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Discussion Starter · #1 ·
One of the things I'd like to do is add an electric axle to my trailer. I've seen that they are regularly built over in Germany, Australia, and other countries. But not sure of the process of conversion from non to powered.

The trailer is standard 16ft cargo trailer with tandem axles. I was thinking of replacing one of them, probably the front axle, with electric. Are there electric axles available here in the US? Are there hub motors that I could possibly use that could replace the brake assembly? This second question is a good question considering that my axles on my trailer have a welded spindle. So the hub motor would have to be able to bolt onto the brakes existing bolt holes and not replace the spindle.

Any pointers in this would be greatly appreciated. This isn't a task I'm planning on doing in the next month, or two. Right now I want to do as much research to get all my ducks in a row first to understand what needs to be done first.

Thanks in advance
 

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Discussion Starter · #3 ·
Can you reference the ones in Europe?
This is one that I found. There were a few others

I know these are all the same company. So maybe it's something relatively new and this one company is making this move. A few weeks ago I did a search and I had found some others as well. Maybe they weren't German, but another country that was making them. As one of them was a full RV trailer, not one of these camper trailers.
 

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I think there will be high demand for this, however it's so new it will be expensive. The liability issues that would come from a DIY version are scary for me. Can you imagine if the trailer pushed itself into a crash? I really want this for my camper and other trailers but the tech to make it work safely wow.
 

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This topic has been discussed on this forum already fairly recently.

Please do a search to further that discussion vs scattering the topic all over the forum, making it difficult for those in future to land on ONE topic vs dozens.

Assuming, of course, they do a search first like they are supposed to.
 

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Discussion Starter · #6 ·
This topic has been discussed on this forum already fairly recently.

Please do a search to further that discussion vs scattering the topic all over the forum, making it difficult for those in future to land on ONE topic vs dozens.

Assuming, of course, they do a search first like they are supposed to.
I only found 1 post about a vehicle electric trailer assist. The other posts listed electric brakes, electric plugs, or for a bike. If the OP's of those threads used some obscure title for their post instead of a descriptive one, that kinda makes it difficult for others to search for the topic as well.

And that one thread only barely discussed it, and from 2011. Unless i'm not using the right keywords to find the results. If keywords to help me out could be given, I'd be more than glad to look at other threads. But as I mentioned, I'm just starting out and I am unaware of all the terminology. For instance, I didn't know that a mid-shaft electric motor was called a "P4 Hybrid". I know this now so I can look for those threads.
 

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From the article:
"The most critical part of the eTrailer design is the electronic sensor and control system that keeps the trailer operating at the same speed as the tow vehicle, cutting the tow load without negatively affecting the safety, ride or handling."

Sounds like an interesting research project, not sure if it's ready for prime time or diy though.

From the picture it shows the motor inboard of the wheel and brake, clever design.
 

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I only found 1 post about a vehicle electric trailer assist. The other posts listed electric brakes, electric plugs, or for a bike. If the OP's of those threads used some obscure title for their post instead of a descriptive one, that kinda makes it difficult for others to search for the topic as well.

And that one thread only barely discussed it, and from 2011. Unless i'm not using the right keywords to find the results. If keywords to help me out could be given, I'd be more than glad to look at other threads. But as I mentioned, I'm just starting out and I am unaware of all the terminology. For instance, I didn't know that a mid-shaft electric motor was called a "P4 Hybrid". I know this now so I can look for those threads.
Only one? I found 24 pages in a search:




 

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From the article:
"The most critical part of the eTrailer design is the electronic sensor and control system that keeps the trailer operating at the same speed as the tow vehicle, cutting the tow load without negatively affecting the safety, ride or handling."
Of course the trailer operates at the same speed as the tow vehicle - they're attached. What they meant (or would have meant if they knew what they were talking about) is that the system needs to provide the trailer's share of the required driving force, keeping the pulling force of the tow vehicle on the trailer minimal (but still positive, for stability).

That's from the second NewAtlas article. NewAtlas material is entirely taken from other sources, usually amateurishly paraphrased, and is notorious for technical questionable content; however, in this case the stupidity originates in the Thor press release.
 

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From the picture it shows the motor inboard of the wheel and brake, clever design.
This setup in the E.Home Coco is nicely packaged, although unfortunately it has high unsprung mass due to the positions of the motors (much of the way out to the hubs on the trailing arms). The E.Home Caravan chassis in the CleanTechnica article shows a more conventional inboard drive unit with only half of the axle shafts as unsprung mass; this was probably an earlier design using available components.

Whatever the location, a powered trailer should have separate motors for left and right sides so that the trailer can be maneuvered at walking speed into or out of a parking spot without a tow vehicle attached, steering by differential wheel speed.
 

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Discussion Starter · #11 ·
the system needs to provide the trailer's share of the required driving force, keeping the pulling force of the tow vehicle on the trailer minimal (but still positive, for stability).
Exactly! Definitely what I was thinking in the designing. I was kinda thinking <50% power. Effectively making my 3500-4000lb trailer about 2000lbs being pulled. At least to start off with and see how things ride.

a powered trailer should have separate motors for left and right sides so that the trailer can be maneuvered at walking speed into or out of a parking spot without a tow vehicle attached, steering by differential wheel speed.
I really liked this idea from the German built trailer. Being able to move the trailer w/o needing to be hooked up to the truck. Would make moving it to a parking space and hooking up a lot easier of a task, for sure.
 

