Lower power (350W? 500W?), lower cost middrive recommendations

[Drizzt321]

So I have a lead on a fairly low priced old Terratrike Rover, and considering buying it and putting on my Dream Bike trike conversion kit (dual freewheel "differential" HOME | tricycleconversion) to turn it into a quad, and having a mid-motor (kinda a front motor on a boom tadpole, but whatever).

I'm not going to need huge power, I don't need to go fast, 5-10mph, but I do want some moderate torque. This will be for various festivals and stuff, no real hills, but some sandy desert surface and ruts and bumps.

Cruise and throttle would be nice, and speed control could be useful to keep me from motoring too fast.

I already have a 48v battery, CycleAnalyst v3 (although might not work with a new motor/controller).

Thoughts? Places to look? I'm very much DIY, looking to keep costs down, but willing to pay a bit for reliability.

 

[neptronix]

I'm betting you'd be happy with a bafang BBS01 or a small tongsheng, if cost is the main concern

 

[Drizzt321]

I'm betting you'd be happy with a bafang BBS01 or a small tongsheng, if cost is the main concern

On AliExpress BBS01 seems to be more expensive than BBS02, at least I haven't found one cheaper in my (brief) searching.

The Tongsheng TSDZ2B actually seems like it's pretty solid, and I like it has torque sensor instead of cadence. Seems to be reasonably well regarded as a good low cost motor. And I found there's some reprogramming?!

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github.com

Neato!

Hopefully I'll be able to make this happen, if not, ah well, there will be another time, another trike.

 

[Chalo]

So I have a lead on a fairly low priced old Terratrike Rover,

Don't use a crank drive. You've already specified adverse operating conditions and low performance goals and low cost. Crank drive works against all these things.

Get a rear hub motor intended for 48 or more volts and a 26" to 29" wheel, and lace it to a 20 inch rim, run it on 24V and the maximum current it is designed for.

But let's be real here. If you only want 5-10 mph, why are you messing with electric power? Do you not have legs? Do you plan to be so high that you can't find your legs?

 

[Drizzt321]

Don't use a crank drive. You've already specified adverse operating conditions and low performance goals and low cost. Crank drive works against all these things.

Get a rear hub motor intended for 48 or more volts and a 26" to 29" wheel, and lace it to a 20 inch rim, run it on 24V and the maximum current it is designed for.

But let's be real here. If you only want 5-10 mph, why are you messing with electric power? Do you not have legs? Do you plan to be so high that you can't find your legs?

I think you missed where I was going to convert to a quad with a bike->trike with a dual freewheel "differential".

As to why...festival, Burning Man, etc. Yes I have legs that work, but when it's 4am and you're pedaling back against wind it get really, REALLY annoying.

Reason for the conversion, is I am going to be a large(ish) locking box on the back for things like the battery, my backpack, extra water, lighting on the bike, attach a 30ft flag pole, holding layers/coat for later in the evening, etc. I'd like a delta style, but those are quite long typically.

 

[Chalo]

Yes I have legs that work, but when it's 4am and you're pedaling back against wind it get really, REALLY annoying.

But, 5 to 10 mph. Are you 100 years old? That's just not very much power no matter how you slice it.

 

[Drizzt321]

But, 5 to 10 mph. Are you 100 years old? That's just not very much power no matter how you slice it.

No it's not. That's the speed limit (really, truly is, especially for anything motorized) at these events. And why 48v? It's the battery I already have.

 

[Chalo]

No it's not. That's the speed limit (really, truly is, especially for anything motorized) at these events. And why 48v? It's the battery I already have.

I understand the speed limit. I'm just aware that it takes very little power to go that fast even on sand and passed-out junkies.

No hub motor or crank motor is designed to turn that slow on 48V. Partial throttle will get you there only by imitating a lower voltage. So it's kinda hokey to use the wrong voltage just because you have it.

