Sorry, ignore that tyre width sentence, and numbers should be 560kWh, 1120kWh, which makes even more sense.
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Lets work out the Tesla Semi-Truck Technical Specs
- Thread starter lnpurnell
- Start date
Sorry, ignore that tyre width sentence, and numbers should be 560kWh, 1120kWh, which makes even more sense.
I got to thinking about this some more last night.
Why would you think the motors would be light? Maybe they are but you are also doubling them up and you need to transfer that power to the wheels. First of all your transferring several hundred horsepower over long periods of time if you believe Elon's claims, he also claims these units will a million miles without major repairs. Remember he's using motors from a car that uses this kind of power for only seconds at a time and it weighs in at 2800lb (1600lb without batteries) The components required to transfer that kind of power over those periods of time are going to be heavy. Second is you need twice the inverter capacity to transfer twice the power plus do it for long periods of time in extreme conditions, again this is not bursts of power, this is continuous power that needs to be reliable. Also you need to consider attaching these units to the chassis and suspension.
Why are the batteries in crossways? Now you have to build a complex/heavy frame assembly to support the batteries as well as connect the front and rear of the vehicle. Typical frame rails would be far lighter plus they've lost somewhere between a fifty and seventy square feet of potential battery storage. Trucks with conventional powertrains move the engines and related components as far forward as possible, they' actually moved the front axles back to get more weight on the front axles.
A typical unladen highway truck weighs about 10,000lb on the steering axle, in the US they can load to 12,000lb, they accomplish this by moving the fifth wheel forward of the centerline as required so when the tandem drive axles weigh 34,000lb the steering axle will be loaded to legal max weight.
Tesla mounting the batteries midship tells me that battery pack is extremely heavy, it's simple physics.
I'd bet you suspect wrong, most highway truck cab structures are built as light as possible, they've being doing this for a hundred years and most have learned where they can cut corners to lighten trucks up. Aluminum, fiberglass and some composites have been used in the construction of truck cabs for years. Also truck cabs are far simpler than what Tesla appears to be building, Elon stressed creature comforts during his speech. I wouldn't be surprised this unit has motorized doors and other neat gadgets.
The likes of Walmart/J.B. Hunt and others ordering these trucks makes sense in a way as their trucks vary rarely haul max gross weighing loads, their units are designed for maximum cubic capacity, not weight There is also public perception as these companies going "green".
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Not might. Definitely thermal limit. I'm surprised that it can do THAT much. I think that is due to air intake cross section area
being many times larger than on Model S (JKolodziejski, can you estimate areas for air intake between Model S and BAMF?). Plus 2 more motors and all of them more efficient.
If grade goes up (or weight above maximum) due to maximum nominal power drivetrain can handle will stay constant,
maximum sustained speed will drop (and drop will slightly accelerate as less air mass passes radiators if speed goes down)
Maximum peak power and maximum nominal power are two different things. Acceleration requires peak power (just for 20 seconds). Hill climb continues for minutes. Even ten or twenty. Thermally, different scenarios.
RWD Model S has maximum nominal power was 35kW if I remember correctly. Not sure why, but most likely because
it doesn't have fan for coolant loop and power might be measured stationary on the rollers.
AWD Model S overheats within 1 minute at maximum power and maximum sustainable power output at high speed (a lot of air passes through radiators) is around 200kW. Adding cooling capacity won't help much as rotor doesn't touch cooling jacket. And coolant passthrough has not been confirmed (patented).
Not likely with his corporate buyer customers. Simpler is better. With the touch screens the cab has far fewer moving parts than a conventional truck. I hope Tesla doesn't try to redesign the air suspension seat or the air brakes.
The cab looks really simple to me.
Yes. For both power and regen braking Tesla has to design to what it can achieve continuously, not peak.
I don't think their design challenge was hill climbing, but continuous regen on decent. Keeping a heavy truck under control is of far higher importance than a couple extra mph going up a steep grade.
Obviously the truck has relatively massive cooling to charge a 1MWh battery fast. It must have a good size radiator somewhere, probably with fans. My unimog is designed for high power stationary operation. It doesn't rely on airflow from movement over the radiator. This semi will probably be similar.
The noise from the radiator fans would not be acceptable in a car. But this isn't a car.
