majornelson said:
Any sense on how hard the 10T can pull?
Sure - easy to see on the
ebikes.ca simulator. A BMC V2S is equivalent to a MAC 8T and a BMC V2T is equivalent to a MAC 12T. Run them both and the 10T is halfway in between the curves. For getaway torque, you want to examine the Torque/Thrust curve at 0 mph (dead stall) and shortly thereafter at low speeds.
Here was some key advice:
motomech said:
What controller/Amps do you plan on using. That is a big part of the torque equation.
majornelson said:
Good point. I will order the 9 fet Infineon controller from Paul at em3ev. It is rated at 30 amps.
spinningmagnets said:
If I lived in a flat beach community, I would not hesitate to use 35A as the max setting.
An important point to consider is that you are specifically concerned with getaway torque - this is the time the motor is constrained by the controller 'rated amps' setting.
This means the controller capacity is critical to achieving your specific goal - which is a little different than most who are looking for top speed where the amp draw is lower.
Motomech pretty much nailed it - you really need to get a programming cable and re-program your controller to get the amps up to be able to achieve your best off-the-line performance. A plain vanilla 9-FET is not going to let you max out you motor capability
because the controller is limiting things on getaway.
As an example - from your response above which seemed to suggest you thought a 9-FET was an upgrade - I'm guessing you are using a 6-FET on your existing bike. Here's a run in the simulator showing the difference between your bike with 25A 6-FET and an upgraded 35A controller.
You can see a 16% improvement in getaway thrust (70lb-60lb)/60lb = 1/6 by running a 9-FET jacked up to 35A or a 12-FET dialed down to 35A. Interestingly, you see that the top speed is unchanged because the motor characteristics are limiting current at that rpm - the gain was entirely at the low end.
Looking at a similar situation for the 10T, we run an 8T and 12T simulation and estimate the 10T is about midway:
Here we see that you should get about 80lbs of thrust off the line for a 10T on 35A compared to 60lbs with your existing 8T on 25A. This is a 33% improvement off the line. Top speed will be about 27-28mph. (In order to get the simulator to yield a top speed of your claimed 33mph for the 8T I had to use a full tuck position for you - not a standard Mtn bike posture - I'm guessing you were milking it for all it would do. I use this same tuck posture for the 10T to get 27+mph - faster than achievable with standard Mtn bike posture.)
You will need to play this against the battery Ah and C rate to ensure you don't overtax it, but 35A is modest and within reach of the EM3EV 14s6p frame battery with 22P cells (2.1Ah x 6p x 3C = 37.8A max discharge - 35A is fine for brief getaway bursts). You can safely raise the 9-FET to 35A - the high current draw is transient and the 10T current draw at max speed will be less than 20A so overheating on the flat is not an issue.
You should also be getting the 3077 instead of the 4011 FETs in your controllers to get the highest usable amps - you don't need the high voltage rating of the 4011 for your pack.
Another strategy is to change your 14s6p frame pack (84 cells 50.4v 12.3Ah) to a custom 17s5p pack (85 cells 61.2v 10.5Ah). EM3EV has suitable 17s BMSs and chargers. This will give you a higher top speed and more thrust off the line. Although you don't want the top end, it might make the 12T a viable candidate with the extra speed. If you hold down the top speed you will get close to the same range since the battery Wh remains the same - but you will pay for those power-eating getaways. You can get a CA to keep you honest and/or bump up the pack to 29E cells for more capacity. So many options....
In any case, you get the drift of how to do the comparisons. You may wish to look at thrust at 5 or 10mph instead or examine the achievable speeds with a more conventional posture. Have fun!