These are cheap as chips:

25.6v 6ah 153.6wh Lifepo4 Battery with BMS (24v)

These batteries were only used as backup for about a year. They all have good, consistent voltage and a 15a rated BMS. You can parallel these together easily by connecting all the red wires into a busbar and all the black wires into another busbar to build a nice, modular 24v battery. They are...

batteryhookup.com

Each one is good for 15A, so multiply for more current or more range. The only real hitch is your controller has to be functional with that low a voltage.

US 24/36V 500W Electric Bicycle E-bike Scooter Brushless DC Motor Speed Controll | eBay

It can be suitable to three - wire throttle brushless DC Hub Motor under 500W. Regenerative braking is not supported. The battery type can be Lithium battery, Lead Acid battery…. Automatically recognize the motor phase angle and motor right spin direction.

www.ebay.com

On the plus side, you can get a single ~30V solar panel and charge controller to keep it juiced at the fest.

 

[Drizzt321]

No hub motor or crank motor is designed to turn that slow on 48V. Partial throttle will get you there only by imitating a lower voltage. So it's kinda hokey to use the wrong voltage just because you have it.

Not sure what you mean by that. You mean just by the sheer voltage (and thus power), even 1-2a @48v it'll run faster than 5-10mph? Or that it actually does some kind of voltage conversion to drop the voltage?

I've had a regular bike, upright trike, with a 48v front hub motor for several years, and it's worked fine. Very, very low throttle obviously, but worked fine. However, a front hub won't work well with a recumbent delta, since there's actually fairly little weight on the front wheel, it's almost entirely on the rear wheels. I actually tried it one year with a detla. It just slips too much, and can't grip/provide enough torque. Not on that surface at least.

Thus, me wanting a rear wheel drive, and ideally a 2WD rear, via a mid-motor in order to get enough grip/torque without slipping. Plus, 2 wheels on back provides enough space in between them to attach the bottom of the storage box. Thus needing either a delta or tadpole with 2 wheel conversion on the back to make it a quad, whether 1WD or 2WD, and the box on top of that.

As for 24v vs 48v...do you know of a decent mid-motor 24v? I suppose I could (since I already have the battery, let it not sit around) do a 48v->24v 30a (so if only 15a motor, leaving headroom on the Chineseium buck converter). I found ones like 24V 250W Electric Bicycle Conversion Kit E-Bike Cycling Brush Motor & Controller | eBay around...but seems pretty iffy in terms of build & reliability. I'm willing to pay a bit more for ensuring something will work in a harsh environment. And something that wouldn't require any sort of jack shaft in the middle of the chain, but preferably sits at the bottom bracket or thereabouts (so at the end of the boom in a tadpole/quad configuration). I don't have a welder, but can use bolt brackets or the like to figure out a mounting plate or something if needed.

On the plus side, you can get a single ~30V solar panel and charge controller to keep it juiced at the fest.

I've got 400W with 280Ah LFP 12v at my trailer, so I can easily charge other batteries up just fine with proper CC/CV boost.

 

[lnanek]

Brushless electric motors have a property called KV. It's basically the top speed RPM per volt, and it's determined by the windings, which can be more or less turns. Running higher takes advanced controllers capable of techniques like field weakening that can stop the back EMF from preventing the motor from going faster, but those use a lot of amps to get only a small bump in top speed over the KV determined value.

Chalo is pointing out you can take a motor designed for and performing best at 30MPH at 48V, run it at 24V, and then it's effectively designed for 15MPH. These motors are most efficient at high RPM, which is why geared rear hub motors can be so much smaller than direct drive motors, since they typically run the motor at 5x the RPM of the wheel.

You can burn out a motor by running it very slow uphill. So if you use Chalo's method instead of just using low throttle, you are still closer to the motor's most efficient RPM (which is half as much at half the voltage). A controller at low throttle still sends battery voltage, it just cuts in and out enough to end up not pumping as many amps into the windings. So it's a bit different.

