Astral Rune build thread

[ferret]

Hi everyone.
This thread will document my new project. I will post photos and description of the process, feel free to ask if you want more details.

This build is based on a Banshee Rune V2 frame. This is the only frame I could find that ticks the following boxes:
* Modern high quality mountain bike with at least 160mm travel.
*BB width 73mm (or less).
*Rear dropouts width of 150mm (or more).

Bare frame:


The first stage of the project was building up the bike (human powered).
Complete bike:

 

[ferret]

Now the electric conversion can begin.

Chainring:
I used a Cyclone 73mm ISIS BB. Since I'm using it with standard ISIS cranks (with no freewheel), I need to turn some chainring spacers to get the correct chainline.

Spacers and assembled chainring:





Rear wheel:
I had a "Tophat" adapter made that mounts a 130mm BCD chainring to the rear hubs brake disk flange:



The 150mm rear spacing allows room for both sprocket and a standard brake caliper, although a custom caliper adapter is required.



View from back:

 

[ferret]

Motor and motor mount:

As you might have guessed, the motor chosen for the build is an Astroflight (3215 7T). Plates are used to mount it to the frame. They allow the motor to be moved for chain tensioning and they clamp it from both the front and the rear for effective heat removal.

 

[ferret]

Reduction:
The build uses a 2 stage reduction. A #25 chain connects the motor to to the "jackshaft" and a single speed chain connects the "jackshaft" to the rear wheel. The"jackshaft" contain a left hand freewheel and is floating on the BB spindle.

 

[ferret]

Chain management:

To compensate for the full suspension's chain growth I had to use a spring loaded tensioner. An additional pully is used to prevent the suspension interfering with the chain as well as to increase chain wrap around the small sprocket.

 

[recumpence]

Hmm, that adapter looks familiar. :wink:

Matt

 

[ferret]

Everything seems ok on the stand.

[youtube]Yb3w6CxgLME[/youtube]

Avner.

 

[ferret]

A few updates over the last year:





View attachment 3







Switching to sensored motor and controller made a huge difference when riding slow technical terrain.

Avner.

 

[whereswally606]

Hey Ferret,
Stunning build, a lot of features that are superbly thought out. I like the top hat style adapter for the rear sprocket and brake, the LHS jackshaft on the isis BB. Also, that's a nice touch using one of burtie's opto boards on a grin phaserunner. Its a great choice of frame too, thanks for sharing the build.

 

[ferret]

Thanks,
it took more than two year, but it's finally coming together. Slowly but surly

The Phaserunner made using Burtie's sensor PCB really easy to install. I simply glued it at a position where the wires will be shortest and the Phaserunner automatically detected the sensor angle relative to the winding. In most controller I would have had to find the angle the controller expects by a lengthy trial and error process.

Back when I started, it was hard to find a modern frame with "narrow" BB and "wide" rear hub spacing. Since then, Boost 148mm rear hub spacing became common so there are many other suitable frames.


Avner.

 

[DanGT86]

Nice work! Did you have to turn down the bottom bracket spindle?

 

[flat tire]

That's a nice build. Where will the batteries go??

 

[ferret]

I did turn down part of the spindle by a few hundredth of a millimeter.
The bearings I used for the freewheel adapter have the same dimensions as the BB bearings, which are pressed on the spindle. I wanted to be able to install and remove the freewheel adapter without using a puller or high temperature, so I reduced the diameter of the part of the spindle where the adapter is located so it would easily slide on and off.

The batteries (2x6s 12Ah Multistar Lipos) go in a backpack.
One of the reasons is to reduce the mass of the bike and allow it to handle as close to a human powered mountain bike as possible. The bike weights 20.5 kg and does not feel as nimble as my non electric mountain bike.
The second reason is that I used a battery box on my previous build and the batteries became deformed/squished, probably as a result of harsh landing from drops and jumps. I guess a ton of padding could have prevented that but it would have been very cumbersome.

Avner.

