Dogmans 72v Mongoose Blackcomb Dirt bomber

[dogman dan]

This one's been a sloooow build. Got the bike last summer, but spent the summer riding instead of wanting to spend time moving stuff from my old mongoose dirtbike to the new one. Finally I trashed the motor and rim a bit, and ended up taking some time to get all that sorted.

Basic components. 2810 (6x10) winding 9 continent rear hubmotor, 72v 40 amp 12 fet Lyens controller, 20s lipo for 72volts.

The whole bike. 81 pounds including 72v 15 ah battery.

2810 9 continent rear hubmotor in 26" rim.

Detail of no weld pinch dropout on the wire side of the motor. Regular nut on the other side. The beauty of the mongoose blackcomb is a steel rear swing arm. So lots of flat space, and no worries about an extra hole where needed to bolt on some 1/4 " thick angle iorn. The second angle could be bolted on too, but seems to not need it so far. We'll see how this holds up when I get around to higher amp and higher volt controllers. For now, it's working good on 72v 20 amps. Next ride I'll put the CA on, to see what the peak wattage is. I'm expecting about 1600 watts, so about 2 hp.

Here are some of the clearance issues. Maybe the pic too small, but there is a freewheel spacer behind the screw on disk brake mount that gives me just a hair of space between the caliper and the motor cover. Then there are a few extra washers on the axle to get the alignment of the disk good with the caliper. Disk and rear hubmotor is a pain in the rear, but I'm loving disk brakes on the new bike, even if they are cheapos with cables. I feel a lot better descending hills on some steep pipeline roads now compared to canti brakes.

Fat rear tires for floating in sand are nice, but continental diesels in 26 x2.5 lead to some tight fits. Had to take the kickstand off and grind down the mount to clear the fat tire. And I better keep this rim straight as I can with this little space on the sides. View attachment 1

Controller can be changed to anything I want very quickly. I've been riding this bike a bit on 48v 20 amp. That can be nice, because it allows me onto the local blm singletracks. Right now it's sporting a 12 fet Lyens 72v 40 amp. later I may lower it to a 20 amp wattage that I hope will run the motor cool enough to keep riding 72v all summer in 105F temperatures. I did lose some halls last summer, but only after a LOT of riding. Now that it's nice and cold though, I will do at least some riding with a controller that can go as high as 120v. I'm riding now with 72v 40 amps.

Battery box. More on how I built it in a later post, but for now just a shot of it loaded up with 72v 15 ah of hobby king lipo. The pack is 2 zippy 20c, paralelled with one turnigy 30c then 4 of those blocks series connected. Ends up a lot of wire. There are much neater ways to do it, but I do it a bit the hard way. The reason why is I require the abiltiy to reconfigure my lipo stash one way for this bike, another way for the death race bike, and no telling what I'll be up to next. So no nice neat paralelled permanently rigs for me yet. The box is huge eh? but that is so it can take whatever I want to put in it, up to about 30s 10 ah.

How does it go? SWEEEET! Yes the cheap bike needs upgrades, particularly the rear shock. And the front shocks are nuttin special too. But the bike frame is super stiff, and feels great. My old mongoose dirtbike had a swingarm design that allowed a lot of flop like a dog wagging it's tail. I got used to it, but never liked it. This bike is solid, and I really feel exactly what the rear tire is doing.

The 2810 is the perfect motor for dirt. I'm gonna go over the bars, so how fast do you want it? Slower is fine with me on dirt, where a huge hole can appear in the road at any moment. It could hit 20 mph on 48v. I haven't put a speedo on it yet at 72v, but it sure feels close to 30 to me. About the max I want to go flying over the bars! :lol: Now that I've put 72v to the 2807, I really feel like the torqe I've been craving is there. I can't quite climb straight up 30 degrees of sand, but I'm real close to it. I think there will be very very few places this bike won't go now.

Now that I finally commited to lipo, I can put the battery where it belongs. and the handling stays nice whether I ride with 6 pounds or 20 of battery. The huge box does bonk my knees just a bit though, so I may swap it with my race bike boxes eventually. Those hold 72v 10 ah, and should be better when I start riding in shorts come summer.

 

[dogman dan]

For the pix of the battery box build later.

Inner sides, 1/8 aluminum sheet. Plywood would work too of course. Also some spacers to make it fit the blackcomb frame better. Attach the inner sides with furniture screws, seclected for thier flat low profile heads.

