.

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Re: Mid drive motor with spur gear instead of chain

Post by izeman » Feb 26 2015 5:38am

this of course is the best solution if you can get those gears.

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Re: Mid drive motor with spur gear instead of chain

Post by recumpence » Feb 26 2015 5:14pm

Looking at your design again, I realized the gears will be running at low speed. Straight cut should be ok at the rpm you will be running. The sound should be minimal.

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Re: Mid drive motor with spur gear instead of chain

Post by Punx0r » Feb 27 2015 4:06am

A timing belt is the narrowest of the available belt options to transmit a given load.

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Re: Mid drive motor with spur gear instead of chain

Post by avandalen » Feb 27 2015 4:50am

Punx0r wrote:A timing belt is the narrowest of the available belt options to transmit a given load.
Do you know a suitable timing belt that handles 350W and what is the width?

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Re: Mid drive motor with spur gear instead of chain

Post by recumpence » Feb 27 2015 7:37am

avandalen wrote:
Punx0r wrote:A timing belt is the narrowest of the available belt options to transmit a given load.
Do you know a suitable timing belt that handles 350W and what is the width?
8mm pitch Gates Polychain in 10mm width should do the job. 14 tooth is the smallest tooth count in that pitch and belt type however.


Matt
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Re: Mid drive motor with spur gear instead of chain

Post by Miles » Feb 27 2015 8:11am

avandalen wrote:Do you know a suitable timing belt that handles 350W and what is the width?
To be honest, this is a bit of a nonsense question...

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Re: Mid drive motor with spur gear instead of chain

Post by avandalen » Mar 06 2015 6:31am

recumpence wrote:
avandalen wrote:
Punx0r wrote:A timing belt is the narrowest of the available belt options to transmit a given load.
Do you know a suitable timing belt that handles 350W and what is the width?
8mm pitch Gates Polychain in 10mm width should do the job. 14 tooth is the smallest tooth count in that pitch and belt type however.

Matt
Thank you Matt. Here is a solution with the Gates Polychain 8mm pitch, 10mm width:
Crankshaft pulley diameter 160mm, 62T
Planetary gear pulley diameter 35mm, 14T
Can you help me with these questions:
1. What is the power loss when the power is 350W and the speed is 100rpm for the large pulley?
2. What do you thing about the Polychain carbon belt version http://www.gates.com/products/industria ... rbon-belts
3. The gear ratio is 4.4 which is quite small, is there any strong, more flexible timing belt with a smaller pitch?

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Re: Mid drive motor with spur gear instead of chain

Post by recumpence » Mar 06 2015 8:00am

Polychain is available in 5mm pitch too. That pitch can go down to 12 tooth IIRC.

One other item related to power handling with toothed belts is tooth engagement. If you add an idler wheel to increase the amount of belt wrap p around the small pulley, you will increase torque handling tremendously.

Honestly, at the RPM you will be running, I would not consider myself with efficiency numbers. At that RPM, losses would be nearly identical no matter what transmission style you choose.

Matt
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Re: Mid drive motor with spur gear instead of chain

Post by avandalen » Mar 07 2015 5:54am

recumpence wrote:Polychain is available in 5mm pitch too. That pitch can go down to 12 tooth IIRC.

One other item related to power handling with toothed belts is tooth engagement. If you add an idler wheel to increase the amount of belt wrap p around the small pulley, you will increase torque handling tremendously.

Honestly, at the RPM you will be running, I would not consider myself with efficiency numbers. At that RPM, losses would be nearly identical no matter what transmission style you choose.

Matt
Hi Matt
I suppose you mean something like this:
Image
Honestly, at the RPM you will be running, I would not consider myself with efficiency numbers. At that RPM, losses would be nearly identical no matter what transmission style you choose.
I want no more than 3% loss, it would be great if this is possible with a small timing belt.

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Re: Mid drive motor with spur gear instead of chain

Post by avandalen » Mar 22 2015 2:57pm

I finally will use a gear, the gear ratio = 95t/12t = 7,917. This is much larger than can be achieved with a chain or belt.

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