 

[Chalo]

Motors have a fixed RPM per volt. Typically that's to go low to mid 20s mph on 36V or 30ish mph on 48V (in a full sized wheel). Controllers effectively lower the battery voltage with pulse width modulation so they can run at lower than full load and speed. But if you know you don't want to go that fast, you can set the voltage closer to the road speed you want, get better speed control and better efficiency. That's why 24V. Instead of using throttle within the bottom 10% of its variable range, you can use most of the throttle's range for more precise speed modulation, less motor noise, and improved efficiency.

 

[Drizzt321]

Oh, so use a 36v/48v like TSDZ2B, but give it 24v? Or would that not work, would the controller not function properly?

And remember in this case, in this design, I'd need a mid-motor, not a hub. Already have a geared hub I've used fine on upright trike, but I really want to do recumbent to be able to sit and lean back to relax more.

 

[amberwolf]

If you gear the entire pedal drivetrain to the wheel to run at the low speed, you'll get more torque as a tradeoff.

If the vehicle is geared to go 5-10mph and you're correctly shifting gears for the motor (assuming it's in your pedal drivetrain) to go those speeds, then there's no need to mess around with hacking it to work at a lower voltage.

If the vehicle is geared to go 20-25mph and you're having to use low throttle to get the low speed, instead of shifting gears down to the speed you want, that's when hacking it to work at lower voltages might be a better option.

 

[Drizzt321]

If the vehicle is geared to go 20-25mph and you're having to use low throttle to get the low speed, instead of shifting gears down to the speed you want, that's when hacking it to work at lower voltages might be a better option.

Define hacking in this case? Using the F/OSS firmware and just giving it 24v power input?

I also potentially want to use this around locally, to a degree, so I do want to ride it (legally) on the streets and bike paths and such around.

 

[amberwolf]

Define hacking in this case? Using the F/OSS firmware and just giving it 24v power input?

Making any changes to the drive system could be "hacking", but I really meant having to run it at lower voltage to make it go slower.

I also potentially want to use this around locally, to a degree, so I do want to ride it (legally) on the streets and bike paths and such around.

If you just make sure that it is geared correctly to be able to ride at all the speeds you want, then thats all you need to do.

If the max speed the drive system will run the pedal drivetrain at is the same as the speed you pedal at, then you can just pedal around at that cadence and see if it's got gears that let you ride at those speeds.

If you have to slow your pedalling down to go those speeds, then you'd want to change the gearing so that you *can* ride at full cadence at the slow speeds.

Alternately you can just get the drive system and install it and then see what speeds you get at full throttle or full pedal input, etc., with various gear shifts. If the lower gears do go the speed you want at full throttle/etc, then you're set. If not, that's when you'd want to change the gearing.

That's part of the point of a middrive vs a hub drive, that can make it worth all the maintenance and other hassles middrives have over hubs.

 

[Drizzt321]

If you just make sure that it is geared correctly to be able to ride at all the speeds you want, then thats all you need to do.

If the max speed the drive system will run the pedal drivetrain at is the same as the speed you pedal at, then you can just pedal around at that cadence and see if it's got gears that let you ride at those speeds.

If you have to slow your pedalling down to go those speeds, then you'd want to change the gearing so that you *can* ride at full cadence at the slow speeds.

Alternately you can just get the drive system and install it and then see what speeds you get at full throttle or full pedal input, etc., with various gear shifts. If the lower gears do go the speed you want at full throttle/etc, then you're set. If not, that's when you'd want to change the gearing.

That's part of the point of a middrive vs a hub drive, that can make it worth all the maintenance and other hassles middrives have over hubs.

Ah, I think I understand what you mean. Try it geared down so the motor can spin fairly fast, while keeping the wheel speeds relatively low. Time for me to go understand gear ratios

 

[amberwolf]

Ah, I think I understand what you mean. Try it geared down so the motor can spin fairly fast, while keeping the wheel speeds relatively low. Time for me to go understand gear ratios

Yes, just like when you pedal, you want to spin the cranks fast rather than having to push really hard on them to generate torque--it's way easier on any power source to do that.

(lots of unpowered-bike riders don't learn to shift gears and tend to leave it in the fastest gear all the time, which is harder on them and the drivetrain parts, wearing everybody out faster than necessary)