Lowracer BMX Conversion

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Hi all, yesterday I got my frame all welded up aside from a few more pieces like steering linkages, a seat mount, and idler mount.

This one is a late 90's Haro Zippo BMX with split toptube which made it easy to do a split tube main frame under the seat with 1" square tubing.

I flipped the front triangle to both slack the headangle and raise the BB to make room for my feet. Fortunately after getting some wheels on it it seems like my heels will clear by a couple inches at bottom stroke.

I'm going to build this as a pedal only at first until i get any geometry and posture bugs worked out, and once it's dialed i'll toss either one or two 20" hub motors on it and haul a small camping trailer setup with solar panels, battery bank, and possibly even a small efficient generator that can fill the gaps of cloudy days.

Anyways, if i can make some progress today i should be able to get the seat and steering built and rigged, then go bomb a few hills and see if i got the geometry close to where i want it. If not i'll cut , bend, and tweak it as needed. This one is pretty much a first prototype anyways and if it works i'll probably copy it with all new metal and lighten it up.
 

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Lowracers are the unsteadiest kind of bicycle, and I don't think towing a trailer with one is likely to work very well.

It looks like a fun project, though. Please keep us updated.
 
Hi, thanks for the advice!

This is pretty much an experiment so if it doesn't work out i'll either tweak it to fit my style or build something else. I think i'm going to try doing a tadpole trike in the next few weeks as well as a delta style. I could also try bolting the trike to this frame and making it a long, low delta trike.

I really just want to get a feel for different configurations to see what fits my needs and riding style. I got wheels and a rough plywood seat on it now, and later today i'll try to swap the cranks from one of my other bikes. I still need a steering arm on the fork though, and also to rig up an underseat set of cruiser bars. I'm thinking of actually clamping the bars right onto a skateboard wheel and welding a bolt stud on the underside for smooth, sturdy steering and then going straight from the bars to the front steering arm. I could use a short stem clamped around a wheel if the steering offset doesn't feel strange or just drill holes through a wheel and use U clamps to center mount it or something.

Does steering arm length matter for underseat steering? Are thre any rules besides the obvious of keeping everything lined up and effectively square? I know that equal length arms will be 1:1 ratio at the pushrod pivot and the bars will give x" arm of advantage at the grips, but as long as i keep the linkage at the pivots at 1:1, does it matter how long the fork steering arm is from centerline? Is there any difference between, say, 4" or 6" of offset if i have thew same corresponding offset and angle underseat?
 
I'm going to try it out as a delta trike, hopefully this week i can weld up the jackshaft fork assembly and steering rod bits and get the electric motor hooked back up to it.

I've been down with sciatica so i didn't really make much progress, but hopefully this week i'll be able to get more done and possibly get it out for a test ride.
 

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That's a good approach for a tow bike. I guess that means a front hub motor? Or are you going to use a shaft motor to drive the other half-axle?
 
The rear is already motorized, i just have the motor unbolted. The motor drivers the axle off a second sprocket which i need to replace with a freewheel once i order the proper shaft adapter. For now it hooks up direct so the motor drags while pedaling, that was the original design of the donor trike.
 
Here's the driveline detail, not adjusted but that's where it sits , currently a 450w geared brushless to a 15mm live axle. The other sprocket will be hooked to the underseat brake jackshaft. Currently the live axle just has two fixed sprockets but once i get a bit further along in the project i'm going to get a freewheel adapter and stick an ACS on the shaft to let the motor freewheel.



With this setup i also have the option for very easy motor swaps, there's plenty of room for anything that'll take a 1/2" chain, i've even got a couple of hot "50cc" 2 stroke gas bike conversion engines laying around that i did all the stuff to, re-ported polished and matched with balanced components and knife edged internals, hemi domed piston with plug cutout, shaved skirt, bored and bumped in compression. I'm not a big fan of infernal combustion as something to rely on, but the mad scientist in me is half tempted to put one on the back. Years ago i built and tuned these things for a living when they were big. I never rode one as a practical machine but i did build quite a few including a bmx with a HUGE Marzocchi bomber fork in it that rode like a little motocross bike. One of the motors i got is from that bike and the rpms peak out at nearly triple the stock limit, and with a tuned intake chamber and exhaust, it winds out and screams like a single cylinder F1 car. The other day i found out that a company makes a wee turbo that fits it as well, and if i hook an arduino up to a fuel injector and the CDI box it'll make silly power for it's size.

