Why left-handed drives? Disk + Sprocket?

[erth64net]

I assume the primary reason for going with left-hand drives (aka: chain sprocket mounted on hub's disk tabs) is because of the torque involved with a higher power setup's acceleration. So, if one wanted to keep their disk brake, then a dished-out sprocket bolted onto the disk side sounds like the most reasonable option.

For those of us working with "lower power" ~500W continuous (2KW peak) brushless outrunner setups, I wonder if integrating into the existing chainline, ala mid-drive style would be simpler and easier? The maximum torque that my hub can take is ~100Nm. If I ran a Scorpion 4025 16T motor on 24V at a peak of ~80A (~8,000RPM), through a belt/chain reduction to a sane mid-drive output RPM of just 80 (matching my typical cadence)...I wonder what the torque would be at the hub? My motivation for doing this, would be to minimize moving components while freewheeling, as I don't know of any low friction ratcheting freewheels that would fit on a ~77mm bore (outside diameter of my hub's disk tabs).

 

[johnrobholmes]

Anything under 3kw would work great through the existing driveline IMO. If you aren't wanting to go crazy on power, a little bafang would make a good stoker motor IMO. I am wanting to convert my 20mph bike from a rear hub motor to a mid drive.

 

[jbond]

The central idler on a Bacchetta looks like an absolute natural for a Cyclone style mid mounted motor driving the chain line. One chain from chainrings to motor, one from motor to rear cassette. I guess this needs a Schumacher style reduction gearbox and then a double freewheel with 13 or 14t. How much of that is available off the shelf?

BTW. Are there any front and rear fairings that fit the Bacchetta?

 

[erth64net]

The central idler on a Bacchetta looks like an absolute natural for a Cyclone style mid mounted motor driving the chain line. One chain from chainrings to motor, one from motor to rear cassette.

Yep

I guess this needs a Schumacher style reduction gearbox and then a double freewheel with 13 or 14t. How much of that is available off the shelf?

Not certain, but I have a CNC and 7075 stock...

BTW. Are there any front and rear fairings that fit the Bacchetta?

Yep, and they're made by some really awesome folks just down the street from here: http://www.windwrap.com/

 

[Miles]

If I ran a Scorpion 4025 16T motor on 24V at a peak of ~80A (~8,000RPM), through a belt/chain reduction to a sane mid-drive output RPM of just 80 (matching my typical cadence)...I wonder what the torque would be at the hub?

Knowing the velocity constant (Kv) of your Scorpion 4025, you can calculate its torque constant (Kt) and therefore the torque it produces at 80amps. Multiply the figure for torque at the motor shaft by the reduction ratio of your drive-train (minus a bit for losses) to get the torque at the hub.

Kt in Newton-meters per amp
Kv in rpm per volt

Kt = 9.549/Kv

 

[erth64net]

If I ran a Scorpion 4025 16T motor on 24V at a peak of ~80A (~8,000RPM), through a belt/chain reduction to a sane mid-drive output RPM of just 80 (matching my typical cadence)...I wonder what the torque would be at the hub?

Knowing the velocity constant (Kv) of your Scorpion 4025, you can calculate its torque constant (Kt) and therefore the torque it produces for 80Amps. Multiply this figure for torque at the motor shaft by the reduction ratio of your drive-train (minus a bit for losses) to get the torque at the hub.

Kt in Newton-meters per amp
Kv in rpm per volt

Kt = 9.549/Kv

Delta or WYE?

A stock Scorpion S-4025-16 is @ 332 RPM/V (Delta)...currently rewiring for WYE though.

 

[Miles]

Divide by 1.732 to get the Kv for Wye.

 

[erth64net]

Divide by 1.732 to get the Kv for Wye.

Yep...in hindsight I realized that the Kt would jump with the respective drop in RPM/V for WYE...

Ok, let me make sure I've got this correct:

• Delta Kv=332 RPM/V
• WYE Kv=~191 RPM/V (Kv/1.732)
• At 24 Volts (V) thats 4584 RPM (Kv*V)
• For WYE, Kt=.04999Nm of torque at 1A (9.549/Kv)
• For WYE, Kt=3.9992Nm of torque at 80A ((9.549/191)*80)

So, tossing in a two-stage transmission with, let's say, 6% loss:

• RPM/Cadence = needed gearing reduction (R): 4584/80=57.3R
• Gearing reduction loss multiplier = .94
• (R*Kt*A)*.94=Kt at transmission output

So, a two-stage 57:1 reduction transmission has a peak possible power output of 214.3Nm@80RPM when the 191Kv motor is powered at 24V/80A. Does this math look sane?

BTW, Google is not being too helpful, what's the basis of the 9.549 constant?

 

[Miles]

BTW, Google is not being too helpful, what's the basis of the 9.549 constant?

It's the conversion from radians per sec to rpm

Kv is the reciprocal of the back emf constant Ke

Kt = Ke (V-sec/rad)

Kt = 1/Kv (radians per sec/V)

Kt = 9.549/Kv (rpm/V)

 

[andyinchville]

HI,

I often wondered the same thing....it is interesting to note that the small Chinese engine kits run the same way....drive on the left side.

It is possible to run on the left side AND use a disc brake by using A Super Sprocket and Top Hat Sprocket Adapter from Kings sales and Service
(kingssalesandservice.com)

On the flip side you can run a jack shaft kit and power through the existing drivetrain (doing this you can actually use all the rear gears as well).

Hope this helps.

Andrew