Building my first trailer - dropouts vs through frame etc.

I'm building a power assisted trailer - lots going on and problems I'll have to solve for sure - but at the moment I'm looking at 1"/25mm square tube aluminum to build a frame for the wheels - they will be based on 27.5" laced grin all-axel front hub motors.

I haven't done CAD or milling in a couple decades. But I understand the basics / can read plans so I'm hoping to find either suitable parts or something easy to modify OR someone who can point me in the right direction (will pay for help). I don't want to get so mired in construction challenges that I can't worry about programming or building my body or riding lol

My thought was to go with 15mm through axels. But I have to allow for torque arm installation, and either some sort of through axel nuts with drop outs etc.

With just the 1" frame, I could drill a 15mm hole, and a larger hole on the outside edge to insert and bolt the through axel in. But I also have to deal with the brake caliper mounts. Grin has a variety of those available however most are for special purpose bikes and quite expensive and won't accommodate the square tube frame. Link below.

I've also thought of milling my own (I'd send it out / contract it) drop out adapters from 5mm flat stock - I'd be able to allow for mounting their DIY torque arm, and also include holes to mount a caliper on it.

Here's a couple sketches. Details below - I appreciate any and all feedback - including people questioning my sanity as long as they have reasons for it

If anyone has experience or ability to suggest a place to get torquearms / brake mounts milled if custom ones are required or anything else... thank you!




Front wheel diagrams:

Torque arm adapters:

Where in my sketches I've shown a straight tube structure (specifically in the case of the long ladder frame), I believe it might need to be built into a beam with angular bracing - but I didn't want my drawings too complex:
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The trailer is intended to carry its own weight, plus about 400-500 pounds of total payload. Likely only about 300 typically.

Here goes:

* Ladder frame from 1" square tube approx 8' x 2'

* The front part of this frame will need sheeting on the front / bottom as part mud guard / part support. There are 4 batteries going in that area (approximately 100 pounds). Sheeting the entire bottom with something like diamond plate is something I'm considering as it would enable me to use the underboay for long cargo storage (poles, canopy, etc.)

* 2-3 bolt plates which will be installed in the trailer body (not illustrated here)/ leaving bolts protruding to mount to base. They will be blind in the trailer body hence the plate. Matching holes in the ladder frame required.

* A second small frame approx 32" x 36" which would hold two more wheels in "drop outs" or a through axels. By each of these would need to be an accurately placed block for a disc caliper for brakes.

* The second frame would be connected to the first with scooter shocks (4) arranged in a trapezoidal form. This will allow for multi direction flex (vertical as well as twisting to deal with rough road, pot holes, etc.

Thanks for taking the time to read!

Cheers

Mitch

Check out Carla Cargo. It's a design that lends itself to big loads and a hub motor on the steered front wheel. I would not bother trying to motorize through-axle wheels; it restricts your motor options too much.

Traction motor on the front wheel only, and brakes on the rear wheels only, mean that both motoring and braking reduce any tendency to jackknife.

Chalo said:

Check out Carla Cargo. It's a design that lends itself to big loads and a hub motor on the steered front wheel. I would not bother trying to motorize through-axle wheels; it restricts your motor options too much.

Traction motor on the front wheel only, and brakes on the rear wheels only, mean that both motoring and braking reduce any tendency to jackknife.

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I've looked at that unit. I'm building my own for a variety of reasons though I'm sure I saw a set of plans somewhere with mechanical drawings of the types of pieces I'm looking for. For one thing, one some of the grades I'll be dealing with the front wheel model won't produce enough torque. For another my drive system and control will be quite different from the one they built - although using a bike headset is similar for sure - it was part of my inspiration. They also lack suspension and ground clearance I need. basically a *lot* of reasons. Oh - and I need the brakes on the outside for maintenance.

But I'm not worried about the jackknife issue although dealing with it does factor into my design and programming - this is a prototype I'm prepared to have to deal with challenges

I'm primarily going with the through axle wheels as they support regen as well as disc brakes and I want the strength vs a single side mount.

Thanks for the idea though

Is this intended to be used/pulled on public streets? Used solo or pulled? If pulled/towed, with what vehicle? What speeds intended?

Papa said:

Is this intended to be used/pulled on public streets? Used solo or pulled? If pulled/towed, with what vehicle? What speeds intended?