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dhanson865
Well-Known Member
dhanson865
Well-Known Member
You are using the word "pack" when you should be using "module". The Semi has 4 packs, I don't know if it has 48 modules but I'll take your word on that for now.
I didn't say the motors would be light - I said there's no way that they would weigh 2,000 pounds more than the existing axles/differentials. I haven't seen anything on the Model 3 drive motor weight yet, but the much more powerful original S motor weighs 70 pounds, the complete original rear assembly with inverters and gears and differential is around 300 pounds, and a pair of Rimac motors without gears is 212 pounds.
I'm pretty sure the reason a traditional semi has those massive longitudinal frame rails is to resist the motor torque - and you still seem them twisting several degrees when they accelerate hard at low speeds. That's exactly the kind of structure Tesla needs to remove for weight, because they don't need it without the big diesel torquing things up.
I think the crosswise battery pack arrangement is for two reasons - it's more efficient use of space since the spaces to the outside of the pack between the rails would be wasted, and it makes for easy removal from the side if required.
I'll predict that the motor used in the truck is a different part number than the car. I think using the exact same motor probably turns out to be aspirational.
But I do think that Tesla will have excellent economies of scale on the truck by not doing a lot of custom battery and propulsion work.
Given that the motors are integrated with the gearing and inverter and mounted to the rear axle, I'd say you are correct.
Core stator and rotor could be carry over though.
Two observations that interest me.
1. I have not seen any statement of vehicle weight. This is important because I assume it is deducted from the GVW of 80k lbs and thus defines maximum load.
2. One of the models shown has external mirrors and what appear to be rear facing cameras. The big silver/White Model only has what I assume are rear facing cameras. Is Tesla betting they can get video rear cameras to replace mirrors approved for trucks?
1. I have not seen any statement of vehicle weight. This is important because I assume it is deducted from the GVW of 80k lbs and thus defines maximum load.
2. One of the models shown has external mirrors and what appear to be rear facing cameras. The big silver/White Model only has what I assume are rear facing cameras. Is Tesla betting they can get video rear cameras to replace mirrors approved for trucks?
Tesla has been demonstrating cars without mirrors for years - they keep hoping that the NHTSA/FMVSS requirements will be updated to remove the explicit requirements for mirrors - which a lot of the industry is pushing for I believe, and which the government had said they were going to do a while ago I believe.
Olle
Active Member
Good observation. Do the driveshafts look like 3 piece 2 joint shafts?
What do you think of front suspension? Hard to see in the renderings. Something Volvos new individual suspension?
No drive shafts, Basically, take a differential carrier and turn it into a drive unit,then mount two of those. Drive unit has reduction gears and bearings, axle shaft slides into splines, sizing may allow for shaft to attach to drive before it is inserted. Or there may be an access cover underneath to secure them. Or they are floating... Not sure what is needed.
Elon said independent front end, but I haven't looked at that part.
Olle
Active Member
Got it. Kayman's video explains it all. So drive units are unsprung. Pretty hight demand on cable and hose management I guess since it will be moving with suspension
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True, but it definitely simplifies the axles. It's not a rock crawler, so total displacement won't be too bad.
dhanson865
Well-Known Member
Olle
Active Member
I read that too but can't make sense of it. Model S has 9.73:1. (what could it be on M3?) Given the 50% bigger wheels on a semi, the motor speed would be same as Model S at approximately 15:1. One would think the motors would need to spin much faster in the truck than in a Model S to give enough wheel torque. What am I missing?
This is what I predicted in post #2.
I bet they will tune one ratio to get IDEAL motor+inverter efficiency at ~60mph. Long distance trucks travel at very very constant speed.
And the second pair will be more efficient at lower speeds.
Though now it makes me wonder, how the heck are motors connected to packs.
All 4 packs must be in parallel (or at least 2 packs for left motors, 2 packs for right motors) otherwise a pair will be depleted much earlier.
Without calculations I expect motors will utilize the most of that maximum kW range.
Like I said, 70mph as nominal max speed. Above that power starts to taper anyway.
This is why BAMF will do 65mph at 5% grade. All 4 motors will likely be at peak available kW.
Semi top speed can not be motor top speed. There is not enough power near motor top rpm.
BAMF doesn't need more torque at lower speeds. It kills all other prime movers anyway.
Don't have data for M3 PM motors but this gives the idea:
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