# Help with Hub Motors



## Ausdroid (Apr 29, 2020)

Hello, we are building a 6 wheel drive 500kg robot vehicle and are stuck in our design flow as we have to choose between using a standard 2kW brushless motor and then building a hub with reduction drive, or using hub motors.

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?

Any help in trying to find a 2kw waterproof hub motor would be great.


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## Duncan (Dec 8, 2008)

Hub motors are very rare - because they are a bloody silly idea for most applications!


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## Ausdroid (Apr 29, 2020)

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.

Silly me!


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## Duncan (Dec 8, 2008)

Ausdroid said:


> 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.
> 
> Silly me!


So overwhelmingly popular that you can't find any!!

Great for bikes and other light vehicles - totally crap for road vehicles!

The problems are
(1) Torque is proportional to weight - so we usually use a gearbox to increase the torque - Tesla uses a 35 kg motor to give the torque that would have required a 300 kg motor

(2) Additional unsprung weight is a BAD idea

The result is hub motors are used for Bikes - low powered motor bikes 
AND
Huge great mining trucks where the speeds are low

For something car sized and operating at highway speeds - CRAP


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## Ausdroid (Apr 29, 2020)

Duncan said:


> For something car sized and operating at highway speeds - CRAP


Sorry, i thought I posted this on the Non Road Going thread.

Oh, I did!

Tesla are very clever, however that is a CAR!

Did I fail to mention this is an off road 6x6 that only weighs 500kg. How would you suggest that I drive six wheels without having motors on the hubs? Run six axles and CV joints?


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## Duncan (Dec 8, 2008)

Ausdroid said:


> Sorry, i thought I posted this on the Non Road Going thread.
> 
> Oh, I did!
> 
> ...


500 kg is car sized - and yes if you want it to go fast then you should run six driveshafts

If you are happy with 5 mph - then - even then nunning driveshafts is better


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## brian_ (Feb 7, 2017)

Ausdroid said:


> 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.



Ausdroid said:


> 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).


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## brian_ (Feb 7, 2017)

Ausdroid said:


> 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.




Ausdroid said:


> 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.


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## brian_ (Feb 7, 2017)

Ausdroid said:


> 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.


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## Ausdroid (Apr 29, 2020)

Brian,

Thank's for the engineering lecture.

Our vehicle is skid steer, it needs to be able to turn in its owns space. The suspension is long travel which eliminates the ability to use shafts and CV joints as they don't have the range. Even if we reduced the suspension travel to what CV joints could cope with, and we were to accept the additional wear, they can't cope with the torque at highly articulated angels.

In addition, there is a requirement to be able to easily change out a wheel and suspension assembly as it is expected they will be damaged often.

So we are stuck with motors on the wheels.

The only question, which I attempted to highlight in my first post, is whether we will have to design our own reduction drive into the hub, or whether we use hub motors.

Cost is not an issue as we have an appropriate budget.


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## ishiwgao (May 5, 2011)

Ausdroid said:


> The only question, which I attempted to highlight in my first post, is whether we will have to design our own reduction drive into the hub, or whether we use hub motors.
> 
> Cost is not an issue as we have an appropriate budget.


Since there aren't many small able-to-fit-in-a-hub motors available, in my opinion, a reduction drive into the hub may be a better option because it increases the range of motors you can use (ie using the reduction gear to gain as much torque as you need)

This of course increases cost, complexity and space constraints since you need to design an extra gearbox inside the hub

But as others have mentioned, you'll probably need to do your own casing with the hub that can be IP protected. motors don't usually withstand such harsh conditions; moreover yours is an off-road application


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## Duncan (Dec 8, 2008)

Skid steer
6 wheels 
Off road 
500 kg

How about using swinging arm suspension with a motor co-axial with the swinging arm and enclosed chain drive from the motor to a simple hub - one for each wheel 

That keeps the motor up on the chassis - gives you some gearing options - and is relatively easy to seal


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## RickHoran (Apr 5, 2020)

Ausdroid:

If you haven't already done so, check out www.endless-sphere.com. There you will find tons of information regarding direct-drive and geared hub motors.

Good luck with your project! Sounds exciting!

Rick


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## CivicEV (Aug 1, 2015)

Is there a reason you wouldn't consider hydraulic wheel motors. Mount you electric motor in a safe place and drive a pump. I love electric everything but in harsh environments, hydraulics are so proven and reliable and solves the problems you alert to.


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## Paxelrad (Feb 13, 2020)

Wish I could help. I've been looking for these for several years. I'm trying to build a lightweight amphibious vehicle. Similar weights, low speed and power requirements. Nearest I've got is a company in Estonia building experimental drives for military purposes. They weren't really interested in my R&D.


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