- Feb 19, 2020
- Reaction score
- Houston, Tx
- 3 motor Cybertruck, highly modded 2014 Ford Focus SE, dead 1998 4-Runner
- Space Cowboy
The answer is that it will depend on conditions. The heaviest load is the inertial load we have been talking about and, of course, that load is short lived. Going up a long steep grade isn't. An empty CT (3000 kg) going uphill at 60 mph will pull about 7.8 kW per percent grade above the approximately 24 -30 kW at 0 grade. Pull 14,000 lbs and that load is going to about 24 kW per percent. We can be sure of 2 things. One is that the engineers have examined this question at length drawing heavily on what they have learned with the semi where this is really, really important. The other is that with all those sensors the computer will know if there is impending danger and will take protective action (such as simply limiting the power that can be drawn) and offer the driver a host of warnings, messages, and chimes.People have spent a lot of time talking about the range when towing, but there is another factor that comes into play. We know the CT can put out super high torque and power for 2.9 seconds at a time. What can it do for an hour at a time? Is it going to overheat (or thermally-self-limit) its motors or batteries or electronics pulling a heavy load up a sustained uphill road (through a mountain pass)?
Yes Ryobi batteries suck bad! Buy an Ego and it will cover your 1.5 acres and more and you’ll never have to return the battery. I’ve been using them for 6 years now and they are the real deal.I used an electric weedeater about 40 years ago (yes, in '80s). It was a torque monster. But it was a pain to stretch the cord all around the 1.5 acres. The 2-stroke I finally bought was much better--they still are. 40 years later a battery weedeater still can't really finish that 1.5 acres. The batteries would peter out. And need replacement after 1 season. But my little 80 year old neighbor loves his for light work. He brags that Home Depot keeps taking the batteries back on return after they fail early (lifetime battery on Ryobi?)
I've been using ryobi batteries 4Ah lithium+ and I didnt realize they suck. The ninth and nicd ones certainly did. I've never really used anyone else's although instinctively I know Milwaukee is better but their tools are expensive and I dont imagine their batteries last much longer.... ego lawnmower works well but cant really use a 10Ah pack on hand tools.Yes Ryobi batteries suck bad! Buy an Ego and it will cover your 1.5 acres and more and you’ll never have to return the battery. I’ve been using them for 6 years now and they are the real deal.
Trust me you don’t need a battery that big for hand tools. I don’t even own a 10 only the 7.5’s and smaller. I own a lawnmower, weed eater,trimmer, blower and the generator of theirs and between owning the different size batteries and having the fast charger it all becomes a non issue. Unfortunately my experience with Ryobi is with the batteries with their hand tools and they just don’t last long the big or small ones.I've been using ryobi batteries 4Ah lithium and I didnt realize they suck. I've never really used anyone else's although instinctively I know Milwaukee is better but their tools are expensive and I dont imagine their batteries last much longer.... ego lawnmower works well but cant really use a 10Ah pack on hand tools.
I'm sure the good Professor Singh would approve of the use of calculators provided that you retained enough understanding of the physics to appreciate that 121 kW consumption at 14.6% grade ( 8.3 °) is not consistent with 88 kW at 6% grade (3.4 °).I daydreamed through my motors class 30 years ago (and stared at my professors turban), but I found a calculator at "robot shop.com"
A 20,000 cybertruck (with load) going up the steepest wheelchair ramp allowed (8.3 degrees) for an hour (at 95% efficiency), and maintaining 60 mph on that hill with that load requires 121 KW. ( assuming no air, no rolling resistance, spherical chickens, etc.).
A 6% grade requires 88 KW.
Let's not get too carried away. 200 kW at 400V is several hundred for sure (500) but if I were driving along and saw my power meter nearing full scale and staying there I would certainly back off the pedal.That's a lot of juice. The amps are up there for sure--many hundreds of amps.
