Front sprocket mid-drive

[Auroa]

Absolutely aware there have been other threads on here with the exact same (more or less) build, including businesses like Cyclone, but I thought I'd make a thread for my specific build to make sure it's alright
I thought to ask the wizards with about...15ish years of experience with Dumbasses Who Are About To Kill Themselves, so they'd recognize if I was one.

24v JGB37-545 with about 35 kg.cm at 60-80 RPM, or something similarish, either on a 26T or 44T sprocket and connected with either a trimmed chain or a child-size bike chain (which I realize is probably not strong enough for the hell this'll go through), otherwise, 6S1P 18650 battery, a motor speed controller with a POT for PWM, and a motor driver or other device for current limiting (though I have no idea what I'll go with).
curious as to whether this is over or under powered for any meaningful results, should also ask about freewheels since I'm not sure how to attach one to the motor that'll only engage when its on and not when pedaling.

Thanks/Sorry in advance!

 

[lnanek]

What's the intended use? A 1P pack with something like Samsung 35E cells would only be able to do something like 8A continuous discharge. Not really strong enough to do anything on a bicycle.

It would run out of capacity in 30 minutes too. It might get you one boost up a hill per ride and the rest pedal power?

Even for my kid's power wheels vehicle, I have about 5 Milwaukee 3S2P M12 packs in parallel and she can still use up the capacity going to the local park and back. If I don't plug in at least 3, then the voltage sag when she hits the pedal trips the separate low voltage cutoff device I have installed too. So it isn't even all about capacity.

 

[Auroa]

well yes, the motor itself is around 1.5-2A.
As long as those motor specs are competent enough (for eg: this calculator tells of 10-18 MPH based on the front sprocket) then I think it'll be sufficient enough.
Obviously low, but could help greatly with the hills I suffer with.

 

[lnanek]

I think that's just a gearing calculator. If you gear a 2A motor to run 18MPH, it isn't going to be delivering any more torque than a light breeze. My rear hub ebike needs more like 20A to achieve that.

Maybe you should try a motor simulator instead? Like Motor Simulator - Web Tools - Resources

 

[Auroa]

Maybe you should try a motor simulator instead? Like Motor Simulator - Web Tools - Resources

Yup, 10m-...kph? huh
Anyways, that's lower than I thought and probably not very useful, and that's using inaccurate specs since more accurate specs just yield...no simulation.

It isn't going to be delivering any more torque than a light breeze. My rear hub ebike needs more like 20A to achieve that.

Emphasis on rear hub, I'd imagine that needs more torque than a mid drive, and I could always pivot to focusing on straight power.

 

[Auroa]

Realized I'm being a comically large clown (see: Dumbasses Who Are About To Kill Themselves), the 35 kg.cm figure is stall, and the wattage of the JGB is too weak.
Switching to a 775 (80 watts, which is decently ass) creates a different problem, there aren't any geared versions available to me, which means I need to gear it down multiple times with jackshafts because the RPM is so high (or find a different solution).
Sorry for this slip-up, genuinely ridiculous.
Edit: TQ42-775 seems to be the best motor so far, but it seems a lot more expensive, and atp I'm just thinking of fuckin around with the JGB or getting some e-scooter motor instead.

 

[Auroa]

Comically dumb person writing again.
My previous self writing about the same idea had saved me: get a drill you dipshit.
significantly lower price and better performance and pre-included batteries because #Capitalism and #ScaleEconomy or something.
Parts left are the PWM Pot and board, and a current limiter so it doesn't do the aforementioned Killing Me.
I'll update in the month that this'll take, I think.

 

[lnanek]

I have seen some amusing TikTok's where people repurpose drills and angle grinders into ebikes. And a couple people on the forums have handled the insane gearing needed for RC airplane motors to get the RPMs they need. So it does happen.

Old motor hubs range from free for Bionx stuff to like $50 off Facebook marketplace around here, though. So just never made sense to me. A Milwaukee drill costs twice that. Even here in the forums someone is selling a Cycleanalyst display, Infineon controller, and 9C motor hub for $100.

 

[Auroa]

around here, though.

