Thoughts on electric-assist push bike trailer

[_g_]

I currently have this, which I made for getting more 'stuff' into Glastonbury (yes, that is a full single mattress for my festival camping!):

I would like to 'upgrade' it with electric assistance - with 125kg+ on it, it gets pretty nasty up the steeper hills!

Ideally with some quad bike style tyres (and wheels) for the nasty mud.

Looking for general thoughts, such as:

Drive:
Two hub motors (I already have one 500w/36v front, easy to get another).
This could cause some steering problems, but be the simplest, lightest and avoid the need for a diff.

Axle with chain driven motor.
Plug straight in from a cheap quad, but would likely have problems turning tightly.

Single motor driving axle through a diff.
More complexity and weight, but the best technical solution maybe.

Controller:
I'm thinking something akin to the way I believe car trailer brakes work.
I'd have two sections of metal that slide together (like suspension forks etc) connected to a variable pot for the throttle.
Probably need to be damped.
So, as the front bit is pulled away, power is applied.
Possibly then also used with a braking system as per our trailer brakes - so if it's compressed past 'neutral' position, the brakes are applied. However, this would cause problems if I needed to revers.

Now, I could just get a rear hub motor for the bike, which I may end up doing this year, if I do anything at all (I designed the trailer so a lot of force is put through the rear wheel, to give it the best chance of traction with the extra weight), but I'd like to be able to use it off-bike too if needed - so I could pull a big load up a hill with little effort by hand etc.

 

[Rassy]

g, I think two matched front hub motors would be your best solution. You also need to use two matched controllers. The way you constructed the trailer frame should make installing the motors real easy. You may need to add some torque arms.

I have made several two wheel two hub motor trailers. One was used behind a cheap mountain bike with a side hitch like a two wheel child's trailer uses. It worked good with no cornering issues. I just used a single throttle with all three wires paralleled to the controllers. The battery pack was shared also so the voltage going to each controller was always the same.

Then all you need is another throttle that plugs in by the hitch where your bike throttle would normally be plugged in and you have a nice self propelled trailer. Of course it will want to run over you. Maybe you could run it from the back with a couple of handles sort of like a wheel barrel.

Good luck with your project.

 

[Tommy L]

Hello!

I built a pusher trailer. Live Axle.....is a NO! Very hard to do a tight turn. I started with
Live Axle and then cut it in half

Two Hubs and two controllers sounds good. Just make sure that you have enough battery so you
don't strain the pack. If you run two 20amp controllers, then a 20ah pack that is capable of
at least 2c is in order. Also, two hubs when not powered up in a tight turn will work well

A pusher trailer was my first project. Check link below in my Signature block.
Peace and Nice Camping Bed! 8)

Tommy L sends....

 

[_g_]

Cheers for the thoughts.

I hadn't really thought of it in terms of a pusher trailer, but of course it's basically the same thing.

Current design wouldn't accommodate being pushed from the rear as weight is over the front. However, if I rebuilt with quad bike wheels, I'd probably put them in the middle.

I think a sensible first step would be to make it with two push bike hubs - try and get a second matching 500w/36v to go with my current one maybe.
Then a hand throttle rather than automatic.

See how that goes and go from there - either to hub powered quad style wheels, or even two seperate chain driven wheels.

[edit]
Actually, just looking; if I had the cash, something like this could be quite good:

10" 500w/36v scooter hub motor.
I wanted quad style wheels both for traction in the mud (this and deeper is the sort of thing it has to deal with) and so that I can have a flat bed with things sticking off the side. Wonder how the hub motor would stand up to getting wet, however, as it'd be fairly low down.

It does have some wheel guards now to stop stuff rubbing on the wheels, but it'd be nice to make it totally flat, which the smaller wheels would also help with.

 

[Tommy L]

a design similar to this would allow you to place your bed vertically

Tommy L sends....

 

[Tommy L]

Here is another commercially built unit. Might not be for you design wise, but gives ideas.

Tommy L sends...

 

[_g_]

I really want it flat if possible - initially it was partly for ease of transport, but also so it doesn't get blown about etc.
It's not just the mattress - I'll normally do a second trip with a load of firewood. Then I'd have to try and stop the wood falling in to the wheels with the current design (though now got gaurds over the wheels, as I say.)

