Cromotor + MethTek Monster 24FET + 20S lipo build

[hjns]

Some stills of my commute this morning. I will upload an edited version of the movie into Youtube later this week.

 

[hjns]

And another nice view of this morning's ride.

 

[Alan B]

Modding these controllers to bypass the limits has its risks.

I take issue with the phrase "bypass the limits". ...

-methods

My apologies. No disrespect intended.

I thought the factory design of these controllers shut them down as soon as the current exceeded the design by some amount (regardless of programming), the shunt voltage triggering a hardware shutdown and so it was necessary to change the shunts to prevent this, bypassing that safety feature (or at least moving it to another (less safe) level.

It looks like a great controller, I was going to get one but they were all sold before I knew they were actually available.

 

[hjns]

The cold weather (between -5 and 2oC) is affecting my lipo performance severely. In this weather, with a 2kW draw, I have a voltage drop from 84HOC very quickly to LVC at 72V.

In the graphs, you can see that my bike is stored in our wintergarten at around 3oC, as the motor thermistor is nicely showing. Battery voltage starts around 82-84V, and within a couple of minutes decreases to a maximum of 78V, and a minimum of 72V, which is dictated by the CA. In the kWatts graph, the power is limited to just above 2kW. NOT because I set a power limit of 2kW, but because if I want to apply more power, the lipo voltage wants to drop to lower than LVC (72V), which is then inhibited by the CA.

It's not that bad to drive around with only 2kW, because it is a bit slippery, and even with only 2kW, I get to speeds of 50-60kmh.

 

[John in CR]

Since your battery starts off nice and warm, wouldn't a nice layer of insulating wrap help it maintain capacity with the internal resistance helping to maintain a pack temp closer to the toasty 30°C ? Some big bubble wrap from shipping seems like just the ticket and give the pack some extra protection in case it hits the ground in slippery winter conditions.

 

[hjns]

Hi John,

Good idea. I like some passive methods to keep the lipo's warmer. I am hesitant to try out something more active that generates heat around lipos.....

 

[John in CR]

Hi John,

Good idea. I like some passive methods to keep the lipo's warmer. I am hesitant to try out something more active that generates heat around lipos.....

+1. I don't even like the sun shining on my lipo enclosures. I'll leave the cold to you guys though. Snow is for winter vacations, and I'll stick with temps always in the 20's C, IOW a nice spring day every day.

I take it that you have to use spikes on your tires and all that stuff?

Stay warm,

John

 

[Lebowski]

Hi John,

Good idea. I like some passive methods to keep the lipo's warmer. I am hesitant to try out something more active that generates heat around lipos.....

+1. I don't even like the sun shining on my lipo enclosures. I'll leave the cold to you guys though. Snow is for winter vacations, and I'll stick with temps always in the 20's C, IOW a nice spring day every day.

I take it that you have to use spikes on your tires and all that stuff?

Stay warm,

John

-------------------------------------------------- :wink:

 

[hjns]

+1. I don't even like the sun shining on my lipo enclosures. I'll leave the cold to you guys though. Snow is for winter vacations, and I'll stick with temps always in the 20's C, IOW a nice spring day every day.

I take it that you have to use spikes on your tires and all that stuff?

Stay warm,

John

Agreed, no sun on my Lipos. However, my lipo enclosure is good. A couple of months ago, I have tried putting the enclosure in the sun with the lipos inside. Enclosure got real hot, almost too hot to touch. Lipos were nice and cool inside though.

Snow is fun. At least, to me. I just don't like rainy cold days. Give me snow and sun anytime.

I will start using my spikes when I really need them. Probably only in January....

 

[hjns]

Commute this morning.

 

[hjns]

 

[hjns]

Look at the temperatures. I never had to pay attention to any possible overheating. The CAv3 really kept the motor below 100oC. I may want to change the treshold to a slightly less conservative range. Now it is "standard" at 90-130oC. However, the analogger says that the motor never became warmer than 100oC. Therefore, I will set the cutoff range from 110-130oC. We will see what happens.

 

[hjns]

voltage shows a different story.

I used the first part of the charge to get from my home to Hofstetten. Therefore, starting voltage is already low to 76V at rest (3.80V cell level). What is then very obvious, is that battery voltage slowly drops down to 72V (3.60V cell level) during which most of my power is being delivered. After that there is a steep descend down to 66V, which was my LVC set in the CA for this trip. Note that I do NOT recommend people to go down to 3.30V cell level with LiPo, unless you are sure they keep balanced and will not overcharge when charged again. After I got home, cells were perfectly nice at 3.3V (+/- 0.05V). Total used Wh was 850Wh out of a total battery capacity of 1kWh (11.5Ah out of a total of 13.5Wh).

The voltage graph and the power graph show that the combination of the temp limiting and LCV has a big impact on performance. Whereas initially, I could request 6kW, it quickly went down to 3kW after the motor started heating up. After that, I still frequently hit the LVC and therefore was limited to less than 2kW. After resting voltage was around 72V, I hit LVC more and more often, until there was no power left above 66V. I had to pedal the last km with support from the motor of less than 100W.

 

[Lebowski]

With the weather being better, maybe soon we can try my controller ?

 

[hjns]

Most definitely, Lebowski. I also have Zomies 24FET4115 controller in, so I can start rewiring my bike for testing. I also probably want to start using the external shunt again, so that I don't have to recalibrate everything while testing different controllers.

 

[hjns]

When going downhill (literally), it is very clear that this is a very heavy bike with a heavy rear wheel. Where my trusty rear Avid Juicy 7 and new front Avid Elixir 9 with 203 disc would have sufficed a lighter bike, now I was wishing for a bit more breaking power, especially for the rear. I did some research, and found this review from BikeRadar that showed the Formula R0 to have the strongest break strength (124Nm). My Elixirs come in at 99Nm (Juicy's were not tested), so theoretically it should be an increase of 25% in brake power. I hope it justifies the price difference.....

