My RC Mid Drive with Single Stage Reduction

Discussions related to motors other than hub motors.
This includes R/C motors, botttom bracket, roller and geared drives.
FZBob   100 W

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Jul 11 2019 1:31pm

thepronghorn wrote:
Jul 09 2019 3:30pm
FZBob, I really like this very simple and clean design. I have been following closely and am thinking about making my own. I also wanted to offer some technical equations for torque and phase amps that could maybe inform some of your motor, current limit, and battery choices.
...

Perhaps you can use some of the above math to help explain why different motors feel different from each other. I would be interested in what you are trying to optimize when you play with VESC current limits as well as what low and high rpm mean when you are reading your watt meter.

Since you have plenty of voltage headroom on your VESC but are butting up against the current limits, lowering Kv will help to move the volts/amps combination away from the current limit.
Thanks for your post. Lots of good information here! I have started to add it into my Excel motor sheet.

My "Low RPM" is about 40, and "High RPM" is around 100-110. I'm estimating, as it has been decades since I've had a cadence meter on a bike, but I'm probably within +/-15%.

I've been setting up the VESC current limits as follows. (Note: I'm not an electric motor expert!) I set the Battery Amps to what is listed on the motor spec. Then I increase the Motor Current Limit (Phase Amps) until I see cogging at low RPM and full load/power, and back off about 5%. I have never seen peak amps on my wattmeter come close to the battery current limit I set, so I don't worry about that parameter. I'm not sure if I'm setting the Motor Current correctly, but it seems to work for me. Since I rarely use over 200-250 watts for more than a few seconds, I may be operating in a very forgiving fashion.

(By the way, just to keep the record straight, I'm using 53 Amp phase current on the orange (D5035) motor.)

So if I was to switch from my 125Kv motor to a 100Kv motor, would you expect a need to change from 4S to 5S ? When I tried a 60Kv motor, it needed 8S...

One thing which has puzzled me for a while. At "Mid RPM", (say about 60 RPM), and even "Low RPM", if I hammer the throttle I see Watts and Amps on my Turnigy wattmeter much higher than expected/predicted. Almost as high as at High RPM, over 400 watts. If Torque is more or less constant over RPM, and I believe it is, I would expect power to be proportional to RPM, and therefore the wattmeter should not show a lot of watts at low and mid rpm. Where is the extra power going? I'm guessing heat?

fixvid   10 mW

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Re: My RC Mid Drive with Single Stage Reduction

Post by fixvid » Jul 11 2019 3:15pm

FZBob wrote:
Jul 11 2019 1:31pm
I set the Battery Amps to what is listed on the motor spec. Then I increase the Motor Current Limit (Phase Amps) until I see cogging at low RPM and full load/power, and back off about 5%.

By the way, just to keep the record straight, I'm using 53 Amp phase current on the orange (D5035) motor.
How could you set the limit so high ? If i set motor amps higher then 30A i get cogging at full load. I tried increasing battery amps but that didn't solve it(lowering it solves it, but then power decreases), the maximum motor current without cogging is 29A. At this level battery amps barely hit 20A, so not more than 300W total.

Here is the phenomenon:
https://youtu.be/Q2mATFNtfxk

FZBob   100 W

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Jul 11 2019 4:30pm

fixvid wrote:
Jul 11 2019 3:15pm

How could you set the limit so high ? If i set motor amps higher then 30A i get cogging at full load. I tried increasing battery amps but that didn't solve it(lowering it solves it, but then power decreases), the maximum motor current without cogging is 29A. At this level battery amps barely hit 20A, so not more than 300W total.

Here is the phenomenon:
https://youtu.be/Q2mATFNtfxk
Just watched your video. Mine has always done exactly the same thing on my bike stand. However, since I never use full power at almost stall, it has never been an issue for me in actual riding. In my mind, that's just the motor stalling out.

I determine my motor current by riding up a steep hill in a very low gear, like 22/36, at about 35 to 40 RPM pedaling, and full throttle. I increase motor current until it cogs (less severely than in your video) and back off about 5%. In actual riding I never use full throttle at low RPM, and only rarely at mid or high RPM, when I really have a tough climb, and then I'm working hard too.

Lately I have been occasionally using just a bit of assist from a dead stop when starting in the middle of a steep technical hill, where I would not be able to start without a bit of assist. Not a lot of power, but just enough to help get the pedal moving while I get my other foot up.