The plywood spacers fit a recess in the frame. Two holes in the frame drilled large enough for the fastener.

Then the alloy sheet bolts to the frame through the spacers. View attachment 4

Once that is fitted and sorted out, cutting the bolts to length etc, attach the sides and bottom of the box. I used poplar wood for it's strength, and light weight. 1/2" thick stock, pricy but avaliable at most builders supply megastores.

You definitely pre drill all the screw holes, and get the whole box assembled. I used a taller piece of metal for the outer side, to protect the wires sticking up from the batteries. View attachment 2

The remove the outer panel, and attach to the bike. On this frame, I was able to put a 2x4 block across the top tube and screw in in for additional support. It will also give me easy attachment of anything usefull, like lvc buzzers or such if I want it that way.

Replace the outer panel and nearly done. Not pictured is a coroplast lining to the box. The bottom is cushioned by a sheet of coroplast, and the bolt heads on the inner side are covered by coroplast, so there is no bolt or screw heads touching the lipo. On the outer side, after inserting the batteries I stuff a strip of coroplast about 2" wide into the box snugging up the batteries real good. I've already proved that no further attachment is needed to secure the batteries. Allready passed the flip the bike and fly over the handlebars test. :lol: .

When riding, I put one strip of packing tape over the top of my battery pack, just to tuck down and secure the wiring rats nest. I can still see my lv buzzer lights through the plastic tape. In this pic, you see an earlier idea, for a strip of metal to secure the batts. Wasn't needed. The final mods were moving the whole box forward and down one inch, to give me just a bit more knee clearance, and rounding off the back of the box where I still rub a knee occasionally.

 

[StudEbiker]

Looks fun for sure!!

 

[NeezyDeezy]

Nice job! 8)

A perfect config for hot weather. Thanks for sharing.

 

[neptronix]

Cool build, man!
would really love to do one of these when i don't live in an upstairs apartment.
I hear the mongoose is like 40-50lb .. is that true? O_O

 

[TylerDurden]

I hear the mongoose is like 40-50lb .. is that true?

A bare Blackcomb frame with fork weighs about 18lbs.

 

[neptronix]

Dudes on walmart say it's 46lbs.
I wonder how the components can possibly be that heavy.
I suppose there is room for swapping out components then.

 

[dogman dan]

It's pretty heavy. Once you outfit it with fat tires, thick tubes, and two cups of 4x4 slime in each tube, 45 pounds might be pretty close. That 45 may include the shipping box? Seemed to me to be closer to merely 40 pounds. I didn't think to weigh it before I started. On the bright side, you could just about ride it up the stairs. 8) Seriously, you could walk it up stairs and use the throttle to roll the back wheel up the steps for sure.

I haven't put it on a scale finished, and never thought to weigh it before I started adding stuff. The Y frame is alloy, and though huge and stout, shouldn't weigh all that much. But the rear swingarm is all steel, and really adds a lot to the weight of the bike compared to more expensive all alloy bikes. Then top it off with cheap everything else. a gram here on the handlebars, a gram on the stem, quite a few grams on cheap wheels, and disk is just heavy compared to canti brakes. In the end it's at least 5 pounds heavier than my specialized FRS for sure. The blackcomb is a horrible bike to pedal, but it sure is a nice bike to stand on the pedals and rip sandy arroyos on. It makes a nice commuter too, my other blackcomb is set up with a rear 2807 on 48v.

Edit, 81 pounds including 72v 15 ah lipo battery. Not a bad weight for a small motorcycle. Should be able to go for 25 mile dirt road rides on it. 50 miles on paved might be possible. No more putting the bike on the car to ride in the local mountains. I can just ride there now, and back.

 

[dogman dan]

Aww shoot. after about 45 min of admitedly brutal hard riding, climbing hills up to 20 degrees, etc something melted in the motor. Not running a thermometer, thinking a coldish day would be fine. Sure enough, when she gave out, I could barely hold my hand on the motor cover. Dang, I hope it's just the halls again. I was really having fun on that thing, but maybe I should stick to the 20 amp controller next time.

 

[torker]

Finding the "limits" for us again I see I know when I was younger I used to ride gasser dirtbikes and one time a friend let me borrow a bike and we went thrashing in the deep sand. Needless to say I seized the piston for him. Nothing worse than sand for that constant load it can put on a machine.

 

[dogman dan]

Knew I was going to need that motor and controller tester soon. It shows the blue hall nonfunctional, but also all three phase wires dead. Ouch. I was riding up hills I've never been able to ride an ebike up before.