Some other threads have mentioned the Gatorbrakes, but unfortunately they were not tested either, and I am hesitant as to obtaining pads and parts.

 

[MadRhino]

Rear brake doesn't need to be very powerful, especially DH when the rear is unloaded and very easy to lock.
The true advantage is modulation in those circumstances, you should be comparing models for brake pad surface size and lever adjustment options. Precise braking and independent regen button are doing miracles for the tail.
Next is custom tuned rear suspension to match the weight of your wheel.

For the front you need a lot of braking power, after all it is all the weight of the bike and yourself that is going there when you do a quick stop. Heat dissipation, modulation, system volume and piston pressure, you need them all for this one.

 

[hjns]

Rear brake doesn't need to be very powerful, especially DH when the rear is unloaded and very easy to lock.
The true advantage is modulation in those circumstances, you should be comparing models for brake pad surface size and lever adjustment options. Precise braking and independent regen button are doing miracles for the tail.
Next is custom tuned rear suspension to match the weight of your wheel.

For the front you need a lot of braking power, after all it is all the weight of the bike and yourself that is going there when you do a quick stop. Heat dissipation, modulation, system volume and piston pressure, you need them all for this one.

Hi MadRhino,

I will bow to your experience. Note that I already disabled regen altogether. And it is not the "quick stop" that I am looking for, but going DH relatively fast. Therefore, maybe you can explain to me the following?

I am not really a fast nor experienced DH person, I just take the occasional DH trail when I see it, and would like to go faster than I do now. When going downhill, I find it easier to control the speed of my bike by modulating BOTH front and rear wheel. I tend to use the front brake less than the rear for fear of losing traction and then slide. I find that I need to modulate both rear and front in a different way, to prevent locking but still being able to reduce the speed as appropriate.

The physical mass of the rotating rear wheel makes modulation of the rear brake very heavy and near impossible. With my rear Avid Juicy 7, there is this relatively light braking for a long time and then suddenly the rear wheel locks up. Although I agree that the rear wheel in theory is "unloaded", I find the rear wheel with its 10kg motor is actually quite loaded even when going down a steep slope. According to all MTB rules, I have my weight completely over the rear wheel, and the addition of the motor in the rear wheel means that it seems I should be able to apply significant braking power to the rear wheel. But maybe I am wrong? I also find that even with a locked rear wheel, I am able to navigate loose ground like loose stones or leaves.

With my front Elixir 7, modulating is fine from light to moderate braking, but even with broken-in pads it is difficult to really lock the front wheel, which I find not that much of a problem. I do wish for more modulation when heavy braking. It may be that I need to bleed it in order to be able to modulate even better when braking heavily?

Regarding the rear suspension, I would assume that custom tuning is only of value when the rear keeps losing traction due to it jumping around at high speeds. At this moment my 7.5" Fox Float RL does the job in keeping the rear wheel in contact with the ground, so I may be just a DH beginner here.

 

[MadRhino]

This is about how you ride and how you are using brakes.

If you keep braking long stretches, no bicycle brake is enough to shed the heat, and when a brake is too hot it doesn't work fine anymore.
If you use the brakes in bursts, quickly decelerating before a turn or obstacle, then release and accelerate ASAP; many brakes can do the job and selection is a matter of personal preference among the good brakes available.

As for traction, a heavy hub is too much for most bike suspension systems to control the rebound.
Lift your bike 2 ft and let it fall on its wheels. If the wheel bounces more than twice, you need to set a slower rebound. If your wheel is spending 5% more time on the ground, that is 5% more time available to effectively play with the brake. Also, when the wheel leaves the ground it has no more rolling resistance and is likely to lock if you are braking when it happens. Suspension tuning plays a big part in braking and cornering performance, and the faster you ride the more important a factor it is.

PS: If you ride with your weight on the tail, you are losing front traction and average speed. Shift your weight on the tail before a hit or hard braking, to the front in hard acceleration, keeping it in the middle otherwise.

 

[hjns]

Thanks, MadRhino. I need to try and follow your advice before I can write anything useful about it. Short strong braking instead of long continuously and trying out a 2 feet drop is my take home message.

 

[MadRhino]

Not taking a 2ft drop with the bike, dropping the bike alone from 2ft high to check the rebound. :wink:

 

[hjns]

These just came in (front and rear): 203mm Formula rotors and Formula R0 "oval piston" brake calipers.

 

[hjns]

First commute with the Formula R0 and 203mm rotors. It is really really amazing. Controlled stopping power from 45mph (74kmh) within a couple of meters using just one finger on each brake handle. When modulating, they make this nice whoozing sound. In the wet, my front brake squealed a bit, but less so than with my Elixir. Absolutely amazing. I can go faster, because I can brake better. Traffic, in the woods, you name it. Super! And the calipers look sculpted and blink....

Conclusion: Expensive, but you get what you pay for, and they are really much better than my Juicy 7 or Elixer. If you have the money, go get them.

 

[hjns]

Got Premiere working. I uploaded this 2m50s sequence of 900Mb at highest quality (h.264 MP4 1920x1080p 29.97fps 48Mbps) but I am still not happy with the quality produced by the Youtube encoder when going full screen. Anyone any ideas how to improve quality? Sorry, no music yet.

[youtube]8Wr1NGWkeAU[/youtube]

 

[MadRhino]

...I am still not happy with the quality produced by the Youtube encoder when going full screen.

The vid quality is very bad, even for low resolution. Compression level too high, obviously.
Was this vid neat before uploading to Youtube ?