But for practical use, this thing is probably going to get a 1000-1500w motor with lower gearing for serious hill torque. I'm thinking of doing a body frame from a few critical pieces of EMT tubing and using some pvc for supporting a lace -on fabric body. I'll bend a piece down the middle as a spine to get the profile, a couple pieces on the sides as longerons, and some pvc "tent poles" as stringers and formers.
 
Well, today i loaded up all my stuff on my trailer and dragged it into town where i can plug my welder in.


I managed to get pretty much all the parts fabricated and welded, the biggest one being the jackshaft in the pics. It's got a fixed sprocket,a freewheel,and a drum brake. This is basically the setup from the red trike i stole the rear end from.

Right in front of it, not pictured, i drilled out a mounting hole and made a steering assembly using a seatclamp welded to some cruiser bars. The seatclamp is the perfect size to securely clamp a stack of skateboard bearings in it and bolt it to the frame where the square downtube joins the frame at the seat. I also welded a couple of tie rod mounts, one on the fork at 3" offset and 90deg and the other on the bars to remove the offset that my bearing clamp thingy has, so steering arms are both effective 3" for a 1:1 ratio.

I left room on the fork tie rod mount to redrill holes if i want to change the steering sensitivity, i can go +/- 1/2 either way if needed. Right now my tie rod is a piece of EMT tubing with the ends peened together and drilled. For now i'll just shove a nut and bolt through it and replace it before it wears through with something more legit, like heim joints with a turnbuckle or summat as i get the rest of it sorted.

I'll take pics of the whole thing tomorrow.
 

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Well here it is, almost. Still need a longer bolt to drop the bars into the right place but that's about it. It's ready to get a battery pack plugged in and the tires pumped up tomorrow and i'm going to see how it rides.

And yes, that seat is a custom carbon fiber piece, an old pool skateboard deck with two layers of carbon fiber turned into my ghetto style seat. :D
 

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Thanks, it's been a fun build!

Brakes are a drum opposite the drive side on the jackshaft.
 
Rusty Mustard said:
Thanks, it's been a fun build!

Brakes are a drum opposite the drive side on the jackshaft.

External contacting band brake? That's what I've seen, and installed, on trikes that had freewheels. They're pretty non-awesome, but way better​ than no brakes.
 
Chalo said:
Rusty Mustard said:
Thanks, it's been a fun build!

Brakes are a drum opposite the drive side on the jackshaft.

External contacting band brake? That's what I've seen, and installed, on trikes that had freewheels. They're pretty non-awesome, but way better​ than no brakes.

Yep, one of those things. It's slightly better than crashing into cactus to stop but it gets the job done if you survive the brake steer. :shock: This is one of those "Don't do as i do" things, and it's use is based on what i had left in the graveyard this week. As i said before, once i know the geometry and all that works out, i'll toss the V brake posts up front, i've got brand new bosses of straight and offset ready to weld but i want to make sure i'm not going to swap forks for some reason before i commit the posts to it.

Next week i'm thinking of doing a tadpole from scratch if i can find the time. I'm also tossing around the idea of doing a pedal electric bucket rod as a fun project. I'm thinking of copying a model A front suspension and chassis, but leaving out the parallel frame rails and just keeping the A frame going back to the rear wheel. I want to use a galvanized tub from the feed store as the body and make it all desert-steampunk-ratrod style. I could put a gas motor converted to run on propane up front and spin a generator to charge the system, as well as to have the open motor hot-rod look. A pile of batteries just aren't as cool looking or sounding as a tiny v-twin would be.

I'm also thinking about trying to get a shop where i can actually work on stuff, i live up a mountain and have to pack everything in and out of my place up and down a section of trail with exposure. I've almost lost a few bikes down the cliff when a trailer or trike wheel wider than the trail loses its footing. But, if i had a shop that had better access and enough room to work indoors i could build at least one bike like this in a few hours. Back when i built motorized bikes for a living i had a full shop at my disposal and it was no big deal to build 3 bikes a day.
 
