Flat towing a Rivian

OP
C

CappyJax

Well-Known Member
Joined
Dec 26, 2018
Threads
8
Messages
228
Reaction score
53
Vehicles
Subaru Forester
  • Thread starter
  • Thread Starter
  • #61
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.
 

stank65

Well-Known Member
First Name
Rich
Joined
Apr 1, 2019
Threads
0
Messages
48
Reaction score
19
Location
Coopersburg, PA
First Name
Rich
Vehicles
Tesla Model 3, Chevy Tahoe, GMC Acadia
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.
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.
 

Hmp10

Well-Known Member
Joined
Mar 7, 2019
Threads
3
Messages
454
Reaction score
274
Location
Naples, FL
Vehicles
2015 Tesla Model S P90D; 2018 Honda Odyssey
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.
 
OP
C

CappyJax

Well-Known Member
Joined
Dec 26, 2018
Threads
8
Messages
228
Reaction score
53
Vehicles
Subaru Forester
  • Thread starter
  • Thread Starter
  • #64
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.
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.
 

stank65

Well-Known Member
First Name
Rich
Joined
Apr 1, 2019
Threads
0
Messages
48
Reaction score
19
Location
Coopersburg, PA
First Name
Rich
Vehicles
Tesla Model 3, Chevy Tahoe, GMC Acadia
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.
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.
 
OP
C

CappyJax

Well-Known Member
Joined
Dec 26, 2018
Threads
8
Messages
228
Reaction score
53
Vehicles
Subaru Forester
  • Thread starter
  • Thread Starter
  • #66
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.
Articulated pusher bus. Look it up. It has been done before.
 

PaulMLAS

New Member
Joined
May 29, 2019
Threads
0
Messages
3
Reaction score
3
Location
Las Vegas
Vehicles
BMW i3, BMW 740i, Toyota Tacoma, Monaco Diplomat
I will disagree with one premise here. Towed vehicles and/or trailers ALWAYS transfer energy from towed to the towing vehicle during braking, and there is no problem with this. This is the reason why it's important for tow bars to be close to level; if not, the force/momentum from the toad can either lift the back of the coach or potentially be lifted/levered up into the back of it.

The reason you can't back up with a toad has to do with lateral force, not the front/back.

However, propulsion from a toad would be complicated, and not worth the effort IMO.

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.

Screen Shot 2020-02-06 at 8.21.08 AM.png
 
Last edited by a moderator:
OP
C

CappyJax

Well-Known Member
Joined
Dec 26, 2018
Threads
8
Messages
228
Reaction score
53
Vehicles
Subaru Forester
  • Thread starter
  • Thread Starter
  • #68
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.
 

stank65

Well-Known Member
First Name
Rich
Joined
Apr 1, 2019
Threads
0
Messages
48
Reaction score
19
Location
Coopersburg, PA
First Name
Rich
Vehicles
Tesla Model 3, Chevy Tahoe, GMC Acadia
Articulated pusher bus. Look it up. It has been done before.
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.
 

stank65

Well-Known Member
First Name
Rich
Joined
Apr 1, 2019
Threads
0
Messages
48
Reaction score
19
Location
Coopersburg, PA
First Name
Rich
Vehicles
Tesla Model 3, Chevy Tahoe, GMC Acadia
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.
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.
 
OP
C

CappyJax

Well-Known Member
Joined
Dec 26, 2018
Threads
8
Messages
228
Reaction score
53
Vehicles
Subaru Forester
  • Thread starter
  • Thread Starter
  • #71
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.

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.
 

stank65

Well-Known Member
First Name
Rich
Joined
Apr 1, 2019
Threads
0
Messages
48
Reaction score
19
Location
Coopersburg, PA
First Name
Rich
Vehicles
Tesla Model 3, Chevy Tahoe, GMC Acadia
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.
Under panic stopping the towed vehicle is braking...............
 
OP
C

CappyJax

Well-Known Member
Joined
Dec 26, 2018
Threads
8
Messages
228
Reaction score
53
Vehicles
Subaru Forester
  • Thread starter
  • Thread Starter
  • #73
Under panic stopping the towed vehicle is braking...............
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.
 

stank65

Well-Known Member
First Name
Rich
Joined
Apr 1, 2019
Threads
0
Messages
48
Reaction score
19
Location
Coopersburg, PA
First Name
Rich
Vehicles
Tesla Model 3, Chevy Tahoe, GMC Acadia
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.
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.
 
OP
C

CappyJax

Well-Known Member
Joined
Dec 26, 2018
Threads
8
Messages
228
Reaction score
53
Vehicles
Subaru Forester
  • Thread starter
  • Thread Starter
  • #75
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.
 
Top