Trying to pick between rear hub motor versus pusher trailer

I am stuck in a design-hell loop, over here, and I hope that maybe one or twelve of you fine folks could sound off and give me some fresh knowledgeable opinions to chew on. I have never built an e-bike, but I have done a bit of robot-hacking, so I am not wholly ignorant of electric motors and controllers.

I want to build a big bike trailer to move two kids, or keg-weight cargo. The trailer design is something I feel pretty good about, and have sketched out some possibilities. I have some hitch ideas that look doable, and commercial hitch backup plans if my own ideas don't work out. But one of the kids is getting awfully heavy (not keg-weight by himself, but maybe both of 'em together might match a keg), so I want to add some electric assist to get them to school on time and myself to the office without being drenched in sweat. I would wind up getting a bike-camping trailer as a side benefit.

Problem is, I can't decide where to put said assist. I've been going back and forth between pusher-trailer and rear hub motor for weeks, now. Cost is my main limitation, here, and one of the reasons that I am leaning in the pusher-trailer direction is that it would be much easier for me to scrounge up a brushless motor and a controller for trailer-mounting than it would be for me to either afford a hub motor kit, or to fab up a waterproof mid-drive. I mention "waterproof" because I live in Portland, and this is supposed to be a wet-weather commuter. The trailer is inspired by velomobiles, b/c the kids know that I am obsessed with Coroplast fairings for velomobiles, and they both like the idea of reclining in comfy chairs under an insulated Coroplast fairing while they, I dunno, watch Pokemon and drink hot apple cider.

I have next to no metal-fab expertise, so making my own waterproof mid-drive out of a scavenged motor and homebuilt parts strikes me as unlikely. However, making a waterproof Coroplast fairing on top of a Bikes-At-Work-clone cargo trailer sounds easy, and that would leave me with a dry, insulated place to put my scavenged electric motor drivetrain. (And kids.) I can also mount A Lot More Battery in a nine-foot-long trailer than I can in the frame triangle of my tourer or MTB. On the other hand, a commercial hub drive is probably easier and ostensibly more reliable than whatever I can put together out of repurposed forklift motors and a cheap Chinese controller. (Also, I could leave the empty trailer at school all day long and not worry about some enterprising person boosting a lithium battery out of my velotrailer.)

Few of the hub motor kits I've looked at mention ingress protection, and I don't think that I want to commute in Portland rain without an IP67 rated drivetrain. Are these things dry-weather tools? (Toys?) I also gather that the average Ebay hub-motor kit is not to be trusted, and need to be pointed to some reliable and trustworthy North American vendors of same so I can do my cost comparison.

Lastly, my commute is mostly flat with only one real hill, but if I build this trailer at all, then myself and the five-year-old are going to want to ride it over the Coast Range. So I don't need to build regenerative braking in at the outset, but it will be pretty mandatory for its intended summer use.

So: I suspect that some of you have tried both hub motors and pusher-trailers, right? What elements am I missing in my cost-benefit analysis? I must be overlooking at least one major something.

Pusher trailers can exhibit wheelspin resulting in the trailer stepping out in corners. Also, pusher trailers can induce a wobble in the tow bike. Attempts to mitigate one of these problems can often exacerbate the other. While I have only used a single wheeled pusher trailer, it was consistent enough about doing both these things that I eventually left it behind. I would strongly discourage the use of a pusher trailer if the trailer's weight is at all similar to or in excess of the tow bike's weight.

My inclination in your case would be to use a large hub motor in the bike's rear wheel, to hitch the trailer near the bike's left rear axle, and to keep the trailer as short and lightweight as it can be while meeting its design requirements. This layout would tend to maintain weight on the driven wheel while minimizing feedback into the tow bike.

The 12T version of the MAC motor is probably the most suitable hub motor for this job, because it can make plenty of power efficiently at a usefully low RPM. It isn't the budget choice. Nor does it support regenerative braking. Maybe dogman dan can recommend a direct drive rear hub with an appropriately slow wind? I don't know of one.

What do you plan to use as a tow bike? If you're constrained to a large diameter drive wheel, it cuts down on your suitable motor options. The bike also has an effect on what batteries you can carry onboard.

Thanks! Comparative weight is not something I had thought about very hard. The pusher with cargo will be outweighed by myself & the bicycle, but not by much.

I was planning either a two-wheel trailer or perhaps a three-wheel trailer not unlike the Carla Cargo. I thought that the trike cargo configuration, at speeds not exceeding 15-18 mph, would make trailer sway a non-issue. Maybe I am wrong in this assumption?

Maybe I should hang up my trailer ideas and go out and buy a stick welder, and just make a very large cargo bike. That would solve trailer wobble fairly conclusively, I think.