Here's a rough mockup of the aero shell for it, i'll probably cut the centers and put 45 deg elbows in them, secure this under tension to a EMT tube frame hardpoint, add a few stringer and former pieces, then wrap the whole thing in cloth, lace it tight and give it the sort of looks pre-ww2 airplanes and rigid frame zeppelins have. I'm gonna wrap it in the same cloth i use on my business awning, 2" yellow and white striped "Lemonade Stand" style awning canvas. I've got enough material right now to cover that entire frame and it's inexpensive per yard to get more. The fact that it's going to look like an aerodynamic circus tent should hopefully make me visible since i'm low, as well as the reflections from all the solar cells that i'm eventually going to put into the fabric somehow.

This is where i need some "futuristic" tech like pv yarn or paint that we've been hearing about for years. I hear that zinc/clorophyll nanopaint is like $5 a gallon to produce if one can get nanozinc, maybe i'll dive into their research papers and see if i can electrolyze or chemically produce the nanocrystals and dope it over something like alumanized mylar or even old school silver oxide aircraft primer. I'm sure if i read the literature i can figure out a diy way to make some sort of solar fabric, paint , or laminate or summat.

I'm gonna go downtown soon, pump up the tires, and see if i can't make it to the other side of downtown to the noodle shop on the janky frankentrike with a sack of rc airplane lipos.
 

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For what it's worth, those band brakes come in several different diameters, and the large 90mm ones are not too bad. It's easy enough to use two of them on a twin cable lever if that helps.

Some of the cheapest and nastiest Chinese pedicabs have only a single rear band brake, and ugly things can happen when they're put to the test.
 
Success!

Today the machine hit the road and it was one of the most uneventful first rides ever! I dragged it down the hill with some flat tires, got it aired up and gave it a final once over, a few adjustments, plug the battery, and hopped on. Using pedal and motor, i did a lap around the block,climb, descent, downhill S turn dodging peds and traffic, and then a climb back up the block. This thing handles great, i love it! My gearing is absurdly high so i'm going to drastically drop like 12 teeth or so down into the mid 20s somewhere.

My bars still rub the chain, i went to the store and got a bolt but it wasn't quite long enough so i got some 8mm threaded rod that i'm going to weld to a sturdy adapter plate between the frame rails. It's not a problem , the chain slightly rubs the bars but other than making a bit more noise than it should, it all ran smooth.

One thing i noticed once i actually got rolling is that my frame has a slight twist, about 1/2 to 1 degree to the right which wasn't surprising considering i just tacked this thing together by eye and feel out of plans in my head and then just dove in and welded it. It could even just be from warping while laying down the big center frame beads, but it shouldn't be too hard to cold bend out once i have an extra set of hands to help me lever one end of the frame with a couple of breaker bars.

Other than the slight twist causing a barely perceptible bias towards the right, the feel is pretty much what i imagined when i said i wanted a firm, but smooth and compliant ride. It definitely rolls smooth, and has a bit of give over rough stuff and potholes and handles well on gravel without understeer. The overall stiffness though is confidence inspiring and doesn't feel mushy at all. The turning circle is sufficiently tight that i can really maneuver when i need to but is solid and locked in at speed.

So now that i've got this project pretty much finished as far as mechanical stuff, i'll pick away at outfitting it as i begin the next build, some sort of MBB thing or something. I've got a cracked frame i'm going to steal a nice rear triangle from and stick on the front of an old, size small rigid fork mtb that already has a seattube cut flush, so it's pretty much ready for a seat and some kind of wheels, as to be determined.

Hopefully by this time next week i'll have an MBB bike so i can see how it rides and if i like it, yay!

This was a fun build and it should do pretty well once i get the frame straightened, add a front brake, body, solar, and whatnot. Thanks for the advice everyone!
 
Rusty Mustard said:
A pile of batteries just aren't as cool looking or sounding as a tiny v-twin would be.
It wouldn't have the sound, but there's a number of ways ot make a v-twin look with the battteries (and/or the motor). There's a few builds around here that do that. One of them was by Juiced riders I think. There's a few pics of differnet types in the show us your homemade battery housing thread, IIRC.


