My RC Mid Drive with Single Stage Reduction

[FZBob]

I was afraid you'd say you customized that 90T sprocket. A little outside my skillset

I just received this sprocket from Rebel Gears. Turn-key - No modification required. It's aluminum, 90T and set up for the standard 104 bcd bicycle pattern. It is "custom", ie I specified center hole diameter, mounting hole size and hole circle diameter (see post above). I probably spent less than less than 5 minutes on the phone with them. It did come with the lightening holes, which I did not expect. It is on a 1/4 inch thick blank, which I also did not expect. It all worked out, and this sprocket weighs 230 gm, which is close to my electric scooter parts sprocket - after I spent a day drilling holes! I'm probably going to spend some time trimming this sprocket, and hopefully get it down to about 65 grams. This is a much nicer solution than modifying an electric scooter parts sprocket!

 

[falcongsr]

Nice! That looks like the solution to the biggest barrier preventing me from trying this. I look forward to seeing your progress.

 

[FZBob]

I suspect the weakest link of this build is probably the #25 chain, so I took a look at wear. After 4 months, 34 rides, 350 miles, and 33,000 feet climbed, the chain has stretched by 0.5%

I don't ever clean my chains, but I do apply Rock & Roll Gold lube before every ride. All riding was on dirt trails in Northern California summer conditions - moon dust. I typically climb at 100 to 240 watts with occasionally bursts up to 450 watts or so. Bike & rider are about 300 lbs. This is the Electric Scooter Parts Heavy Duty chain.



What is the allowable chain stretch spec? Lots of answers...
My Park tool gauge works out to 0.6% and 0.8%
A motorcycle website lists 1%
The Diamond chain website lists 1.5 to 3%

I will probably replace the chain at around 1% stretch so I don't wear out sprockets. If the chain wears at a consistent linear rate, (probably not...), then I can get 8 months to a year per chain, which is about 1/2 of what I get on my bicycle chain. These results are better than expected, and very acceptable to me.

 

[falcongsr]

I've been testing my friction drive and I intenionally went out riding on looking for issues with the motor/tire interface, and I found that paved bike/jogging paths in nature preserve areas around me have that same moon dust. It does compromise the friction drive, but if I move over to the adjacent road where vehicle traffic clears the dust the friction drive does fine.

When I figure out a good method of mounting a motor and can source a decent set of sprockets I'll add a drive like yours to my MTB frame.

 

[FZBob]

I found that paved bike/jogging paths in nature preserve areas around me have that same moon dust. It does compromise the friction drive

Do you have the belt sander material on your motor? I'm I'm working on installing a friction drive on the same bike to compare...

 

[falcongsr]

Oh I should have been more clear. My friction drive is on a road bike meant for higher mileage commuting. It is metal motor housing direct on tire.

For wet/offroad riding I'm leaning toward some kind of direct motor connection to the drivetrain on my mountain bike frame.

 

[FZBob]

When I figure out a good method of mounting a motor and can source a decent set of sprockets I'll add a drive like yours to my MTB frame.

So the Rebel Gears sprocket that I received last week is turn key, and it bolted right on. As it is custom, you can specify the number of teeth. Also, as a side benefit, the tooth area is 1/8 inch wide, but the blank is 1/4" thick. This is nice, as I put the flat side out, and the thick side in. I don't need any spacers to allow for clearance between the two chains! (YMMV...) Also, the bike chain can't drop into the space between the bike sprocket and the motor sprocket and get stuck, which happened twice with the steel sprocket.



As for the motor sprocket, I just used the Electric Scooter Parts 9T D-Bore. I also have the 10T and 11T. I used a round file to remove the D shaped flat area, and a square jewelers file to file a keyway.

I used a Shaft Collar from McMaster Carr - P/N 9520T4 - to retain the motor sprocket.



I made a key out of scrap steel with a hacksaw and file. A couple of spacers from brass stock I had laying around (the motor comes with one spacer included...)

 

[Timelord]

This chainring might just be big enough for a medium power single reduction with a bicycle chain. Serious. Might be OK on a road bike as long as it didn't drag in corners. There are custom sprocket makers out there who can make these...

Big Chainring.jpg

My bicycle gearing is 22-40 on front and 11-40 on back. I climb a lot.

I had an idle thought a little while back about a two-stage reduction mid-drive sort of like that. The jumbo sprocket would be on the left side, replacing the left crank completely. Just big enough so you can have a threaded hole inside the outer radius to attach the left pedal to. To avoid the wear and rust problems you've been having with chains, I wanted a belt drive from the motor pulley to teeth on the outside radius as the first stage reduction. Assuming a 1" diameter motor pulley, a 15" diameter crank pulley would provide a 15:1 reduction just from the first stage. Put a 4:1 planetary gearset inside the pulley and you'd have 60:1 total reduction.

