The Brevette "Winchini": a push baby-trailer

[Erogo]

Man, sometimes I wish I had more skills. And forethought. Skills and forethought. Like last night, when I hit the go button, and everything flew apart. Stink.

So I've been building up this drive for our baby trailer.



We've got a real steep driveway, and when the mama gets home with the bubba, 16 degrees of concrete slab just looks a bit much. (That turns out to be 35% gradient, for those who prefer to think in centimal). Some form of assistance was needed.

I thought for a while about rigging up a cable with a pulley and a switch and a controller, and it just seemed a bit fraught. How to stop the other people from activating it, how to reset it for another haul up the hill etc. Onboard propulsion was needed.

I was vaguely aware that electric motors span quickly, and would need gearing down. Maybe these would do?



I probably thought about them for a wee while, read about the robot people, read about locking out the torque limiter... I guess they might do something, but then somehow I came across the 'sphere, the joys and promise of brushless, of lithium polymers, of ESCs, BECs, STs and HKs. Awesome.

I was still thinking the electric drill gearbox might be a starter, one of those ones in the picture is made out of real Metal. But then, I remembered the winch that I'd salvaged from work, and had thought about setting up as a sort of ropetow on the driveway. Wondered what sort of gearbox was in that puppy, cause surely winches handle grunty power and torque... sure enough, it's a metal planetary gearbox, with a 100:1 reduction. Perfect for the eventual operator, who had expressed a powerful disinterest in firing the bubba up the driveway at anything greater than a moderate pace.

View attachment 3

So, some calculations and mathematics, and it all appeared to be feasible, if the mumma was willing to do a little pedalling for her own propulsion. There wouldnt be much spare traction, with limited load bearing down through the single driven wheel... Give it a go. Ordered a turnigy 50mm motor and 100A controller, to give a bit of leeway over the estimated 4A required to drive a 40kg load up a 16 degree incline at 2.8km/h at 22v.

Now, bit of engineering required. Somehow the winch gearbox has to turn a cog that runs a chain to the trailer wheel. Hmm. I built up a new bmx wheel with a mountainbike hub, so that I could fit a cog to the trailer wheel. That was easy enough. Then I drilled a couple of holes in a bike cog, tapped them M3, and bolted it to one end-plate of the cable bobbin that used to be in the winch. Pics of that can come later. (BTW drilling and tapping stainless cogs is hard when you don't know what you're doing).

When the motor arrived, I transplanted the shaft out of the old winch motor into the turnigy motor. I'd made sure the shaft diameter was same same. It needed a groove machined into it for the circlip, and a flat buffed onto it for the grub screw. I did that with some powertools, used in an Inappropriate Manner.



That worked reasonably well.

View attachment 1

I didnt want to drill too many holes in the gearbox, because I find it hard to judge what I'm doing, and didnt want to run the risk of drilling right into the internal gubbins of the gearbox. I was keen to reuse some of the holes that the original manufacturer had already drilled and tapped, apparently quite carefully as they missed the inside bits. So instead I built up an adapter plate to go between the motor and gearbox. I can't remember why now, but for some reason I actually ended up with two adapter plates, which can just be made out in the picture of the partially disassembled winch, above. At the bottom of the black can (the old motor housing) the silver band is the first adapter plate. That one's round. The second one is the big square piece of old frying pan.

For the record, reciprocating saws and animalium frying pans make quite a racket.

Anyhow, after a bit more sawing, drilling and tapping I had enough adapter plates to get the motor to screw onto the gearbox with its borrowed shaft sticking into the little input bit.

Then I used some bolts, and bolted it to the frame of the baby trailer. Somehow the cog on the drive lined up quite nicely with the cog on the wheel, so I got teh piece of bikechain that I'd nicked out of the skip behind the bike shop, and laid it over the cogs and joined it together again.

Hmm. Without any means to move the drive or wheel back and forth, there was no adjustment in the chain tension. So I swapped an old derailleur for a handful of feijoas, hacksawed half of it away and hammered the other part flat, then ran the chain between the two jockey cogs. Personally, I think this is an Excellent chain tensioning device. I havent tried it out yet though.


Note the motor is hidden inside that cup thing on the right hand side. I'm worried about cooling issues, but we'll see.

I'd been thinking about the electric control side of things, figuring out how relays work etc, and I think I've got a good idea for how to control this setup, where throttle control isn't really needed (as it will have a top speed of 2.8 km/hr). But I was so excited by having the drive on the trailer that I thought I'd spark it up just with the servo tester and whatnot.

Hmm

The old winch had a sort of a U-shaped bracket that held the bobbin, with bearings at either end. I did away with that in the interests of doing a really rough job, and so now have no outboard bearing. The driving cog is bolted to one of the end plates of the old bobbin, which mates with a sort of a pinion sun gear output from the planetary box. That pinion sun thing just pushes into the end of the box, then the end-plate pushes onto the pinion. It's not really a snug fit or anything, just kind of floppy. So when the chain tension pulls on it, it just pops out!

Grah.

