Mongoose Pug on/off road

Barncat

1 kW
Joined
Oct 26, 2020
Messages
357
I'm back at the FL headquarters for another winter, so that means more ebike projects and Endless-sphere! May as well document this one- my third Mongoose brand build, so a stable of Mongooses, Mongii, Mongeese, take your pick...

Cost me 120 bucks off Craigslist. A kids 8 speed fat bike with nice surprisingly light disc brake alloy wheels that I'll upsize into an adult off road capable unit.

It will get a 20 inch fat bike air fork that'll lift the front end a bit and add suspension. Fortunately, adapter headsets are available to swap a 1-1/8 fork into a 1 inch steerer tube. Rear will stay hardtailed and I'll extend the dropouts about 5 inches to add wheelbase. The fat tire will soak up trail riding, I'm not going to be doing anything extreme, just gravel roads and civilized single track.

I've already cleaned and checked the wheels and repacked and adjusted the hubs. Spent over half an hour with a hair dryer removing all the lousy decals Mongoose plasters on their products.

It will get another nominal 3000w MY1020 motor running at more like 5000w with my 20s battery pack, and will use the generic 24 fet controller pictured that says 55A. Motor will mount on lower chainstays just behind the seatpost with chain drive of course to a sprocket and freewheel. It occurred to me that I could physically mod the controller by cutting the shell a bit shorter. It will now fit inside the front triangle. Also rerouted the battery leads to come out what will be the upper end for a much shorter cable run to plug into battery, which goes on the top tube as per a couple other of my builds.

I do have one question for you more advanced controller guys- should I attempt a shunt mod on this? It's an inexact procedure and a bit tricky in this case with close quarters. I'd really like to bump this to roughly 80A from the rated 55...
 

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Keep in mind that those bikes are make from compressed garbage, and their quality and structural integrity ranges from barely good enough to do the intended job, to not nearly good enough to do the intended job. Under no circumstances would I consider cantilevering the rear wheel five inches behind dropouts and rear stays that are very marginal to begin with.

I assume you're not child sized and don't weigh as much as a child. And you won't be going at speeds that would be characteristic of a child on a pedal bike. Whether you are playing with 4000W or 6000W doesn't make much difference. It's a terrible idea either way.

I think that bike would be an acceptable donor for a 250W e-bike conversion FOR A KID. (Especially if it's a kid you don't like.) It's still crap and will still disappoint, because that's what department store garbage bikes do. But it probably won't maim anybody because it's crappy when it's going 10 mph with an 80 pound kid on it. Very different story when it's a full sized adult going 40 or 50 mph.
 
I see you're off your meds again Chalo.

Not only will I successfully mod and safely thrash this new frame as desired, I already built one with close to 2000 miles on it.

AFAIC, you need to STFU.
 

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Great new Fat Bike project Barncat :thumb:
I'd love to see what you will come up with and how well it will perform.
 
Barncat said:
I see you're off your meds again Chalo.

Not only will I successfully mod and safely thrash this new frame as desired, I already built one with close to 2000 miles on it.

AFAIC, you need to STFU.

Yeah, why listen to me? I only repair and restore bikes, good and bad alike, every working day of my life. So what would I know about them?

Here's a second opinion from another bike professional:
https://www.southcoastbikes.co.uk/No_BSO.asp

How would you regard someone's opinion of a car they'd driven "close to 2000 miles"?
 
Look Chalo, I'm probably older than you are, have a mechanical engineering degree, and I've been modding, building and riding all types of frames for decades, including a short run of my completely custom designed full suspension mtb frames of 7005 series aluminum. That's one of the most difficult machining and TIG projects anyone can take on. Oh, plus 20 cafe racer motorcycles- where your life is really at risk.

So when somebody calls me an idiot, they're by god gonna hear about it.

I don't want you posting in any of my threads- now or in the future. This kind of personal animosity has no place on this website.
 

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Other guys above, thanks.

This is a pretty simple project overall, and I've developed something of a formulaic style with these chain drive MY1020 motors and generic controllers that are inexpensive, durable, lighter than hub motors, and are very good performers.

I should have the dropouts and motor mount done soon. Still waiting for the special headset and air fork to see the final geometry.
 
