My RC Mid Drive with Single Stage Reduction

fixvid said:

FZBob said:

I used the same current limits as the Turnigy 6374, since I worry about cooking the VESC.

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Why worry ? just set the MOSFET temperature start and limit values and power will be gradually reduced from start to end limit tempeature. I would say 60C to 70C is pretty safe.

FZBob said:

The Mystery 6384 has a fairly harsh and somewhat louder sound in comparison.

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That's an interesting point because for me this motor had a more satisfying 'brushless' sound with a characteristic whirl and high pitched sound. Although at a specific RPM it resonates but it's not very problematic. When i turn by hand both motors the turnigy is indeed smoother but somehow in my application Mystery had a better sound and the transmission was smoother too. The shaft of the motor is 10mm thick which is a BIG plus because i have no longer have to support the end of the shaft - D5035 was bending like crazy at high loads causing all sorts of chain problems.

FZBob said:

Overall I like this motor. I just wish it was a bit quieter & more pleasant sounding. However, for the price it's a bargain. I pay more for a tire!

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Don't overpay for tyres. Buy Continental and Schwalbe tyres from www.bike24.com
Their top tyres are between 30E and 40E. I don't know if you have to pay import taxes, if any, because they are from Germany. For a speedy rear tyre i use Conti Race King 2.2 or if i want more grip and cushion than Schwalbe Rocket Ron 2.6. For front tyres with more grip i use Schwalbe Rocket Ron 2.2 - 2.8 or Conti CrossKing 2.4.
These tyres are lightweight and if you are agressive or ride in harsh environment chose the Protection(Conti) or SnakeSkin(Schwalbe) carcass or go with their more agressive pattern tyres which are more robust (Conti Mountain King, Schwalbe Knobby Nic, etc).

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My VESC is set to:
Motor Current 75 Amp
Battery Current 40 Amp (I often see 44+ Amp peaks on the wattmeter after my ride...)
MOSFET temp cutoff start 85C (default)
MOSFET temp cutoff end 100C (default)
But remember, I only use high power for a few seconds... I ran a few tests when I had the metr working, and at high power the MOSFETS were getting up around 85C in under 30 seconds. I occasionally think about the big heavy duty VESC...

The sound thing is interesting. My motor mount is all aluminum, bolted to the frame. I wonder if the noise may be transmitted more, due to the solid mount. Is yours similar?

I do have a taste for Maxxis Minion DHF front tires...

FZBob said:

Motor current 75amps

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I have no ideea how you achieve such high powers.. [75 phase amps] .. even if i set it to 50 amps it feels inefficient and rough, probably because of small 10t sprocket. I set it to 30 amps and it feels good and smooth enough.

I've never seen more than ~350W on VESC app, with 30A battery limit. If i set the current limits too high the motor cogs and i don't like it. I'm really into smoothness. I think you have Lipo batteries which also sag less than my 4s6p li-ion.

My motor is mounted to an aluminium plate and this plate is mounted via ABS adapters to the frame. I remembered that i was using a bearing to hold the end of the shaft and that amplified the noise. For Mystery motor no such need because the shaft is thicker.

Anyway i built the first prototype of my second drive unit with 24:1 reduction. There is just no comparison between this drive and the new one. It's like driving a sports on the weekend vs a daily average car used to go to work. It climbed the steepest hill without breaking a sweat until i had a fatal failure. I was expecting it and im redesigning the bearing housings. I'm using the D5035 which in this application feels like a mini rocket. I was testing it with 10s li-ion but i'm planning to go 12s on the final version. I'm trying to keep torque as low as possible because even like this im afraid of stressing too much the bike.

My primary bike had not been getting much use since I motorized my Reign. So I added a motor to it last December and have been riding it ever since. I have about 35 rides on it now.

It's a 2013 Giant Trance 29er, modified to be as close as possible to my Reign. I installed a Reign suspension link and longer shock for 157mm travel in back. https://forums.mtbr.com/giant/reign-shock-link-trance-29er-838322.html
A Fox 34 150 fork and a 1.5 degree angleset give 66.25 degree head angle. I have the same tires on both bikes, on wide rims. Not surprisingly, both bikes ride almost identically. The 29" wheels on the Trance are about 5% faster/more efficient, and feel just a bit more planted in the loose stuff. The Trance is also a few pounds lighter, which I don't notice.



Since I didn't want to drill holes in this frame, I used Nylon pillow blocks. I put a bit of helicopter tape on the frame first to protect it.


I had to space the 90T sprocket further out from the spider than on the Reign, as the front derailleur would not go high enough to clear.


Water Bottle bolt through the top pillow block to prevent the mount from sliding.


