Another gearbox discussion

[just-an-allusion]

Well that is, by definition, what a transmission (or a gearbox) does, which is the topic of this thread. My concern (i.e. my reason for replying) is that your posts suggest gaps in understanding. I've suggested some topics you could look into to fill those gaps.


If with all that you're trying to say Tesla should make a better motor, I'm sure they're working on it. What they have now with DT1.5 is working pretty well, though.

No, no, no.... It's not that I'm missing some "gaps in understanding", it's that I'm merely leaving out what I view as unnecessary components, the results of an attempt at cross-application integration of two clearly divergent technologies.

What I'm suggesting/questioning is why not merely use the "motor" itself as the "transmission" (multiple "poles"=two birds...one stone) instead of (IMHO) needlessly over complicating a basically straight forward process of poer management?

It would be helpful if you had some background in/experience with the varieties of induction motors...do you?

[donauker]

It would be helpful if you had some background in/experience with the varieties of induction motors...do you?

Based on your posts I would estimate that my understanding of AC inductions motors is greater then your understanding of the part played by reduction gears.

I would be very interested in seeing your motor specifications for your AC induction motor which will produce approximately 8 times the torque of the motor built by Tesla Motors. Please include weight, size, efficiency and the method of cooling used for the rotor.

[ChargeIt!]

Ok ... pardon me for "gearing in" ... but "inspiration" is not giving me the proper "inspired drive" to satisfaction ...

I would agree that direct drive is the most efficient and simplistic ... but you need a REDUCTION gear. Let's try some simple geometry and 'rithmetic with a motor directly driving the wheels:

Assume at 125 mph your motor turns 14,000rpm. Meaning your car travels 125 miles or 125*5,280 feet in one hour, or 125*5,280/60 feet per minute. Since your drive wheels are thus traveling 11,000 feet in one minute while the 14,000 revolutions happen, each revolution is 0.79 feet. This would match the circumference of your drive wheel, or 12*0.79 measured in inches or an equivalent 12*0.79/PI inches DIAMETER.

Sorry but I would prefer not to run my Tesla Roadster on 3.0 inch wheels which spin at 14k rpm.

I would prefer a final drive ratio of .... oh say ... hmmm ... what would be a nice number ... how about 8.32 ? That would allow me to drive a single-speed gear reduction transmission on wheels with 8.32*3.0 = 24.96 inches diameter. I think an 17" wheel with Yokohama 225/45R17 tires might just work out (45% * 225 mm * 2 converted to inches plus the wheel diameter).

Did I miss inspiration's point and am I way off subject ?

(Notes: 1) No insults intended; 2) my cursory search did not find the actual final gear ratio for the Tesla Roadster.)

[graham]

2) my cursory search did not find the actual final gear ratio for the Tesla Roadster.)

Is this what you were looking for?

Tesla Motors - technical specs

Transmission
Single speed fixed gear with electrically-actuated parking lock mechanism and mechanical lubrication pump
Overall Final Drive 8.28:1
Reverse Reverse direction of motor, limited to 15 mph
Final Drive Ratio 3.12:1

[ChargeIt!]

Yeah! Thanks! That's it. I was close (8.32 vs 8.28) !
( I had guesstimated the ratio so that the calculations would match up with the tire size. )

[power]

its not really a problem . the rotor mass is still yet a fraction of what a combustion engine inertia would be. a sequential gear box with a 80% rpm drop would be more than achievable. again, this is what the porscheGT3 cup car does all day long with near 500hp and at 7-90000rpm.
a one gear change would certanly be very easy, relatively speaking.

mk

Yeah a flywheel would definitely work against their goal of trying to get the eMotor to change RPMs as quickly as possible. It sounds like the existing mass of the rotor was too much as it is.

If they ever need variable ratios it would be good if they found a CVT that could work.

[power]

no he is refering to the gear box alowing the available power of the motor to be utilized by the tires at any vehicle speed in question. Forget about motor torque for a minute, its the torque at the rear wheels at any vehicle speed that is being talked about. to maximize this, max power is needed. (not max torque) the gear ratio tesla selected is like a 1st gear on most cars. the motor can extend near the same torque as a internal combustion engine to double the rpms with out the risk of bending valves . But, the power available is much lower later in the vehicle top speed, for which a gear box, even a second speed , could help with.
Gearing doesnt create power, it helps better utilize the power you have available. With the Tesla roadster, this happens near 8000rpm for max power, even though max motor torque falls off at 6000rpm.

mk

Are you referring to LF as it equates to a tire's properties of deflection and recovery during operation as it relates to peak-to-peak, first harmonic, second harmonic, and higher-order harmonics?



Or another form of LF?