Barncat said:
So when somebody calls me an idiot, they're by god gonna hear about it.

Show me where I did that.

My well-founded animosity towards department store bikes isn't a reflection on those who assume they are fit for purpose. They should be, but they mostly aren't.
 
LewTwo said:
play nice boys ...
I've noticed that there's a unwritten rule or etiquette, in the build section, where most are either asking questions related to the build or providing general support, especially when the OP is using a thread to document their build, and not really asking for input. Just an observation, since the build thread section seems different from the other subforums in that way.


Barncat said:
It will get a 20 inch fat bike air fork that'll lift the front end a bit and add suspension. Fortunately, adapter headsets are available to swap a 1-1/8 fork into a 1 inch steerer tube. Rear will stay hardtailed and I'll extend the dropouts about 5 inches to add wheelbase. The fat tire will soak up trail riding, I'm not going to be doing anything extreme, just gravel roads and civilized single track.

I should have read more carefully. I'm interested in how the geometry works out, since I'm planning something similar for a bike for my wife, but a different approach, but also a kid's bike. I'm planning around a 24" Specialized HotRock, but mounting 20" wheels and a 26" ~130mm travel fork (with 20" wheel) to slacken the geometry. This results in the slacker head angle and the longer chainstays, relative to a 20" frame, and provides a rear disc option. 20" 6 speed Leaf motor, and hailong pack mounted under the downtube, and controller in the triangle would complete the setup.
 
E-HP- all my builds thus far have 20 inch rear wheels for proper final drive ratios with the available #25 sprockets, with 24 inch front wheels for decreased rolling resistance and better safety over potholes and pavement irregularities. They handle great. Speedway bike styling. A 26" front for example would look aesthetically odd, and would not handle as well. Disc brakes are always preferable when possible, especially with the 45mph + speeds my builds have, and the disc fat wheels on this project are the main reason I bought the bike. The fat 20 inch front will float over rough stuff.

At any rate, don't do anything that looks too odd or departs too far from convention and you should be ok.

I'm in a holding pattern waiting for parts before I can start cutting and welding...
 
Hi barncat, nice looking piece of compressed garbage :p look forward to seeing you turn it into more fun like your other builds. Don't forget to install an anchor to stop you.

Those controllers could have a factor 5 difference in the mosfet current capability, but 80 seems reasonable if they haven't cheaped out too much and it's a decent quality design and assembly. I'd personally run it at the rated current, keep an eye on temperatures and then jack it up accordingly.
 
Hey mx- I've already put quite a few miles on that controller which was on my first build- the white bmx pictured above. I swapped a Flipsky 75100 onto that one as described elsewhere...

At any rate, this controller running on 20s never even got warm. I assume it's nearly identical to the units the same manufacturer claims are 80A. It appears to be quite well made. Is the Amp rating primarily controlled by the shunt wire, assuming the downstream components can handle it?

I've run into a minor problem with what I thought was a headset that would adapt a nominal 1 inch steel head tube to accept a 1-1/8 inch air fork steerer. As in they may not exist. The bearing cups would have to press onto the outside of the head tube. If my lathe was here I could modify the head tube by welding on a couple extender rings... also considering turning frame into full suspension but that might be more trouble than it's worth.
 
Barncat said:
At any rate, this controller running on 20s never even got warm. I assume it's nearly identical to the units the same manufacturer claims are 80A. It appears to be quite well made. Is the Amp rating primarily controlled by the shunt wire, assuming the downstream components can handle it?

Indeed the shunt wire(s) generate a voltage drop proportional to current and then there are amplifiers to convert that to a larger MCU readable signal.

Options are...
1) wedge conductive stuff onto the shunt (crude but effective)
2) modify the opamp circuit to have a lower gain (easy if you're comfortable with soldering small things and much more controlled)
3) reprogram it if that's an option the device supports.

If you locate the amplifier we can probably work it out, APL did a similar thing in his thread.
 
Sounds to me as though the personal animosity was one-sided, although the more egregious element is attacking Freedom of Speech, something I would have expected the mod(s) to address.
 
I love how easy this conversion is! I am not a fan of fat tire bikes but I might just get one of these frames...

