Mongoose Blackcomb

[Barncat]

Picked this up yesterday for 75 bucks. Will be intended as a street ride to smooth out the inevitable bumps and potholes... the bmx build I just did is fantastic and precise on smooth pavement but a bit harsh on less optimal surfaces.

Cool aluminum main frame that will lend itself to attaching a battery and controller. Swing arm and rear stays are steel so there's a small weight penalty but better to weld a motor mount to without post-weld heat treat problems. Will have to cut upper seat post tube off and also the vestigial front derailleur tube. It'll be fairly light after tossing all the other crappy steel parts. Crank will be gone, just footpegs. Power mode only. Probably an air fork.

I'd like to use an 80100 outrunner motor on this one but will start another thread in "motors" to ask a bit of advice on that.

Will use a 20" rear wheel with 25H chain drive and 24" front wheel again.

[amberwolf]

FWIW, that's a bike that has made a number of conversions here on ES. I went looking for some of them but got lost down a rabbithole and then dozed off...if I find any of them that were middrives (vs hubmotors) i'll link them here if you're interested.

[spinningmagnets]

Doctor Bass, one of his first hot rods...

[Barncat]

Cool. So it has a pedigree! Saw it on craigslist a few days ago and said I have to have that

This shouldn't take too long. Learned a lot from the first project and i have the mods pretty much worked out. I may order the Flipsky 80100 and their FSESC 6.6 single later today. Those two items will knock about 9lbs off relative to my bmx build. And theoretically perhaps a 75% power increase. I may just buy some lipo packs for this setup as current is of the essence.

Having suspension will be good. One must ride sidewalks etc from time to time as a stealth ebiker. A couple decades back I built my own line of full suspension mt bike race frames from 7005 aluminum... the supply of 70's vintage Japanese motorcycles to chop up has dried up so it's ebikes now.

[Barncat]

Finished taking the frame apart this afternoon. The main frame is very light and fortunately there were no cracks in the swingarm bottom bracket area. All the nylon or delrin bushings are in good shape too so no need to replace any of that stuff. Will probably do some surgery on frame tomorrow. Some PO really messed it up with black paint, sadly...

The swingarm and stays are reasonably light. It appears that the 20" rear wheel will allow plenty of space for the motor so I won't have to modify the dropouts, but instead tension the chain via swingarm mounted motor adjustment.

Was surprised that the shock linkage plates are steel, so I'm going to make aluminum replacements.

The forks are actually in good condition and will clean up well but they're not a high performance item... may use for now.

[amberwolf]

None of the pics of Doctorbass's bike are still around the forum (lots and lots of pics have disappeared relatively recently) but there's a bunch here:
http://www.evalbum.com/1947
including one of him towing a schoolbus with it


This finds threads with still-good pics easier than any other way I tried
https://www.google.com/search?q=endless ... b&tbm=isch

[Barncat]

With all due respect, that bike is aesthetically not for me.

Not trying to offend, but I'm a minimalist.

[Barncat]

After hours of research and some advice from member mxlemming on another thread, looks like going with that Flipsky 130kv motor is not a good idea. You'd need 2 stage reduction. Plus big lipo packs are hard to come by quickly from reputable sellers...... nothing is easy.....

Looking at a different performance motor with proper kv but no sensors. My understanding is you have problems with a standing start w/o halls, correct? This would potentially be mated to a flipsky FSESC 6.6 single rated at 60V and about 150A. Does FOC (which it has) work without sensors? And I suppose a pot style throttle would work?

[Barncat]

I did pull the trigger on a like new Tiger Motor U15 80kv yesterday, so that's in the mail. Great ebay deal unopposed bid surprisingly.

I found and read through the Lebowski "sensorless standstill" thread, which I only understand in general terms, but trying to get up to speed on mating this motor to a sensorless controller- wherever credit is due to those designers.

So build is on pause for a bit while I sort out components. It's a rob Peter to pay Paul series of tradeoffs as I wanted to just swap on my 20s battery pack...

[Barncat]

Oops. Deleted double post.

[Barncat]

Swapped a new alloy QR disc brake rear hub into a 20" front wheel I had lying around. Turned out well. You can buy a pair of these hubs on amazon for like 25 bucks. Unbelievable. However, in the course of adjusting the cones I noticed an intermittent hang up which was really odd. Turns out there was an extra ball bearing inside the hub dragging on the axle...........

Have to relace the 24" front wheel with a disc hub also. Need different spokes.

The Flipsky 6.6 controller arrived today. Have pretty much decided to build a new high current 21700 pack with new Molicel p42a's. Has anyone bought from bulkbattery.com in Smyrna GA and are they legit with genuine products?

[Barncat]

These custom projects always get slowed down by decisions, waiting for parts and solving design problems...