I didn't realize 6 percent angle is different from a 6 percent grade. I was just plugging numbers into a calculator. I think I implied that. I bet Jane could tell some stories. And Scott. Are you always like this?I'm sure the good Professor Singh would approve of the use of calculators provided that you retained enough understanding of the physics to appreciate that 121 kW consumption at 14.6% grade ( 8.3 °) is not consistent with 88 kW at 6% grade (3.4 °).
A truck traveling at 60 mph covers about 1600 m in one hour. On a 6% grade (3.4 °) it climbs 6% of that (0.06*1600) = 96m. If it weighs 20000 lbs its mass is (20000/2.2) = 9090.9 kg and (20000/2.2)*9.8*(1600*0.06) = 8.55273e+06 joules potential energy was gained (supplied by the motors in addition to all the other energy they supplied in covering this mile). 9.8 m/s/s is the nominal gravitational acceleration. That's a lot of joules equivalent to 2.375 kWh (a watt hour is 3600 joules) required to pull the rig up the hill over one mile to which must be added the other loads which are at least 700 wH/mi for a total consumption of about 3 kWh/mi which is 6 - 7 times the expected consumption of the unloaded truck so the 500 miles nominal range would be reduced to 70 - 85 miles or so. But note that this 3 kWh is consumed in a minute so that the power consumption is 60*3 or 180 kW - 142 of them just for the uphill load which would be, of course, the dominant one.
Now let's try to put that in perspective. A Model X has a nominal consumption of 280 Wh/mi and so the nominal power delivered at 60 mph is 14.8 kW. But the first mark on the power meter is 75 kW with full scale being 300 kW and it's not uncommon to see power levels get up to and above 75 kW in the course of normal driving in country that is not hilly. Thus even the X is designed to a couple hundred kW power levels if briefly. Nonetheless we do hear stories of current Tesla vehicles operating in the desert in the summertime having power restrictions imposed with reduction in cabin cooling to protect the battery. So this is a very good question.
Here's a chart showing the power used for going up hill as a function of vehicle weight and speed. Where towing 14,000 pounds up an 8% grade (and there are those that persist for a couple of miles in the US) on a hot day you are going to have to slow down.
Let's not get too carried away. 200 kW at 400V is several hundred for sure (500) but if I were driving along and saw my power meter nearing full scale and staying there I would certainly back off the pedal.
I have never seen angle represented as a percentage but I have seen it represented as a fraction (of a circle). The angle of a road with respect to the horizontal is related to the grade through the tangent function: grade = tan(angle). If the angle is expressed as 2*pi*fraction of a circle ( "radians") then grade and angle are approximately the same for angles less than about 0.21 radian ( 12 °). Degree measure is just 360*fraction of a circle.I didn't realize 6 percent angle is different from a 6 percent grade.
I was suggesting that perhaps a bit of caution is wise when using a calculator "found on the internet" if you are hazy on the principles on which the calculator works.I was just plugging numbers into a calculator. I think I implied that.
Yep.I bet Jane could tell some stories. And Scott.
Most of the time. I love playing with numbers and tech. Check Dilbert and "The Knack".Are you always like this?
I will address range in the 3rd Video.The CT will be a towing God? How much stamina, endurance, and life-span does God status require?
The CT towing 14k+ will be like a champion powerlifter competing in a Crossfit contest. I agree with the comments that up to a certain speed a Tesla torque curve is flat in a good way.
I used an electric weedeater about 40 years ago (yes, in '80s). It was a torque monster. But it was a pain to stretch the cord all around the 1.5 acres. The 2-stroke I finally bought was much better--they still are. 40 years later a battery weedeater still can't really finish that 1.5 acres. The batteries would peter out. And need replacement after 1 season. But my little 80 year old neighbor loves his for light work. He brags that Home Depot keeps taking the batteries back on return after they fail early (lifetime battery on Ryobi?)
