How to get higher top speed from DD motor

I just setup a rear direct drive system from ebikes.ca and I was hoping that someone could help me with trying to get a faster top speed.
I got a all-in-one kit from Grin that includes a 9c rh212 motor (standard 8.5 winding), a 52v 20mah battery(40a continues) with a baserunner (with 45-50a continues) and the ca3 cycle analyst. I have it on a hard tail mountain bike and i get right at 28-29mph top speed on the flats (crouch down using full throttle). I only commute to work using 300-500w of PSA but i'm needing the ability to use the throttle for very small sections of the commute (keep up with traffic) and would really like to get it close to 35mph. It seems that at 28mph while using full throttle the motor uses less watts and just maintains that speed of 28-29. I have looked in the software suite for the baserunner controller (it just uses the phaserunner suite) and noticed that the max power limit for the motor is set to 1200w and the max battery current is set to 30a. If i increased the max power limit to 1750w and max battery current to 35a, would that increase my top speed? and will it hurt anything doing that? Do i need to use the top speed overdrive feature (field weakening)? I didn't know if having the 8.5 winding on the motor limited my rpm or something. Even on slight downhills i get about the same. I live in central Florida so there are almost no hills to speak of.

I know these are beginner questions but you have to start somewhere right? :wink:

Thanks for any info you can give.

Around 750w typically gets you to 28MPH or so, depending on aero and conditions. If you've already got more than that, then more power probably won't increase your speed.

You'd probably need higher voltage, a larger diameter wheel, or higher speed winding of the motor, or you can try the field weakening features--There are some threads discussing how that works, if you're interested.

If you want to figure out what is limiting you, you can also use the http://ebikes.ca/simulator , read the entire page to learn what evertyhign is and how it works, and then put your components in there (or similar ones), under differfent condtions, to see how it responds. I dont' know if it has FW available, but you can simulate increasing the voltage to increase teh speeed.

amberwolf said:

Around 750w typically gets you to 28MPH or so, depending on aero and conditions. If you've already got more than that, then more power probably won't increase your speed.

You'd probably need higher voltage, a larger diameter wheel, or higher speed winding of the motor, or you can try the field weakening features--There are some threads discussing how that works, if you're interested.

If you want to figure out what is limiting you, you can also use the http://ebikes.ca/simulator , read the entire page to learn what evertyhign is and how it works, and then put your components in there (or similar ones), under differfent condtions, to see how it responds. I dont' know if it has FW available, but you can simulate increasing the voltage to increase teh speeed.

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Thanks so much for your reply... I have been trying to figure out the simulator but still a little confused. I will keep plugging away at it and keep trying to learn more. If anyone else has ran into this or have anymore insight that would be great. Thanks again for your reply.

Yes almost everyone who wants to go fast runs into that very problem. You need more voltage or more flux weakening. In the end after getting your feet wet with this setup you'll probably upgrade motor, battery, and controller for REAL POWER!!!

You may need to go to a 16S or 17S battery.

https://www.ebikes.ca/tools/simulator.html?motor=MGRIN2708&batt=B5220_GA&hp=0&cont=BRZ9&axis=mph&cont_b=BRZ9&motor_b=MGRIN2708&batt_b=B662A123&bopen=true&hp_b=0

flat tire said:

Yes almost everyone who wants to go fast runs into that very problem. You need more voltage or more flux weakening. In the end after getting your feet wet with this setup you'll probably upgrade motor, battery, and controller for REAL POWER!!!

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thanks for the reply... Yes, unfortunately no upgrade will be happening. $$$$ I need to make due with what I have for years to come . I really like the setup but I so hoping for a top speed of 34-35mph. My main 20 mile commute is perfect at a 22.5 mph average with PSA using 300-500w. It just would be nice to have that throttle up to 35mph to get out of the way at certain spots or some small downhill spots.

E-HP said:

You may need to go to a 16S or 17S battery.

https://www.ebikes.ca/tools/simulator.html?motor=MGRIN2708&batt=B5220_GA&hp=0&cont=BRZ9&axis=mph&cont_b=BRZ9&motor_b=MGRIN2708&batt_b=B662A123&bopen=true&hp_b=0

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I'm defiantly just going to have to work with what i have. I just need that magic speed button mounted on the handle bars :wink:

I've been playing with the simulator some more and it looks like the top speed for the motor, controller, battery is 28mph. Maybe the field weakening would work for that top speed increase.

biker5500 said:

I've been playing with the simulator some more and it looks like the top speed for the motor, controller, battery is 28mph. Maybe the field weakening would work for that top speed increase.

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Field weakening may work for speed, but may also significantly reduce your range, so there's a trade-off. But, since you have a baserunner, it would just take a few clicks to change the settings to see if it gets you what you want.

E-HP said:

biker5500 said:

I've been playing with the simulator some more and it looks like the top speed for the motor, controller, battery is 28mph. Maybe the field weakening would work for that top speed increase.

Click to expand...

Field weakening may work for speed, but may also significantly reduce your range, so there's a trade-off. But, since you have a baserunner, it would just take a few clicks to change the settings to see if it gets you what you want.