So I'm thinking some sort of overly-complicated cantilevered retaining device, arching over from the side of the gearbox housing, with a little pushy bit reaching over the chain to press down in the centre of the bobbin plate. I think I'll be able to locate a bearing on top of the plate so that when it turns the pushy bit won't cause too much drag. Actually the pushy bit doesnt have to do much axial pushing, just counter the radial force from teh chain tension. So hopefully that'll be loading the bearing appropriately.

Does that sound like a good enough idea to suit the kind of Mickey Duck approach I've been following so far? I have to admit I do have concerns that its mechanical implementation is somewhat out of my skill level, but we'll see.

BTW if I get this sorted, someone with a video camera said they'd include me in their documentary they're making for the television!

Eric


edited to reinstate images

 

[Erogo]

Well, I had a requirements capture meeting with the client, who proposed I adopt design principles of reliability and sturdiness over flimsy vulnerability. So to that end I'm thnking the bearing support will be a firmly located stub of shaft, secured with smaller radius shaft steel passing through it and this second transverse shaft fastened to sheet metal that spans the whole gearbox, effectively shrouding the output cog and chain engagement point, and screwed into the gearbox housing making a real concerted effort not to drill right into the inside where the magic happens.

 

[etard]

That's pretty cool man, although I'm not sure why you didn't just use the electric drill motor going into the winch with a brushed controller controlled by an on-off switch on the handlebar? Then Amberwolf could put his freecycle stamp of approval.

For the sprocket retainer how about using a rectangle scrap of metal ( maybe 1" x 3"?) mounted to the gearbox mounting holes and drill a hole in the center where shaft would go and mount a bolt through sprocket to shaft to hold in place. A brass spacer or washer could be used with some grease to create lower friction where any moving and non-moving parts meet to act as a bushing which for your purposes should be just fine.

And if this doesn't work, just build a simple friction drive.

 

[Erogo]

Etard, you the man. Yes I think you're right in retrospect, a brushed drill motor or three could praps have driven through the winch gearbox to power this baby uphill. The calculated current draw and power requirements certainly suggest that would be possible. You see? That's what I mean about forethought. One drawback I do see to going that route though, is that then I wouldn't get to use a brushless motor. But yes, if the client had specified simplicity as a guiding principle, that would have been an excellent approach.
And, regarding the retention plate concept you put forward: it's going to be hard to prove this convincingly, but I was moving more in this direction already. I'm well impressed though that you gained sufficient understanding of the setup from my efforts to describe it, that you could suggest an excellent solution.
So yes, I had moved away from the sheet metal shroud. This has the attractive side effect of not having to drill the gearbox casing, and potentially plunging the drill bit into the internals, shattering it against the hardened steel cogs and leaving a trail of abrasive shrapnel to wreak havoc. But that wasn't what motivated the shift in thinking. The motivation was realizing I only had a top tap. Or is it a bottom tap. The one that can't do blind holes.
So yes, another plate, mounted via existing holes to exert some compression to the stack, but probably still with some of this shaft steel I got out of an old printer that fortuitously just perfectly fits the bearing that I've already mounted, using a disc of polythene holesawed out of an old breadboard. I like your idea of pressing it in with a bolt though, rather than a cantilevering crossshaft. Fits client's design principles better.
E

edited to change key details

 

[Erogo]

Dear Sirs,

please find attached further imagery regarding the current efforts toward powerising our baby trailer. This first shows the underside of the driven output plate, and the splined pinion sun gear cog that engages with it. You'll note the heads of six bolts visible under this plate, the purpose of which should become clear in later images.



In this second image, the drive cog becomes visible as I tilt the output plate toward its engaged position. One can also see the standoffs, through which are inserted the bolts whose heads we saw in the previous image. These standoffs keep the cog far enough from the output plate that when I finally apply a drive chain, it should not foul against that output plate. The standoffs were made out of animalium rod, hacksawed, drilled and filed. The cog is a used mountainbike cog, rescued from a skip or dumpster behind the LBS. Drilling through it was rendered somewhat difficult due to the hardness of the material, and the lack of knowhow of the operator.



A smaller disc of plastic, possibly nylon, possibly polyethene, is fastened to the animalium output plate, using six wee M3 bolts through existing holes in the drive cog. The heads are not visible in this picture, due to being sunken down into the plastic, to ensure enough thread in the plate. Visible also is a bearing, pressfitted into the plastic disc.



Now, the trouble arises when chain engages cog. Tension on the chain causes the whole subassembly (b) to disengage from the housing (c), via lateral movement of parts e through f on cog shaft spline pinion (tt).



This shaft to me appears to have potential. Just the fact that it fits so snugly buggly in the bearing, it has to be good for something doesnt it? So I'm thinking a plate, bolted to the bolts that you can see at each corner of that upper face of the gearbox housing, with maybe a stub of that shaft in the bearing and the plate pressing down on it. But I think I'll still need to have something through the shaft sideways to prevent it from just sliding in through the bearing. And also a depression in the plate to stop the shaft pulling out sideways.

So a sideways something and a depression something.