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It's intended to fit between bike trail bollards - my plan is to make it 3' wide as I'm unable to find any sort of standard that exists even in the greater vancouver (BC) area. I'd like a little more space - 4' would be IDEAL - but I was worried about narrower bike lanes so was trying to constrain it to the width of a trike.

Once I put significant miles on the next one may be wider. My plan was to put whiskers on it and tie into my logging (contact sensors extended 10" on the corners to allow them to bump anything they need to / logging where I ran out of room).

Max speed off road will likely be about 50km/hr depending on surface. On road in Canada 32.

I will be pulling it on roads in North America - will be traveling within the speed limits as varied by laws province and province / state to state. It will be self assisting - will be riding a bike in front - depending on the trip that could be a gravel bike, or an ebike - possibly a tadpole trike. The trailer is designed to put no hitch load on the "towing" bike.

The way I'm configuring it, the motors will support regen for speed reduction as well as ebrakes/parking based on hydraulic capilers.

I am in the planning stages of a power assisted bike camper trailer build myself. There are so many questions and concerns since I will effectively live in this build up to two years, long enough to sight see the lower 48 and possibly Alaska as well depending on how my health holds out.

You didn't mention how thick this 1" aluminum square tube will be which is of critical importance. Personally I thought long and hard about using aluminum and decided against it for many reasons. The deciding factor ended up being most any service station has a MIG welder or at minimum a stick welder. Very very few have a clue about welding aluminum! So being able to repair it if needed is more important to me than a few pounds of weight. This however may be different in your circumstances.

As to mounting the axel in that 1" tubing. Have you ever seen anything more substantial than a BBQ grill made that way? I've custom built a lot of stuff over the years from dump truck bodies and heavy equipment trailers to 8 second drag cars. There is no way I would through mount any kind of load bearing or powered axle crossways through a thin tube! That's begging for trouble in the long run IMO.

Check out this little camper. I will likely end up building something similar.

Tiny Two Roomtour​

Claudi's Abenteuer

Might give you some different ideas.

I live off grid two miles from pavement and have for nearly 20 years now. When I go sight seeing I want to be able to be off road for weeks at a time and need full suspension and most likely powered wheels at each corner to do that. I can't make my trip until 2028-29 or there abouts so I have plenty of time to plan and research.

I would love to follow along as you make your build happen.

MitchNotMitchell said:

It's intended to fit between bike trail bollards - my plan is to make it 3' wide as I'm unable to find any sort of standard that exists even in the greater vancouver (BC) area. I'd like a little more space - 4' would be IDEAL - but I was worried about narrower bike lanes so was trying to constrain it to the width of a trike.

Once I put significant miles on the next one may be wider. My plan was to put whiskers on it and tie into my logging (contact sensors extended 10" on the corners to allow them to bump anything they need to / logging where I ran out of room).

Max speed off road will likely be about 50km/hr depending on surface. On road in Canada 32.

I will be pulling it on roads in North America - will be traveling within the speed limits as varied by laws province and province / state to state. It will be self assisting - will be riding a bike in front - depending on the trip that could be a gravel bike, or an ebike - possibly a tadpole trike. The trailer is designed to put no hitch load on the "towing" bike.

The way I'm configuring it, the motors will support regen for speed reduction as well as ebrakes/parking based on hydraulic capilers.

Click to expand...

You NEED to see this one it may be the answer you are looking for. They only show a quick glimpse of it but be sure to notice the box trailer. It would be a great camper conversion.

BiggKidd said:

I am in the planning stages of a power assisted bike camper trailer build myself. There are so many questions and concerns since I will effectively live in this build up to two years, long enough to sight see the lower 48 and possibly Alaska as well depending on how my health holds out.
....
I would love to follow along as you make your build happen.

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We're on similar pages. I can for sure try to keep you posted / if I don't feel free to poke me but I expect I will "live here" for a bit as I build. I'm semi-retire right now - burned out on my things - this has been my goal a while - but I'm not getting younger. I'm starting by crossing Canada - from Tofino in the west to Newfoundland in the east. Along the way I'm going to be exploring tiny housing villages and other issues related to the housing crisis.