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Using a typical trailer brake controller's output to control the trailer's regen braking should be trivial in a project like this.

Getting the trailer to harmoniously follow a car and accelerate, deceleration in unison without pushing or pulling or doing anything dangerous is just a matter of tuning the PID loop of your trailer controller. I would think it could work the same as those self-propelled vacuum cleaners that can reverse direction and follow your hand movements effortlessly.

Nothing off the shelf. All DIY. Lots of people come to this forum looking for a shopping list of things to buy and bolt on, but the reality is you have to design, test, and build your own.

A few years back I built a system of someone else's design that uses a Roboteq controller to move a motor back and forth along a track to passively follow another object below it using a potentiometer on a string. It worked really well.
 

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Discussion Starter · #14 ·
Using a typical trailer brake controller's output to control the trailer's regen braking should be trivial in a project like this.

Getting the trailer to harmoniously follow a car and accelerate, deceleration in unison without pushing or pulling or doing anything dangerous is just a matter of tuning the PID loop of your trailer controller. I would think it could work the same as those self-propelled vacuum cleaners that can reverse direction and follow your hand movements effortlessly.

Nothing off the shelf. All DIY. Lots of people come to this forum looking for a shopping list of things to buy and bolt on, but the reality is you have to design, test, and build your own.
Yeah, not looking for the off the shelf bolt on. I already tried looking for some of that availability and that's how I found the German/Aussie sites. I didn't see anything really locally for this project. Still looking up information about the items needed.

I was thinking along the same lines with the regen braking. More current being ran to the back causes the regen to engage more. Pretty proportional from there.

Just going electric assist on the trailer only (and not including the hybrid addon in my other thread) would drastically increase the amount of fuel saved. I was looking at both options to see which one would probably be more economical and logical. I think this system with the trailer would be the best overall.
 

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Discussion Starter · #16 ·
Licensing your contraption for road use will be interesting as it'll no longer be a trailer, but a motor vehicle...
It'll be interesting, indeed. Will see what happens when that comes to pass.

Considering the amount of "crap" that is on the road now, might not be an issue, tbh. We have idiots here that drive with trucks having the front bumper 4ft in the air, rear bumper barely 2ft off the ground, and police do nothing to them. And that's definitely illegal considering they can't see in front of their trucks.
 

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Just going electric assist on the trailer only (and not including the hybrid addon in my other thread) would drastically increase the amount of fuel saved. I was looking at both options to see which one would probably be more economical and logical.
If you want economical and logical, then reduce the trailer weight from 4000lbs to 2000lbs. Or better yet, take the Prius, and bring a tent :D!

How drastic exactly do you think the fuel savings are going to be? Pulling any trailer is going to incur extra aero drag, so your actual mileage improvement will depend on speed. As an exercise, run through the numbers: how many miles are you going to pull this thing, how much MPG improvement will that cause, and how long is it going to take to pay back the ten or twenty thousand it will take to build?

Here is a good calculator:
At 5$ per gallon, driving 10,000 miles and going from 15mpg to 18mpg will save you $556! I suggest finding another justification beyond the merely pecuniary, as these projects rarely if ever save money.

I also live in a hilly place, and have had a vehicle pushed around by a trailer. Going down a slope with a turn and then loosing traction on the tow vehicle is scary as shit without the trailer trying to keep on going. I am sure that the controls to make this safe are not rocket science, but it is also not something to trifle with.
 

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Yeah, just saw the whole other thread with better numbers to use as examples, etc. Seems like it has already been done to death over there: Hybrid systems will not save money. Moving the hybrid system to the trailer will not only not save money, it will also be adding extra danger.
 

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Exactly! Definitely what I was thinking in the designing. I was kinda thinking <50% power. Effectively making my 3500-4000lb trailer about 2000lbs being pulled. At least to start off with and see how things ride.
(y) Of course the trailer will be power-limited under some circumstances; for instance, when you climb a 6% grade (typical of our mountain passes) at highway speed (anything under 80 km/h or 50 mph is stuck in the slow lane with the tractor-trailer rigs) even 50% of the power needed would be more than you're likely to make available in the trailer, so it will just do what it can. Under braking I would want to go for as high a fraction of the appropriate retarding force as possible, coordinated with the trailer brakes to make up the right total.

Control design would be an interesting. The articles don't mention what sensors would be used.
  • The most obvious (and least likely) is a force transducer in the towing coupling, so the trailer motor(s) can provide whatever power is needed to keep the pulling force low (and provide regenerative braking to keep pushing of the tow vehicle low); this is similar to "surge" or "over-run" braking used in some trailers.
  • Acceleration could easily be used (as it is for electric trailer brakes, as Electric Land Cruiser suggested), since acceleration and the (known) trailer mass implies the required force (for speeding up, braking, climbing grades, and containing speed descending grades), but that ignores aero and rolling drag so it wouldn't do anything at steady speed. Acceleration-based trailer braking normally acts only when the tow vehicle brake pedal is pushed, but in this application regenerative braking should be enabled without tow vehicle braking to control speed and recovery energy at steady speed on grade descents.
  • Drag could be estimated from speed and appropriate power applied.
  • If dependence on a specific tow vehicle is acceptable, tow vehicle power and braking could be monitored, and trailer power proportional to that could be used.
Obviously no even moderately intelligent design would apply power when the tow vehicle is trying to brake; any reasonable design would assist the trailer's brakes both for better braking performance and for regenerative energy recovery.
 
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