Strange. I was pretty sure my car did "beep-beep-beep" and didn't get into reverse if I was still moving forward. That was a while ago though.. by now I am used to stopping so maybe they changed the software to allow it now?
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Can I cause any harm by switching from Drive to Reverese at < 5mph?
- Thread starter PhilDavid
- Start date
Strange. I was pretty sure my car did "beep-beep-beep" and didn't get into reverse if I was still moving forward. That was a while ago though.. by now I am used to stopping so maybe they changed the software to allow it now?
P85DBeast
Side tEsLa
I've done this in my S and even in ICE cars and I've never had a problem. Once a few months my wife was driving her moms 2017 Lexus ES 350 and while she was turning into the neighborhood her purse fell off the center armrest and hit the gear shift and the car shifted into Neutral (at about 20 MPH) and it caused no damage to the car's transmission, it just shifted into neutral. So I suspect it shouldn't cause any problems to the S or any car for that matter.
Uncle Paul
Well-Known Member
Can't be doing the drive line any good, but the slower the speed you reverse the easier it is on the mechanics.
Makes slow speed direction reversals a little easier, but has risks.
Is a little like using regeneration to slow your car from speed.
Makes slow speed direction reversals a little easier, but has risks.
Is a little like using regeneration to slow your car from speed.
Today I observed how it feels to suddenly switch at 5mph, it does not instantly switch it decelerates then slowly accelerates, I dont see any harm that can happen from this switch.
PACEMD
Active Member
What does Tesla officially say for the model S in the manual? The model 3 manual says:
Reverse
Push the lever all the way up and release. You can only shift into Reverse when Model 3 is stopped or moving less than 5 mph (8 km/h). If moving less than 1 mph (1.6 km/h), you must press the brake.
Drive
Push the lever all the way down and release. You can shift into Drive when Model 3 is stopped or moving less than 5 mph (8 km/h) in Reverse. If Model 3 is moving less than 1 mph (1.6 km/h), you must press the brake to shift into Drive.
Reverse
Push the lever all the way up and release. You can only shift into Reverse when Model 3 is stopped or moving less than 5 mph (8 km/h). If moving less than 1 mph (1.6 km/h), you must press the brake.
Drive
Push the lever all the way down and release. You can shift into Drive when Model 3 is stopped or moving less than 5 mph (8 km/h) in Reverse. If Model 3 is moving less than 1 mph (1.6 km/h), you must press the brake to shift into Drive.
busaman
Member
going to drive from reverse at 5mph is no different to flooring the pedal from a standstill.the motors will never exceed the preset torque limit.
I wish Engineering Explained could do a video showing the math and physics for this.
I believe the Model S manual states something similar so I assume changing direction < 5 mph is safe.
I'm not an engineer or physicist, but the math is actually easy, kinetic energy (KE=1/2 mass X velocity^2). The engineers can chime in with the calcs and kg and m/s conversions. The answer is the amount of energy in joules required to stop the car.
I think he meant if the ICE Porsche had 1 forward gear. One way or another you’d have to make up a lot of momentum in the wrong way.
this is related to the post somewhere about is it bad to use the accelerator to keep at a standstill on a hill except that you do have mechanical slack in the drivetrain to take up when you reverse direction. Ideally that should be close to zero. Aside from slack, the wear and tear upon a clutch or hydraulic transmission are non issues with the electric motors
Uncle Paul
Well-Known Member
At low speeds, perhaps no damage. You will just use more energy, slowing to a stop and then accelerating.
It sure makes 3 point turns easier.
It sure makes 3 point turns easier.
Uncle Paul
Well-Known Member
This is because we are kind of guessing at the accurate answer.
The prudent thing would be to do this as few times as we can.
Certainly will not do the driveline any good.
The prudent thing would be to do this as few times as we can.
Certainly will not do the driveline any good.
I'd also like to think if there was risk of any harm, Tesla would not allow it. They specifically woite the software to allow a Reverse to Drive change at less than 5mph and I don't think they would have done this if there was any issue.
I hope it causes no harm, because I do it fairly often, and have been for 4 years or so.....
I hope it causes no harm, because I do it fairly often, and have been for 4 years or so.....
If one day the car refuses to go from Drive to Reverse, do let us know!
ucmndd
Well-Known Member
My admittedly somewhat elementary understanding of AC induction motors leads me to believe there's no reason to think this could be a problem the same way it is with ICE engines and actual mechanical transmissions where you literally have gears and carriers spinning in opposite directions.
3-phase AC induction motors are powered by the rotation of magnetic fields. There is no physical mechanical connection between the application of rotational force and the motor's output. Direction of spin is determined by simply reversing the phase of the applied current. When you aren't applying any accelerative force, the motor is essentially "free wheeling" and there's no force applied when changing from reverse to forward. There's nothing that's going to cause the motor to "buck" or otherwise suddenly apply a sharp force the way someone suggested earlier on.
The transition might be more abrupt if you don't let off the accelerator, but again we're not talking about a hard physical connection - just reversing the spin of the induced magnetic field that propels that car in the intended direction. Foot off the accelerator, shifting from reverse to drive while still rolling backward? I can't think of any possible way this would cause harm.
3-phase AC induction motors are powered by the rotation of magnetic fields. There is no physical mechanical connection between the application of rotational force and the motor's output. Direction of spin is determined by simply reversing the phase of the applied current. When you aren't applying any accelerative force, the motor is essentially "free wheeling" and there's no force applied when changing from reverse to forward. There's nothing that's going to cause the motor to "buck" or otherwise suddenly apply a sharp force the way someone suggested earlier on.
The transition might be more abrupt if you don't let off the accelerator, but again we're not talking about a hard physical connection - just reversing the spin of the induced magnetic field that propels that car in the intended direction. Foot off the accelerator, shifting from reverse to drive while still rolling backward? I can't think of any possible way this would cause harm.
"There is no physical mechanical connection between the application of rotational force and the motor's output."
There is force against the wheels and ground. For a demonstration, hold the chuck of an electric drill and press the button. That force ripping both your wrists off just cost the battery/electrical source a small amount of energy. That force you experienced on your wrists would be transferred to the mounts holding your wrists in place if they were mounted stationary. That force can mitigated by torque limits/current limits on the motor so it will not apply all the current all at once to force that chuck to spin, but allow it to slow or give without ripping your wrist off the mounts.
There is force against the wheels and ground. For a demonstration, hold the chuck of an electric drill and press the button. That force ripping both your wrists off just cost the battery/electrical source a small amount of energy. That force you experienced on your wrists would be transferred to the mounts holding your wrists in place if they were mounted stationary. That force can mitigated by torque limits/current limits on the motor so it will not apply all the current all at once to force that chuck to spin, but allow it to slow or give without ripping your wrist off the mounts.
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