I understand the concerns re repairability - it's cool to be able to have that discussion with somone else who's been on the fence themselves. I estimated about 50 pounds difference in total weight - which is about 10% - it makes a fair difference in daily range based on the motor simulator Grin has online - but I was also thinking about the dissimilar metal corrosion issues I've seen lately. Bike motors, brakes, shocks, etc. are all aluminum. If I had a steel frame and sprinkle in some road salt, I wondered about the galvanic reaction - with steel I could patch a cracked weld myself - but I'd probably also have to powder coat it. Thing is it's been a challenge in a big city to find a fab shop with time to work on it - so that's pushing me to reconsider steel again - so I'm conflicted too. But that corrosion issue could be big being in the outdoors in all weather. I'd appreciate any other thoughts you have. Would you paint or powdercoat steel? Milling is harder for custom parts.

I think you're 100% correct about the stupidity of dripping the tube wall - but threw out the idea for comment anyways for discussion. I think my goal would be to get milled plates to mount in and tack weld or bolt them to the square tube frame. But that's a place aluminum makes it easy - I can use a local maker shop to mill my own - steel I'd have to send out for laser cutting or something which would mean I need to find a shop and someone who uses cad to draw it up and send it out.

Cheers!

Another thought I already had about the trail bollards width. This guy Jeremiah Brown has already done it and he built his trailer 40" wide and had a few tight places. I think I'll go 48" and just deal with less bike paths and more roads or off road for the extra stability and space! I noticed our local rail trail removed the bollards recently....

MitchNotMitchell said:

We're on similar pages. I can for sure try to keep you posted / if I don't feel free to poke me but I expect I will "live here" for a bit as I build. I'm semi-retire right now - burned out on my things - this has been my goal a while - but I'm not getting younger. I'm starting by crossing Canada - from Tofino in the west to Newfoundland in the east. Along the way I'm going to be exploring tiny housing villages and other issues related to the housing crisis.

I understand the concerns re repairability - it's cool to be able to have that discussion with somone else who's been on the fence themselves. I estimated about 50 pounds difference in total weight - which is about 10% - it makes a fair difference in daily range based on the motor simulator Grin has online - but I was also thinking about the dissimilar metal corrosion issues I've seen lately. Bike motors, brakes, shocks, etc. are all aluminum. If I had a steel frame and sprinkle in some road salt, I wondered about the galvanic reaction - with steel I could patch a cracked weld myself - but I'd probably also have to powder coat it. Thing is it's been a challenge in a big city to find a fab shop with time to work on it - so that's pushing me to reconsider steel again - so I'm conflicted too. But that corrosion issue could be big being in the outdoors in all weather. I'd appreciate any other thoughts you have. Would you paint or powdercoat steel? Milling is harder for custom parts.

I think you're 100% correct about the stupidity of dripping the tube wall - but threw out the idea for comment anyways for discussion. I think my goal would be to get milled plates to mount in and tack weld or bolt them to the square tube frame. But that's a place aluminum makes it easy - I can use a local maker shop to mill my own - steel I'd have to send out for laser cutting or something which would mean I need to find a shop and someone who uses cad to draw it up and send it out.

Cheers!

Click to expand...

I bought a cheapo plasma cutter nearly ten years ago for about $200. Might be something to consider. I prefer cutting steel with a portaband and or 4.5" angle grinder with a composite or diamond blade. My hands aren't steady enough for the plasma cutter and straight cuts. lol

Ever consider galvanized steel? Also paint is a lot better today than it was 50 years ago...

I've been working this rabbit hole for a few months now and I have lots of ideas, some are good, really good others well sometimes even a bad idea can lead to a good one. You can put solar on the trailer roof and gain charging all day everyday while you ride and when you don't. I'll be packing as much solar power aboard as possible. I'm less worried with weight or speed than enjoying myself when I go! I've even got a sliding solar panel array about half worked out in my mind to put 4) 200W flexible panels on the roof. The top most panel will always work but those under it will only connect when extended out as a set of awnings. That only accounts for three panels though. The fourth will be a littler trickier and will depend on the height of the trailer to bike and rider height. But another panel cantilevered off the front of the trailer over the bike and rider is the idea.

BiggKidd said:

Ever consider galvanized steel? Also paint is a lot better today than it was 50 years ago...