That chainring wouldn't drag in corners. The pedal would hit long before it would. But you wouldn't want to use it on a mountain bike.

 

[FZBob]

I had an idle thought a little while back about a two-stage reduction mid-drive sort of like that. The jumbo sprocket would be on the left side, replacing the left crank completely. Just big enough so you can have a threaded hole inside the outer radius to attach the left pedal to. To avoid the wear and rust problems you've been having with chains, I wanted a belt drive from the motor pulley to teeth on the outside radius as the first stage reduction. Assuming a 1" diameter motor pulley, a 15" diameter crank pulley would provide a 15:1 reduction just from the first stage. Put a 4:1 planetary gearset inside the pulley and you'd have 60:1 total reduction.

That chainring wouldn't drag in corners. The pedal would hit long before it would. But you wouldn't want to use it on a mountain bike.

I'm not an expert on road bikes, but it does seem like you could run a pretty big driven sprocket, which in combination with a low KV motor might allow for higher voltage on a single reduction system, and therefore more power.

By the way, that's not rust, it's dust! Life's too short to clean Mountain Bike chains!

 

[neptronix]

Glad to hear that rebel gears came through as promised.

Yeah friction drive is kind of a dead end if you have the wrong conditions for it to work all the time.
I'd say what you have is very close to the ultimate solution.
Did you get a bigger sprocket on the motor itself? that help the chain stretch factor.. you are not running a ton of watts here after all..

 

[FZBob]

Glad to hear that rebel gears came through as promised.

Yeah friction drive is kind of a dead end if you have the wrong conditions for it to work all the time.
I'd say what you have is very close to the ultimate solution.
Did you get a bigger sprocket on the motor itself? that help the chain stretch factor.. you are not running a ton of watts here after all..

I really liked dealing with Rebel Gears... Nice sales Lady, amazingly fast, and excellent quality.
I spent a bit of time trimming out extra metal that I didn't need.




Still running the 9T on the motor. The bike is working very nicely now. I was out riding in the hills yesterday, and the experience was very natural. The drive system integrates with the bike really seamlessly. I almost forget the motor is there, even when I'm using it!

I did order an Alien 120KV motor which is much lighter than the yellow Turnigy motor. In theory, it should provide the same power... We'll see... It's in limbo on a slow boat somewhere between England and here. If it works well, I may order their 90KV motor, which would allow me to go to a 11T or 12T motor sprocket, which should be quieter.

 

[falcongsr]

Wow that's quite a trim job! Beautiful work. I would have left more material - out of ignorance mostly.

 

[SlowCo]

:lol:
You removed more material then there is left over...
It seems you have the tools and skills to have made the entire sprocket yourself including the teeth. Why didn't you?

 

[FZBob]

:lol:
You removed more material then there is left over...
It seems you have the tools and skills to have made the entire sprocket yourself including the teeth. Why didn't you?

Thanks! I wish I had the ability to fab sprocket teeth. That's far beyond my capabilities! I believe you need a CNC mill or Gear Hobbing equipment in order to form the correct tooth profile.

I would have left more material

Hopefully as long as I don't use it as a bashguard, I'll be OK. I compared it to some lightweight bicycle chainrings, and then cut a bit further because this sprocket is 1/4" thick. I'm sure a strong rider would put more force into a chainring than my little motor...

 

[FZBob]

I received the Alien 5065 120KV motor on Friday. (on the right). Half the weight of my favorite motor. (The large black one, previously orange...) In "theory", the Alien should make close to the power of the big Turnigy... We'll see...

I also have some concerns about the open frame design and dust. The bearings on all these motors are Shielded, not Sealed. I suspect at some point I'll need to replace bearings with sealed units (Boca Bearings...)

Note the short shaft on the Alien. Not enough room for the collar to retain the sprocket.


Drilled and tapped the shaft for an M3 Cap Screw. (I did cover the bell in plastic before machining)




Temporarily mounted the motor to my existing mount, for Testing Purposes Only. If I like it, I'll need to make a new mount, as the Alien bolt pattern is totally different than the Turnigy motors, and I can only catch two bolts on the existing mount.
View attachment 2

Went for an exploration ride Friday with a couple of friends. I had the only E-Bike . Lots of long steep (22%) loose gravel grades. 11 miles, 1700 feet of climbing. I cleared all the grades (barely), the really strong rider did not clear all of the grades, and the third rider, who is somewhat stronger than me, had a tough time. If I had been on my non E-bike, I would have had a bad day... I used 87 Watt Hours, out of 100 WH available in my new Zippy 4S 8AH pack. I carried a spare 5.8AH in the fanny pack. I'm liking this light weight setup a lot - its not too hard to throw the bike over gates & fences...

