Wow. Again, I really appreciate everyone taking the time to share their experiences here.
A few people have mentioned various direct-drive motors by referring to part numbers in the format of "2810" and so forth. I do understand what this system of measurement means (width x windings) but one thing I've always wondered, and never been able to get an answer on, is what the equivalent size of the Amped direct-drive motor is, as that's my only real-world basis for comparison in such matters...
chroot wrote:Here another MAC 10T tested by Hightekbikes at 20% grade hill in SF so 12T will be more faster climb up the hill at ease than on 10T MAC. Here the video show
Chroot, this video is the single most convincing thing I have seen thus far. That is actually similar to the area in which I live, although our hills are not quite as severe. If a 10T motor can climb that incline on 48v at 1,5kw (which would make it a 30A current draw) then I suspect this is probably the motor / controller combination which I need. Thank you.
GMUseless wrote:If you are staying under 60V, you really don't need the 4110 fets...the 3077s will run better (less heat) at that voltage....and they cost less.
Well, I'd like to leave my options open for the future. And, to be honest, the difference in efficiency between the 4110 and the 3077 should be so trivial as to be immeasurable.
Looking at the International Rectifier's datasheets for the two devices, the 3077 has a maximum steady-state RDS(on)
of 3.3mΩ as compared to 4.5mΩ for the 4110, and the VDS
and recovery curves appear virtually identical. So if we assume a constant 30A load, then in a worst-case scenario the 4110 would dissipate 4.05 watts at a forward drop of 0.135 volts vs the 3077 at 2.95 watts at 0.099 volts. (Granted, current in a polyphase inverter is not steady-state, however I assume that the operating frequency of the device is so low as to be functionally indistinguishable from DC to a device whose rise and fall times are well under 100ns, and whose dynamic properties are specified in the Mhz range.)
I think I can live with 1.1 watts and 0.036 volts.
o00scorpion00o wrote:cell-mans triangle battery and bag might be worth the extra money if your triangle can take it ?
Huh, I didn't even realized he offered one. I planned to take the measurements of the triangle battery with me when frame-shopping, however. Worst-case I can always go with a rectangular pack and hang it off the front tree or beneath the rear cargo basket.
o00scorpion00o wrote:How would you feel about LiPo ? IF you don't know much about it I would stay clear, but the reason I asked is because the 12T would probably give you only 15 mph on 48 volts, so I would go with 60 volts.
Well, I have no first-hand experience with it, as I've never been an R/C enthusiast. My knowledge of LiPo basically consists of:
- Single-cell prismatic LiPo batteries in consumer devices (eg: cell phones) tend to be reliable at extremely low c-rates.
- Multi-cell LiPo packs sold to the hobbyist community tend to be of variable quality, burst into flames occasionally, and scare me.
Given the relatively good availability of LiFe battery packs, I'm not really considering LiPo.
o00scorpion00o wrote:The other thing about the 10-12T is how fast will it actually go up the hill is what you need to ask cell-man or someone who actually has those motors, you might find that 48 volts is awful slow while climbing!
Well, the video that chroot posted on that subject seems fairly convincing, assuming that the data presented in it is true.
I would also tend to assume that, should I wish to increase the battery voltage at some point in the future, that there's no reason why I could not install a 36v battery pack of equivalent Ah rating in series with the main battery. I'd have to check out the BMSes to ensure that there are no components in them with an inadequate voltage rating. Perhaps this is something I will ask cell_man about directly.
Lebowski wrote:If you want speed and hill climbing, get a 12T and a 80 to 100V battery.
Something to consider for sure. I'm not sure what the single-block BMS options for such a battery would be- I need to figure out with certainty if the series-BMS idea is valid. Two 39V packs in series would really be something.
dogman wrote:Very true. Most of the people I have steered towards the 2810 9 continent are running them at 72v, and very happy with 30 mph top speed. And even happier when they have a steep hill to climb. But if you run that motor on 48v, it's too slow for most people, at 19-20 mph. It definitely will climb 15% without any problems, even on a lame 48v 20 amps.
To be honest, I've been leaning in the direction of a geared motor for other reasons as well, principally weight and free-wheel ability. I just didn't realize that there were such capable geared motors out there, given that most of the ones I'd seen previously tend to carry rather small wattage ratings.
And like I said- speed on electric-only mode is not a high priority in this build. If I can cruise comfortably along a 5% grade at 20-25 MPH with a 50/50 split of pedal power and the electric wind, that would suit me just fine. My only concern for speed on the more severe hills (which tend to be relatively short in length, no more than 100-200 meters typically) is that the system be capable of actually getting up them without stalling or slowing down so much that the motor overheats. That's the big problem I had with the Amped system.
dogman wrote:The advice about making a really good bike the first priority remains. The rest is an easy solve, the only problem is deciding which slower winding motor to choose, and what voltage to run.
Interesting that you say this, as I've finding the problem to be quite the opposite. There are a number of good bike shops in my area, so it's easy to browse around, sit on bikes, ride them, operate the controls, and get a feel for how they work. (For instance, I rode a bike with disc brakes for the first time this past Monday at one local shop, and I'm absolutely hooked. I'd have never imagined the difference vs. linear-pull rim brakes could be so dramatic!)
By comparison, all I have to go on for selecting a motor and battery is what I can read online. No ability to go into a shop and test-drive them, so it's a much more vexing problem, at least for me, given my present level of (in) experience with them.
The concept of "average" requires that 50% of the population be below it.