[brian_]

So far, we cannot find any wheel motors that have a decent IP rating. Why is this? Do electric vehicles not go through pools of water? Do they not get submerged up to the hubs?

Electric vehicles deal with the same driving conditions as non-electric vehicles, but roadgoing EVs (cars) don't use hub motors. The motors which they do use are well sealed and at least splash-proof, and likely "waterproof" for minimal immersion for a limited time.

That probably explains their overwhelming popularity. I thought it would be more to do with their more compact use of space, lack of requirement for reduction drives, transmissions and associated losses, reduced weight etc.

Hub motors are popular in electric bicycles, and some types of equipment (such as some robotic devices), but rare otherwise. I realize that this thread is about a robot vehicle, but this should be understood to be a specialty application.

Hub motors do have the same requirement for reduction gearing as other motors. With any motor location there is always a tradeoff between the cost, bulk, and weight of a reduction drive, or the cost, bulk, and weight of a much larger motor that is required if the motor must operate at wheel speed due to the lack of reduction drive. The location of the motor in-wheel or inboard is not related to the need (or lack thereof) for multiple transmission ratios.

The only advantages of in-wheel motors are packaging, and the avoidance of an axle shaft (especially in some cases such as where ability to steer the wheel through the large angle is valuable).

 

[brian_]

Tesla are very clever, however that is a CAR!

Did I fail to mention this is an off road 6x6 that only weighs 500kg.

Why do so many people seem to think that Tesla is the only manufacturer of electric cars? Weird...

But yes, while the example of electric cars may not seem directly applicable to a 500 kg vehicle, the technical issues are similar. The most notable difference is that cars are more sensitive to unsprung mass than low-speed and heavy-duty vehicles, and so in-wheel motors are particularly undesirable. Since cars don't use in-wheel motors they can use only one motor per axle to save expense, leading to a common configuration which may not be ideal for other applications.

How would you suggest that I drive six wheels without having motors on the hubs? Run six axles and CV joints?

Assuming that you have suspension or steering at each axle, then yes... with a motor or motors not mounted on the hubs you would need CV joints. There have been many 6X6 vehicles of various sizes, and nearly all of them have three conventionally powered axles (either live beam axles, or independent suspensions and jointed drive axles).

In this case, hub motors might make a lot of sense, especially if individual wheel speed control is desired for skid steering or tight turns. In a low-speed and low-powered vehicle the disadvantages of in-wheel motors might not matter, especially compared to the packaging advantage and lack of axle shafts.

 

[brian_]

While we would love to use hub motors, we can't find any with an IP65 or IP67 ingress rating. As this will be used in hostile, muddy wet environments, this is a requirement.

So far, we cannot find any wheel motors that have a decent IP rating. Why is this? Do electric vehicles not go through pools of water? Do they not get submerged up to the hubs?

Motors need cooling. Liquid-cooling a hub motor means coolant lines to and from the motor, which would be an unpopular choice. Cooling entirely via a sealed housing is not very effective. That leaves most small motors air-cooled, and so likely incompatible with even splashed water, let alone submersion.

It seem like there must be applications which require sealed in-wheel motors, so there must be a source, but it may not be inexpensive or readily accessible to the public. There would be very little experience with this specialized type of application in this forum.