How do you size the right Mid Drive?

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geosped   100 W

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How do you size the right Mid Drive?

Post by geosped » Oct 15 2020 10:53am

So I'm not new to e-bikes. I built a really cool off road mountain bike that I used for years. BMC Rear hub on 50v made well over 1000w and had plenty of power. Actually with all the weight including the battery on the rear tire it was very sketchy at times. All I do is just ride for fun and exercise off road on mountain bike trails. So I want a new mid-drive but how do I size the right one?

1) Strictly off road mountain biking trails.
2) 250lbs
3) Trails are I ride have some really steep sections with lots of big thick roots. Not uncommon where I have to get off and walk around it.
4) lots of tight single track with lots of switch backs. Very slow and challenging especially when going up hill.

I'm using a 26" full suspension bike. Now the big question is how much power do I need? There are several great mid drives out there. All of the commercial hard core mountain bikes ($3500) and up seem to use a much lower power system and much smaller batteries that what I'm seeing. Tenshong and Bfang offer 500w 750w 1000w on 48v and 750w 1200w 1500w on 52v batteries respectively. Assuming the controller is setup to take the higher voltage batteries. So how do I make sure I get a system strong enough to carry me up the hill with out burning anything out and at the same time not too powerful where it's dangerous? Do I really need 1500w to get me up a steep hill?

Thoughts and suggestions.

Green bike is what I used to ride. This hub motor easily made 1200w but like I said it was very sketchy the way I had the battery pack mounted. Not ideal at all. In the end I burned out the halls sensors and decided to go in another direction.

Blue bike is the new donor bike. Just need help in deciding to go to the 750w 48v - 1200w 52v BBSH02 option OR should I go with the BBSHD 1000w 48v - 1500w 52v option?
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Limbs   10 mW

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Re: How do you size the right Mid Drive?

Post by Limbs » Oct 16 2020 7:55am

I don't have any experience of different powered mid drives, just a 250w Bosch system, but seeing as no one else has answered so far.

I ride with only one arm, plus other health conditions, which that mean I don't have much energy, but I mange to ride pretty much everywhere I want to in Tenerife, which includes some incredibly steep & very rocky climbs. Due to my health issues, I ride almost exclusively in turbo mode and it's great; the beauty of a mid drive is that the motor gets geared down at the same time as you change down for the benefit of your legs. I ride with a couple of other guys, who ride more for the exercise and only use Eco or Tour modes, they have also fitted larger rear sprockets to help on the steep climbs, but they still get off and walk sometimes, where I ride (I carry a spare battery, they don't).

Whilst the Bosch is rated @ 250W, I have seen peaks of 720W on a meter the same as yours.

So, in summary, 250w is enough, but it does depend on your fitness level, how much effort you want to put in etc, I'm half your weight BTW. If you want to put in less effort, go faster etc, then a more powerful unit would be beneficial.

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ZeroEm   100 kW

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Re: How do you size the right Mid Drive?

Post by ZeroEm » Oct 16 2020 8:25am

I'm sure the mid Drive fans will chime in soon!
If he was talking about DD hub then more watts the better. With the mid drive you need to thing about the chain and how fast you want it to replace it all. So I would stay below 1200w.
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Re: How do you size the right Mid Drive?

Post by SlowCo » Oct 16 2020 8:45am

You seem to be a slow (in a positive way) and technical rider. If you don't need speed then it's all in the gearing and a mid drive will help in any gear. Riding such technical climbs weight and CoG are key I think. So you'll probably be happiest with a low weight torque sensor system like the TSDZ2 with the open source firmware. And get the smallest battery pack that will do your longest ride distance.

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pwd   1 kW

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Re: How do you size the right Mid Drive?

Post by pwd » Oct 16 2020 8:58am

The beauty of a mid drive is that you can utilize the bike's rear cassette/freewheel which allows you to tackle those steep; rooty, low speed climbs with minimal power.

