Mid drive motor with spur gear instead of chain

avandalen

100 W
Joined
Oct 2, 2010
Messages
175
Location
Maastricht, The Netherlands
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.

Mid-drive1.jpg


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/Horsepower/horsepower.php

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

Spur-gear.jpg


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?
 
Hi,

A belt drive will be quieter.
 
avandalen said:
MitchJi said:
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_(mechanical)
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.
 
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
 
Thud said:
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:
[youtube]ZpLF1F2anpA[/youtube]

Do you think a chain is better than a spur gear in respect to efficiency, noise and wear?
 
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.
 
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
 
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
 
recumpence said:
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.
 
mfj197 said:
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.
 
izeman said:
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.
 
izeman said:
izeman said:
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?
figu352_2.jpg
 
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.

Matt
 
avandalen said:
Punx0r said:
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
 
recumpence said:
avandalen said:
Punx0r said:
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/indus.../synchronous-belts/poly-chain-gt-carbon-belts
3. The gear ratio is 4.4 which is quite small, is there any strong, more flexible timing belt with a smaller pitch?
 
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
 
recumpence said:
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:
done8.jpg


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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