I had actually wondered about making it a tricycle trailer with a single powered wheel.

The powered trailer means I don't need to put the force down in to the rear bicycle wheel for traction, so more wheels would be ok.
Also I could simplify my current tow arrangement which has to have the vertical pivot by the rear wheel, but horizontal pivot behind the rear wheel - and then a separate 'turning' mechanism for slopes and the like.
A single powered wheel would mean a single motor and no issues with a live axle so less complexity/cost. However, I would have to then make something to allow it to turn, which may mean redesigning the other two wheel so they turn with caster.

 

[_g_]

Was just having a look at a rear hub motor for the cycle and it's listed as a maximum weight of 85kg.

Could see with me (around 80kg, though of course some on the front) and an extra 40+ kg from the trailer pushing down on it, that bearings etc could very quickly disintegrate on bumpy ground.

Any thoughts? Anyone used well over the suggested weight on not-smooth terrain?

 

[jateureka]

Some interesting ideas here, subscribed.

 

[Drunkskunk]

Was just having a look at a rear hub motor for the cycle and it's listed as a maximum weight of 85kg.

Is that on that little motor? Thats 190lbs. if you used two, they would share the load giving you a 380 lbs capacity on the trailer. And I don't think I'd fear going over that.

But if you're in the mud, you might consider a motor on the bike as well, and some nice fat tires. A bike like mine will roll over mud my shoes sink into.

 

[_g_]

Sorry, that was just for a motor on the rear of the bike as a 'quick fix' for this year - I'm seriously running out of time and far too busy with other stuff as it is!
As you say, 85kg each side should be just about ok - I reckon I've had 150kg or a bit more on it (a lot more when a random person jumps on it), but the weight is distributed to the front wheel a bit too in the current design.

I would love to make a 'fatty' electric bike (with a mid mounted motor and lots of suspension travel), but that's a project even further off (I also have a Fantic Koala 'project' - liked the idea of making a motorbike like that in to a 2wd go-absolutely-anywhere vehicle with a front electric motor added - another one in the 'pipe dream' pile probably .)

 

[Milou]

Check this out for possible idea???

http://www.poweredbiketrailers.com/~shop/hot-rod-racing-trailer-3400watts/38486/

 

[_g_]

Check this out for possible idea???

Cheers - interest to see how they do it.

When I was at Glastonbury (with out a powered trailer, but the weather was pretty good, so no cycling up steep muddy hills etc ) I had a quick chat with someone on an electric trike - they just had direct drive to a solid axle with no diff system.
However, a trailer can turn a light tighter (Ie turning with one wheel static and the other rotating around it - even possibly one wheel going the opposite direction.)

However, should be noted that my chain did snap, although when I was just cycling rather than using the trailer. Managed to get that fixed, so not the end of the world - but if I hadn't been able to, a pusher trailer would have been useful at the end of the weekend certainly!

I've been currently thinking about a higher 'axle' powered by a single motor, then with a free wheel at each end, one way or another (be it before or after a chain drive going down on each side) - however, do I REALLY need the extra ground clearance that offers? Not really, but I do have a bad habit of over-engineering.

 

[teklektik]

I'm thinking that with those heavy loads you are really just poking along and much extra speed would be dangerous. I suspect that the slow speed/high load would put many/most hub motors into meltdown - particularly on the hills you mention. You aren't really building a conventional push trailer for normal bike speeds, but more of a truck - low speed and relatively continuous heavy torque (like grinding through those mud flats). Your plan to use a motor and chain drive really looks like the best approach so you can gear it down and keep the motor rpms up in a decent operating region to minimize heat.

An alternative might be a couple of conservative front hubbies running in front of or behind the wheels and chained to the wheels with a disc brake cog adapter. This would keep up the rpms and your ground clearance -- not a difficult fabrication - perhaps a mod to what you already have. Two motors would give you a limp-home-mode in case of a failure.

Mount up some ebrake levers to activate regen 'trailer brakes'.

