Jackshaft DIY Jackshaft / Freewheel / Shift Kit

[210061741]

A Caution About Torque And Ht Motor Output

Now when it comes to just about any type of racing known to mankind, besides engine output, gearing is the single most contributor to acceleration. It will make or break any car and the right gear selection can and will mean the difference between winning and losing a race.

How important is gearing? Gearing nearly makes torque obsolete. Yes, it's that important. In a perfect environment with no limiting factors such as size and weight, the actual peak torque output of an engine would be totally meaningless because of gearing.

How's that possible? It's simple. Gearing multiplies peak torque to the wheels to any amount desired. Increasing the ratio increases torque.

AGAIN
Gearing multiplies peak torque to the wheels to any amount desired. Increasing the ratio increases torque.

Therefor never guess or assume it is safe.
Do the math.
Find the specs.

Our little HT IC Motors can generate massive torque with the gearing
configured to do so.

Time for another short break.

COMING NEXT TORQUE CALCULATION AT 36 T FREEWHEEL.

 

[210061741]

Torque At 36t Freewheel Sprocket

Ok guys i'm getting tired here.
Anyone... calculate the torque at the 36t freewheel sprocket.
I'll give it another run tommorow.

After all those gear calculations my brain is spent.

Have a good night.

 

[210061741]

Torque Calculations

UPDATED SCHEMATIC ILLISTRATING TORQUE AT EACH SPROCKET

SOMEONE PLEASE VERIFY.

THANK YOU

SEE ATTACHED

 

[Fabian]

Hi 210061741

The mathematics are correct in a sense that they do work when using the "optional 48 tooth" chainwheel which SickBikeParts sells on their website.
When creating my schematic i falsely assumed that the standard chainwheel sprocket was 48 tooth but in fact, the standard chainwheel size with all of the kits is "44" tooth.
In ways this could be seen as an error on my behalf.

The jackshaft output sprocket size in the standard kit/s is 10 tooth with optional 9 and 11 tooth sprockets.
Personally i want a 12 tooth sprocket to lower top gear rpm's but it is not produced.

Feel free to redraw my schematic with the various sizes added for future reference.
Better still - please recreate my schematic in a professionaly produced manner

Kind regards

Fabian

 

[210061741]

Gear Schematics

Yes I am basing this on the given gear setup.

The important thing is that the Torque & RPM are correct.
The torque and rpm deterimine the load required to be handled by the bearings.

For our Freewheel which BTW gets the highest torque in the gear train applied to it , we are comparing bearings to the white freewheel.

To get an idea of reliability.

So our bearing can be sized to provide the best duribility, and least possible chance for failure.

These MAX torques will be applied "as stated before" at around starting speed. Very slow speed.

I believe 48 cc ideles around 3600 rpm and 4500 rpm being max torque.
Means a little rev and where there.

However somewhere we should factor into this the torque created at the freewheel when peddaling and using the motor to start off.

Cause like having 2 motors the crank and the motor both will transmit torque simultaneously.

Anyone have the magick number.
I saw an answer earlier.

Once we are moving down the road the torque drops significantly.

AS A RULE LOOK AT IT LIKE THIS.

INCREASE SPEED = LOWER TORQUE
INCREASE TORQUE = LOWER SPEED

That is how it will work with our gear ratios.
So by playing with those we could adjust not only speed. (normal reason)
But to adjust torques if nessessary.

Don't you love math!!!!

It seems we have done alot of work but everything gets easier once your forces are figured.

Find the max force and your system must stand up to it with a factor for safty.

We will use these calculations later to determine the strength required by the shaft and to figure how much we stress the steel plate brackets.

So yes we did all this work so far.
just to find a bearing

Yes at this point in time that appears what we have done.
What did we learn?

NOW WE UNDERSTAND WHAT ENGINEERING IS REALLY ABOUT.
It is more than just picking up pcs off the shelf and putting them together.
Everything must start somewhere so prototypes like that are nessessary.
But once you know it will work, DO THE MATH.

Know the limitations of the system.

I will redraw the schematic in cad.

I appreciate the use of the existing pic.
Thanks for that it saved me time.

Also once i get the whole system modeled in 3d i will run stress analysis software against it. My calculations could be off. I am surly not perfect.
IF ANYONE ELSE OUT THERE HAS TIME TO DO THE MATH.......
PLEASE ALSO DOUBLE CHECK THE FIGURES.
WE DON'T WANT TO BE WRONG HERE

After the complete unit is designed we will stress test it to the point of catastropic failure.

Then we will know the weak points.

I BET IT WILL BE THE BIKE FRAME.

 

[Fabian]

Hi 210061741

I am keenly looking forward to this project gathering a strong head of steam and moving into the design and development stage.

When it's modelled in cad, can it be designed as a moving user interface for input of different optional jackshaft sproket ratios and final drive (to rear cassette) ratios, so people can play with different ratios and see a moving outcome on the screen; rear wheel speed, rpm ratios, tensile stress forces on the chain drive systems and the torque loading on the freehub cassette pawls as they step down or step up torque through the package.

I am curious as to the tensile forces are going through the various drive chains, especially when the jackshaft ratios are changed .

Fabian

 

[Fabian]

210061741

Remember that these chinese bicycle motors only reliably rev to 4000 rpm and are on their way to self destruction at 5000 and completey shot to pieces at 6000 rpm.

The seat of the pants feeling with my motor is maximum torque is around 2500-3000 rpm and max power is around 3500.
Having said that, my engine uses the stock standard exhaust (i feel it boosts low rpm torque compared to the open muffer variant i used before which allowed more rpm but the motor self destructed).

Fabian

 

[Fabian]

Check out this dyno graph of a chinese motorised bicycle engine - i have no data as to it's capacity or manufacturer or final drive gear ratio.

Unfortunately the graph only gives a torque spread vs road speed and a horsepower curve - it doesn't give an rpm curve which makes calculations difficult.

Fabian

 

[210061741]

3d Models

Yes we can generate 3D Models that simulate eyerything.
We can create assosiative assemblys where if 1 component changes it is reflected in the model. This allows to make changes without redrawing the entire model.

Pretty cool stuff.
Cost me $20.000 for that degree.

Getting ready to start modeling soon.

Were gonna take this one to the max.

 

[210061741]

thanks

Thanks for the correction of motor output / rpm.
But that is good news.
It means or torque calculations have a safty factor of
8000 rpm / 4500 rpm = 1.777 safty factor.

72.99Nm / 1.777 = 41.07 Nm actual Max Torque.

DIVIDE THE MAX TORQUE OF THE BEARING BY 41.07 Nm actual Max Torque.
= ACTUAL SAFTY FACTOR FOR THE BEARING.

This means our sprag bearing is a very good selection.

This means as long as our bearing is mounted properly our freewheel should be able to take anything we throw at it.