Click to expand...

I've considered it - however that's where I think you'd get the worst of the galvanic reaction with aluminum parts. Plus treating the joints. I think I'd stick with regular steel and just paint or powder coat - I like the idea of powdercoat as I think it's shown to be more durable and for awkward places like under the frame it might be the ticket.

As for construction for the most part I'm hoping to find the right person to work with me to build the frame - I won't have a problem with the body or electronics - I have some prior experience in that and friends with current experience in microcontrollers, etc. whom I will lean on from time to time - but the frame right now is my bottleneck - so hopefully out of these conversations I can figure out the path forwards for now - I'd like to start building early in the new year.

To sustain the GVW intended and tolerate mildly rough roads, 1" aluminum tubes won't survive without numerous, strategally placed gussets & bracing. Most aluminums have near zero fatigue resistance, which means it has essentially no tolerance for flexy structures. And, when you bolt the aluminum structure together, you weaken the joints even further. If welding the aluminum structure, it'll need to be post heat treated because most aluminum's lose upwards of 50% of its tensile in the HAZ. (heat affected zone).

BiggKidd said:

I've been working this rabbit hole for a few months now and I have lots of ideas, some are good, really good others well sometimes even a bad idea can lead to a good one. You can put solar on the trailer roof and gain charging all day everyday while you ride and when you don't. I'll be packing as much solar power aboard as possible. I'm less worried with weight or speed than enjoying myself when I go! I've even got a sliding solar panel array about half worked out in my mind to put 4) 200W flexible panels on the roof. The top most panel will always work but those under it will only connect when extended out as a set of awnings. That only accounts for three panels though. The fourth will be a littler trickier and will depend on the height of the trailer to bike and rider height. But another panel cantilevered off the front of the trailer over the bike and rider is the idea.

Click to expand...

That's cool - I found a set of panels - flexible and 18" x 48" - so I can put 4 of them (400w in theory) on the curved roof. I can tuck a couple more in the underbelly for additional charging while stopped. The battery array and balancer is built and tested. Solar panels too.

Papa said:

To sustain the GVW intended and tolerate mildly rough roads, 1" aluminum tubes won't survive without numerous, strategally placed gussets & bracing. Most aluminum have near zero fatigue resistance, which means it has essentially no tolerance for flexy structures. And, when you bolt the aluminum structure together, you weaken the joints even further. If welding the aluminum structure, it'll need to be post heat treated because most aluminum's lose upwards of 50% of its tensile in the HAZ. (heat affected zone).

Click to expand...

That's what I was afraid of. Maybe I'm back to steel. If you were going to do steel, would you prep and paint or powder coat? I think I want to avoid stainless or galvanized due to dissimilar metal corrosion - a lot of parts are going to be unavoidably aluminum.

MitchNotMitchell said:

That's what I was afraid of. Maybe I'm back to steel. If you were going to do steel, would you prep and paint or powder coat? I think I want to avoid stainless or galvanized due to dissimilar metal corrosion - a lot of parts are going to be unavoidably aluminum.

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With SS you are back to less repairability and it's often more prone to cracking than mild steel. A lot of people build their frames out of wood but that's not a direction I'd go.

Also while you are thinking and planning try and keep those old popup campers in mind. With those in mind I'm thinking a 4Wx4Hx8L that extends to 4Wx7.5Hx8L or along those lines. I want room enough to not go crazy sitting out a week of bad weather... I am also considering 10 foot long if I copy that first trailer I linked.

MitchNotMitchell said:

If you were going to do steel, would you prep and paint or powder coat?

Click to expand...

Enamel.

Not as effective as powder, but can be easily removed (and spot repainted) for repairs, also easy to do touchups.

In the interests of keeping to simplicity and ease of sourcing repairs and parts I am sort of leaning toward the box tube steel they build carports out of. It's a bit overkill but better heavy than broken! They also sell the galvanized MIG wire for welding it so the welds aren't such an issue with rusting. I bought 10-15 (10lbs) rolls a year or so ago, CHEAP. I want to say I got the whole lot for $75 but I can't remember for sure.

Standard minimum distance between Bollards on a pedestrian / cycling pathway is one meter (39.37")

I meant to ask @MitchNotMitchell why did you choose the motor you did?