I added a 3/8" thick angle aluminum brace to prevent the mount from racking/parallellograming. (pic from under the bike)


I found this top tube bag on Amazon. My 4S 10AH pack and electronics fit perfectly




So far, I have been very happy with this conversion. I initially used my D5035 (orange) motor, then the 6374, and finally I bought a second mystery 6384. I think the 6384 might be a bit quieter on the Trance than the Reign, maybe due to the Nylon pillow blocks damping out the sound vs the hard mounting on the Reign. (It seems like the 6384 on the Reign has also got a bit quieter over time, possibly due to the 11T sprocket breaking in a bit...)

With the 6384 (and really the 6374), I have plenty of power, and now I rarely drop down to the granny ring on either bike. Note that I still put in some effort (but not enough to blow my knee out...)

Inspired from all of you guys, I've started working on my own

The previous version was a friction drive, but it didn't work that well and for some reason I blew a lot of tires with it

Pedrodemio said:

Inspired from all of you guys, I've started working on my own

The previous version was a friction drive, but it didn't work that well and for some reason I blew a lot of tires with it

IMG_0649 (Editado).JPG

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Nice sprocket collection! Just curious, where did you source them?

What motor are you using?

FZBob said:

Nice sprocket collection! Just curious, where did you source them?

What motor are you using?

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Thanks, they are custom laser cut, there is a shop in my city that does this kind off service ridiculously cheap, if I were to convert to dollar, all these parts, minus the chain, would be $26

Shiny ones 304 stainless, and black ones carbon steel, in case the stainless ones wear too fast I will temper the carbon ones, I may have gone overboard with the 115T sprocket, but it doesn't look that bad on the bike

For starts I will use a 6355 230Kv motor I have laying around, since I've been building electric skateboard for the past years I have quite a collection of motors to try

Next in line would be a 6396 140Kv, but it's quite heavy and I'm afraid there will be too much drag when pedaling

By my calculations the 6355 at 60 A phase will be capable of 25% grade with the 9/115 sprockets and lightest gear on the bike, this is without pedaling

Since you aren't using a crank freewheel can you use the slack side of the motor reduction for torque measurement or am I not understanding correctly?

Grantmac said:

Since you aren't using a crank freewheel can you use the slack side of the motor reduction for torque measurement or am I not understanding correctly?

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This is actually a good idea, I will think about for a while

Probably the slack side would have to have a pre load, if we could measure hpw that pre load changes, a pedal torque value may be calculated from it

Pedrodemio said:

For starts I will use a 6355 230Kv motor I have laying around, since I've been building electric skateboard for the past years I have quite a collection of motors to try

Next in line would be a 6396 140Kv, but it's quite heavy and I'm afraid there will be too much drag when pedaling

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The 6396 140Kv motor might not be too bad for pedal drag. I've been running 6384's (120Kv) on both of my bikes for a while, and pedal drag is not really noticeable. I like the feel of the lower Kv motors (120-125) as they seem to lug down like a diesel - as I get tired and my cadence slows the motor seems to get stronger. The higher Kv motors (140-150Kv) liked to spin, so when the going got tough, I needed to increase my cadence. Made my knee sore. (different motors so not an entirely valid comparison...) I did find that the 11T motor sprocket seemed a bit more refined than the 9T.

Looking forward to hearing how it all works out, especially with that 115T sprocket!

Nice to hear that

Yeah, the VESC firmware has a problem with tracking at low duty cycles, on low power builds or/and ones that use a non optimal gearing it gets really apparent

I plan to play with that, instead of dropping the Kv, lowering the voltage may also work since you would increase the duty cycle for the same cadence, in my tests it was bellow 35% ~ 40% that it starts to get noticeable

On my drive friction drive version, if I could keep the speed above 19 km/h it worked great, but if it dropped past that point it sucked, right when you need the most torque is when it lacks. You could off course just pump more current, but it’s wasted energy

It’s in my list for years to build a small dynamometer to measure all that, hopefully this next year it will happen

It doesn't look that bad being huge, I may paint it black to mask a bit

Screwed up a bit on the motor mount design, it cover the rear shifter cable mount, a bit of dremeling may solve that, in the future I probably will do a new mount in front of the pedal, I avoided that because the downtube geometry is complex and would require a bit of trial and error to print a piece to clamp it perfectly

good see too you not stop this

good luck

Are all these builds without freewheels on a motor and a chainring?
What is going on here?

Yep you got it.. no freewheel direct drive, super light..

Animalector said:

Yep you got it.. no freewheel direct drive, super light..

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So, you guys are building calf muscles massage contraptions. Very cool. :lol:

Don't knock it before you try it. Light weight low power eMTB's are the future. Not the perfect solution but its all about compromises that you can live with.

Ecyclist said:

Are all these builds without freewheels on a motor and a chainring?
What is going on here?

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I put 30K miles on a mid-drive with no freewheeling cranks. It is awesome.