Decided to use #25H chain again, and made a 16T sprocket that adapts to the motor. Not easy without my lathe which is elsewhere. I gutted then welded a threaded freewheel as a fixie adapter for the 80T rear sprocket. Had my doubts that it would spin true but it's right on fortunately. The plan is to go direct drive, as there is very little cogging torque from this motor and it feels similar to a freewheel. This permits regen braking if desired and you could also give the bike a wee push from a standstill if necessary since the motor is sensorless. Jury is out on all that. Don't have an appropriate hi current battery built yet for testing/programming...

Last tricky part is the motor mount, then it'll come together fast.

[crazy dreamer]

s-l1600 (1).jpg (112.34 KiB) Viewed 2539 times

100 tooth 25h sprockets are available. i have also seen 110 tooth.

[Barncat]

Good to know. I've seen up to 90T #25 sprockets commonly available here in the US.

My calculations indicate I only need a 5:1 reduction with this motor to drive a 20" diameter rear tire to near 60mph. So the 16/80 fits the bill, and gives a relatively large diameter wrap on the front sprocket which is always desirable. Started work on the motor mount...

Also have 75 new Molicel p42a's on the way. Decided used cells aren't worth the trouble, and these will kick out serious amps. 15s5p. 15s is pushing it with the Flipsky 6.6 controller but plan is to not charge over 4V/cell. Still must learn how to program that by watching youtube vids... thing is tiny compared to that huge generic 55A Chinese controller on my first build.

[Barncat]

Chipping away at things...

The motor mount was a complex affair. It's swingarm mounted to keep chain at constant tension to rear axle. Not easy to locate a motor accurately in space- to have clearance, to be plumb, straight, aligned, adjustable fore and aft for chain tension, and strong enough to withstand over10hp. 1/8" steel plate, 3/8" aluminum angle, 5/16 fasteners.

Finishing up paint today, then assembly can begin.

[Barncat]

Also, I suppose I'll put in a good word for Harbor Freight's Bauer bandsaw. Built a vertical stand for it. It's indispensable for quickly and safely cutting all the small metal parts necessary for building projects like this. I have a larger bandsaw at my shop up north but this is really handy, and portable.

Been using it for 3 months. I've seen one review that said a blade guide broke but so far no evidence of that. Powerful gear reduction motor, easy blade changes, nice accurate cuts, 5 1/2" working depth. 3 pack of Lenox blades (the best IMO) 20 bucks at Lowes.

Had a little stainless dipstick lying around that was fashioned into the trigger clamp. Wear earplugs when using. It's loud up close.

[SlowCo]

Nice project
I'll be following your progress. Good luck and enjoy building!

[owhite]

I really like the single pivot soft tails. Do you have drawing for where you plan on putting your battery?

[Barncat]

Thanks SlowCo.

owhite- battery will be the 2nd of my no weld no solder design, rectangular, and mounted on top of the top tube. Will make that soon after completing the rolling chassis.

Slapped on some paint and fabbbed a couple aluminum shock linkage plates to drop about 1lb. Note the frame surgery vs stock...

[Barncat]

Battery porn . 75 brand new 21700 hi current cells 15s5p.

[owhite]

It's a nice layout! How much clearance do you have between the mid-motor and the dropouts in the back? What size tire are you planning for the rear? Also, are there any bearings going in where you are putting in your shock plate linkages or is it just surface to surface with bolts?

[Barncat]

Wheel specs listed earlier in thread. Rear suspension is stock barrel bolts and nylon bushings, no bearings.

[Barncat]

Rolling chassis mostly complete. Still need to fab some footpegs, put the kickstand on and spray some flat black on the plywood seat, which is believe it or not more comfortable than a conventional bike seat, and 3" closer to the ground for low CG. I may decide to do an irreversible frame mod to get seat pan 2" lower still, but no one could ever put a seat post on it again...

Disc brakes front and rear. My previous build has a caliper front brake (and disc rear), which is adequate but not great, plus the rim will slowly wear. With the power this motor should generate, ya gotta be able to stop.

I have more $ in the 24" front wheel than what the whole used bike cost... good luck finding a 24" disc brake model. Had to buy wheel, hub, spokes, tire and tube. Brake disc swapped from original 26" front. Spokes were slightly too short and useless for 3 cross and slightly too long for 2 cross , so I put a couple #8 stainless washers under each spoke nipple. It's nice and true now, hope it holds tension.

I figure it's at about 35lbs once pegs and kickstand added. 12 more for the battery brings it in at 47 or so, pretty light for full suspension. I'll probably swap out for better lighter forks and stem after test riding. Easy to do and will drop 3lbs.

Last phase is custom battery and learning how to program the vesc.

[99t4]

... good luck finding a 24" disc brake model.

Aren't there some high quality youth bikes (24" wheels) with disc brakes out there? Seems like the 24" wheel/disc combinations should be around?

[Barncat]

They exist and show up on Craigslist rarely but then you've got to buy the whole bike. And they always have knobby tires, not suited to street use. So there's no cheap easy work-around.

Commonly available 26" fronts are a poor and unsightly match for the 20" rear required to get proper gear reduction. Plus there are basically zero 20" disc rear wheels around used, so I built both wheels.