My RC Mid Drive with Single Stage Reduction

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Re: My RC Mid Drive with Single Stage Reduction

Post by SlowCo » Oct 19 2018 2:56pm

This is a great DIY mid drive idea!
I might use it on my bike next year. Thanks for sharing and keep enjoying your bike!


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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 19 2018 3:34pm

falcongsr wrote:
Oct 19 2018 1:28pm
Would using a 60kV motor such as this one: https://alienpowersystem.com/shop/brush ... 0kv-1800w/ potentially open up higher voltages or simpler reductions?
That's an interesting motor. Looks like it can handle lots of current and power. If I had an 8S pack, I would be very tempted to order one.

As a side note, I did run a small light motor on this bike for a while to see how small I could go. It was about the same weight as the Alien motor, but about 1/3 the power rating.
5045 motor.jpg
5045 motor.jpg (43.25 KiB) Viewed 631 times
This tiny motor was 336 gm, and rated for 15 Amps. I typically ran it on 3S, at up to 190 watts max. It saw almost 17 Amps, but was not happy over 15 Amps. This motor was ALMOST good enough. For 85% of my riding it was fine, but it had no torque reserve at all. Also, it wanted to run at higher RPM for maximum power, so I had to pedal like mad to get up steep hills, which kind of defeated the purpose.

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 19 2018 3:36pm

falcongsr wrote:
Oct 19 2018 1:28pm
Would using a 60kV motor such as this one: https://alienpowersystem.com/shop/brush ... 0kv-1800w/ potentially open up higher voltages or simpler reductions?
You just cost me money! :D :D :D

I just ordered the 120KV version. I was not aware of Alien motors! Thanks!

(I think I got the last one :) )

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Re: My RC Mid Drive with Single Stage Reduction

Post by falcongsr » Oct 19 2018 3:45pm

Sorry! :D

If you were starting from scratch would you choose a lower kV motor if you had access to them?

I picked up a Kepler Friction Drive for my road bike and I'm delighted with it on 6S power. Now I'm thinking of a single-stage reduction for wet weather riding.

Can you share how you mounted the 90T wheel sprocket to the chainring? Your sprocket doesn't look like these: http://electricscooterparts.com/sprocke ... wheel.html

Thanks!

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Re: My RC Mid Drive with Single Stage Reduction

Post by Tommm » Oct 19 2018 4:20pm

Most of the higher rated ones have an open design, others have very low voltage ratings making them impractical for high powered ebike use. That vent seems to be the reason they are so small and light but high rated. Cyclones are closed.
These RC motors are not made for bike applications at all. A good motor that isn't a cyclone and has high quality is the qs motor 2000w mid drive. It blows these out of the water.

Then again for your application a bosch 250w mid drive would suffice, with much higher reliability.

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Re: My RC Mid Drive with Single Stage Reduction

Post by neptronix » Oct 19 2018 5:15pm

Tommm wrote:
Oct 19 2018 4:20pm
Then again for your application a bosch 250w mid drive would suffice, with much higher reliability.
No way, man. Lots of gears and proprietary components in those. I've seen my shares of failures of these at a local ebike shop, and the cost of the parts.
His drive is the perfect answer to these issues. Order a spare motor for $100. No CANBUS or proprietary parts, but an open source controller instead. Run whatever ratio you want. Pop over to a scooter shop and pick your replacement parts up on the spot.

I also have in my posession a bosch battery which is perfectly fine, except the BMS got hit by a suicide switch in the programming. X amount of cycles and bosch considers the whole thing a throwaway.. WTF!
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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 19 2018 6:59pm

falcongsr wrote:
Oct 19 2018 3:45pm
If you were starting from scratch would you choose a lower kV motor if you had access to them?
Thanks!
If I was starting from scratch, and there was a good selection of 60 KV motors, I might go 8S. Same for 80KV and 6S. Just size the battery pack for the same number of Watt Hours.

