Thread: Electric 4WD crosses Simpson Desert

Good to know it wasn't crazy talk on my part. I always thought the advantage of hub drive was that you didn't need conventional brakes as you can have a braked motor. I was playing around with them in the 80's so I know they exist.

Originally Posted by JDNSW

A question I have been wondering about since my teens! Hub drive was first used before the first world war, and has periodically appeared in prototypes ever since. None have been successful. It is difficult to see obvious reasons, although one is that the wheel hub is already pretty much occupied by a brake assembly, and fitting both a motor and a brake assembly in the space means at a minimum that both must be designed to integrate with each other. This is an area of design where there is neither experience in design nor experience in manufacture. By contrast, using a conventional drive train uses technology and tooling that already is in place in the factory. This means that the conventional drive train is a lot cheaper to build.

Very few if any revolutionary car designs have not used existing components wherever possible. To quote just a couple of examples - the first Landrovers used an existing engine design, admittedly one that had not yet entered production, although it was already being tooled up, and a gearbox and differentials introduced in 1932. The only new part of the drive train was the transfer case. A second example was the Citroen DS - which was decades ahead of anything else on the road - but the engine was an updated version of an engine that had entered production twenty years previously, and the gearbox and final drive were a copy of the existing gearbox and final drive with a fourth gear.

There is enough new tooling and design in an EV that an existing manufacturer will do everything they can to minimise it - a bit easier for a company entering the business for the first time (e.g. Tesla), but they have a much harder row to hoe anyway, because they don't have the existing technology they can use. But they have the advantage that they are not likely to be trapped by using existing technology when there is a better way of doing it by starting from scratch. (Better means either cheaper to build or sells better or both - there is no data to convince the bean counters that either is the case for hub drive!)

Unsprung weight is a major issue. For a four wheel drive vehicle to have a motor for each wheel mounted inboard and connected to the wheels by driveshafts solves that problem, and allows the brakes to remain on the wheels - though using the motors for regenerative braking helps too. Having one electric motor for each wheel allows very precise computer control of the drive applied to each wheel. You could end up with a very effective off road vehicle!

But I think a hybrid works better than 100% electric. Far less battery capacity is needed, and the range becomes just as good as a conventional vehicle. A diesel or petrol motor running at constant speed to keep the batteries charged, supplemented by regenerative braking, and perhaps solar panels.

Lots of possibilities, but research and testing needed. Also, hopefully, a less polluting source of batteries than lithium.