 

[bh4801]

Nice work!
I like how cleverly you attach to existing frame features, the freewheel spinning on crank spindle, the motor mounted to pivots.
I am curious as to your motor selection, it would seem the overall ratio is ca. 24, with 27.5 wheels, 145 Kv motor and 45V average battery your top speed should be ca. 35km/h.
I would have thought at 45V * 145 Kv = ~ 6300 rpm you are only taking advantage of 1/2 of the rpm band, and therefore 1/2 of the power band of the 3215?
Why not a lighter & cheaper 3210-5 ?
Is that correct? Is this how you planned it?

 

[ferret]

You are pretty much spot on with your calculations.

I mostly ride singletracks so I'm not too concerned with "powered" top speed. I reach my highest speeds using gravity by letting off the brakes going downhill without touching the throttle.

With the Castle controller on 12S "hot off the charger", the motor should reach about 7300 RPM. I check the rpm at "hot off the charger" voltage because I want to make sure not to exceed the rated rpm and explode the rotor. The motor is rated to 10000, I can get there by either adding cells or using the Phaserunner's field weakening feature. By raising the RPM (and/or by changing the reduction ratio) I could get higher top speed, but right now I don't feel the need.

Deciding on a motor frame size between 3205 and 3200 involves trying to guess how to trade off between cost and weight vs power potential and heat soak resistance. Fortunately didn't have to agonize over it. I had one constraint that forced my decision; the sensor PCB could only fit the 3215 (without extensive modifications).

I guess what I wanted is a "mountain bike on steroids" that will allow me to climb steep technical singletrails and be an alternative to shuttles and chailifts that take you to the top of mountains (which are practically non existent here). That is quite different from the commuters, cargo bikes, fast roads and fast trail bikes that many of the forum members are building. The is why my build has relatively uncommon features such as sensored Astro motor, low power direct drive with a rear disk brake and a small capacity battery in a backpack.

Avner.

 

[flat tire]

The batteries (2x6s 12Ah Multistar Lipos) go in a backpack.

Terrible idea considering you should be standing most of the time. Put them on the frame, it will be much better.

 

[ferret]

As I mentioned, I already tried both frame mounted battery and backpack mounted battery and prefer the latter.
Not trying to convince you or anyone, especially not knowing your riding style, I feel that a backpack is better for me for the following reasons:

* More nimble handling.
* Less impacts to the battery because in is suspended by the arms and legs.
* Battery weight is dynamic, moving with my body instead of being fixed to the frame.
* Easily replace battery with one of a different size or carry multiple batteries (without building a different battery box).
* Easily charge battery off the bike.
* In case of Lipo fire, backpack can be quickly ditched and won't burn down the bike.

Avner.

 

[neptronix]

Wonderful build!

 

[Deafcat]

Very clean work, well thought out and well executed.

 

[ferret]

Thanks guys!


Avner.

 

[armandd]

Nice build. I always wanted to build something like this! If I may ask, did you use this type of sprocket for the Astroflight RC motor?

 

[ferret]

Yes I did,
The Astro standard motorshaft diameter is 3/8" (9.375mm). IIRC I bought sprockets with 8mm internal diameter (http://www.staton-inc.com/store/index.php?p=catalog&mode=catalog&parent=45&mid=0&search_in=all&search_str=&pg=2) and drilled them out to 3/8".

Avner.

 

[armandd]

Yes I did,
The Astro standard motorshaft diameter is 3/8" (9.375mm). IIRC I bought sprockets with 8mm internal diameter (http://www.staton-inc.com/store/index.php?p=catalog&mode=catalog&parent=45&mid=0&search_in=all&search_str=&pg=2) and drilled them out to 3/8".

Avner.

I see, thanks.. What kind of throttle did you use?

 

[ferret]

Using the WUXING 108X (on the left side).
After running it stock for some time, I shortened the lever with a grinder to get less linear throw and more sensitivity.

Happy with it.

Avner.

 

[afzal]

[necroing this to avoid derailing another thread where you posted recently]

Why did you prefer a mid-drive instead of hub motor for a single speed transmission?, to have a lighter motor ?