Thanks for documenting this
 
mx- thanks as always for the detailed tips. I'll probably experiment with a quick and dirty shunt mod or just leave it alone.
 
Barncat said:
Look Chalo, I'm probably older than you are, have a mechanical engineering degree, and I've been modding, building and riding all types of frames for decades, including a short run of my completely custom designed full suspension mtb frames of 7005 series aluminum. That's one of the most difficult machining and TIG projects anyone can take on. Oh, plus 20 cafe racer motorcycles- where your life is really at risk.

So when somebody calls me an idiot, they're by god gonna hear about it.

I don't want you posting in any of my threads- now or in the future. This kind of personal animosity has no place on this website.

Nice cafe build! I went a different direction with a hardtail build around my XS650 motor.
20221203_184947.jpg

I did do a cafe build back in 2015 around an XV750 though. I still own this one which I plan to hand down to my son.
20221203_185239.png

Always dig running into other bike builders! :bigthumb:
 
Nice bikes. And we shall end our ICE show and tell here lest we be banished from the forum :). I prefer the ebikes lately and don't ride the XS much here in Pinellas county anymore. Lotta traffic, no twisties. I have several other cafes at our place on the TN/NC border.

Made some progress on the Pug. Rear dropouts extended, and axle/chain adjusters done. Will weld a couple straps across the lower stays to mount the motor. Must weld a bracket on left side for brake caliper. Motor end caps need to be drilled out for ventilation as per my other motors. Will run 12T front and 80T rear sprockets for street use, and swap an 11T on for trail riding- not that there's much of that in my vicinity, and it's mostly loose sand that's not motor friendly. Will take this bike up to TN in the spring.

As alluded to, a problem developed in terms of adapting an air fork to this 1 inch headtube. Without my lathe here I have to go prehistoric and file two steel rings out to 33.9mm ID, then weld them to the headtube to accept the new 1-1/8 headset...... not fun. Missed a great craigslist deal on a mini lathe the other day by a few hours...........
 

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Any plans to make further mods to the motor since you are already takings the side covers off to drill out the vents?

I have seen a lot of people on Facebook that replace the phase wires with thicker gauge or shorten them and put on better copper phase connectors and upgrade the bearings to make these a little more stout for the higher wattage longer run time they like to push through them.

Also, I know you are probably still annoyed that your last vesc adventure ended with some fireworks last year (I'm annoyed for you) but there are now 2 new offerings at Flipsky that are supposed to handle 200 or 300 phase amps and have better thermals. Any temptation there or just keeping this one simple and staying with the components you have?
 
Hey MOK- astute observations... I did wrest the end caps off the motor a couple hours ago for drilling. Need to finish one up in the morning. No plans to do anything else to the motor other than as you suggest, optimize all major wiring to be as short as possible. Not the best or tightest winding job on the stator, but I did see the rotor was balanced with some blue epoxy compound on both ends. Thus far the stock bearings have been 100% cool for me on the other bikes.

Indeed I have in hand a shiny new Flipsky 75200 with nice rugged aluminum case. I'll be wiring that into the sidelined Blackcomb build within a few weeks. Word is that the latest vesc tool firmware has some upgrades from non other than that very bright fellow across the pond, mxlemming. That bike is also getting an ultralight integrated carbon handlebar/stem, and will be receiving nearly all of my attention soon.

I suspect these MY1020's could be pushed to their limit with the 75200 if one had active cooling. They're incredibly smooth running on the 75100 but need more amps for torque.

Finished the motor mounts. Disc brake and headtube next.
 

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Motor installed. End caps were more difficult to remove and replace than previous motors. Chain line is right on, and everything's rock solid.

Probably get the disc brake mounted tomorrow. Fairly easy since I traced the original dropout before cutting the tabs off. The relationship between the axle and those two bolt holes is critical. Like all of these mods, accuracy is paramount.
 

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Disc brake mount done.

I am stuck on the headtube mod. Trying to accurately file the ID of a short length of steel tube out by .084" is insanity... a lousy 10 minute job on my lathe that's in NY :evil: Have to find some hobbyist with a lathe here.
 

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:bigthumb: thank you! Brilliant!
 
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