Flat towing a Rivian

Discussion in 'Rivian General Discussions' started by CappyJax, Mar 4, 2019.

  1. CappyJax

    CappyJax Well-Known Member

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    Propulsion from the toad to eliminate the load of the toad would be simple. To assist the towing vehicle would be more complicated. But both would be possible.
     
  2. stank65

    stank65 Well-Known Member

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    Not sure how this could be done simple, safe, or efficiently.

    1. You would run the battery out because you would recapture energy at a slower rate than expended

    2. Propulsion wouldn’t work because the application of the force through the single point of the hitch would destabilize the RV. Acceleration on any curve would push to fishtail the RV.

    3. The tow arm to handle this would probably be more expensive by a factor of 3 or 4 times.
     
  3. Hmp10

    Hmp10 Well-Known Member

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    In one of my favorite “Big Bang Theory” episodes, Penny asks the guys to help her assemble an entertainment wall unit she bought. They immediately begin postulating every possible scenario for which the unit could be used. In short order, they decided it needed all kinds of special wiring, cooling capacity, radiators, etc. to the point that they had to rush off to a junkyard for material. Meanwhile, Penny quietly assembled the unit to ready it for its rather straightforward intended use.

    This discussion reminds me of that episode.
     
  4. CappyJax

    CappyJax Well-Known Member

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    You would have far more range than operating the vehicle by itself because of the reduced drag. You could simply have an algorithm to use only so much energy in the batteries just like any hybrid. Same with applying power in turns. The hitch would not be standard. You would need something more stable than a regular bumper pull and with a pivot point closer to the rear axle.
     
  5. stank65

    stank65 Well-Known Member

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    I think you are discounting how incredibly complex this is. How this would require real-time data from both the car and the RV, and probably a multiple new sensors. Some of which would have to be on the hitch.
     
  6. CappyJax

    CappyJax Well-Known Member

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    Articulated pusher bus. Look it up. It has been done before.
     
  7. PaulMLAS

    PaulMLAS New Member

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    Of course you're correct as every time I brake without the Brake Buddy engaging (it only engages for heavy braking), it'll be pushing forward. I didn't work my physics correctly on that one. It makes sense that my bent bars that came from backing up just a couple of feet in a pinch in heavy city traffic at a tight intersection I couldn't clear--that would be the lateral force you're talking about. And that was backing up with a 2700# Mini Cooper, not a 7200# Rivian.

    Then again, pushing forward with the Rivian to "help" up a grade would somehow have to be always perfect at not inducing lateral force under any circumstance.
     
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  8. CappyJax

    CappyJax Well-Known Member

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    If you don't use some propulsion from the toad, either to reduce to load or assist the towing vehicle, then you are just going to waste that energy away when the toad batteries are full.

    And the reason you can't back up a toad is because the caster on the toads wheels will make them turn all the way in one direction and there is no way to straighten them except to go forward.
     
  9. stank65

    stank65 Well-Known Member

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    Articulated buses are completely different. They are meant for low speed urban environments, and there are studies that show they are inherently less stable because they are pushers.

    https://trid.trb.org/view/293829

    The articulated pusher buses also have an enormous advantage in their construction and design because they whole system of the whole unit is manufactured together. In Rivians case this advantage does not exist. Separate manufacturer for both car and RV. Dimensions, handling characteristics, etc all different RV by RV. Gas vs Deisel is an enormous difference and the system would have to be able to handle both. Hitches on RVs designed to handle tension force and not compression. Tow arms designed to handle tension and not compression.

    This would require an enormous amount of engineering and design and up front expense to even have a chance to do it right and it is likely that states would outlaw it due to safety concerns. Honestly, IMHO, this is a problem that doesn't need to be fixed. Even if this saved me $40 per full tank of gas (which is an unbelievably massive stretch -- that would be over a ten percent savings), the likely additional outlay on this would probably be a couple thousand dollars. That would take me 50 full tanks (100 gallons) to make it up -- that is 50k miles of driving to make up that cost.
     
  10. stank65

    stank65 Well-Known Member

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    THIS^^^

    You guys should take a look at how flat tow bars are constructed. They simply aren't built to handle compression of any form and any hiccup would destroy them in compression. An entirely different system would have to be designed that would have to be significantly more heavy duty by a factor of 3x or 4x to handle this.
     