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Ok, thanks. I'm going to try that tomorrow (more like when the sun comes up again). Haha.
I did try changing the max power on the battery from 30 amps to 35 amps and increased the max voltage from 1500 to 1750. The result from that was a very noticeable torque and acceleration but no top end speed difference. I will try the field weakening in slow increments to see how that goes. If I activate the field weakening does it only activate when I go past the 28 mph of the normal speed of the motor? I have been on the forums for hours now trying to find some more info on the field weakening but not having much luck. The good news is that I am getting more familiar with the simulator on the grin's website.

A basic property of permanent magnet electric motors, like almost every motor here, is that as the speed of the motor increases, the motor increasingly "fights back". Flux weakening does some voodoo shit to keep the motor from fighting back as much. But it doesn't happen for free.

In other words, the basic problem with field weakening is that it is less efficient; in fact, it is significantly less efficient for non-IPM motors which yours is.

A more pressing consequence than reduced range is your motor will heat up much faster. This is bad because unless there is an internal temperature probe, and it is working, and properly setup, you will burn your motor out while trying to go fast. For all intents and purposes this will completely destroy the motor because even if the magnets are OK (magnets are permanently weakened by high temperature) it is not realistic that you will rewind your motor very well.

Oh and don't think for a second you'll ride this ebike for "years to come" unless you come to the conclusion that it sucks and that means it just sits unused. Ebikes are so much fun that it will soon be something like an addiction and you'll try to fund "a good bike" by any means necessary!

Finally make sure everything is tight including your torque arms before doing 35 cuz you don't want to fall down on the street at all, especially at that speed.

biker5500 said:

I've been playing with the simulator some more and it looks like the top speed for the motor, controller, battery is 28mph. Maybe the field weakening would work for that top speed increase.

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Originally I was led to believe that field weakening is extremely inefficient. Maybe in some cases it is, but that isn't my experience.

After some testing on my bike (Nucular 12F/MXUS3K4T), I concluded that the additional power consumed by the field weakening process is still far less than the additional power required to ride at the increased speed. The added consumption of field weakening was small enough to be within the margin of error of my experimentation.

IMO, learn to live with what you have, including searching for an alternate route. Even a fairly long detour can be worth it to avoid that one section where you need 35 mph.

Dead serious dude,, even if you get faster one way or another, YOU ARE RIDING THE WRONG ROAD. If there is any alternative. Sometimes there is none, like getting to the other side of a freeway. But look hard, and look in weird places for a better way to avoid that stretch. Behind the big box stores can be a great route sometimes, or down a bit of dirt trail down a drainage ditch, or whatever it takes.

You can have 40 mph, with that motor pretty easy. But its a very very expensive upgrade to change your controller and battery to 72v. At this point, my advice is ride what you have till its time to get new battery, then consider higher voltage then. You can add 2 miles to your route with out much pain, once you have that motor to help. You can take the long way, or the steep way, to avoid that busy road with no bike lane.

My numbers are similar to yours. I'm ran my Phaserunner max Watts at about 1650 and I got about 28 mph without F.W. I am now using 10 Amps of Field Weakening and now get about 33, maybe 34 mph all other conditions being the same. Does it really matter if it's inefficient if you're only using it for a short portion of your ride? For me, no. I rarely reach that top speed but I want it available if I need it.

dogman dan said:

IMO, learn to live with what you have, including searching for an alternate route. Even a fairly long detour can be worth it to avoid that one section where you need 35 mph.

Dead serious dude,, even if you get faster one way or another, YOU ARE RIDING THE WRONG ROAD. If there is any alternative. Sometimes there is none, like getting to the other side of a freeway. But look hard, and look in weird places for a better way to avoid that stretch. Behind the big box stores can be a great route sometimes, or down a bit of dirt trail down a drainage ditch, or whatever it takes.

You can have 40 mph, with that motor pretty easy. But its a very very expensive upgrade to change your controller and battery to 72v. At this point, my advice is ride what you have till its time to get new battery, then consider higher voltage then. You can add 2 miles to your route with out much pain, once you have that motor to help. You can take the long way, or the steep way, to avoid that busy road with no bike lane.

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You have definitely got a point there and I really do appreciate your input. I will probably try the field weakening just to see what it will do but realistically you're right on point. Thanks so much for your reply

BVH said:

My numbers are similar to yours. I'm ran my Phaserunner max Watts at about 1650 and I got about 28 mph without F.W. I am now using 10 Amps of Field Weakening and now get about 33, maybe 34 mph all other conditions being the same. Does it really matter if it's inefficient if you're only using it for a short portion of your ride? For me, no. I rarely reach that top speed but I want it available if I need it.

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Thank you so much for your reply and I will definitely try it at the rate that you stated just to see how it runs. This morning I'll commute in the motor never got over 33 degrees Celsius here in Central Florida. So I think I have some playroom with the temperature And like you said it's only those very short distances that I would be using it.

I see that Grin has a YouTube live presentation this weekend on how to optimize a motor and when it is needed. I'm looking forward to watching that