Coincidentally, an hour ago I received a new motor in the mail - Turnigy SK8 6354-140KV. 630 grams vs the current 125KV motor which weighs 780 gm. The heavier 125Kv motor has a pretty flat torque curve on 4S, which is really nice. The new lighter motor seems to have a Torque curve which increases with RPM on 4S. I don't think it will matter most of the time at 200 to 250 watts, but there is one short steep 30% hill - TBD...

Now I'm really curious now about that Alien motor - 120KV and 380 gm, rated for 55 Amp.

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 19 2018 7:14pm

falcongsr wrote:
Oct 19 2018 3:45pm
Can you share how you mounted the 90T wheel sprocket to the chainring? Your sprocket doesn't look like these: http://electricscooterparts.com/sprocke ... wheel.html
Thanks!
Yup, the 90T sprocket on the bottom of the page. I turned the center out and drilled a bunch of holes. I'm fortunate to have a lathe and a small mill with a rotary table. You might be able to do the same with a hacksaw, file, and drill, or take it to a machine shop. I drilled four holes for the standard 104 BCD bicycle pattern, and used really long chainring mounting bolts.

https://www.amazon.com/Chainring-Bolts- ... extra+long

Then I drilled a bunch of holes to make it lighter. That thing is thick heavy steel!

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Re: My RC Mid Drive with Single Stage Reduction

Post by falcongsr » Oct 19 2018 10:24pm

Thanks for the details and gearing info FZBob. I was afraid you'd say you customized that 90T sprocket. A little outside my skillset - I'd need to buy a few spares for sure!

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 19 2018 11:23pm

falcongsr wrote:
Oct 19 2018 10:24pm
Thanks for the details and gearing info FZBob. I was afraid you'd say you customized that 90T sprocket. A little outside my skillset - I'd need to buy a few spares for sure!
I hear you. The trick would be to find about 10 other guys who want the same thing. Negotiate a group buy of sprockets. Find a machine shop with a CNC mill and negotiate a good price. I suspect the machine work could be done for under $30 each. If anybody wants to take that on, I would be happy to provide the autocad drawing file...

Or - work with one of the custom sprocket manufacturers to have aluminum versions made... Probably about the same price in the end, depending on quantity, and a better part. Again, I can provide the drawing, and I would buy at least one of the chainrings!

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Re: My RC Mid Drive with Single Stage Reduction

Post by Kepler » Oct 20 2018 2:11am

Thread has gained some well deserved traction. Low power lightweight builds are sadly lacking on this forum and I think this build has been a nice change of direction.

I total disagree that RC motors are not suited to ebikes. coupled with a Vesc controller (or similar), I think they are the perfect combination for those ebikers who prefer their bike to remain a bike after conversion. I now look forward to seeing what transpires now we have seen what can be done with a bit of lateral thinking.

Don't get me wrong, I still love high powered builds also but for a completely different reason.
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Re: My RC Mid Drive with Single Stage Reduction

Post by wineboyrider » Oct 20 2018 12:55pm

Nice to finally find a decent sensored turnigy motor 8)
ES IS SAVED! THANK YOU JUSTIN.

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 20 2018 2:16pm

wineboyrider wrote:
Oct 20 2018 12:55pm
Nice to finally find a decent sensored turnigy motor 8)
Just curious - What's the deal with Turnigy motors - Reliability? Performance? I haven't used them very long, so wondering what I can look forward to... By the way, I'm not using the sensors, so I don't know if they are decent or not.

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 20 2018 3:46pm

Tommm wrote:
Oct 19 2018 4:20pm
These RC motors are not made for bike applications at all.
"Turnigy D5035-125KV Sensored Brushless Motor ideal for Electric Skateboard Conversions". Quote from Hobby King. All the SK8 motors say this. I know a skateboard is not a bike, but they both operate in dusty environments and propel a human at similar velocity...

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Re: My RC Mid Drive with Single Stage Reduction

Post by edblanch » Oct 20 2018 5:28pm

Bob,

Great build, that I would like to replicate here in Australia.

I had a couple of questions :
1 Where did you get the motor mounting bracket from ?
2 What Voltage battery pack are you using as I've got a 48V 10AH unit I would like to use.