[power]

I follow you here, but that is not really the question (which is getting more and more convoluted)

I think its agreed that the tesla 8.3:1 reduction is almost perfect for the motor and drive electronics. my point was to get another gear in there , with a 80% rpm drop to not only take the top speed up, but give much better acceleration in a key area of performance, that being in the 80 to 120mph range.

electronic gearing, as what i see as being suggested, is not just as simle as pulling out a few motor poles! there are switcing losses in the control circuitry, back emf, winding impedenace, etc. There never will be one electric motor that can provide constant power. If there was, it would waste a lot of technology and cost to do what an advanced gear ratio could do. (i.e a CVT -IVT ).

Part of the confustion still boils back to the ole power vs torque discussion.
power determines the torque at the wheels that gives the acceleration. maximize the power at ANY vehicle speed, and you maximize your acceleration.
Remember, Acceleration = Power/(mass x velocity). So, if you can get the Tesla Roadster at a higher power range (i.e. near 8000 motor rpm) then you will maximize its accelertion potential.

mk

Ok ... pardon me for "gearing in" ... but "inspiration" is not giving me the proper "inspired drive" to satisfaction ...

I would agree that direct drive is the most efficient and simplistic ... but you need a REDUCTION gear. Let's try some simple geometry and 'rithmetic with a motor directly driving the wheels:

Assume at 125 mph your motor turns 14,000rpm. Meaning your car travels 125 miles or 125*5,280 feet in one hour, or 125*5,280/60 feet per minute. Since your drive wheels are thus traveling 11,000 feet in one minute while the 14,000 revolutions happen, each revolution is 0.79 feet. This would match the circumference of your drive wheel, or 12*0.79 measured in inches or an equivalent 12*0.79/PI inches DIAMETER.

Sorry but I would prefer not to run my Tesla Roadster on 3.0 inch wheels which spin at 14k rpm.

I would prefer a final drive ratio of .... oh say ... hmmm ... what would be a nice number ... how about 8.32 ? That would allow me to drive a single-speed gear reduction transmission on wheels with 8.32*3.0 = 24.96 inches diameter. I think an 17" wheel with Yokohama 225/45R17 tires might just work out (45% * 225 mm * 2 converted to inches plus the wheel diameter).

Did I miss inspiration's point and am I way off subject ?

(Notes: 1) No insults intended; 2) my cursory search did not find the actual final gear ratio for the Tesla Roadster.)

[just-an-allusion]

Based on your posts I would estimate that my understanding of AC inductions motors is greater then your understanding of the part played by reduction gears.

I understand both the necessity and practical application of the reduction drive unit(s), i.e., inasmuch as a single stage reduction gearing setup requires the input shaft (motor end) to complete two(2) rotations to every one(1) of the output shaft (wheel end), and that a second stage reduction gearing setup would require the input shaft to complete four(4) rotations to every one(1) of the output shaft's, slowing it's overall revolutions as a byproduct, I fail to see the benefit since everyone appears to desire more performance/speed from their cars, but that's not what I'm getting at as I (as you can hopefully tell by now) feel that switching to a two-stage/two-gear setup would be defeatist at this point.

I would be very interested in seeing your motor specifications for your AC induction motor which will produce approximately 8 times the torque of the motor built by Tesla Motors. Please include weight, size, efficiency and the method of cooling used for the rotor.

Intellectual Property("IT") is IT only for as long as someone doesn't blab about it out in some public forum/I'm sure you would.

[just-an-allusion]

Ok ... pardon me for "gearing in" ... but "inspiration" is not giving me the proper "inspired drive" to satisfaction ...

I would agree that direct drive is the most efficient and simplistic ... but you need a REDUCTION gear. Let's try some simple geometry and 'rithmetic with a motor directly driving the wheels:

Assume at 125 mph your motor turns 14,000rpm. Meaning your car travels 125 miles or 125*5,280 feet in one hour, or 125*5,280/60 feet per minute. Since your drive wheels are thus traveling 11,000 feet in one minute while the 14,000 revolutions happen, each revolution is 0.79 feet. This would match the circumference of your drive wheel, or 12*0.79 measured in inches or an equivalent 12*0.79/PI inches DIAMETER.

Sorry but I would prefer not to run my Tesla Roadster on 3.0 inch wheels which spin at 14k rpm.

I would prefer a final drive ratio of .... oh say ... hmmm ... what would be a nice number ... how about 8.32 ? That would allow me to drive a single-speed gear reduction transmission on wheels with 8.32*3.0 = 24.96 inches diameter. I think an 17" wheel with Yokohama 225/45R17 tires might just work out (45% * 225 mm * 2 converted to inches plus the wheel diameter).

Did I miss inspiration's point and am I way off subject ?

Yeah, pretty much, other than the point of increasing the inherent inefficiency of the gear reduction drive unit that much further by adding yet another gear/stage.

(Notes: 1) No insults intended; 2) my cursory search did not find the actual final gear ratio for the Tesla Roadster.)

None taken. I'm use to people not understanding/misunderstanding the ideas/concepts that I attempt to convey...it comes with the territory.