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DIY EV Mechanical Transmissions - Page 2

Page 1        Page 2       Page 3

 

3. Double Reduction Stage Drives

Related Components

 

Electric Motors

Bearings

Chains & Sprockets

Gearing

Shaft Steel

 

 

 

Typical electric drive motors will have maximum shaft speeds around the 2500 - 3000 rpm mark. A single stage reduction will give maximum reductions of roughly 5 or 6:1, given practical constraints on the sizes of available sprockets and space to fit them in. This leaves drive wheel speeds of  roughly 400 - 500 rpm when the motor runs at top speed. For many small wheeled slow speed EV's this is too fast, and the lack of reduction ratio can also mean lack of drive torque at the wheels (and conversely torque overload at the motor shaft).

 

At the bottom of Page 1 a solution is described using electric drive motors with built-in gearheads, however these are not always available and the solution might be to build your own two stage speed reduction.

 

Some examples:

 

Two Stage Roller Chain Drive

Double Reduction Roller Chain DriveWith this set up a bearing mounted intermediate shaft is driven by the roller chain stage from the electric motor output shaft. The intermediate shaft carries a second sprocket which drives a second roller chain stage to the vehicle's road wheel - here the final drive sprocket is mounted directly on the wheel hub which is bearing supported on a fixed shaft.

With, say, 5:1 reductions at each stage this arrangement will give a 25:1 overall speed reduction. This will reduce a motor shaft speed of 2500 rpm to 100 rpm at the road wheel with a proportionate multiplication of drive torque through the transmission - there is a lot of scope for adjusting the overall speed ratios by changing either or both of the stage sprocket sizes.

 

 

Roller Chain + Geared Drive

Double Reduction Roller Chain & Gear Drive

 

Here a combination of roller chain and straight spur gear stages are used to produce a two stage transmission. The roller chain element allows flexibility in the mounting of the electric motor and the spur gear stage provides a compact high reduction stage.

 

Both shafts rotate and are bearing mounted and the vehicle's road wheel is torque fixed to the final drive shaft. Note how the final shaft diameter is the larger - it has to deal with both larger drive torques and bending loads from the road wheel.

 

The intermediate and final shaft separation has to be carefully controlled to maintain the correct centre distance for the gear mesh. 

 

Double stage chain drive

Double stage chain drive as used in the Voiturette

 

Combined chain & gear drive as used in the 500W Kart

....... go to Page 3 - More Double Stage Reduction Drives

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