Gee, I guess it's kinda bad to stall a hubmotor and pour 2600 watts into it? I guess if I get it working again, all I need is a 5 ah battery box. 72v 40 amps, it's a short ride bike.

 

[thewmatusmoloki]

Hey nice build dogman.
Good to see the batteries in the frame, handling must be pretty good.
Bummer about the motor. I've just had a hall sensor's go out on me because of heat. (you get that in oz summer tho.)

Maybe a couple of sprays of rattle-can black on the otherwise excellent looking torque arm, if I may be so bold.

I also have a spacer behind a screw on disc adaptor on one of my bikes, been using it for awhile now with no probs, however a few people have reported problems with the thread shearing off, so keep those front brakes tuned up !

Hope your controller is OK.

I had never riden a 72volt bike until just the other day when I took Oldhaq's 72v headway, beefed up cruiser for a blast. Wow, was it fun!! Scary type fast tho at top speed with no suspension.
He also did a hall sensor in on the first 72v ride.

 

[Doctorbass]

Nice built Dogman!

The day you'll try to put the battery down and appreciate the better handeling.. you'll never go back ! puting The battery just between the frame and the front wheel make a HUGE difference!!


Yes.. a thermometer is.. something that all ebike overclocker MUST install in the hub motor!!!

I never blown any of my hub motor since i began installing these temp sensor in the motor. Cheap.. like 4$ on dealextreme or 15$ at your local home depot.. I preffer those for BBQ.. they can display higher temp

2600W is normal for a 9C... but you must watch temp :wink: otherwise.. by my own experience it will only take few second to jump 50 to 100 degree higher while accelerating!

Put the probe directly on the winding.. it is better and more accurate!.. so accurate than when you twist the throttle, you see it increase.


BTW.. I measured the weight of my new Mongoose built... 140 pounds!! with the tire at 40 PSI( indoor)

80 on the rear wheel and 60 on the front.

Doc

 

[amberwolf]

It shows the blue hall nonfunctional, but also all three phase wires dead.

With luck it's just the solder melted on the lap-solder joints inside the motor, so that the phase wires fell off, rather than burned or shorted windings.

I think you ought to start installing internal thermometers at the windings on all your motors, so you know what's happening before they go blooey.

 

[dogman dan]

Yeah, silly me, I always have a thermometer at least on the ouside of the motor. But being a fairly chilly day, 50F, I figured I could just feel the cover from time to time and be OK.

Then I got to riding and grinning, and wham. This motor has been getting hot before, so maybe it's a case of the straw that broke the camels back. I definietely need a better temp montior than the ol, feel it with your hand trick for 72v.

Batteries mounted higher, because this is a real dirt bike. I need ALL the ground clearance and fork travel. It might handle better with lower CG, but really, even the battery i'm packing is not all that heavy. I can flick this bike around on the trail pretty good, even at the very low speeds where the lowest possible CG would be an advantage. Only 81 pounds, so not so bad to handle.

In fact, heat may be only one factor in the failure. It stopped instantly immediately after hitting a huge bump. This bike was being ridden very hard, on very rough and rocky roads. I may have simply shook stuff loose inside.

 

[dogman dan]

Opening it up, sure enough, all three phase wires had the solder melted off where they connect to the windings. Amberwolf called it exactly.

Also all the string tie stuff inside was burned up, and in pieces about 2" long. Nylon I presume?


So what temp would that be typically to melt that solder? 250F? Higher? I have found keeping a motor under 180 F sure makes em last.

 

[jimw1960]

You can get different solder alloys with melting points all over the map, but melting point for typical lead-tin solder is about 315F. Must have gotten hot enough to bake cookies in there.

 

[amberwolf]

FWIW, the interwoven lapjoint I prefer, at the bottom of this post:
http://www.endless-sphere.com/forums/viewtopic.php?p=345771#p345771
would have let you keep riding, although the solder would still have been melted. (well, more like just getting "soggy", then the bump probably jarred the wires off, it wouldn't have to be totally fluid yet, just very very soft).

Possibly it's a good thing they did come undone, but a danged hard thing to fix in the field to be able to get home. If using a thermometer inside it (at the windings) to monitor temperatures (or even to activate the ebrake to shut it off), then the interwoven lapjoints would prevent having to take it apart to repair it, and you could just sit and let it cool down and then ride home.