-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Lets work out the Tesla Semi-Truck Technical Specs
- Thread starter lnpurnell
- Start date
Try drawing a free body diagram of that to get the answers.
No reason you cannot have drive at any or all wheels.
Aerodynamic drag is proportional to the product of the drag coefficient times the frontal area. there are other variables like speed and other factors.I guess it is good that the Tesla Semi has a drag of 0.36 then.(Under the 0.4 that you say would be necessary.)
Tesla is only quoted as saying that it will be under 2kWh/mile. And 1.6 kWh/mile is under 2.
JRP3
Hyperactive Member
Fatigue from what? If the motors are already capable of sustained 50hp output, which I'm quite sure they are, then the bearings are as well.
I think you misunderstood the discussion. I'm saying all four rear wheels are driven, but the frame does not experience a twisting momemt along the axis where the drive shaft would normally be. Nor can you remove the reaction torque that tries to raise the front end (like a rear wheel drive car on a hard launch).
Well, I'm not a trucker, but if I was and had to drive backward after parking my truck, I walk a circle around it to see what's behind it, but if only the truck got camera's, then autopilot can never work, because it doesn't know weather there is someone behind it or not.
There are currents induced in the bearings due to the high magnetic fields which wear them out.
I think you refering to milling issue on early S (X?) drive units. The issue was resolved on the AC induction motor type.
The 3 PMSR type should not exhibit the root cause to the same degree, but it also has a rotor grounding contact on the encoder end to prevent current flow through the bearings.
I heard they are using insulation on the bearings to prevent the flow of the induced currents into the housing through the bearings. Will see how long they last.
I think S/X have ceramic bearings. Without an AC motor's inducted rotor current/ flux, the PMSR should not have that issue. If you come across articles on the 3 motor design, I'd be interested in reading.
I see.
I don't have a lot of details. I think it is similar to the LAGER (Boeing) motor mentioned here (not the GTM), slide 12: http://images.spaceref.com/fiso/2015/071515_frank_eichstadt/Eichstadt-Jones_7-15-15.pdf
JRP3
Hyperactive Member
No, but even if that were the case, how would that differ between using the motor in the Model 3 vs the Semi?
The motor used for the 3 and Semi is a switched reluctance permanent magnet (SWRPM) motor. That presentation doesn't mention the LAGER unit being reluctance type, and from the diagrams it appears to use a novel rotor/coil/stator layout. I believe they are different motor types, although the 3/Semi motor may also use Halbach arrays (conjentured in the Munroe teardown).
As @mongo has pointed out, not being an induction motor means the 3/semi motor doesn't have the eddy currents in the rotor for the bearings to deal with. In the Model S, ceramic bearings are indeed used, as are shaft grounding brushes to bleed off the current to avoid arcing past the ceramic bearings.
The LAGER from 2007 doesn't have the special stuff from the 2015 presentation, just the Halbach arrays. Rest of the presentation is about the newer GTM design.
And the Model 3 rotor has the Halbach magnets. This is why I said it's like the LAGER motor which is a Halbach motor, but not switched reluctance. Model 3 rotor appears to have the mix of Halbach magnets and non-permanent magnetic poles.
Attachments
I don't think a pure Halbach array can be switched reluctance. The only way that's possible if there is a mechanism to move them. So this always works as a PM motor. And if Tesla calls it switched reluctance, then they might have combined these two systems.
EDIT:
I figured out these are called permanent magnet assisted switched reluctance motors.
So Model 3 motor is a SRM in the first place. LAGER is a PM.
Last edited:
I think you are conflating things.
Many motors may use magnets. Some use them to directly react with the corresponding switched electromagnetic field to attract/repulse a rotor creating rotational torque, such as PM motors.
Other motors use magnetic inserts to shape the lines of flux through the magnetically conductive core, such as SWR motors.
A Halbach array is simply a way of optimizing the flux pattern generated by the magnets. It doesn't change the basic nature of the type of motor itself.
I believe a later teardown showed they are not actually halbach arrays. My thought is that the magnets direct the flux from an inner set of stator poles and the outer set of poles act as a typical reluctance motor. That allows twice as many poles, reducing the torque ripple.
To see what I mean, compare the number of stator slots (54) to the number of rotor sections (6). Each pair of rotor sections form a pole pair, giving 3. This is a three phase motor, so requires 6 slots for a full set of stator pole pairs. That gives us 54/3/6=3 sets of stator poles per rotor pole pair. Thus, there is a set of poles formed between the stator poles which align with the rotor shape. Here, the uppercase are the stator poles that align to the rotor reluctance sections, and the lower case are the stator poles that align to the permanent magnet section. The periods correspond to the undriven phase.
NN.ss.nn.SS.nn.ss. repeat 3 times
Net result: large rotor flux sections and small stator phase angle, giving high power and low ripple. Without the magnets, the adjacent stator poles would be 'shorted' through the rotor.
Similar threads