No hub motors (or any e-bikes really) reach egypt without being hypergentrified (which tracks for e-bikes), I saw a used rear hub motor on a sale website for 1.5k EGP, in comparison to a drill with its battery included coming out sometimes at 600-900 EGP, the only thing I'm losing out on is the max use cases.
And yeah, I saw those airplane outrunners and I got so confused, "How the hell would you even gear for this???", the gearing for a drill at about 700 RPM wouldn't be too insane at a mid-drive.

 

[neptronix]

This thread might be of interest to you:
My RC Mid Drive with Single Stage Reduction
Guy used a cheap RC motor and ran it at low voltage.

Can you buy things from aliexpress in Egypt? that's hub motor heaven..

 

[Auroa]

Can you buy things from aliexpress in Egypt? that's hub motor heaven..

If you can imagine something worse than no shipping; it's probably shipping that's 3-5x the price of the actual product, for a hub motor on AE I'd pay up about...14K? I've seen organs that expensive.
Tx for the thread.

 

[neptronix]

Wow, rough to be an ebike enjoyer out there.

Let me suggest you one thing;
The crank speed is very slow ( ~90rpm ), so you will need a much oversized motor for the power you're looking to put out.
Ideally the motor has a few reductions inside.

It would be much easier to drive a left hand sprocket on the wheel; this way you can get a huge reduction, if you don't mind a sprocket almost as big as the wheel

I wonder if you can get your hands on robotics or RC type motors. Something brushless at least.

 

[Auroa]

It would be much easier to drive a left hand sprocket on the wheel; this way you can get a huge reduction, if you don't mind a sprocket almost as big as the wheel

Like I said, the drill can be reduced from its 700 in a single stage 6:1/5:1 (reminder this is the absolute, very unrealistic maximum) to one of the bigger front sprockets if we have an especially small motor sprocket (or freewheel, I'd love to understand these properly because it could be useful when the motor is turned off).

There's tons of robotics and RC motors, but they're all similar wattage and statistics to something like the JGB because they're for those arduino classes and small cars.

 

[AnthonyC]

Drills are meant for use in short bursts, how long do those Youtube videos last?

 

[Auroa]

Drills are meant for use in short bursts, how long do those Youtube videos last?

In short bursts at full power because of current and cooling, we're simply not using the full power most times, we can get a small fan and attach on the shaft, already how a lot of motors cool themselves.
Plus, we're forgetting we're in a moving vehicle with tons of air.

Also for the record, never seen a drill diy setup before lol

 

[lnanek]

There's dozens of search results for it, top one with 4.7M views:

 

[ChapinB]

Check the link above. Its what inspired mine.

Finding the right kv motor and the right gearing is the hard part.

 

[Auroa]

Neat! I thought about having to carry multiple batteries, but maybe the Ah is better if I don't use it's full power.

Finding the right kv motor and the right gearing is the hard part.

Im Fafoing, and 5:1 or 6:1, thanks!

 

[lnanek]

I'd definitely need multiple in parallel. My commute to work takes 20Ah. I've been collecting DeWalt FlexVolt tools to eventually switch over to tool packs for my eBike. It's slow going, though. I need 4 15Ah FlexVolt batteries (which are only 5Ah at 60V) before I can switch.

It's hideously expensive too. One FlexVolt pack is $419. Meanwhile the last 20Ah Reention pack I bought that was made with Samsung 21700 50G was only $400. So 4x the cost to use tool packs. Essentially free if you need the tool and a pack for other reasons anyway, though.

 

[ChapinB]

Neat! I thought about having to carry multiple batteries, but maybe the Ah is better if I don't use it's full power.

Im Fafoing, and 5:1 or 6:1, thanks!

I have a 6384 motor, 120kv, 6s (22v) and 11:1 ratio limited to 18amps/400 watts. With my ratio and setup, the motor struggles to provide any real torque below a cadence of ~40 rpm. The 11:1 was a noticeable improvement over my previous 10:1. A 6:1 reduction wouldn't provide any meaningful power on my setup. Unless your pushing big amps or have another reduction, that ratio likely wont provide what you are looking for.

Read this thread, he plays with different motors, ratios and settings. Including rough estimates on battery use and chain life. Good read for anyone looking to go this route.