Towing EVs are almost in their infancy. But they must get born first. After a pregnancy. The parents haven't even been picked yet. (Isn't Tesla still searching for a site to build the Cybertruck? Isn't Tesla trying to figure out ventilators? While working remotely? Wait, aren't they trying to figure out big rigs? Which reminds me, heck, aren't they trying to figure out batteries?)
I have an electric bike--I love it. For 20 miles. No comparison betwix it and my motorcycles. I have a battery chainsaw and three that are heavy duty (ish) and gas. To make my echo battery chainsaw badass enough to beat my Stihl Farmboss, the echo would last 1-5 cuts.
I am starting to wonder about the wisdom of spending 90K (all in) on a replacement for my 18 year old 7.3 F250. I did rough numbers in my head one day and think battery degradation alone (from abusing the battery towing) in addition to electricity costs will be ballpark 50 cents a mile for towing. I need to do a spreadsheet though with actual guestimates. At a minimum I'm thinking of going back down to 1 motor and keeping the diesel for towing. I mostly just want a "truck" and FSD.
...and this is why I decided to use a wrench to explain torque. Because explaining torque with math is more accurate but way less understandable for most of us.Here are some more musings on torque which I hope will help in clarifying some of the confusing material in the video. Perhaps an edit or two is possible.
The motor(s) in a truck are there for the purpose of providing a force on the truck in the direction of desired travel. This force does several things but the most significant of them is getting the truck moving that is, accelerating it to desired speed. Force is also needed to lift the truck up hills and push air out of the way but lets focus on getting the truck moving for now. The required torque is the required force multiplied by the wheel radius (this is the definition of torque) and the required force is the product of the mass of the truck and the desired acceleration. In symbols this is F = m*a which is Newton's second law and the basis for all classical mechanics. Since torque is simply force multiplied by arm (the technical term, here the wheel radius) we can multiply both sides of F = m*a to get F*r = T = m*r*a from which it is clear that the faster we want to accelerate the more T, torque we will need. The more torque we can obtain the faster we can get from 0 - 60. Thus we want all the torque we can get but there is a limit to what drive train components will tolerate before failing. In the sketch below the maximum available torque, let's mark it T, is denoted by the solid horizontal line in the "Torque Limited" part of the diagram which plots torque on the left vertical axis against wheel speed.
Now lets go back to the Newton law and multiply all terms by w, the angular speed of the wheel. This gives F*r*w = T*w = m*r*w*a. As r*w is the distance the car travels in a unit time, i.e. it is the speed of the vehicle, and as force times distance is energy and energy per unit time is power each of those terms is the Power transferred to the truck. The dashed line shows how that power, read off the right vertical axis, varies with speed . When the torque is held constant It increases linearly with speed. Eventually a point is reached where the motor's power capacity is reached. It cannot, or cannot safely, produce any more power and at speeds above this critical speed the power is constant at the maximum value the motor can produce. As power is the product of torque and wheel speed the torque must go down as speed continues to increase and this is shown by the solid curve in the "Power Limited" part of the chart. As acceleration depends directly on torque it is clear that the vehicle will not accelerate as swiftly in the power limited region as it does in the torque limited region. An electric motor, conversely, has a torque characteristic that is quite like the sketch.
I don't know how good a job I did of explaining this but a whole lot of the story is tied up in this graph.
I can't begin to tell you how upsetting that is to me. American kids leave high school without being able to comprehend what F = m*a means. That's pretty pathetic but not the upsetting part. The upsetting part is that kids coming out of school in China do understand it. The irony is that torque is a mathematical convenience which makes the mechanics of rotating systems easier to explain....and this is why I decided to use a wrench to explain torque. Because explaining torque with math is more accurate but way less understandable for most of us.
First, I meant no disrespect. I can see how my comment would come off that way. I apologize. I hope that you can tell by watching my videos that I appreciate education and learning.I can't begin to tell you how upsetting that is to me. American kids leave high school without being able to comprehend what F = m*a means. That's pretty pathetic but not the upsetting part. The upsetting part is that kids coming out of school in China do understand it. The irony is that torque is a mathematical convenience which makes the mechanics of rotating systems easier to explain.
