Does "suck up huge amounts of power" for a seal imply "generate lots of heat"?

If so, is that heat another issue or is it a "don't care" because the heat is over a large enough surface?

It absolutely matters. Every Watt of energy that doesn't become torque at a rotational velocity is just heat.

Contact seals work by contact and friction, friction generates heat proportional to linear velocity and linear velocity goes up proportionally with radius.

The motors I designed were intended for food production washdown areas, and if I were designing large motors for use in road environments, I would use a lot of similar methods, including high quality contact seals.

Teflon seals would probably have the required capabilities, but they will get destroyed by dust and grit. Nitrile seals would do it too with the detraction of a huge power loss at the seal. I wouldn't trust a plain labyrinth seal to do the job.

> Every Watt of energy that doesn't become torque at a rotational velocity is just heat.

Do you have any rough numbers to put on this? If there was 1000w of electrical power going to a wheel like this, what kind of heat loss are we talking? 5%, 10%, 30%?

Depends on the seal manufacturer. Those numbers are usually provided through their engineering data system. Their data will be fit to a particular tolerance for seal race surface finish, which will be influenced by the reality of manufacturing.

Right, but are we talking closer to 5% or 50%?

Allow me to embrace my engineer nature and hedge my bets. A contact seal of that size is usually specced for a power transmitting shaft. An (assumed) 20" shaft is going to transmit a huge amount of power. So much that the seal losses will be negligible. Those same losses would exist on any shaft/seal combo of that size, but would take a greater fraction of total motor power, given the size and power constraints given by an internal motor design.

This is an offshoot of a motorcycle manufacturer. They have this product on the market already, so there must be something you missed?

https://arstechnica.com/cars/2024/07/sci-fi-looks-high-end-p...

I cannot speak to their actual means and methods. Maybe they've figured it out. But my experience designing and manufacturing similar products informs my skepticism.

I also look back in history and see many "revolutionary" technologies in the automotive/transportation space that didn't turn out as the inventors hoped. A veritable graveyard of "good on paper" ideas that failed due to the harsh realities of environment, maintenance, safety and manufacturing.

As I said in another comment, I want them to succeed. I am familiar with the great efficiency that a direct drive motor can offer. They can be great motors in the right application. But my evaluation of what I can glean through the marketing is that this particular product will end up in the graveyard.

The way I understand hubless wheel designs (powered or not) is that you don't build them as one big bearing, wasting huge amounts of load bearing capacity in all parts of the rotation that aren't the ground contact point. I assume that the moving part is the rim is designed as a rail, with tiny trucks (as in the rail car component) riding on it that are fixed to the non-moving part. You'd have a high density of strong trucks near the floor, some at the three and nine o'clock positions for braking and acceleration force and perhaps some flimsy guiding on top. Those trucks would not necessarily require more sealing (outside their own small bearings) than the rail/wheel contact in railroads need sealing. And moving that rail a little hubward, behind a lip that extends rimward would already get you strong centripetal forces driving out all ingress in contact with the moving part, and adding some overpressure (that you might need for cooling anyways) would help even more. I think it could all remain contactless on that first, whole-wheel level, at least if you don't design for routine wading.

Plus there's the unsprung mass. At least traditionally part of suspension performance is reducing the unsprung mass as much as possible because mass and spring rate inversely correlate.