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DIY EV Mechanical Transmissions

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The different ways in which electric drive motors can be connected to vehicle drive wheels is an area of interest for many DIY kart and buggy builders.

 

Over the years I've tried a number of approaches and here are a few suggestions -

 

Starting with the simplest.

 

Component Details

 

Electric Motors

Bearings

Chains & Sprockets

Shaft Steel

 

1. Fit the Wheel directly on the Motor Shaft

 

..... don't! This won't work unless you are using a "hub motor" - ie a type of low speed, high torque electric motor that is specifically designed to carry a drive wheel. Generally these are quite expensive, and the more commonly available drive motors run too fast and with too low a torque for a direct drive to the wheels. You will probably need at least a single stage speed reduction.....

 

2. Single Stage Speed Reduction Stage

 

Most of the drive motors I use come fitted with a small roller chain sprocket on the output shaft ready for assembly with a chain transmission. Single stage reductions can also be implemented with toothed belt transmissions or geared transmissions.Single Stage Electric Motor Drive

 

 

The image shows a single stage roller chain drive to a rotating drive axle. The wheel is fixed to the axle and the axle is bearing mounted (either directly housed or by pillow block) on the vehicle chassis. This type of arrangement works with vehicles with relatively fast turning wheels as the size of the speed reduction that can be achieved is effectively limited by the size of larger chain sprocket.

 

Extending the axle to carry the second rear drive wheel provides a simple dual wheel drive, however one with no effective differential action for cornering. To introduce good differential behaviour use either an electric motor for each wheel (below left) or fit a differential gear box (below right - single stage reduction drive on a commercial kart).

 

 

 

Single Stage Electric Motor DriveDual Motor Electric Drive

 

Geared DC PM MotorThe single stage arrangement can be used for slower speed wheel drives if used in conjunction with a drive motor with a built-in gear box (see image left). These transmissions are effectively double or triple stage reductions with the "gearhead" on the motor providing the first reduction stages. The outcome is a lower speed / higher torque drive to the wheels better suited to lower speed vehicles with smaller wheels or for higher speed vehicles with larger wheels - in both low wheel rpm and high drive torque is needed.

Component Details

 

Electric Motors

Bearings

Chains & Sprockets

Shaft Steel

 

 

The type of gearing in the motor will affect it's behaviour - be careful with worm geared units if you need regenerative braking.

....... go to Page 2 - Double Stage Reduction Drives

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