Think of a pound of butter. Gravity exerts a force of 1 pound on it. If you pick it up off the floor and put it on a counter 3 feet higher than the floor you have worked against gravity. The amount of work you did is 3 foot-pounds. You have transferred 3 ft-lb of energy to the butter (2,655,224 ft-lb is equivalent to 1 kWh).
A motor has a torque specification. For example, the 5.0L V8 in the Ford 150 delivers 400 lb-ft at 4500 rpm (which I guess is it's peak). Note that the units, lb-ft, are those of work/energy except that lb is customarily written first when speaking of torque but that doesn't matter. Torque numbers are still energy values. A torque of 400 lb-ft means that this engine is capable of delivering 400 ft-lb of work per unit angle of shaft rotation. As there are 2π units of angle in a complete rotation that means that a 400 lb-ft engine delivers 2π400 ft pounds of work per shaft rotation.
The engine is geared down through the transmission and differential. Let's say it is geared down in a 10:1 ratio so that for each rotation of he engine the half shafts only make 1/10th of a turn. Ideally, the transmission is lossless (not, of course, the case in the real world) and that means that all 2π400 ft-lb of energy would make it through to the half shaft but is is delivered in 1/10th of a turn so that the torque, (work per unit angle of rotation), must be 10 times higher at 4000 lb-ft. Thus torque is "multiplied" by the gear ratio. Shaft speed is divided by the gear ratio so the half shaft speed is 450 rpm and as the wheels are connected to the half shafts the speed of the vehicle (in feet per minute) is 2π450 rpm times the radius of the tire (in feet). The thrust from the wheel is the torque divided by the wheel radius and the thrust is, of course, what we need to determine vehicle acceleration, overcome drag and ascend hills but it occurs to me that I've probably lost many already. Maybe some kid in China will get something out of this.
I did not think your comment was at all disrespectful and I did not think it came off that way at all.First, I meant no disrespect. I can see how my comment would come off that way.
Thanks but no apology necessary, I worry a lot about the US falling farther and farther behind in STEM but it is hardly your fault.I apologize.
I hope that you can tell by watching my videos that I appreciate education and learning. [/QOTE] I can indeed.
I think we share the goal of trying to come up with meaningful explanations of what torque is and how it relates to motor vehicles.Secondly, we are, respectively, trying to solve different problems.
I think most here are familiar with what a torque wrench is as most probably also know by experience that if you put a long extension on a socket wrench you don't have to pull that hard to "torque the head off a cap screw". But I don't think that so many would have thought of torque as energy delivered per revolution which is the aspect of it that is pertinent when discussing the movement of a vehicle (towing or not)..On the other hand If I tried to explain torque in the way you're trying to do, I would lose a lot of casual viewers who aren't really trying to understand the finer points of torque, but rather trying to frame the capacity of the Cybertruck relative to other vehicles they may have some familiarity with and within the specific application of towing.
I don't recall anything major. There were some comments about "delivering torque faster" which I wouldn't use and a statement that electric motors deliver torque more smoothly which is questionable as they are subject to "torque modulation" sometimes called "cogging". On the reciprocating engine side we have flywheels to smooth out the impulsive power delivery.With all of that said, do you think I fundamentally missed or misrepresented something in the video?
Thanks for responding. All analogies are flawed and there are terms that I will use colloquially, which may be ultimately be incorrect relative to their engineering or scientific use. You obviously know your stuff. I'm neither an engineer or mechanic. Just an enthusiast who got tired of non truck people telling me why I shouldn't like the Cybertruck and got tired of yelling at them via my phone screen. My only goal is to provide good information in an entertaining enough delivery to get people to the end of my videos. That said, If I get something wrong, I want to know.I did not think your comment was at all disrespectful and I did not think it came off that way at all.
Thanks but no apology necessary, I worry a lot about the US falling farther and farther behind in STEM but it is hardly your fault.
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