By the way, how's your motor mount working out? I'm thinking about doing the same clamping arrangement on my nice bike, as I don't want to drill holes in the frame.

fixvid   10 mW

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Re: My RC Mid Drive with Single Stage Reduction

Post by fixvid » Jul 12 2019 3:50am

FZBob wrote:
Jul 11 2019 4:30pm
By the way, how's your motor mount working out? I'm thinking about doing the same clamping arrangement on my nice bike, as I don't want to drill holes in the frame.
It's pretty good but it does have some flex to it. The corner sides of the motor plate crack because of the printing/layer orientation but it's still holding up. I will reprint the motor mount with another orientation and that should solve the problem. I could also increase the temperature, because the crack was the result of insufficient layer bonding. This was just the first usable version, i feel it can be improved but i'm lazy nowadays.

I tried to connect the HM10 bluetooth module and i had no luck even though i tried every combination possible. The app sees the bt module but it won't receive any data from VESC. There is one more module 'NRF type' which is used by the mobile VESC tool beside the more expensive metr module. This costs 10usd.
https://flipsky.net/collections/accesso ... rd-ws82013

fixvid   10 mW

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Re: My RC Mid Drive with Single Stage Reduction

Post by fixvid » Jul 13 2019 4:15pm

Today i reprinted the motor mount in PLA. Took it in my hands and it felt very stiff .. stiffer than ABS for sure.
Image

I thought to myself: Nice, i won't have any more problem with chain become slack and climbing on the chainwheel teeth. Guess what ? i was wrong.. and the culprit is (drum-roll pls): the bloody motor shaft. It's flexing like hell when i pinch the chain. So not the printed mounts induce that much slack but the shaft itself. I was thinking that it's a nice hardened steel. Well, 8mm is not enough and it should be supported by bearings on the end. Like your motor cover FZBob which you bought from hobbyking. That should solve the problem.
It should be supported anyway, otherwise i'm very skeptical that the inside bearing will last 1-2 years.

FZBob   100 W

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Jul 14 2019 1:12pm

fixvid wrote:
Jul 13 2019 4:15pm
Today i reprinted the motor mount in PLA. Took it in my hands and it felt very stiff .. stiffer than ABS for sure.
Image

I thought to myself: Nice, i won't have any more problem with chain become slack and climbing on the chainwheel teeth. Guess what ? i was wrong.. and the culprit is (drum-roll pls): the bloody motor shaft. It's flexing like hell when i pinch the chain. So not the printed mounts induce that much slack but the shaft itself. I was thinking that it's a nice hardened steel. Well, 8mm is not enough and it should be supported by bearings on the end. Like your motor cover FZBob which you bought from hobbyking. That should solve the problem.
It should be supported anyway, otherwise i'm very skeptical that the inside bearing will last 1-2 years.
Is the chain climbing the teeth on the big chainring or the little sprocket? I'm wondering what's causing this because I have never had the issue even when my chain is floppy loose.

I just went out and squeezed my chain, and my motor shaft flexes too. I was actually expecting the bearings to fail from dust, as they are only shielded, not sealed, and I ride very dusty conditions. I will continue to run without the outer bearing support just as a stress test. I got a year and 850 miles on the orange motor before I changed it out last month. When I get some spare time, I will convert my good bike using the old orange motor, and continue testing.

That little sprocket cover with the built in outer support bearing is structurally really helpful. It also looks really nice.

By the way, my motor shaft was definitely soft, as it got tore up when I tried the belt drive and the set screws slipped. I was easily able to file it down. Note that shaft flex (elastic deformation) is not really a function of hardness, as the Modulus of Elasticity is about the same for all steel, hard or soft. Shaft diameter is by far the major factor, as stiffness is proportional to thickness cubed.

fixvid   10 mW

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Re: My RC Mid Drive with Single Stage Reduction

Post by fixvid » Jul 17 2019 3:00am

I made a shaft support with a bearing:

Image

Image

It made a big difference in chain slackening. No more shaft flexing. The problem with the chain climbing on the big chainwheel i think it's because my motor is right above the chainwheel and the chain is tangent(vertical) to it. I saw that your motor is mounted more to the front of the bicycle and chain is not vertical like mine. Probably that's why you were trouble free.

My steel chainwheel is also not true because my crank wasn't designed with chainwheels mounted on the exterior. I have to take it to a milling shop to flatten the mounts then buy a nice aluminium chainwheel. Maybe NateTN made some progress with the water jet cut chainwheels.