You might consider a Cycle Analyst V3 to give you pedal assist to control the trailer - just adjust the boost factor and pedal. An alternative is to use a strain gauge on the tongue rigged to the V3 as the PAS torque input - Justin is using a strain gauge sort of like this on a cargo bike prototype and could provide more details. The V3 would give you control of power ramping up/down and overall system gain so things would pull smoothly without surging.

 

[_g_]

Three years on, and back on the idea, but this time *after* Glatonbury, so might actually have a chance of getting it done, as opposed to a month before the Festival when I've got far too much to do!

This year I had a 1kw rear hub motor on the bike pulling it, which was probably useful as it was considered 'the muddiest Glastonbury ever' which compounded a missing section of metal path in a main walkway leading to a very wide and muddy section with a gentle uphill grade.

Considering I still managed it without trailer power (though probably not great for the motor I did have as a lot of high throttle low speed), I'm currently thinking to go for a couple of geared hub motors. Should be enough to keep it moving in the worst bits and keep the 1kw DD motor cooler. I like the simplicity of hub motors and I've got far too much else on to spend a lot of time fabricating etc.
Where I park now, the hills aren't as bad, so mud's the main issue (and hopefully will be less so next time if they get path down).

I'm thinking to go for 20" wheels, possibly with mx tyres.
48v makes sense, as can use the same 2x6s lipo setup I've got for the 1kw motor on the bike (and may add to it - also the option of using 4x100ah pb leisure batteries I normally use in 2x 2p separately in the van and caravan.

So; looking for suggestions on 500w+ geared hub motors I can get fairly cheaply in the UK and use in a paid.
"48V 500W 8Fun/Bafang" currently at £129 delivered from China. (This definitely isn't the right time to be buying from abroad here, but such is life!)

 

[dogman dan]

Nothing wrong with the push trailer idea, but did you ever consider just adding a geared motor to your bike's front wheel?

Coasts when you don't need it, Can run on same throttle as your rear, but have a push button or other switch on the bars, to run it or not run it.

The advantage is just one additional motor, and it can be run at 1000w, if you get the larger type. I'm sure 2000w will pull your trailer ok.

 

[_g_]

Yes, cheers.
I would consider it anyway at some point - even if just for using the bike alone when it's really muddy/better acceleration in daily use!


However:
I designed the trailer with the wheels towards the rear to put pressure on the rear wheel to give it better traction as that's the main driven wheel.

The pivot point is just forwards of rear wheel spindle. So the trailer wheels and rear wheel get 'most-all of the cargo weight and half my weight.
I suspect the front wheel would be much more likely to slip in mud and not offer much up any bits of steeper hill.

Powered trailer would also offer the option for the trailer to be used by hand with power-assistance - a big part of the bike is being able to move heavy stuff with very little effort.
It also means it can still be used to get stuff back if I have a problem with the bike.

This was it a good few years ago (as picture in the first post seems to have gone):

 

[amberwolf]

I don't know if it's in your pricepoint, but Cycleezee should have the Ezee hubmotors right there in the UK; I expect they'd do what you're after. Get the "slowest" winding there is, if there is more than one availavble.

 

[_g_]

Cheers; they do, but starting at £800 a set (that may be with batteries, not entirely clear), that's definitely a good bit past my price point unfortunately!

(Judging by other kids, that probably is including a battery - cheapest seems to be just under £500 without a battery, which unfortunately is still far too steep for me!)

 

[_g_]

If I push the budget a bit, seems two 12t MACs laced onto 20" bmx rims with 16" MX tyres would work pretty well - well, possibly complete overkill, but that should mean for typical use, they won't be stressed at all.

I've got until next June to get it sorted.

Wondered if with the above, it could make a nice little 'up lift' for "bike parks", though that might then be pushing the internal gears a bit.

 

[_g_]

4 years later, we have this...
Ezee 200rpm motors with 43mm 20" Unicycle rims and 100mm wide 16" motocross soft/medium rear tyres, 2x40A 12fet controllers with fancy bluetooth stuff.

After sorting out various teething issues; it did the job well enough. Wasn't quite as good as it could have been. Might need to look into a better cooling system.