Finding the rated RPM per volt (Kv) of your motor with Fardriver

[@imho7250]

0:00 Finding Motor Kv 0:16 set pole pairs correctly so you get the correct RPM value from the Dashboard 0:30 ensure WeakResponse is set to 7:none, which turns off field weakening. 0:35 Next increase MaxSpeed to about 2x what you think the rated speed is so it doesn’t interfere 0:48 set all Ratios in Speed to 100% so it doesn’t interfere and increase speed limit to 2x max speed 1:20 with the motor free to spin, slowly increase throttle to 100% 1:28 my motor did 1430 rpm at 63.4v, so 1430/63.4= 22.6Kv. 1:47 now we change WeakResponse from 7 (off) to 6 (first level field weakening) 2:09 you can see rpm went to about 1785 this time. Under load this would be slower, but faster than with field weakening off under load 3:31 I turn field weakening off because my ebike goes faster than I want without it after upgrading from 13s (48v) to 16s (60v) battery. 5:20 LimitSpeed doesn’t seem to do anything. Lol 5:38 Now I set my Ratios In Speed to start governing at 1200RPM@50% phase current. 1300RPM @25% 5:47 then 1400RPM@1%. It will not let the motor run faster than 1400 rpm, even if i set field weakening to maximum 6:05 the taper should be over a few settings, then 0% down to the bottom. This gives stable overspeed protection 6:37 you can see under no load, max rpm is just under 1400. On the road it would be closer to 1300RPM max or 1200RPM if going uphill 7:00 finally I set MaxSpeed to 675 which corresponds to 45 kph. Boost will override this and I can go to about 80 kph if I’m stupid

[@je7647]

DOES it make that beeping noise until you set it up? ive tried all the temp sensor types and it still beeps still havent auto learn yet as ive got it sort out my chain

[@imho7250]

Which beeping noise? There are some for error with is a steady beep and there is dot-dot-dash telling you its in autolearn waiting for you to run it. If its a steady beep make sure temp sensor is set to NONE, check your voltage is set correctly, and verify your low voltage settings is correct for your battery. If its the autolearn signal then it will keep going until you run autolearn. You can do this with the chain off or on, as long as the motor can run full speed forward or backwards without any hinderance. If you fully twist the throttle and it only runs one direction, just twist the throttle again and it will run the option direction to complete the autolearn, and then it will automatically exit autolearn.

[@je7647]

@@imho7250 my bms will cut off the battery anyway I assume. will I be able to go between a 72v and 60v because II have both? im noob at this. Ill learn.

[@imho7250]

@@je7647 , you can change the voltage settings each time you swap between 72v and 60v to ensure regen cuts out before the BMS closes the port. Regen is cut by the Fardriver when it thinks the battery is above 90% SOC. This is roughly established when you set battery voltage and lithium battery type. If you leave the fardriver set for 72v but use a LVP of 48v it will allow you to run either 60v or 72v pack, but with the 60v pack regen will never be disabled. This can be a problem if you fully charge and then go down a hill using regen. So you should at least try to change batteries voltage if you swap between 60v and 72v. LVP can stay at the 60v level since if the BMS discharge port closes it won’t damage the controller like if the charge port closes during heavy regen.

[@MrDeceptacon88]

Hi again Ok i will do these steps 1. Set all ratios in speed to 100% 2. Turn off FW 3. Set max rpm to 2000 4. Jack up the bike and twist full throttle with a fully charged battery to see my unloaded max rpm So far sound ok?

[@imho7250]

Yes, that will give you the no-load rated rpm. As a baseline. Then right after that if possible make a top speed run with same settings and screen recording, holding top speed for about 5 seconds if possible. This will give the loaded rated rpm, but equally important it will show how many DC and phase amps are needed, and how many volts the battery is sagging. If it’s not sagging much at top speed then you have some overhead to work with.

[@MrDeceptacon88]

@@imho7250 ok thx..but after the steps i listed, couldnt i test the FW while the bike is still unloaded instead of riding?

[@imho7250]

@@MrDeceptacon88 , i just tested all levels of weak response unloaded and couldn’t really see any difference. I think because it can easily reach high rpm with very little current for torque. And my motor is only needing about 10a of FW current to get up to speed. But if you test it be gentle with the throttle and let off if the rpm goes way too high. Once you find your rated rpm you might want to add 20% to that and set the ratio on speed table to 0% at that speed. Example, if you get 900rpm without FW, you can set 1000rpm 50% and 1100rpm 0% and that will prevent runaway. You can always back these off later if you see you can run 1000rpm no problem. Note that your loaded rpm without FW will likely be 10%-20% less than your unloaded rpm , depending on many variables.

[@MrDeceptacon88]

@@imho7250 yeah a road test full throttle would be better. So check my unloaded max rpm then road test max rpm with FW off. If the road rpm is lower than unloaded..do I turn on FW to get it high or turn up the amps and phase with FW off?

[@imho7250]

The unloaded no FW test is just a reference. Then the loaded no-FW rpm will be less, due to more torque needed (which needed more differential between your battery voltage and the Back EMF), and due to voltage sag. Every volt sag will decrease rpm by about 10-12rpm (depending on your motor turns (3.5 or 5t). When you turn on FW, in addition to the normal phase amps it was sending for torque, it will also send in additional amps to weaken the flux creating the back EMF. At the same time the torque will be less for the same amps so you need even more amps. Thats why the FW will really pull the battery down if weak because 10% more speed might need 30% more amps.