I've been leaning toward geared hub motors since they seem to get weight moving better.. They would need to be welded up for regen.

BiggKidd said:

I meant to ask @MitchNotMitchell why did you choose the motor you did?

I've been leaning toward geared hub motors since they seem to get weight moving better.. They would need to be welded up for regen.

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Because of that very issue - I need regen however I didn't want to end up on my first ebike trailer build to be going back and forth between a motor company, no warranty due to the weld, and a separate controller company etc.
Grin is close - they seem to cater to DIY - which is better than a big company catering to bike manufacturers I think. I might do it again after the first one, but I figured I'd try to keep it simple. Their motors have a good reputation - and are reported to run well under load due to a liquid cooling injection ("statorade") - I've seen motors for much less - however I've also seen a lot of broken motors amoung friends and ebikes - considering the weight of the trailer and the miles I intend to put on it - I didn't want to cheap out on something like a motor and have it blow out in the foothills. I'd be interested to hear other people's ideas - but mine was one of simplicity - had to make some decisions and this seemed to be easy (if more expensive than some).

I bought a pair of single-sided, direct-drive 1500w hub motors from Leaf for my cargo trike build. They're in 20x4 rims.
My first build with single-sided motors. The plus is you don't have to take the wheel off to change a tire, and maybe gain some cargo platform width.

48V 52V 1500W single side shaft hub motor

MitchNotMitchell said:

It's intended to fit between bike trail bollards - my plan is to make it 3' wide as I'm unable to find any sort of standard that exists even in the greater vancouver (BC) area.

Click to expand...

That's a good reason to use normal front hub motors in the rear (if just one in the front won't do). Doing so will allow a low floor, which combined with narrow track width will help prevent flipping the trailer over in hard maneuvers or off-camber turns. It's not entirely clear from your sketch, but it looks to me like you placed the deck at axle level. Lower is better, especially when you don't have long overhangs on the trailer.

Another point in favor of conventional front hub motors rather that through-axle is that you can get geared motors in that format. If steep grades are a design constraint, you can get more torque more easily and cheaply with geared motors. If regen is part of your plan, you can use a direct drive hub in front (or a disabled one way clutch in front) for that.

gromike said:

I bought a pair of single-sided, direct-drive 1500w hub motors from Leaf for my cargo trike build. They're in 20x4 rims.
My first build with single-sided motors. The plus is you don't have to take the wheel off to change a tire, and maybe gain some cargo platform width.

48V 52V 1500W single side shaft hub motor

Click to expand...

Nice. Cool to hear what others are building. I gotta admit I like the idea of not having to drop a wheel to fix a flat, but on the other hand, using good tires with liners have virtually eliminated flats for me. What worried me about the single side was the amount of force on that axle - especially if loaded. The wheel itself becomes an amazingly strong lever to multiply force into the axle / wheel mount. Using smaller wheels will help. I've been going back and forth on the motor simulator with different wheel sizes for a bit now. 20" vs 27.5" would drop my load 3.25" which isn't insignificant. But I also think about ground clearance in some locations... Likely this will be the first of many builds. But if I build for 27.5, I could always drop to 20 without a rebuild.

Chalo said:

That's a good reason to use normal front hub motors in the rear (if just one in the front won't do). Doing so will allow a low floor, which combined with narrow track width will help prevent flipping the trailer over in hard maneuvers or off-camber turns. It's not entirely clear from your sketch, but it looks to me like you placed the deck at axle level. Lower is better, especially when you don't have long overhangs on the trailer.

Another point in favor of conventional front hub motors rather that through-axle is that you can get geared motors in that format. If steep grades are a design constraint, you can get more torque more easily and cheaply with geared motors. If regen is part of your plan, you can use a direct drive hub in front (or a disabled one way clutch in front) for that.

Click to expand...

I haven't really figured a way to drop the floor. I know the center of gravity will be high. But the frame design gets a LOT more complicated to maintain some ground clearance, allow for suspension, and have the floor below the axle. In theory I could do it by making the wheels independent. That might be something to consider for version 2. Once I have the miles on it, I'm sure I will learn a lot of things I want different.

This first one is going to be a bit of an overland / highway proof of concept. But I'll see how much clearance I needed. And when I could have dropped it for stability.

Cheers