"Transformer" push trailer

[zap]

I call this a HEAT/SC
Hauling Electric Assist bike Trailer/Shopping Cart

His 'full' name is Woodrow Prime. He goes by 'Woody'.

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Here he is in shopping cart mode.

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Power is from a 450 watt Currie geared motor controlled by an I-zip I500 scooter controller overvolted from 24v to 36v.
The power transmission is through a typical 5 speed gear cluster from an old 10 speed bike which is shifted with an old drill off of it's own NiCd power pack. Limit switches and diodes were added to the drill to make a home brew linear actuator.
It's controlled with a rocker switch under the left brake lever.

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At the top of this photo is the hitch safety strap and wiring harness made from and old mother board power connector.

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The long gray plastic box is the main battery, a 36v 10ah(?) lithium(unknown exact chemistry) borrowed from a Tres Terra Europa.

The trailer is a modified Burley and total weight is around 46lbs. I added a telescoping caster to the front for shopping cart mode.

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Set up as it is, it's not technically a 5 speed. Spacers I had to add for the derailleur were not long enough and now it's just about impossible to get into 1st gear... although it really isn't needed. I shortened the trailer as much as I dared and now the 'chain path' suffers badly from cross chaining in 2nd gear. This could be eliminated with a geared hub or by moving the motor in and out as the shifting occurs. I might try the later if I can figure out some kind of dovetail mount for the motor.

I tried to keep the cost down for this build so I tried to use junk I already had lying around.
The motor was $45 plus shipping (along with other items) from http://www.allelectronics.com The motor is now sold out.
The trailer was $40
The scooter was $30
Other misc. items brought the total cost, as best as I recall, to somewhere around $210 excluding the Europa's battery.

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Specifications
I don't have too many miles on it so specs are limited.

'Wheel off the ground' WOT showed 30.9 mph in 5th gear.
I've got about 20 miles on the trailer so far and the fastest speed I've seen with it pushing me and no pedaling was 26 mph on a slight downhill.
Woody held up fairly well in those 20 miles. A solder joint on one of the linear actuator's diodes came lose on one trip but you can still open the trailer up and turn the 'screw' by hand to get it into a different gear if need be.
One trip hauled around 35lbs. of groceries. The trip to the store is uphill and the loaded portion is all downhill. I've seen 35 mph downhill and the trailer trailed just fine.

I'm a fair weather rider and I doubt Woody will see much use till the Spring thaw arrives.

Changes/improvements
I'd like to shorten the trailer's width and length but it does work as is and will clear a 2' 8" door.
As mentioned earlier, a geared hub or enabling the motor to move as it's shifted.
The Currie geared motor does make it whine but it's not horrible. I've read many of the Currie posts about grease and oil... I'm thinking of trying a belt drive modification.


This longer version of this story was originally published on fieldlines.com (http://www.fieldlines.com/story/2009/11/10/16828/297) and linked to ES by spinningmagnets under the post "Revisiting a Push Trailer"... thanks again spin, your linking the story made me decide to join ES and post the story here.

Comments and/or questions welcome,
zap

[davespicer]

The Currie geared motor does make it whine but it's not horrible. I've read many of the Currie posts about grease and oil... I'm thinking of trying a belt drive modification.

If I understand you correctly, this suggests that at least part of the Currie whine is due to vibration from the motor's gears being carried into the chain. Then the chain would become like a "sounding board" for the whine, making it louder...

[zap]

I'm not sure how much of the noise is being transmitted through the chain. I did have this temporarily mounted on steel Bell trailer for testing but I didn't put enough miles on it to know whether that one was really any quieter although it seemed like it was.

This trailer box sides are 13 ply Baltic plywood and the top and bottom are luan hollow door skins bonded to Tuff-R polyiso insulation. The whole thing is a speaker box for the motor! :(

[zap]

The front range received an early glimpse of summer yesterday and I managed an endurance/shake down ride with Woody in trail.

I learned I will most likely need a bigger "shifter battery" and I probably need to consider some sort of ventilation for warm weather operation.

I drug the trailer to the Platte River trail and rode a circuit of around 2.6 miles. Somewhere around mile 5 or 6 I noticed the shifter was no longer working and I got to my turn around point and opened up the trailer to check it. I determined the battery (sub-c from an old camcorder battery set up for 9.6v) was about dead and I finished the rest of the test in 5th gear. I also took a temperature reading of the motor... 167°F!

This part of the trail is fairly flat with a difference in elevation of about 12 feet from the start to the mid 'turn around' point.

The BMS cut out at mile 12. I didn't bring a meter but the battery was at 31.9v when I got Woody home.

Some "no pedaling" numbers:

12 miles
16.7mph average
22.5mph was the highest speed recorded.
43 minutes

I have no CA or anything on the bike or trailer but my Kill-A-Watt reported 450wh to charge the battery so I guess it's about 37.5wh/mile.
I think I may have been able to add a quarter to a half mile to the ride if the shifter battery hadn't crapped out. It's pretty sluggish and I imagine the amp are pretty high starting out in high gear so I had to baby the throttle quite a bit.
Most of the ride was done somewhere around 3/4 throttle.

Other than the shifter battery and warm motor, I was pleased with how well Woody performed.

[mwkeefer]

WOW!

I've never been a fan of push trailers but this is inspirational!

The flipping deck reminds me of GoPed ESR design and the "woody" look is classic and simple while inside.... you have managed a really nice low cost setup with I think the first homebrew power shifter / automatic transmission!!! Using a drill for an actuator to shift that 5spd cluster is brilliant..

The frame looks very similar to the frame for my child trailer - what were the origins of yours? I could see adding another "transform" mode to such a trailer, with a cage (aluminum) and optional canvas along with a seat for my son (on shocks this time, he is getting picky about ride quality).

For the transmission / shifting I will assume at 9.6v the current is below 1A or less you can use an LM317T with appropriate voltage input divider (to drop the input voltage from maximum of 43 down to 36v) and resistor bridge to set the output voltage to 9.6v (and a heatsink) If you need current > 1A @ 9.6v there are plenty of buck step down converters out there, just find the one which puts out enough current and meets your input and output voltage requirements.

-Mike

[zap]

Thanks Mike.
I had come to the conclusion that the lack of comments on Woody meant no one really liked it... glad you did

Just to clarify... the shifting isn't automatic, just remote.
I did consider using a LandRider shifter or something similar for automatic operation but I had all the stuff for this on hand.

The frame is from an old Burley D'lite.

This ride was 'no pedal' just to get some numbers. All other times I pedal and pedaling should lessen the amount of shifting needed. I'm hoping the next ride will be a range test w/pedaling and I can check to see if the current shifter battery is enough.

[amberwolf]

I had come to the conclusion that the lack of comments on Woody meant no one really liked it... glad you did

Actually, I just somehow missed it, I guess. I've seen the pictures somewhere before; probably in the trailer thread, but that's all I remember.

I really like the shifter idea, and have been considering something based on it for my trike that will have front 3-speed hubs driven by powerchair motors, since I will A) need them to shift at the same time and B) would like it to be automatic based on demand speed, load, and actual speed.

[zap]

If you're following and participating in a half a dozen or more other threads and doing the same thing on another board or two, building, riding, working... I certainly understand missing some posts.
Thanks for the reply.

You're trike sounds very interesting.
I really wanted to use a Sram DualDrive on Woody to help with the chain path but they're so darn expensive and I was having a hard time finding a Strumey Archer at a decent price. I've never even seen a DualDrive and it's probably been around 4 decades since I've been on anything with a Strumey but I assumed if I went that route I'd need a little more precision shifting and would probably need to go to some kind of stepper motor control to get the precision.

What is your idea for taking care of the automatic side of things on your trike? Something like the LandRider or are you leaning towards something electronic?

[amberwolf]

I really wanted to use a Sram DualDrive on Woody to help with the chain path but they're so darn expensive and I was having a hard time finding a Strumey Archer at a decent price. I've never even seen a DualDrive and it's probably been around 4 decades since I've been on anything with a Strumey but I assumed if I went that route I'd need a little more precision shifting and would probably need to go to some kind of stepper motor control to get the precision.

I got lucky on the hubs and got some from the city dump via Spinningmagnets and Ejoness. They're old and apparently well-used Shimano 333's and Sachs types (2 of each). I also have an SA from the same era (70s or 80s) found at a bike swap meet not long after I got those. I'm still working on how to build a disc-brake adapter for them, too, probably going to layer some aluminum panel scraps together and cut on the lathe, bolt them to holes drilled between the spoke holes on the flanges.

I'm not sure exactly how I'd do the shifting motorization, but probably I'd count the number of turns needed to shift it one gear, then build a little incrementable/decrementable counter and set it up to turn off the motor after that number of turns. So it would be just commanded to shift one gear at a time with a pulse from the shift control (be that a button on the bars or an electronic command). It'd be easier to do with a PIC or AVR or something, I'm sure, but I already have a bajillion old boards with 74xx series logic gates on them, so I can use those for free instead of buying an MCU kit, and then having to figure out how to program it (I suck at that kind of stuff). I'd probably just dead-bug wire up the gates and stuff.

What is your idea for taking care of the automatic side of things on your trike? Something like the LandRider or are you leaning towards something electronic?

Not familiar with the LandRider; looked it up on google and found it uses weights to shift, I think. I'd probably instead be basing it on current draw from the motor, since the front wheels would both be motorized, and the pedals only run the rear wheel. As the current draw increases beyond a setpoint I'd have to determine, it'd trigger a shift down. As it decreases below a slightly different (lower) setpoint, it'd shift up. I'd likely also put +/- buttons on the bars, that would override that automatic shifter until I press a "cancel" button.

The current measurement can be done with a simple shunt in the motors' power path, and amplify that with an op-amp, with a couple of comparators to determine if it sends a shift up or a shift down pulse, which can trigger a 555 for whichever one it needs to do. As long as the shunt is in the path leading to both motors, before it splits to feed each separately, it will measure total motor power and shift both of them at the same time. I just have to put enough hysteresis between up and down for it to not try shifting all the time, especially under the following conditon:

To keep it from having to shift under load I'll probably also put an interrupter to the throttle circuit, which will momentarily take power from the motors during the shift, then reapply it just like it was before. That will cause a current surge so I have to be sure that the current measurement/shifting doesn't shift until the current has been high for a certain period of time. Also the current drop when power is cut has to be prevented from shifting up.

This whole method might not work at all, but since I am mostly trying to have the gears there for it to be more efficient rather than to run at any particular speed, it should do what I am after. I think.

I've also copied this post over to the ARTOO thread, so I won't forget about this later on when I get back to the fancy stuff for that trike.

[DarthSensate]

Love the trailer design.
I especially like the power drill derailleur design.

I have one more kit ready for a typical front hub install to do and then I am going to look into taking my old GM motor and putting it in a tandem/tag-a-long I have as a pusher.

But I do love the idea of being able to gear the Currie-style motors for hill climbing to speed running.

[zap]

Thanks Darth... I've put some more miles on it and it everything seems to holding up well.
I hope to get a video up sometime soon... too many other projects.

[Whiplash]

Agreed with others, a very cool build and good idea with the push button shifter!

[zap]

Thanks Whiplash... appreciate it.

I did a performance ride the other day jut to see what the trailer could do. WOT 70-80% of the time with moderate to heavy pedaling 100% of the time.
The battery hit lvc at around 18 miles and the Kill-A-Watt reported 450 watt hours for the recharge.
I averaged 17.2 mph up to lvc.

25 wh/mile seemed pretty good to me.

[DarthSensate]

OH! And I forgot... +1 on the GT hardtail!!

[zap]

Heh... it's hard to beat an old GT. The energizer bunny of bikes.

Yours looks like it's in a little better shape than mine but I'm not complaining. I've put around 1700 miles on it and it just keeps going.
Not bad for a bike pulled out of a trash pile.

[John in CR]

Zap,

I especially like the transformer aspect, so you don't leave the goodies outside. Now you got me trying to dream up a folding cargo bike that transforms into a shopping cart, which would be perfect for my morning market and grocery store run.

John

[zap]

That's a darn good idea John.

I have a couple of Currie folders where the wheels come together when folded. I think you'd need some sort of double hinge so when folded the wheels would stay far enough apart for stability or maybe some type of outrigger?
If you could keep the wheels apart when folded, and still lined up parallel, that seems like it would probably ease using panniers.

Did you see this post?
http://endless-sphere.com/forums/viewtopic.php?f=3&t=21263&p=309768&hilit=escart#p309768
I like it... there's bound to be some ideas hiding there.

[John in CR]

The eSCART is cool, and I love that it has a real ball and socket trailer hitch. My goal would be something that can go on the street as well as in the store or the crowded outdoor fruits n veggies markets every weekend, leaving no way for the ebike to be stolen. Even with bigger wheels the eSCART would have to be too slow on the streets, and no way the long handle is going to cut it at the market.

Keep in mind that I've never seen a folding bike in person or really looked at them in detail, though some fold all kinds of ways into compact sizes. Yes folding to parallel wheels is the way I'd go. I spent a couple of hours of mental exercises and haven't come up with a way to eliminate the need to move the load around after transforming back to a bike.

I keep coming back to the idea that it should be a delta trike. I'd want a leaner though for stability and narrow width for the rear wheels. Then the cargo area as both a cart and a trike can remain static. I think the type of leaner with only the front wheel leaning is just the ticket. Then the transformation could be as little as flipping it up on it's end, lock the lean mechanism and handle bars to become a shopping cart. I'd need to build one and use it for a while to determine if the front wheel needs to come off, but hopefully just turning it out of the way so the handlebars double as the cart handle is practical enough.

I'm all over this, if only to get the looks from people seeing me use it. I've got just the stuff from McDesign's parts score out of customs and waiting for pickup at my courier service. I've been wanting to to a leaning trike for over a year, and this the perfect reason to accept lower performance, while at the same time being an even more practical vehicle.

John

[zap]

I've had a chance to think about this more. The Currie folder would be almost perfect and you don't need a double hinge... at all!
I think I have a photo or two of one of the Curries folded, if not I'll try and get one but I think it would work perfect for your idea. Once folded, the front wheel can still steer so even though the wheels will be staggered a little, they'll still be parallel... all that's needed is a way to lock the front wheel in it's parallel position.
Right now the steering tube folds forward but I think that can be moved 180­°.

Tonight I folded one of the bikes and left enough room for 7 inch wide, hard sided panniers. I measured somewhere around 27 inches total width, outside of front tire to outside of left (looking from behind) pannier. Woody is right at 29 inches wide.
So far it's looking good.
Some type of caster up front and it's a done deal!

[amberwolf]

Locking the front wheel can be done with a hole drilled thru both the steerer tube and the headtube, and a bearing-type cotter pin passing thru the holes to latch it. I've got this planned for a parking steering lock on a bike once I find the pins I know I have somewhere (so the front wheel can't flop around while it's parked and allow the bike to fall over easier if bumped).

If you don't want to potentially weaken the steerer or head tubes, you could add a bracket pair to the headtube and stem that has the holes needed, vertically, so the pin drops down between them. Same effect, just requires extra fabrication.

[John in CR]

I've had a chance to think about this more. The Currie folder would be almost perfect and you don't need a double hinge... at all!
I think I have a photo or two of one of the Curries folded, if not I'll try and get one but I think it would work perfect for your idea. Once folded, the front wheel can still steer so even though the wheels will be staggered a little, they'll still be parallel... all that's needed is a way to lock the front wheel in it's parallel position.
Right now the steering tube folds forward but I think that can be moved 180­°.

Tonight I folded one of the bikes and left enough room for 7 inch wide, hard sided panniers. I measured somewhere around 27 inches total width, outside of front tire to outside of left (looking from behind) pannier. Woody is right at 29 inches wide.
So far it's looking good.
Some type of caster up front and it's a done deal!

I'm sure you could have the pieces that fold over or pull out of the panniers to form the shopping basket also lock the front wheel into place.