I'm also thinking about trying to get a shop where i can actually work on stuff, i live up a mountain and have to pack everything in and out of my place up and down a section of trail with exposure.
[/quote]
What about building up a big shed to hold generator, tools, welder, etc.? If you had money to burn you could also put solar and batteries and inverter in there, to run stuff silently, rather than a noisy generator, but it'd take a chunk of change to do that for welding.
 
Rusty Mustard said:
Other than the slight twist causing a barely perceptible bias towards the right,

No reason not to align the frame as pefectly as you can manage, but do keep in mind that delta trikes always pull to the downhill side. On a crowned road bed, that makes them want to head for the gutter all the time. Before you decide what behavior your trike is exhibiting, ride it on the left edge of the road and see if it changes its mind.
 
amberwolf said:
Rusty Mustard said:
A pile of batteries just aren't as cool looking or sounding as a tiny v-twin would be.
It wouldn't have the sound, but there's a number of ways ot make a v-twin look with the battteries (and/or the motor). There's a few builds around here that do that. One of them was by Juiced riders I think. There's a few pics of differnet types in the show us your homemade battery housing thread, IIRC.

I've seen stuff like that back when i built bikes, vaguely remember something like a V-twin looking battery box that fits three 12-12's that a customer had. I'm not really a big fan of internal combustion in terms of practicality and daily use, i don't want to depend on burning fuel, but on the other hand, i love to build and work on them, they're much more fun to tune and mod than electrics. Electrics are great, a solid state mystery box makes a wheel turn when you twist the go thingy that doers what is says on the box. Cool, but that's just boring to me. What's really neat though is that with the mechanical engines there's so much tuning possibilities in such a dynamic system. I like all the attention to detail that goes into making a cacophony of metal bits jiggle and spin around several thousand times a second in a high performance manner. I get to play with stuff like fluid thermodynamics in practical applications, as well as general physics, resonant harmonics, and even chemistry when it comes to custom fuel blends and such.


I'm also thinking about trying to get a shop where i can actually work on stuff, i live up a mountain and have to pack everything in and out of my place up and down a section of trail with exposure.
[/quote]
What about building up a big shed to hold generator, tools, welder, etc.? If you had money to burn you could also put solar and batteries and inverter in there, to run stuff silently, rather than a noisy generator, but it'd take a chunk of change to do that for welding.[/quote]

The big problem with where i am is where i am. I already have solar, and soon i'll upgrade my inverter to one big enough to weld at home, but my biggest problem is access. There's just no reasonable way to get materials into and finished product out of my yard. I live on a terraced canyon wall, and i have access either by 150 narrow, winding stairs, or a narrow section of sketchy singletrack with exposure. And all of that is after climbing like 200' vertical over less than 1/4 mile. My trikes and trailer are too big for the stairs.

The hardest part of building this trike has been packing it, the road bike and trailer i towed with plus all my tools up that climb and through the trail. Just today coming home on the trail in the dark i almost lost the trike over the cliff face trying to get through the rock garden on one wheel so the motor would clear. I don't even know what i did but somehow my elbow is all sore and bleeding from wrestling it down the trail. I really want to build a pedal powered hovercar, i have all the parts but i'm hesitant because i'll have to get a few people to help me pack it out to the trailhead just to get it on the trailer.

So i'm looking at motor upgrades for the lowtrike, and i see this 1800w brushless setup all over ebay, says it does 4500rpm at 48v and has a 9t sprocke. I'm assuming that the 4500 rpm rating is it's no-load max ans suspect the working rpm under load is lower. I did the math, and with my current gearing and wheel size, that would put me at well over 200mph with 9/22 gearing. With 44t gearing though then numbers fall down to something more reasonable like a theoretical top speed of 67mph or so at 4500rpn, and more like mid 50's if the load RPM is lower. Not that i plan to ride wide open, but if i cruise at like 55-70% of max power i figure that should let me cruise at 20mph without straining the system, but still have enough power for higher speed runs where appropriate.

Anybody know anything about these motors? I'm trying to find the torque specs and also stuff like load RPM vs no load.
 