Probly won't get back to this for a couple of weeks as unfortunately we won a holiday to New Caledonia, so I've got to go and lie on a beach in the sun for a bit. Suck.

Eric

edited to protect the innocent and infringe copyright

 

[Erogo]

Returning from the adventure that is going on holiday, I have gotten back to this baby trailer project this afternoon.

I've cut a stub of the big axle, but rather than run little axle sideways through it, I took a bearing apart to use the little inner ring to press against the other bearing. After bluntening up a few of my centre punches I gave up on the idea of drilling through this bearing race(by hand, without a drill press I think I was dreaming), and soldered it to the shaft.

[attachment=0]P1060053.JPG[/attachment

So that's cool. The bearing race ring bit stops the shaft pushign all the way through that other bearing that's already housed in the breadboard disc there. I cant remember now what's going to stop that bearing just pushing out of the breadboard, but we'll find out. Then there'll be some more bits of breadboard over the top of that stub of shaft, probly with a hole drilled part way through it to locate the stubby bit, and then firmly held in place with layers and layers of duct tape. Or I might find a bolt somewhere.

E

 

[Erogo]

Grah. Nah, fail.

Solder not strong enough: Hit it with hammer, it goes squelch. Lets go of little piece in middle, pushes through.

Then, got too fun-and-games with the drillers, and ended up with too many funny-sized holes in my piece of plastic breadboard, and the nice metal part didn't sit straight in it, meaning the plate bit could bend over and rub on the moving-around part. Will have to do more Thinking, and Planning.

I had hoped to get grub screws through the little ring piece (no not that ring piece) to hold it on the shaft, but as mentioned, the steel used in making the bearing is too hard. Maybe if I use the dremel to worry a little flat area onto it, the drill will then be able to take hold and work its way through? Worth a go?

The bubba will have outgrown this trailer by the time I finish this off! But not to worry, there's another one in the warming drawer.

E

 

[Erogo]

Yes, so, that other bubba materialized, and turned out to be a girl one, to complement the previous boy one.

And I figured a way to hold the drive together better. The inner race of the bearing stopped moving down that shaft stub when it reached the scrunched end, so that was fortuitous. Then to stop the bearing pushing through the plastic plate, I put the other half of the disassembled bearing (its outer larger race) in underneath the full bearing in the plastic. The parts count on this is rising ridiculously.

Then the solution to the problem of it all flying apart is currently a piece of animalium plate begged off the local boatbuilder, bolts through the gearbox corners, and a central one through the shaft stub. I'd hoped to get four bolts through all four corners, but two of them would have foulen the chain, so instead i've folded the plate down the side and I'll either gun staple it to the gearbox housing, or hotglue it.

Also I dreamed a name for the device, which is "Winchini". I might add "Brevette" to that, for that certain ring. The brevette winchini.

Eric

 

[mylittlepony]

OMG Erogo. This is the BEST build log I've read on ES ever!!!! Please keep the posts coming :lol:

Subscribed.

 

[Erogo]

thanks Pony.

I got another bit done, which is the main retention plate. Simply a fold of aluminium, screwed to the end of the stub of shaft that sticks into the nylon bit that's bolted to the chain ring, and also screwed to the gearbox housing through a little flange bit I hadnt noticed before, and bolted as well to the end plate of the gearbox. In case the multiple layers of redundancy werent enough, I've gone ahead and used five screws to hold it to the housing. Two bolts to the end plate. I'd say probably the vulnerable bit is the single connection to the stub shaft. Mind you that's only needed to stop the shaft pushing into inside the gearbox, which seems pretty unlikely cause I've packed it full of adapter plates in there.





.


Jobs remaining: bolting it to the trailer, possibly via an adapter plate, and doing the electrical wiring.

Eric

 

[Erogo]

Did some more sawing and drilling and filing last night.

Cause I found that when I bolted the newly secure motor to the trailer, the wheel couldn't go round any more. I traced it to the fact that the new retention plate was pressing hard against the tire. Stink. The thing's getting too big what with all the bits I've been screwing and bolting on to it.

So, I have to move it out of the way of the wheel. The wheel's held between two bars of trailer chassis, and the BW is bolted to one of these bars. (The inboard one). To get it out of the way of the wheel I thought it would be good to mount it somewhere else on that bar, like further back. But then, it can only move so far back because of the finite length of that inboard bar, and the last inch or so of this bar is out of bounds, because it's involved in holding other parts of the chassis together. So no space to put extra bolts through there.

So an adaptor plate. Out with the plastic breadboard, the saw, the driller and the file, and some marker pens and a ruler, and before you know it I was sawing and drilling and filing.

I think I'll bolt the bit I've sawed out of the breadboard onto the trailer, and then mount the BW to that. Or maybe the other way round, maybe I'll mount the BW to the breadboard, then the whole subassemby "B" to the trailer "A".

It'd be quite cool if I could set up the bolting somehow so that the BW had some fore-aft travel adjustment, to take up the last little bit of slack in the chain. Turns out this is the wrong application for the very excellent derailleur-cage tensioner I've developed, so I'll keep that for another future project.

Eric