THe problems with motors in the trailer are (besides lack of time to experiment) one of the main reasons I have not yet added motors to any of my trailers, and instead just use massive motors in the cargo bike and trike, which are sufficient to pull several hundred pounds of dogs, dog food, or a piano. (probably not enough to do all of those at once though ).


If you decide to go with building your own bike or trike for the purpose, there are a lot of things to consider depending on the usage, cargo, speeds, acceleration requirements, your riding style, traffic or not, road conditions, etc.

For example:

My CrazyBike2 and SB Cruiser trike have constraints that they must be able to accelerate (with a load) in a few seconds from 0-20MPH, so I am not in the way of the traffic waiting behind me at a light or stop sign, etc., and that they have to be able to haul at least a couple hundred pounds of cargo on the bike/trike itself, and be able to pull a trailer full of cargo weighing at least as much as the loaded bike/trike+rider, at the same time, and still handle well--and be able to stop quickly and safely in any of those modes. I prefer the bike/trike be as light as possible, but given the materials I ahve to work with and my inexpertise at design, they ended up pretty heavy, including the batteries and motors, at around a couple hundred pounds for just the bike, and at least half-again that for the trike. Add another 180lbs for me these days, and another 20lbs for tools and crap I carry with me on any ride, and they're right up there for weight.


But they both handle well on the roads, and carry the stuff I need them to, without any input from me in most cases. They're both 2WD direct drive hubmotors (would prefer some form of middrive, but the hubs are much simpler and more reliable vs the middrives I've built; much less to go wrong as long as the wheels are well-built with the right spokes for the rims), independent throttles, regen braking, etc.

Both were built from scrap bikes and other scrap metal / wood / etc., with a few storebought things. I welded mine up using the basic harborfreight welder at first, and a slightly better HF model nowadays, but it is possible to bolt stuff together without welding, if you don't have access to a welder or experience. Just need a grinder w/ metal cutting discs, drill & bits, hacksaw, files, stuff like that, and assorted old bikes and other scrap metal to make all the parts out of, then bolt them togther once you've worked the ends of the pieces to fit, and in some cases made brackets to connect the pieces.

If you're curious you can follow the builds in the threads in my signature.


One of the first decisions you'll need to make is whether you want the cargo in front of you or behind you. They both have advantages and disadvantages. Iv'e only built the ones with cargo behind me so far, but plan to build the Barkfiet long-longjohn eventually.

Another one is if you want three wheels, or two. They both have advantages and disadvantages.

Then if you want three wheels, do you want a delta or a tadpole. Again, each has it's own good and bad. If you do a tadpole they seem to work better as short wheelbase, but delta works better long. Delta is a lot simpler to build; it's what the SB Cruiser is.


More decision tree stuff later, after you reply.

Yahshoor said:

I was planning either a two-wheel trailer or perhaps a three-wheel trailer not unlike the Carla Cargo. I thought that the trike cargo configuration, at speeds not exceeding 15-18 mph, would make trailer sway a non-issue. Maybe I am wrong in this assumption?

Click to expand...

A three-wheeled trailer might eliminate or at least strongly reduce steering feedback to the tow bike; I just don't know. It certainly would make tongue weight and trailer balance a non-issue. Worth a try, I think. I'd still suggest a hub motor (but on the trailer front wheel) because you'll pay a big weight and efficiency penalty if you use a forklift motor, plus you'll consume space that could otherwise be used for payload. If the trailer's side wheels are on stub axles, the trailer floor can be significantly below axle level and you can even use full sized wheels for better ride quality and lower rolling resistance.

Ebikekit sells a slow wind direct drive front hub motor intended for trikes, which would be a great match for a Carla Cargo style trailer. It, like the MAC geared hub motor, is relatively expensive as hub motors go. https://www.ebikekit.com/collections/tricycle-kits

I thought about a pusher trailer several years ago.
It could work , IF ... the trailer and cargo was very light
and
You would design the trailer to turn slightly the wheels on it when the bike turns. Someone did this on a home made utility trailer for his car/truck.
You would have besides the main hitch ball mount , a hitch ball mount on both sides of that , those hitches and trailer tongue bars would be connected to each wheel , so that when you turn your vehicle to one side it would push back on the axle of the trailer so both wheels would follow the path of the bike/vehicle. note that the turns could not be too sharp so you would have a larger turning radius than usual. On a bicycle and bike trailer that is light weight you could use Heim Joints instead of ball hitches.
https://www.amazon.com/slp/heim-joints/vqhsc99oewx33wr

It is best to just spend the money on a good Rear hub motor.
I have a Mac and they are good hubs. Grin Technologies in Vancouver has all the parts you need as well. An added bonus is that they have allot of experience with Rain and what parts you need for such wet climate's.

No motor on the trailer. Brakes yes.
Low tow attachment.
Rear hub on the tractor bike.
That is the only way to have good handling and safe operation.

I personnally would prefer a front cargo bike. That kind: