8Fun CST 250w and 350w, what is the difference?

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by d8veh » Jul 15 2013 3:43am

The standard CST spline allows 40.2mm for the cassette between the motor side-plate and the inside of the drop-out. I have a 9 speed on mine. I think I had to add a washer to get the top gear clear of the drop-out, but different cassettes have different stack-heights, so you need to measure yours. Whatever size it is, you can always fit washers.

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by friendly1uk » Jul 15 2013 7:48am

I have a 500w cst in a 135 frame. I had to leave out one of the tabbed washers and spread the frame a few mm. I have a nut actually sitting on the inside of my dropout without the protection of a washer. It's a bit undesirable, but OK. IIRC 142mm would of accepted all the right washers. A tabbed washer lost was 5mm gained though. I couldn't use the weather proofing on my cassette either, as the tabbed washer occupies the same space. My cassette is just open ended now. To do the job right a 150mm frame would be better.

I thought about taking the nut off the motors non drive side and trimming it down. I was in a hurry though..

No hope at all of using a disc with my frame.
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Re: 8Fun CST 250w and 350w, what is the difference?

Post by merganser » Jul 16 2013 7:01am

I'm very glad I saw this thread before I ordered my 500W CST from BMS Battery - it wouldn't have occured to me that it might not fit 135mm dropouts. In the end I decided to risk it but I have also ordered a 500W BPM as well as a backup in case the CST won't fit my frame.

I'll report back with the dimensions when it arrives.

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by d8veh » Jul 17 2013 3:52am

merganser wrote:I'm very glad I saw this thread before I ordered my 500W CST from BMS Battery - it wouldn't have occured to me that it might not fit 135mm dropouts. In the end I decided to risk it but I have also ordered a 500W BPM as well as a backup in case the CST won't fit my frame.

I'll report back with the dimensions when it arrives.
I've fitted three 500w CSTs and one 350w one, and they all dropped straight in to 135mm drop-outs. I'm not sure where the idea about 150mm width came from, but it's wrong, as you'll find out when you get yours.

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by merganser » Jul 17 2013 1:32pm

Is it possible the earlier ones were wider?

Anyway, I hope you are right and it does drop right in.

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by chas58 » Jul 17 2013 1:59pm

hmmm. Friendly1 just got his a few months ago. I'm not sure why D8veh and freindly one had different experiences.

odd...
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Re: 8Fun CST 250w and 350w, what is the difference?

Post by d8veh » Jul 18 2013 3:13am

Here's a drawing of it directly from the Bafang website that clearly shows 135mm between the drop-outs:
http://www.szbaf.com/uploadpic/201110171606401.jpg

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by friendly1uk » Jul 20 2013 7:26am

That's not my motor. I just checked a couple of dimensions.

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That should be 33.4mm, and it's not even 31
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Re: 8Fun CST 250w and 350w, what is the difference?

Post by merganser » Aug 07 2013 6:39am

My 500W CST has just arrived and a quick & not very accurate measurement of the OLN dimension shows it is less than 135mm without the torque washers fitted, I'd say it will probably be 135 - 136mm with them fitted. It certainly isn't 150mm though.

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by NiToNi » Aug 23 2013 6:50pm

I would like to use this motor on my build but only if it can take a 10 spd cassette and still fit a 135 mm dropout. Stretching my aluminium frame by even a millimeter is not an option.... I dont care if the largest sprocket is up so tight against the motor I can't use it, but want to be able to use the 11T obviously.

Also, how much power can this motor take compared to say an upgraded MAC? On 52V (15S), would it cope with 30-40A (1500-2000W)?

What would be a killer controller for this? Would Paul's (cell_man) Infineon controllers work? What are these torque simulator controllers sold by BMS battery - gimmick or good?

Batterbikekit.com is selling the CST in two different velocities, 25 and 30 km/h. What RPM do these correspond to? I thought the CST came in 270 rpm only.

What's drag like, especially compared to the MAC?

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by d8veh » Aug 25 2013 5:26am

The 500w CST is 270rpm. The 250w and 350w ones are slower.

If you can't sretch your frame by even 1mm, you'll struggle to find any motor that'll fit. There's nothing wrong with stretching a 262 wheel frame 25mm or more. Why is yours different?

The 500w CST can run happily with 30 amps at 36v and 25 amps at 48v.

Drag with geared hub-motors is a myth from the past.

Why do you need to fit a 10spd cassette if it doesn't matter if you can't use the bottom gear?

The size between the drop-outs of the Bafang CST is 135mm with a space of about 38mm for a cassette. If the stack-height of your cassette is larger than that, you need to fit spacing washers on the axle, and you need to stretch the frame by a corresponding amount.

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by NiToNi » Aug 27 2013 7:49am

Thanks Dave. Sorry for not replying sooner, I was away over the bank holiday weekend.
d8veh wrote:Drag with geared hub-motors is a myth from the past.
Great, good to know.
d8veh wrote:The 500w CST can run happily with 30 amps at 36v and 25 amps at 48v.
So about 1100-1200W then. What speed (loaded) would be achievable at that power (15S) you think with a 29er? Do you think the CST 500W could even take 1500W continuously? What is the best controller available to go with this particular motor?
d8veh wrote:Why do you need to fit a 10spd cassette if it doesn't matter if you can't use the bottom gear?
It is not about the number of gears per se but compatibility with my existing 10-spd drive train.
d8veh wrote:The size between the drop-outs of the Bafang CST is 135mm with a space of about 38mm for a cassette. If the stack-height of your cassette is larger than that, you need to fit spacing washers on the axle, and you need to stretch the frame by a corresponding amount.
I've read that the standard width of 10-speed cassettes is 37.5mm, is that correct? If so, 38mm sounds like it would be OK. You indicated however in a previous post that the space available could be up to 404 mm, or is that wihout any clearance the 11T cog and the dropout?
d8veh wrote:If you can't stretch your frame by even 1mm, you'll struggle to find any motor that'll fit. There's nothing wrong with stretching a 262 wheel frame 25mm or more. Why is yours different?
Well, as I'm sure you are well aware, stretching aluminum alloys can result in metal fatigue. If this was not an issue, I think I'd just go with a MAC 1000W + DNP 10-spd freewheel (138-139 mm) to get the 30 mph I'm looking for.

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by majornelson » Aug 27 2013 10:07pm

I installed a MAC 500w from Paul on a standard 135mm aluminum frame with a nine speed hub (which added an extra 3 - 4 mm). No issues so far and I have almost 1,000 miles on the bike (new Trek 8.4 DS). Goes 35 mph max and can cruise at 30 mph. At 22 mph I get over 60 miles on the 18,5 AH triangle battery.

I wouldn't worry about a 3 - 5 mm spread on an aluminum frame. However, a rear torque arm is key. Paul has the Grin torque arms...
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Re: 8Fun CST 250w and 350w, what is the difference?

Post by lollandster » Aug 27 2013 10:19pm

I didn't buy the 8Fun CST so i can't say how that works with 10speed, but I did buy a qute q100 cst and that needed extra 2mm for both standard 8 speed cassette and my 10 speed Dynasys cassette. The 10 speed cassette isn't much bigger than the 8 speed, the gears are closer and it uses a special narrow chain.
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Re: 8Fun CST 250w and 350w, what is the difference?

Post by majornelson » Aug 27 2013 10:28pm

Funny, I just received the Cute Q100 for a city bike I have today. I'll have it installed in the next week or so...

I bought the 36v version but plan to use a 48v Lipo battery (I have a very short 2 mile one-way commute and will be attempting to use a 5 Ah battery).

It will be interesting to test it against the MAC motor. Very different configurations with different goals for me.
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Re: 8Fun CST 250w and 350w, what is the difference?

Post by d8veh » Aug 28 2013 4:14am

NiToNi wrote: So about 1100-1200W then. What speed (loaded) would be achievable at that power (15S) you think with a 29er? Do you think the CST 500W could even take 1500W continuously? What is the best controller available to go with this particular motor?

I've read that the standard width of 10-speed cassettes is 37.5mm, is that correct? If so, 38mm sounds like it would be OK. You indicated however in a previous post that the space available could be up to 404 mm, or is that wihout any clearance the 11T cog and the dropout?

Well, as I'm sure you are well aware, stretching aluminum alloys can result in metal fatigue. If this was not an issue, I think I'd just go with a MAC 1000W + DNP 10-spd freewheel (138-139 mm) to get the 30 mph I'm looking for.
15S would give a speed of about 37mph, which I think is too fast for the power. Sustained 25mph would be about the limit of this motor, so I think 12S at 25 amps would be enough.

I did a bit of research,and found out that 10spd cassettes are the same width as a 9spd. I have a 9spd, which went on without significant frame adjustment.

Stretching aluminium can't cause metal fatigue. Fatigue comes as a result of changing stresses, not constant stress. The stresses in your frame in the vertical direction are massive compared to a bit of spring in the lateral direction. If you're worried about stress, you should think about that; but of course there's nothing to worry about because your frame can resist all those stresses without fatigue. Looks like you can get a MAC then.

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by NiToNi » Aug 28 2013 12:03pm

majornelson wrote:I installed a MAC 500w from Paul on a standard 135mm aluminum frame with a nine speed hub (which added an extra 3 - 4 mm). No issues so far and I have almost 1,000 miles on the bike (new Trek 8.4 DS)... I wouldn't worry about a 3 - 5 mm spread on an aluminum frame.
d8veh wrote:Stretching aluminium can't cause metal fatigue. Fatigue comes as a result of changing stresses, not constant stress. The stresses in your frame in the vertical direction are massive compared to a bit of spring in the lateral direction. If you're worried about stress, you should think about that; but of course there's nothing to worry about because your frame can resist all those stresses without fatigue.
OK, seems like this issue has been widely overexaggerated then.
lollandster wrote:I did buy a qute q100 cst and that needed extra 2mm for both standard 8 speed cassette and my 10 speed Dynasys cassette. The 10 speed cassette isn't much bigger than the 8 speed, the gears are closer and it uses a special narrow chain.
d8veh wrote:I did a bit of research,and found out that 10spd cassettes are the same width as a 9spd. I have a 9spd, which went on without significant frame adjustment.
Thanks, it is my understanding as well that the 10-speed cassette is not really any wider than a 9-speed cassette. So although the CST specs say maximum 9 speed, I guess I can safely assume a 10-speed will fit too (the XOFO clone specs 10 spd btw).
d8veh wrote:15S would give a speed of about 37mph, which I think is too fast for the power. Sustained 25mph would be about the limit of this motor, so I think 12S at 25 amps would be enough.
OK I hear you. Any particular controller you would recommend? The S12S looks interesting, have you tried it with the CST? However, I can't seem to find any info on how many amps it is capable of.
d8veh wrote:Looks like you can get a MAC then.
I thought so but the next issue seems to be with the fitting of the disc calipers... sigh.... is this an issue also with the CST? If not, I think that would seal the deal for me....

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by majornelson » Aug 28 2013 12:14pm

thought so but the next issue seems to be with the fitting of the disc calipers... sigh.... is this an issue also with the CST? If not, I think that would seal the deal for me....
FWIW, my bike uses a disc on the MAC 500w motor. I had to shim it using washers but there are shims available from Amazon or from ebikes.ca. The discs make any motor installation a PITA, I think. Or at least mine was until I figured out the washer approach *and* found the adjustment screws on the calipers. :)
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Re: 8Fun CST 250w and 350w, what is the difference?

Post by majornelson » Aug 28 2013 3:33pm

You can't see the washers (took 3 on each screw and I have to get longer screws) but you can see the disc- also a torque arm.
torque.JPG
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Re: 8Fun CST 250w and 350w, what is the difference?

Post by d8veh » Aug 28 2013 3:45pm

The BMSBattery S12S is 23 amps, so OK at 48v, but a bit low for 36v. Whatever motor you have, sorting out the brake is easy. You need a disc of at least 180mm. If your bike had 160mm, then you get a 160mm to 180mm adapter. You then remove the caliper, put the anti rotation washer in place and bolt up the axle on that side. Slide the caliper onto the disk, and look to see whether the holes in the caliper line up with the adapter. You have to try to get it central by putting in/taking out washers from behind the anti-rotation washer. You then space the gear side appropriately, which normally means springing the frame a bit. Next, look at the position of the rim, which is now typically off-centre to the frame, so you dish the wheel by loosening the spokes on one side and tightening them on the other by the same amount. You go round 1/2 a turn at a time.

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by NiToNi » Sep 05 2013 3:39pm

Thanks, Dave.

You have me convinced, I will order a CST 500W from BMS Battery asap.

So on to spokes..... are you sure the drawing of the CST 500W is the correct one? Reason I'm asking is that there seem to be a few different drawings floating around, for example this one:

http://m.alibaba.com/product/917618517/ ... wheel.html

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by d8veh » Sep 06 2013 3:09am

NiToNi wrote:Thanks, Dave.

You have me convinced, I will order a CST 500W from BMS Battery asap.

So on to spokes..... are you sure the drawing of the CST 500W is the correct one? Reason I'm asking is that there seem to be a few different drawings floating around, for example this one:

http://m.alibaba.com/product/917618517/ ... wheel.html
I've no idea whether that drawing's correct. All I know is that I use 210mm spokes with the BMSBattery rim in a 2-cross pattern. Working backwards using a spoke calculator gives the rim an ERD of 539 to 540mm, not the 515mm that BMSBattery have on their website, which must be a mistake

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Re: 8Fun CST 250w and 350w, what is the difference?

Post by friendly1uk » Sep 06 2013 5:28am

BMSbattery sent me 186mm spokes to put the cst in to there wheel rim. They claimed it is what they use, but they didn't reach. They were 5mm too short. Many wheel build sites say to ignore the specs and measure yourself. I found the cst spoke holes draw a 165mm circle which has been said by others. I missed what rim you are using though. Not theirs I hope. I ordered two but didn't use them. They looked like they belong on a racing bike, not one likely to hit holes with a lot of energy. Prolonged use by others has shown the spoke holes crack in a couple of thousand miles.

I run the 500w cst with 44.4v(12s lipo) and 15 amps. 26" wheels take me to 27mph with next to no pedal effort.
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Re: 8Fun CST 250w and 350w, what is the difference?

Post by -dg » Sep 06 2013 8:03am

d8veh wrote: Stretching aluminium can't cause metal fatigue. Fatigue comes as a result of changing stresses, not constant stress. The stresses in your frame in the vertical direction are massive compared to a bit of spring in the lateral direction. If you're worried about stress, you should think about that; but of course there's nothing to worry about because your frame can resist all those stresses without fatigue. Looks like you can get a MAC then.
This is not quite correct, especially in the case of chain stays. The bottom bracket moves around a lot due to pedaling forces which puts a lot of twisting and bending stress on the chainstays. Almost all bikes have a bridge between the chainstays a couple inchs behind the bottom bracket. This is not just a handy place to mount a fender, especially on bikes that don't commonly get fenders. It is there because bikes that don't have a bridge break the right chainstay off at the bottom bracket. The bridge distributes the load to both stays. But, it also fixes the the angle of the forward part of the stay. That is, when you spread the stays it bends right at the bridge which puts a lot of stress in a small already highly stressed area. While the stress from spreading the stays is static, the pedaling stress is not and the combination is not. One can get away with "re-spacing" a steel bike because you actually bend the stays so that they are not stressed in the new position. It would not work even with steel if you just spread the stays and shoved the wheel in.

I suspect a couple of millimeters of bend is ok, at least there are some bikes made with 132.5 mm spacing so you can use either 130 or 135 mm spaced wheels. I would not trust more than a couple mm of stretch though.
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Re: 8Fun CST 250w and 350w, what is the difference?

Post by d8veh » Sep 07 2013 6:26am

If it really bothers you, you can push the frame beyond its elastic limit quite easily. Then there's no stress. I did this one by putting a foot on one side and gave a good tug on the other. you only get one chance because of work-hardening, so you have to judge how far to tug.
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