Here is a quick example in the simulator using a BBS02 Motor set to 20A max battery current @52V. I only picked this motor because it is very common and one of the few mid drives available in the simulator. You can see the performance with two different rear cogs selected (You can adjust the grade etc... as necessary):

https://ebikes.ca/tools/simulator.html? ... mass_b=120

If we dial the max current down to only 10A battery / 30A phase you can see the bike will still make the same climb without overheating:
https://ebikes.ca/tools/simulator.html? ... _30_0.03_V

Here is a comparison of 20A battery 60A Phase vs 10A battery 30A phase with the same gear selection:
https://ebikes.ca/tools/simulator.html? ... _60_0.03_V

With more power; you can climb steeper hills more aggressively depending on the size of the motor. Larger motor's (more copper) will be able to take more power before overheating with all gearing etc... being equal. For what it's worth; I really enjoy my Cyclone 3000 motor on 52V /40A batt (not sure what the phase amps are) on "technical" mtb trails. I have tried dialing both the phase current and battery current down to 50% and was still able to do the same climbs; just at a slower rate.
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Re: How do you size the right Mid Drive?

Post by leisesturm » Oct 17 2020 3:50am

geosped wrote:
Oct 15 2020 10:53am
. So how do I make sure I get a system strong enough to carry me up the hill with out burning anything out and at the same time not too powerful where it's dangerous? Do I really need 1500w to get me up a steep hill?
If your choice is between the BBS02 and the BBSHD I would say get the BBSHD. 1500W is not dangerous unless you do something ... unwise. The bigger motor will be built tougher and that will pay off because any kind of off-road puts tons more stress on every part of an ebike drivetrain and motor than any kind of street use.

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Re: How do you size the right Mid Drive?

Post by Skaiwerd » Oct 17 2020 9:12am

I’m with PWD and the cyclone. I have years on mine but don’t run at %50. More is always more. You can always ride under full throttle and have some reserve power for bursts and an out for tricky situations like wiping out or falling over, like something with power can do. More power is less shifting. Find the right gear setup and go single speed if you want, may require 75v to have speed for the flats.

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geosped   100 W

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Re: How do you size the right Mid Drive?

Post by geosped » Oct 17 2020 9:52am

So I went with the BBSHD and 52v 17.5 ah triangle pack. I was torn between the BBSHD and Tenshong. I started looking at the TenShong because I really like the idea of torque sensing and pedal assist. More natural feel more of a real assist. Keeps the bike lighter and more nimble but also let's it feel more like a normal bike. All these positive attributes are really important to me. The big hurdle I couldn't get over was I didn't think it would be strong enough to haul me up. I think with a 52v battery folks have been pushing it to 1000w which would probably be just fine. A bit of fear kicked in since I already burned out my BMC rear hub motor at 1200w. And that's how I made my decision. If Tenshong had a more powerful option I would have probably gone in that direction.

For me getting an ebike is about getting my phat butt up the hill without having to get off and walk BUT more importantly it's about exercise. Unfortunately most of the trails are I ride I half to get off and walk a little. It sounds like I may have to adjust the BBSHD to allow me to work a little harder so I get that good workout and at the same time not having to get off and walk. If it's not so natural that's a consession im willing to make.
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furcifer   10 kW

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Re: How do you size the right Mid Drive?

Post by furcifer » Oct 18 2020 12:05pm

geosped wrote:
Oct 17 2020 9:52am
So I went with the BBSHD and 52v 17.5 ah triangle pack. I was torn between the BBSHD and Tenshong. I started looking at the TenShong because I really like the idea of torque sensing and pedal assist. More natural feel more of a real assist. Keeps the bike lighter and more nimble but also let's it feel more like a normal bike. All these positive attributes are really important to me. The big hurdle I couldn't get over was I didn't think it would be strong enough to haul me up. I think with a 52v battery folks have been pushing it to 1000w which would probably be just fine. A bit of fear kicked in since I already burned out my BMC rear hub motor at 1200w. And that's how I made my decision. If Tenshong had a more powerful option I would have probably gone in that direction.

For me getting an ebike is about getting my phat butt up the hill without having to get off and walk BUT more importantly it's about exercise. Unfortunately most of the trails are I ride I half to get off and walk a little. It sounds like I may have to adjust the BBSHD to allow me to work a little harder so I get that good workout and at the same time not having to get off and walk. If it's not so natural that's a consession im willing to make.
Good choice. The BBSHD gets my fat ass up the hill and allows me to peddle when I want. It's all controlled through the software. Do the shunt mod, I'm doing a 48A controller but 45A is stable from my experience. Don't rely on the motor, give it help and you won't have a problem. I suggest making a cork gasket for the controller because the factory silicone one is a joke.

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geosped   100 W

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Re: How do you size the right Mid Drive?