  11. CappyJax

    CappyJax Well-Known Member

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    This isn't true at all. The max acceleration of an RV pulling is many times less than it can decelerate in a panic stop. I had have to panic stop in my RV. I can go from 60 to 0 in a few seconds. It takes me well over 20 to go from 0 to 60. Therefore, the compressive loads experienced by a tow bar are many many times higher than the tension forces.
     
  12. stank65

    stank65 Well-Known Member

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    Under panic stopping the towed vehicle is braking...............
     
  13. CappyJax

    CappyJax Well-Known Member

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    I have a surge brake system which requires the compressive load BEFORE the toad brake is applied. And basically you are saying that if the brake fails, the tow bar will fail, which is not true at all.
     
  14. stank65

    stank65 Well-Known Member

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    A properly installed ReadyBrake should never hit forces you are stating. The breaks should trigger while the trigger compression is happening and not once it over compresses and slams.

    If a brake fails, your bars certainly could fail. They are over engineered, but that isn’t something I’m interested in testing. Just like trailer hitches can handle more than they are rated for.
     
  15. CappyJax

    CappyJax Well-Known Member

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    No, the bar isn't going to fail ever unless it is overloading, or the towing vehicle gets in an accident. And the electric brakes fail all the time. That is why I went with a mechanical system which requires compression before the toad brake is applied.
     
  16. stank65

    stank65 Well-Known Member

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    #76 stank65, Jun 2, 2019
    Last edited: Jun 2, 2019
    If a quick release isn't properly seated and locked, bar will get destroyed if you put any compressive load on them. They should not fail even if put under full force of the vehicle, but again that is not what they are designed to have happened on a regular basis. There is a massive difference between a system designed to handle these loads regularly and safely vs a system that should be able to handle it in an emergency situation. A surge system would never reach the loads you are stating if it was working properly. The brakes are triggered before the spring/damper is fully compressed and it slams metal on metal. During that time, the only forward load on the RV is the spring/damper force.

    AND if a propulsion system was put in place it makes your surge braking impossible.
     
  17. CappyJax

    CappyJax Well-Known Member

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    No, you are making shit up now.
     
  18. stank65

    stank65 Well-Known Member

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    What am I making up?

    There is no way that surge brakes are designed to take the anywhere near full force of the towed vehicle prior to applying the brake. That makes no sense.

    If there was propulsion from the towed vehicle, it would compress the damper/spring in surge brakes and trigger the brakes.

    Blue OX tow bars have a specific warning about driving distances greater than 1 mile without both of the arms fully locked out. The arms don't fully lock out unless you turn your vehicle in a certain way to get full extension on both arms. If a propulsion system was in place, you would have to drive until you think you are locked and then somehow engage the propulsion from the tow vehicle.
     
  19. stank65

    stank65 Well-Known Member

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    In theory you could have a tow bar that had a three way damper that could trigger brakes in compression, trigger acceleration in tension, and have a middle ground which would be neutral/coast, but that is a significantly more advanced (expensive) version of a surge brake. Even this setup could never give you propulsion, it would only get the towed vehicle to the point of coasting.
     
  20. Hmp10

    Hmp10 Well-Known Member

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    Would someone please explain the point of all this.

    It seems to me the only advantage of using flat towing to charge an EV is so that the battery will have juice to drive the vehicle when you arrive at a place that doesn’t have a charging station.

    This notion of using a fully-charged EV that has been charged using flat towing to then help push the RV that is towing it in order to keep from “wasting energy” makes no sense. The fuel consumption of the RV was increased in the first place by having to overcome the drag that regeneration was creating. (The reason regenerative braking works is that force must be applied to the motors during regeneration. In braking, that energy comes from recovering the kinetic energy of the slowing of the vehicle. In power utilities, it comes from burning fossil fuels, heating water into steam, or capturing the force of running water. In flat towing, it comes from the engine output of the tow vehicle.)

    First, you increase the RV’s fuel consumption to tow the EV while in regeneration mode. The EV battery fills. Then the EV battery drains while helping to push the RV. Then the RV fuel consumption increases again to replenish the battery charge that was drained while helping push the RV. (And remember that regenerative braking is considerably less than 100% efficient. It doesn’t recover all the energy that was used to accelerate the car in the first place.)

    Really, what’s the point?
     

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