 

[ThierryGTLTS]

I'm really impressed.

What about the noise, please :wink:

What is the quiest motor you've tested.

Have a Nice Day.

Thierry

 

[FZBob]

I'm really impressed.

What about the noise, please :wink:

What is the quiest motor you've tested.

Thanks!

I set the VESC speed control to FOC mode. That runs the motors very quietly. The motors all make a very pleasant soft whir. Remember, I'm only spinning the motors at 400-800 RPM, depending on my cadence. Also, since I'm not running a freewheel on the motor, this soft whir is present any time I'm pedaling, whether or not I'm on the throttle. It doesn't change a lot.

I initially tried the VESC in BLDC mode, and that had a bit of an irritating high frequency whine. That was a much bigger difference than between the motors.

The chain going on to the 9T motor sprocket makes a bit more noise than the motor, and it varies by power.

To answer your question, the big Turnigy D5035-125kv is the quietest. It also works by far the best. I really like this motor! The Alien is a bit louder, I think because it's open frame. A bit of high frequency noise escapes. The other two fall in between.

 

[neptronix]

Looks like you're living a dream i had in 2011.

So.. when can we buy a kit from you?

 

[falcongsr]

I think the motor attach is the next issue to solve for a “universal” kit/solution.

 

[FZBob]

Looks like you're living a dream i had in 2011.

So.. when can we buy a kit from you?

I think the motor attach is the next issue to solve for a “universal” kit/solution.

That's a coincidence - In 2011 I built a Cyclone 500 Watt kit. I never really bonded with it. I was interested in the RC stuff back then, but I didn't want to play with two stage reduction.

Making up kits sounds suspiciously like work, and I'm allergic

I just took a look at my Bill of Materials. Everything is off the shelf except the finished motor mount. About $400, not including the wattmeter and throttle, but including the battery. When I get a chance I'll post it.

The motor mount will end up being different depending on the bike. I used a piece of 3" x 3" by 1/4" angle aluminum. I wonder if most DIY guys could do the same thing using a drill and a hacksaw, which is what I did back in the day...

 

[neptronix]

Well..
Make the motor mount and the frame tube mount 2 pieces.

piece #1 is the motor mount that's designed to fit X,Y,Z motor..
Piece #1 hooks to piece #1 and adapts to a tube of X diameter.

So you'd have a kit where the customer measures his seat tube or lower tube diameter, and tells you he needs a clamp of X size. Using some rubber as a shim, there's room to deviate ~3mm or so?

And then the customer is expected to custom cut and link the chain to make up for the distance between the seat tube or lower tube and the crank + desired gear ratio.

Of course the guy is screwed if he has oblong or square shaped tubes, but there's always another bike frame out there.

All you really need to do is machine 2 big aluminum pieces and maybe a motor shaft.. add some bolts, let the user handle the sprocket and chain issues.

 

[FZBob]

I'm looking for suggestions for low KV small motors to try. I would like to find something around 60 to 90 KV, and under 700gm, preferably about 450gm.

I'm thinking about trying 6S to 8S with a very low KV light motor. This might save weight, and allow a slightly bigger motor sprocket, which would reduce noise even further.

I had been looking at the Alien 60KV motor for a while, but I waited a day too long and it went on backorder!

I would love to hear suggestions. I'm only familiar with Turnigy (Hobby King) and Alien.

 

[Kepler]

This motor looks like it could fit the bill.

http://epowerhobby.com/product/e-power-hobby-6354-outrunner-brushless-motor-60kv-2450w/

I like that they offer a sensorless version. Perfect for your application. And they are in stock at the moment.

 

[Uturn]

chain going on to the 9T motor sprocket makes a bit more noise than the motor,

Could a belt drive be lower noise lower maintenance? Or will that assembly take too much space? Or no big pulleys available?

 

[FZBob]

This motor looks like it could fit the bill.

http://epowerhobby.com/product/e-power-hobby-6354-outrunner-brushless-motor-60kv-2450w/

I like that they offer a sensorless version. Perfect for your application. And they are in stock at the moment.

Thanks! I just placed an order.

Everyone please keep the suggestions coming! I would still like to see what's out there...