Post by geosped » Oct 18 2020 6:03pm

furcifer wrote:
Oct 18 2020 12:05pm
geosped wrote:
Oct 17 2020 9:52am
So I went with the BBSHD and 52v 17.5 ah triangle pack. I was torn between the BBSHD and Tenshong. I started looking at the TenShong because I really like the idea of torque sensing and pedal assist. More natural feel more of a real assist. Keeps the bike lighter and more nimble but also let's it feel more like a normal bike. All these positive attributes are really important to me. The big hurdle I couldn't get over was I didn't think it would be strong enough to haul me up. I think with a 52v battery folks have been pushing it to 1000w which would probably be just fine. A bit of fear kicked in since I already burned out my BMC rear hub motor at 1200w. And that's how I made my decision. If Tenshong had a more powerful option I would have probably gone in that direction.

For me getting an ebike is about getting my phat butt up the hill without having to get off and walk BUT more importantly it's about exercise. Unfortunately most of the trails are I ride I half to get off and walk a little. It sounds like I may have to adjust the BBSHD to allow me to work a little harder so I get that good workout and at the same time not having to get off and walk. If it's not so natural that's a consession im willing to make.
Good choice. The BBSHD gets my fat ass up the hill and allows me to peddle when I want. It's all controlled through the software. Do the shunt mod, I'm doing a 48A controller but 45A is stable from my experience. Don't rely on the motor, give it help and you won't have a problem. I suggest making a cork gasket for the controller because the factory silicone one is a joke.
Thx I'll look it up? Did you have to apply any additional grease or have to waterproof anything? I was gonna use a little dialelectric grease on the connectors and some heat shrink.

Is the gear switching sensor a must for mountain biking.
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Re: How do you size the right Mid Drive?

Post by furcifer » Oct 18 2020 11:27pm

geosped wrote:
Oct 18 2020 6:03pm
Thx I'll look it up? Did you have to apply any additional grease or have to waterproof anything? I was gonna use a little dialelectric grease on the connectors and some heat shrink.

Is the gear switching sensor a must for mountain biking.
I added thermal paste to the heatsink between the mosfets and the controller housing when I did the controller mod. You could add some RTV to where the wires come out of the controller, but I found a good cork gasket was more than enough. Adding dielectric grease to the Higo connectors probably won't hurt but they are waterproof anyways. Be careful putting them together, the pins bend easily.

I never bothered with a gear sensor but I've got one coming for my next build. I never found shifting to be that problematic but I've ridden motorcycles all my life. I basically treated the throttle like I would the clutch on a bike. I don't know how responsive the gear sensor is but my gut tells me you've got to be carful not to be on the throttle when you shift even if you have one. Missing a shift makes a horrible noise you just know isn't good.

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geosped   100 W

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Re: How do you size the right Mid Drive?

Post by geosped » Nov 02 2020 10:58pm

Just finished now just waiting for the battery.
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Re: How do you size the right Mid Drive?

Post by furcifer » Nov 03 2020 5:52pm

geosped wrote:
Nov 02 2020 10:58pm
Just finished now just waiting for the battery.
Dude, that's a sick build. If you've got a good chain line you're golden. When you do the mod and start pulling 45A you'll get the full potential out of this drive you'll realize it isn't bad for the price. Good bones on that one.

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Re: How do you size the right Mid Drive?

Post by Manbeer » Nov 04 2020 8:30am

That's a sweet looking setup

I too am torn on my next off road setup. Part of me wants the TSDZ2 as I feel it will ride kind of like the poor man's factory ebike and should be pretty efficient and fluid with the OSF flash, on the other hand the BBS is a bit more bulletproof and will make things fun on faster trails and fire roads unlike the TS where I was expecting it would pretty much just make riding easier and more enjoyable

I'm kind of starting to come to the conclusion that there's no one perfect solution and I'm going to need two different bikes for the two different types of trail around here. Lots of slow tight stuff where I'm afraid that the BBS we'll be over till in terms of weight and power and change the characteristics of the bike too much between it and the battery required to keep it going

on the other hand there are a lot of double track trails and old horse trails and fire roads we're going 40 miles an hour and basically using it almost like an electric motocross bike would be awesome

In the end I'll probably do both, pair the TS with a carbon 29er or a 27.5 plus like the trek Roscoe and try to do a lightweight build focused on single track and efficiency and then slap a BBS HD or a cyclone on a full suspension rig

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ZeroEm   100 kW

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Re: How do you size the right Mid Drive?

Post by ZeroEm » Nov 04 2020 10:24am

I agree the right E-bike for the right ride. Think I will need three before it's all over.
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