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 20 2018 7:05pm

edblanch wrote:
Oct 20 2018 5:28pm
Bob,

Great build, that I would like to replicate here in Australia.

I had a couple of questions :
1 Where did you get the motor mounting bracket from ?
2 What Voltage battery pack are you using as I've got a 48V 10AH unit I would like to use.
Thanks! I built the motor bracket from a piece of 1/4" thick 3" x 3" angle aluminum. I bought some M5 aluminum Rivet Nuts from McMaster Carr, which are an exact match for the inserts Giant uses for their water bottle mounts. Installed one above and one below the two existing bottle mounts. Moved the water bottle up 2", and bolted the motor mount to the remaining lower 2 inserts. I ran a strut from the mount to down under the frame to prevent the mount from tipping sideways. I put a hose clamp at the top of the mount around the frame to prevent pulling on the top bolt. I really didn't like drilling holes in the frame, but it worked out fine.


Batteries. I have run 3S - 11.1V and 4S - 14.8V. I have tried 125KV, 140KV and 150KV motors.

The sweet spot is definitely the big 125KV motor and 4S. This has a pretty flat torque curve, and feels really natural when pedaling. It's easy to forget I'm on an Ebike. Anything between about 40 RPM to 80 RPM cadence just feels good.

The big 125KV motor on 3S felt like a diesel. It wanted a low cadence to make torque. OK, but not great. Not really natural, it required thinking...

The higher KV motors really want to spin to make torque. I always found myself at a higher cadence than I preferred while climbing, which was tiring, and bothered my knee.


So - unfortunately I suspect that your 48V pack will spin the crank way too fast. That's over 3 times the voltage I'm running, which means you need about 30:1 reduction. It sounds like the right pack for a high power build with multiple stage reduction... Can you break the pack up and rebuild it around 15 volts?

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Re: My RC Mid Drive with Single Stage Reduction

Post by Kepler » Oct 21 2018 2:30am

FZBob wrote:
Oct 19 2018 6:59pm
falcongsr wrote:
Oct 19 2018 3:45pm
If you were starting from scratch would you choose a lower kV motor if you had access to them?
Thanks!
If I was starting from scratch, and there was a good selection of 60 KV motors, I might go 8S. Same for 80KV and 6S. Just size the battery pack for the same number of Watt Hours.
Got to ask, why 8S with the 60kv motor? My calcs come up with 6S and 60 kV at 10:1 being a nice combo. Calculated as opposed to real world can be be quite different I know.
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Re: My RC Mid Drive with Single Stage Reduction

Post by neptronix » Oct 21 2018 3:02am

Okay, three things..

1) there's a company in the USA called rebel gears that can cut up pretty much any sprocket you want. I had purchased a custom one from them and it was very high quality..
http://www.rebelgears.com/

2) alien power sells sensored RC motors that go all the way down to 30kv. These are usually in the multi KW range. I don't know how high of quality they are, but if you wanna run 10S-12S for this kinda build, you might find something that's perfect from them.

3) for making a standardized kit that fits muliple bikes, i think a handlebar stem mount to the seat tube could work great. Check this thread for more info:
viewtopic.php?t=79254
My first major build: 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w on a Turner O2 full suspension.
The wheelie machine: 20" Rear Magic Pie II on a Trek 4300 MTB

"The best time to plant a tree was 20 years ago. The second best time is now."- Chinese Proverb

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 21 2018 2:44pm

Kepler wrote:
Oct 21 2018 2:30am
Got to ask, why 8S with the 60kv motor? My calcs come up with 6S and 60 kV at 10:1 being a nice combo. Calculated as opposed to real world can be be quite different I know.
My calculations showed the same thing. However, my calcs showed 3S with 125 KV, and it ran like a diesel - all the torque at low cadence. When I tried 4S, the same motor woke up. Nice flat torque curve. I suspect this illustration might explain it, but I'm not sure. I would love to see a set of real motor curves for my motor, but I suspect they don't exist...
BLDC Torque Curve c.jpg
BLDC Torque Curve c.jpg (23.98 KiB) Viewed 438 times

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 21 2018 3:06pm

neptronix wrote:
Oct 21 2018 3:02am
Okay, three things..