My RC Mid Drive with Single Stage Reduction

I thought you guys might be interested in my RC Mid Drive conversion. I ride frequently in the hills, and I wanted to try just a bit of climbing assist without changing the character of the bike. I ran a Cyclone on and off about 7 years ago, but the benefit to downside ratio was not there, so...

endless-sphere.com

Side note - the chain on many kids toys is a #25h. Iv built many projects with this chain, and up to about 4 or 5kw, they are fairly reliable, albeit a short life span at these power levels. Past that, the quick links becomes the failure point.

 

[scianiac]

In short bursts at full power because of current and cooling, we're simply not using the full power most times, we can get a small fan and attach on the shaft, already how a lot of motors cool themselves.
Plus, we're forgetting we're in a moving vehicle with tons of air.

Also for the record, never seen a drill diy setup before lol

I mean drills already do have fans mounted on them, generally moving a fair amount of air for the size of motor. You can't just keep adding more cooling to get more power. The size of the motor is a practical limit on how much power you can get out of it and a drill motor is very small. Not to mention most cheap drills still use low quality brushed motors which don't like being pushed super hard even more. I mean I've seen people burn up drills all the time just using them slightly hard.

You need to pick what you want here, do you want a super cheap ebike that doesn't require much work but will be really terrible at being an ebike? Drill is not a bad idea. I mean a drill ebike can work totally fine but it will only be able to provide a very small amount of assistance, maybe a little more in short bursts. But also drills generally don't have any thermal protection so you will have to be real careful or you'll burn it up.

Do you want a super cheap ebike that is pretty decent? Well then you need to find a suitable motor from something used, maybe with a gearing or maybe you need to get the gearing from something else but it will take some work. Here are some examples for ways I would build a very inexpensive ebike that would still be pretty decent. Look for a broken electric scooter, hoverboard, electric lawnmower, wheelchair, even some treadmills have useful motors may work. You just need a large enough motor that will operate at the right voltage range then you can figure out the transmission of that to the bike.

 

[neptronix]

Could you do two reductions? that would open up a lot of doors.

 

[Auroa]

I have a 6384 motor ... the motor struggles to provide any real torque below a cadence of ~40 rpm.

I guess we'll have to wait and see. I don't know how much power it would lose in gearing, but it's hard to believe a 400W can't provide torque at that rate.

I mean a drill ebike can work totally fine but it will only be able to provide a very small amount of assistance, maybe a little more in short bursts.

Fine by me!

Look for a broken electric scooter, hoverboard, electric lawnmower, wheelchair, even some treadmills have useful motors may work.

If anybody has these, they're either replacement parts or scrap, I've never seen any of these motors be functional, available, and reasonably priced.

Could you do two reductions? that would open up a lot of doors.

Would need a jackshaft, and I don't know neither how to source its parts nor make it.
Again, I don't think two are needed.

 

[ChapinB]

I guess we'll have to wait and see. I don't know how much power it would lose in gearing, but it's hard to believe a 400W can't provide torque at that rate.

Brushless motors, and controllers for that matter, are inefficient at low rpm/high amps. High phase current causes saturated windings, heat build up in the motor and controller. Could I bump the phase current up to 150 amps and get that torque back? Probably. But none of the electronics would be happy about it for long.
Limiting a motor to 500rpm when it wants to spin at 2700 is leaving a bunch of performance on the table. Perhaps if you can find a 40kv motor for your build, a 6:1 ratio might work? But I'd be willing that would feel fairly gutless without large currents as well.

Your concerned with range or battery life. Why build something that runs at a sub-optimal efficiency rpm?

Not saying my way is the best, Im positive theres better ways of doing it. I can 100% for sure say the motor feels like a dog when I shift into a high gear and pedal with a slow cadence. But wakes up the faster I pedal, to the point I wish I could fit a 15:1 ratio.

 

[glennb]

Mixing drill in low range gear ought to cope with bike applications. But yes, can't imagine a regular cordless drill surviving a hill. If you want to see how quickly they cook when bogged down, stick a mixing paddle in one and attack a batch of mortar with it.