Chalo said:
Rusty Mustard said:
Other than the slight twist causing a barely perceptible bias towards the right,

No reason not to align the frame as pefectly as you can manage, but do keep in mind that delta trikes always pull to the downhill side. On a crowned road bed, that makes them want to head for the gutter all the time. Before you decide what behavior your trike is exhibiting, ride it on the left edge of the road and see if it changes its mind.

It's the frame, it pulls on flat, we don't have crowned roads in town, many are actually the opposite and are troughs and nothing is really level. I put the trike across the same hill both ways and i can see it favors leaning right. I've got a friend who does metal fab and such who will probably stop by in the next few days, when he does i'll have him twist the rear while i do the front with two big bars and cold set it about a degree or so. I may add a bit of 16ga sheet webbing in between the two frame rails and weld it in as a shear web type structure. That should give it more lateral and torsional stiffness without cutting into the vertical compliance too drastically.
 
Got a link for the motor you're thinking of?

For the access problem, it sounds like it's time to build an elevator platform with a winch. ;)
 
Here's an example of the motor,,,

http://www.ebay.com/itm/48V-E-Bike-Brushless-Motor-Controller-for-Electric-go-kart-buggy-1800W-48V-/232242731913

Possibly good news as well, my neighbor just mentioned to me yesterday that he has a bunch of e-bike batteries and electric stuff he inherited from a friend who passed a couple years back (who coincidentally rode a recumbent delta trike with hub motor) that he's said he'll bring by. Hopefully there will be something useful as more batteries coming my way soon!

Even if i had a lift, i'd still have wrestle everything down the trail to get to it :lol:
 
I've seen the brushed version of that motor used on ES for a number of projects (I have one here off a standup scooter I wanted to rebuild, but they made those all illegal here so I put it away for a later project).

IIRC the brushed version could overheat if actually used at 1000w continously, unless additional forced-air cooling was done (to pull air thru the motor).

I don't know if the brushless one would have the same problem, since it would be more efficient (assuming geared correctly for speed used at), having no brush/armature losses/heating.

But it could also be cooled by forced-air, and also could have finned heatsinks added to the outside, if necessary.
 
Right on, it looks like they come with a 9t sprocket, so a 44t on the axle will give me 5:1 reduction. They claim 4500rpm from it but that's probably no-load so under load i'm guesstimating based on similar class motor's specs that i'd have like 3800 rpm under load, and if i go with 20" wheels in the rear i should be within the range of reasonable.
 
I scored some swivel eye ball joints this week, went into the auto parts store with a friend and asked if they had any, they said there might be some around, dude dug 3 hardened 1/4" swivel eyes and told me "Just get 'em out of here and they're yours".

So i welded a couple of bolts into the ends of the EMT tubing and stuck 'em on with locknuts as jam nuts. Now my steering is like silk, with either bearings or ball ends on anything that moves i'm not as worried as i was about my steering linkage falling apart while bombing down a hill.

I've also got all the steering and chainline alingnment issues solved with some proper hardware. I shortened my rear chain by one link and moved the axle forward as much, allowing me the adjustment range i need to raise the jackshaft and balance the the tension under load properly. Since the frame has a bit of sag under my weight at the jackshaft, when unloaded the chains are slightly loos but with rider weight they fall into proper tension nicely.

This week i'm going to try tvo get some cells and tabbing wire ordered and build a spot welder with some stuff i've got around and build a couple of packs. I'm thinking of doing two 10s5p packs with 18650s, maybe a marine battery selector, some switching and wiring to swap packs between charging and discharging from solar.

I've got a panel that pushes 1.5a i'm going to install and charge a bank of standard 12-12 gel cells running at 12v and fed by the solar charge controller. This will be my "house" battery where i'll pull 12v for lighting, device charging, etc and also feed the charger for the drive packs. Alternating between packs, i'll be able to charge one while drawing from another, switching the packs to keep them between, say 40 and 80% to extend life. It'll eventually get more panels, probably a couple of 320w flex panels contoured to the aero shell.

Once i get as far as having batteries all working with manual switching, i'll probably hook it all up to an arduino or pi or other pic with bluetooth capability and control it with an app. If i write an app from scratch it's pretty trivial to utilize the phone's capabilities to do stuff like voice control, and use gps and power system state to calculate stuff like actual range and a whole host of other data points that can be used to maximize battery life and range.
 
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