I found a weakness with the printed motor mounts and it's not flexing but heat disipation. I climbed some smaller hill (and on longer flats) the motor is heated to 65C where i set the VESC to start to cut power. It heats up too easily. The PLA mounts do not disspiate heat and it probably don't help that motor is half enclosed. I need to make an aluminium angle mount, it's just hard to find.

c_saayman   10 mW

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Re: My RC Mid Drive with Single Stage Reduction

Post by c_saayman » Jul 18 2019 6:58am

So I've started the build on my 12 speed Polygon N8.
Polygon N8.jpg
Polygon N8.jpg (376.9 KiB) Viewed 65 times
For this ebike conversion the gearing on FZBob's bike is very good (22T front and 40T back). With the SRAM 12 speed the smallest sprocket is 32T, and a big 50T cassette at the back. Compare the two and FZBob is still better for keeping the motor RPM up during climbing.
His gears meters develop compare to mine.JPG
His gears meters develop compare to mine.JPG (41.34 KiB) Viewed 65 times
It was a great suggestion from Briangv99 to use the bash guard ISCG mounts to mount the motor. I started of with the steel 80T sprocket(cheap), just for testing, but ordered the 90T Rebel Gears to keep the price down. She did not ask me again for CNC setup, just $62+ shipping to Australia.
I am concerned about the ground clearance, but will give it a go first. I had to add the round hollow pipe to my bash guard to go from 80T to 90T. Still waiting for the 90T.
Bash guard with motor mount.jpg
Bash guard with motor mount.jpg (139.11 KiB) Viewed 65 times
Bash guard fitted.jpg
Bash guard fitted.jpg (504.63 KiB) Viewed 65 times
I don't have any bag space on the frame. The idea is to build a very flat battery out of 18650 cells, 4S4P, that mounts under my down pipe. Unfortunately all the extra aluminium make it impossible to keep the weight down.
Polygon N8 with motor.jpg
Polygon N8 with motor.jpg (480.01 KiB) Viewed 65 times
I want to use a push button throttle.
s-l500.jpg
s-l500.jpg (10.22 KiB) Viewed 65 times
Push the green button, power. maybe 200W. Push the red button in, double the power on the green button (turbo). Maybe cruise control on the right indicator and completely off on the left indicator. This is the idea, with a basic resistor network connected to the ADC input of the VESC controller. Any suggestions on this will be appreciated. Kepler had a great idea with using the Arduino throttle, but I would like to simplify that even more. Not sure if it can be done. Unfortunately, until I finish the battery I cannot run anything. I still have to figure out the controller and the VESC software tool.
Everything is going to be completely sealed, so I ordered the Metr Bluetooth transmitter, so that I can make adjustments later without having to open the box every time.
Any suggestion will be appreciated.

FZBob   100 W

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Jul 18 2019 2:36pm

fixvid wrote:
Jul 17 2019 3:00am
I made a shaft support with a bearing:

I climbed some smaller hill (and on longer flats) the motor is heated to 65C where i set the VESC to start to cut power. It heats up too easily.
Nice support. Do you notice any difference in chain noise? My aluminum support increased noise a bit, especially in the harsh sounding higher frequencies. I suspect it might have been "ringing" a bit...

Just curious - do you know how many battery amps you are seeing when the motor heating occurs? Also, have you noticed if your VESC FET's are getting warm? I think my FET's heat up more than my motor.

FZBob   100 W

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Re: My RC Mid Drive with Single Stage Reduction

Post by FZBob » Jul 18 2019 2:59pm

c_saayman wrote:
Jul 18 2019 6:58am
So I've started the build on my 12 speed Polygon N8.

It was a great suggestion from Briangv99 to use the bash guard ISCG mounts to mount the motor. I started of with the steel 80T sprocket(cheap), just for testing, but ordered the 90T Rebel Gears to keep the price down. She did not ask me again for CNC setup, just $62+ shipping to Australia.
I am concerned about the ground clearance, but will give it a go first. I had to add the round hollow pipe to my bash guard to go from 80T to 90T. Still waiting for the 90T.

I want to use a push button throttle.

Push the green button, power. maybe 200W. Push the red button in, double the power on the green button (turbo). Maybe cruise control on the right indicator and completely off on the left indicator. This is the idea, with a basic resistor network connected to the ADC input of the VESC controller. Any suggestions on this will be appreciated. Kepler had a great idea with using the Arduino throttle, but I would like to simplify that even more. Not sure if it can be done. Unfortunately, until I finish the battery I cannot run anything. I still have to figure out the controller and the VESC software tool.
Everything is going to be completely sealed, so I ordered the Metr Bluetooth transmitter, so that I can make adjustments later without having to open the box every time.
Any suggestion will be appreciated.
Nice looking bike! I really wish I had ISCG tabs.

Just a suggestion, you might consider running a light strut from the motor mount up near the motor over to the frame, just to stabilize the mount and keep it from wobbling/vibrating.

I like the push button throttle idea. I had considered something similar, possibly with a toggle switch for around 150 watts cruise control, and a turbo button or possibly a throttle over-ride. I agree it could be done with a voltage divider resistor network. (and maybe a couple of diodes if using a throttle over-ride). I would be curious what resistor values you come up with, I never got that far. I would assume pretty high values, as it should not take much current. Might be worth starting with a potentiometer in the circuit in order to dial in the power.

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