Cute 128 BB drive on a Surly 1x1

[Qwiksand]

I bought a couple of the Cute 128 motors from BMSbattery last year with the intention of building a bottom bracket driven set-up (or two); a year later and I finally got a little time to start work on the project. This first build is a test sled of sorts, to work out the kinks and see what needs to be improved as I'd ultimately like to power my Kona Stinky with a small geared hub running either a BB drive or some jack shaft variant. The frame is a 22" Surly 1x1 I picked up on closeout from one of the big online bike stores a while back. I didn"t take any before pics of the bike, but it looked a little something like this.



I stripped the orange paint (well, most of it) and then welded a 1 1/4" square tube to use as a mounting point for the hub motor. Don't look too close at these welds, they're ugly enough to blind ya! I was a little nervous mig'ing the 1/16" thick square tube to the THIN walled cromo frame.



When I started this build a couple weeks ago, I was using simple U-channel I bent out of 1/8" x 1 1/4" bar stock to hold the hub motor as a mock-up. I decided to try running it under power with this design, but It quickly bent and derailed the chain. so back to the drawing board I went and came up with this monstrosity.





Weighing in just shy of 2 lbs.



There's two axis of adjustment built in: fore/aft and right to left.





Here's a couple pics of the motor I'm using. That's a 17 tooth sprocket bolted on. I used the three side bolts and shimmed the sprocket out with some washers.





Weighs in around 6 lbs 6 ounces.



I've used u-bolts and electrical conduit straps to mount controllers and battery boxes to frame tubes on prior builds, but was never really happy with the result. So I decided to try building my own. I picked up several different inside diameter sized pieces of cromo tubing from aircraftspruce. The idea is to chose a tubing size for your clamp that just fits around your frames tube. To illustrate the process, this is how I made my battery mounts.

I cut a 2" piece of tubing and then used a jig I made to mount some 3/8" tubing (for the bolt holes) perpendicular to the main tube.







I then ended up with these (the 1" version I use to mount the controller to the seat tube).



I cut those in half, as well as cut-off a couple M6 x 1.0mm bolts.



I then cut a few slots in the smaller bolt tube so I could get a little better bite on the stud with the welder.



I put the other half of the clamp on to make sure it'll fit after welding and then hit it with the mig.





To make the battery holder part, I used 1/8" x 3" flat bar and drilled some holes in the corners to hold a couple u-bent bars.





I tacked the bottom of the u-bend into the flat stock from the underside to leave a clean surface for the batteries.



With the clamp mounted to the battery holder.

[neptronix]

Nice! Lots of ingenuity here.. Watching..

[spinningmagnets]

I'll be very anxious to read the final performance numbers. The Cute motor is considered somewhat small for a hubmotor, but as a BB-drive I believe it may be a great size, since the motor will have the bikes gears to help keep the motor RPMs up.

I really like the process by which you made the brackets, and I very much appreciate the way you set the order of the pics to show that.

[amberwolf]

Definitely a good post on how to go about doing this; the pics and order are a huge help to those wishing to emulate it.

[recumpence]

It is good to see some unique innovation. I agree, that is a small (read weak) motor, but through the gears, it should be a really good performer, light weight, and overall a good reliable performer. Also, with minimal power, the freewheel on the crank should survive just fine.

Matt

[Qwiksand]

Thanks for the replies and feedback, guys! The goal for this build is better weight distribution coupled with higher efficiency and range. With the controller I'm using (22 amp limit, but spikes to 25 amps), this motor run on 37 volt nominal batteries (10s konions from fatpacks) will peak around 900 watts.

I used a rough estimate of 255 maximum unloaded Rpms for the motor and then calculated crank Rpms using 204 Rpms (80% of 255). With a 17 tooth motor sprocket and a 48 tooth crank sprocket, I get a reduction of 2.82:1 or a crank rpm/pedal cadence of approximately 72. That's a comfortable pedal cadence so I'm hoping for a bit better efficiency than I was seeing from my 9c rear at the same power level. I'll provide data when I have it.

[RWP]

I like it - very nice work!

[DAND214]

If those Cute 128's are a year old, you will be amazed how stong they are.

The new ones are the weak ones with single reduction gears. the old ones had double reduction gears and were mush more powerful than the newer ones.

Wish I could find gears for the older ones.

As for the build, IT ROCKS! Can't wait to see it in action.

Dan

[Grinhill]

Great work!

I love the tubing clamps, and that is some very fine welding on them too!

[Whiplash]

YES! The clams are very slick! Easy way to get it done!

[Qwiksand]

Got some spacers (4mm length, 10mm width, 5mm bore) and shorter (button head) headed screws for the sprocket mount from Mcmaster.



I had to enlarge the flat mounting area around the 3 bolt holes to fit the washers I was using as spacers (used a router bit in the drill press- isn't pretty, but it works). With the new spacers, I don't think I would have needed to butcher the case.



This little piece of angle iron adds a bit of torsional rigidity to the motor mount and acts as a place keeper of sorts when you remove the mount from the bike. As long as you don't touch the angle iron, you don't need to realign the motor sprocket to the chainring.





Mounted back on the bike.



This is the controller and wire hiding box attached to the seat tube- used clamps like shown in the first post.





This is the battery all mounted up and secure. This is a 10s4p pack of konian cells, my bigger pack died (I abused it, left it plugged in to the controller last summer and it finally died). I'll be upgrading to lipo in the near future and will probably mount the majority of the pack to the down tube, just in front of the motor assembly.



And here she is fully assembled and in operating condition. Weighing in at 53 lbs 6 oz.

[Qwiksand]

I installed a Cateye Astrale 8 bike computer, it has a cadence function that is perfect for my application.

Some quick data:

No load RPM at the cranks- 90 rpm
No load max rear wheel speed (44t chainring, 11t rear sprocket @90rpm)- 28.5 mph
No load amp-draw in low gear (34t rear sprocket)- 1.3a
No load amp-draw in high gear (11t rear sprocket)- 2.0a

I've only run it around the block without the computer so no real world data yet.

[Whiplash]

VERY clean! I love it! How is the torque in low gear and what's the low gear top speed??

[spinningmagnets]

This is a GREAT project. Thank you for posting this. If somebody wants raw power, its not hard to just throw a lot of money at a bike. The great thing about an efficient set-up is that you can get the same miles from a smaller, lighter, and less expensive battery pack. Plus by giving the motor some gears, it keeps the controller and motor heat down.

The only performance compromise IMHO is that you have to slow down (downshift to keep motor RPMs up) to tackle a steep hill with a smaller motor, but what is great is that, you CAN still tackle a hill with a smaller motor. Great hill climbing and you can still do 30-MPH on the flats...

[Qwiksand]

VERY clean! I love it! How is the torque in low gear and what's the low gear top speed??

Torque is ok, but not phenominal. It is difficult to stop the rear wheel and it will pull a wheelie, but it needs a little crank input from the rider to get the front wheel off the ground. I'm sure torque could be increased easily by dropping the tooth count on the drive chainring, but I'm more interested in cruising speed with this build- lots of flat here in the DC metro.

Low gear unloaded top speed is 9.4 mph (90rpm, 44t chainring, 34t rear sprocket).

[Whiplash]

Thanks! I am trying to figure out my gearing for my MAC mid drive build...