Warren said:

Ecyclist said:

Are all these builds without freewheels on a motor and a chainring?
What is going on here?

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I put 30K miles on a mid-drive with no freewheeling cranks. It is awesome.

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Can I see your build please? 30K miles sound like a lot.

Ecyclist said:

Warren said:

Ecyclist said:

Are all these builds without freewheels on a motor and a chainring?
What is going on here?

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I put 30K miles on a mid-drive with no freewheeling cranks. It is awesome.

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Can I see your build please? 30K miles sound like a lot.

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Sure. Click on the link under this post.

Warren said:

Ecyclist said:

Warren said:

Ecyclist said:

Are all these builds without freewheels on a motor and a chainring?
What is going on here?

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I put 30K miles on a mid-drive with no freewheeling cranks. It is awesome.

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Can I see your build please? 30K miles sound like a lot.

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Sure. Click on the link under this post.

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Thanks. :thumb:
I will check it out.

No freewheeling and no suspension is definitely not for me.

Finally after a long time it’s rideable, first test went really well, it was just a short ride around the block since it is late

First thing that needs to change is the controls, right now it’s the same as my friction drive, 1 button press 25% torque, 2 50% and 3 100%. Right now it’s really easy to get hurt with that, a throttle will probably be the way to go, maybe slit in two, a button that you press to activate and deactivate the motor and a lever that controls the torque

It was quite a bit of work getting here, first I had to chamfer the chain ring and pinion since the engagement was not good, and probably assembled and disassembled everything at least 10 times playing with spacer, cutting the mounts to increase the adjustment range and all that until I got a chain line that I was happy with

Also I need to increase the motor current, right now it’s at just 30 A, and since the previous setup has no airflow on the vesc it was fine since it throttled to just 20 A continuous, right now it’s just held by Velcro straps to the tubes for testing and seeing how much current I can run with plenty airflow

I also rebuilt the battery, it’s a 6S4P made of NCR18650B from a old pack that had a lot of use a few years back and sat on a shelf for at least 4 years, surprisingly good capacity left on the cells

@FZBob
Great engineering congrats!
How did you manage to get the correct shape for the nylon pillow blocks around the Trance frame?
Safe riding!

Ecyclist said:

No freewheeling and no suspension is definitely not for me.

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For years I believed a motor freewheel was necessary. I put a lot of thought into freewheel mechanisms. If you take a look at the very first pic in the first post on this thread, you can see a big ol' FREEWHEEL on the left side of the crank, allowing for pedaling past the motor. It was noisy and heavy...

Then I did an experiment. (3rd pic, first post...) No freewheel! I was pretty surprised when the bike pedaled just fine. Motor drag ends up about 6-10 watts as near as I can tell. Way less difference in drag than switching from a fast rear tire (Spec. Slaughter, Kenda Small Block 8, etc) to an aggressive rear tire (Kenda Nevegal, etc). (I have a 2' stack of tire experiments up in the attic...). On THIS PARTICULAR SETUP, with the low reduction ratio, these little motors spin easily. Not at all like the Cyclone I had 10 years ago which would require a pipe wrench to back-drive.

The freewheel weighed 211gm and the Crank & BB required to use it weighed 169gm more than the original crank, for a total delta of 380gm. The freewheel was noisy. Without the freewheel, pedaling without the motor is pretty quiet. (just a touch of chain noise). Also, the freewheel had a "take up clack" when adding power. Without the freewheel, the motor is already spinning, so the take up is pure silk...

At this point, I have about 3300 miles of very hilly & varied technical off-road on my two bikes. I ride about 3x per week, and I DO NOT use the motor when pedaling on flats, downhill, or slight uphills. Believe me, if the drive was draggy, I would have put the freewheel back!!! At this point, I don't think much about the drive system. I lube the motor chain when I lube the bike chain (before every ride), and replace the motor chain & drive sprocket when I replace the bike chain. In use, it's really transparent. My right thumb is trained to flick on the cruise control on long climbs, and I use the throttle in tight technical terrain.

I'm with you on suspension.

frenchie said:

@FZBob
Great engineering congrats!
How did you manage to get the correct shape for the nylon pillow blocks around the Trance frame?
Safe riding!

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Thanks!

Pillow blocks - :lol: :lol: :lol: - Total PITA! I used CAD (Cardboard Aided Design...). Then eyeballing about 50 little cuts on the mill. Cut, fit, re-try.

I did put helicopter tape (?) under the mounts, so as to not scar the paint. It's a tight fit, and the top pillow block has the water bottle bolt passing through to prevent rotation.

The benefit of pillow blocks is distributing motor reaction forces over a large area of thin aluminum frame tubing.

But installing a few nutserts in the frame sure is easier. I used nutserts on my brown bike, and I have not seen any sign of cracking or deformation in that area so far. YMMV!