1) there's a company in the USA called rebel gears that can cut up pretty much any sprocket you want. I had purchased a custom one from them and it was very high quality..
http://www.rebelgears.com/

2) alien power sells sensored RC motors that go all the way down to 30kv. These are usually in the multi KW range. I don't know how high of quality they are, but if you wanna run 10S-12S for this kinda build, you might find something that's perfect from them.

3) for making a standardized kit that fits muliple bikes, i think a handlebar stem mount to the seat tube could work great. Check this thread for more info:
viewtopic.php?t=79254
Just curious - about how much did the custom sprocket cost? What size was it?

Just found the Alien website - lots of cool stuff! Ordered a 50mm 120 KV motor, and would really like to get a 50mm 90 KV, but I need to slow down on buying motors...

Yup, the trick for making a kit of this would be the motor mount. Maybe offer a few options - Handlebar stem mount, water bottle bracket, something like Cyclone has (Yuck). I'll leave all that for someone else... I'm retired, and that sounds a lot like work. :D

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Re: My RC Mid Drive with Single Stage Reduction

Post by falcongsr » Oct 22 2018 1:06pm

FZBob wrote:
Oct 21 2018 2:44pm
My calculations showed the same thing. However, my calcs showed 3S with 125 KV, and it ran like a diesel - all the torque at low cadence. When I tried 4S, the same motor woke up. Nice flat torque curve.

I noticed my no-load "eRPM" that my bluetooth module logged is ~17% lower than my expected motor RPM calculated by motor kV * Battery Voltage.

So either the motor kV is lower than what the manufacturer says or FOC mode doesn't put out full battery voltage, or both.

Does anyone know if the FOC algorithm these VESCs uses reaches full battery voltage on the motor outputs? I wonder if the motor spins faster in BLDC mode...

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Re: My RC Mid Drive with Single Stage Reduction

Post by neptronix » Oct 22 2018 2:22pm

kV under load is always 10%-20% lower than unloaded kV in an old fashioned PWM controller.
This figure can vary more in a FOC controller.. based on the settings you use.


as for the rebel gears sprocket.. i bought it 5 years ago and forget the price. In the $50 range for a custom 39T 415 sprocket with a bicycle disc brake mounting pattern.
My first major build: 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w on a Turner O2 full suspension.
The wheelie machine: 20" Rear Magic Pie II on a Trek 4300 MTB

"The best time to plant a tree was 20 years ago. The second best time is now."- Chinese Proverb

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Re: My RC Mid Drive with Single Stage Reduction

Post by falcongsr » Oct 22 2018 6:09pm

neptronix wrote:
Oct 22 2018 2:22pm
kV under load is always 10%-20% lower than unloaded kV in an old fashioned PWM controller.
This figure can vary more in a FOC controller.. based on the settings you use.
I'm seeing 17% lower RPM with no load than kV * Vbatt in FOC mode. I suspect it might be because of FOC/settings. Which might explain FZBob's preference for 4S vs 3S?

I'm pretty new to this, thanks to all for weathering the ignorance and questions.

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Oct 24 2018 2:11pm

neptronix wrote:
Oct 22 2018 2:22pm
as for the rebel gears sprocket.. i bought it 5 years ago and forget the price. In the $50 range for a custom 39T 415 sprocket with a bicycle disc brake mounting pattern.
Thanks Neptronix! I just ordered a custom Aluminum 90 tooth #25 sprocket from Rebel Gears. About $46! They were very nice to deal with. I requested a 3.47" dia center hole and 4 ea 0.390 dia mounting holes on a 4.094" circle. This should match the standard 104 bcd bicycle chainring pattern and bolt right on my standard crankset. Plain disc, with no lightening holes. It will need to be spaced outward with some washers for clearance. The new aluminum sprocket should weigh 200 grams as built, and I will probably lighten it to 64 grams.

For comparison, the current steel chainring from Electric Scooter Parts cost $30, and I had to spend a full day modifying it to fit my crankset and drilling lightening holes. It weighs 200 grams after all the mods.

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