Dave's 80:1 RC mid drive kit build log

another...
It now has dirtbike pegs instead of the machined ones. I should update my pic!
 

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That's a sweet bike. Did you make that battery compartment, or did you get it somewhere? The Tangent has so much raw torque that a 24T is gonna be too low, 24 X 36 is a .66 crawl ratio, even my granny is .80 and the rest of the Tangent guys probably think I'm nuts for running a gear that low. You're probably going to want something in the neighborhood of 30-34 teeth somewhere. At 34 x 11, running 8 psi, on a ~60 lb bike, with a 220 lb rider, I can hit 34.5 mph.
 
Yeah, I made the battery housing. The adaptto controller is also inside it.
I make my own sprockets, so it's easy to experiment with different ratios :wink:
 
Hi Dave how heavy is the whole motor setup compared to the bafang BBSHD ?

I.e how heavy is all the parts the chainwheels, the bottom bracket, chain, controller, mount and motor, i.e everything except the throttle so I can compare.

And also what is the peak power of the standard 3210 motor 4kw ?
 
1454278447934.jpg

White Industries HD freewheel + Truvativ Gigapipe 148mm BB + 52 links of chain = 840g (quality components)

Another 150g (ish) for the 32t chainring and spider

Total= 3950g (8.7lbs)

Peak power of the Astro motors isn't given, it depends on many factors. The 3210 7turn is most efficient at 24A but doesn't start to feel even warm until 40A continuous. I've pushed 130 phase amps through my 3210 for a 10 minute, 40mph ride before it was too hot to touch (simulating a 3220 testing the 20:1 gearbox). These motors are made for abuse and handle thermal and power transients like a champ. The Ascent's housing clamps around the motor for the best possible thermal transfer and does an excellent job of moving heat away from the motor (you can feel the temperature gradient as the unit warms up).

-dave
 
Quick update, build still in progress.

zerode right.jpg
zerode iso.jpg
zerode close side.jpg

Zerode G2 with 7kW of awesome. This is running a 3220 at 150A phase current, 20:1 Tangent gearbox, BAC2000 speed controller with 12S 32Ah LiPo (for now) and is good for 11.5k motor RPM. The motor freewheel is a 16t while the Shimano Alfine 8 IGH uses 16t receiving cog and I've also matched the cog at the rear wheel to the IGH's output cog (26t->26t) so the only reductions are the 20:1 Tangent and the ratios inside the IGH. The Zerode normally uses a 21t at the rear wheel but I've increased that to reduce the top speed and stress on the IGH.

There is a small amount of flex in the mount because I'm not running the chain to the BB as designed. I'll rotate the downtube brace clockwise to put more metal above the freewheel and more inline with where the chain is pulling. The IGH is handling the torque fine- some quick math:

3220 4turn @ 150A-> 6.4ft-lbs
6.4x20= 128ft-lbs on a 16t sprocket
-------
200lb person standing on the cranks= 115ft-lbs (200lbs x 0.55ft) on a 32t sprocket

So, even at 7kW the IGH and bicycle components handle the forces fine. The motor will make at best double the forces an average person would but in a smooth and constant manner. The fun is the drive outputs 500RPM with this power. From Sheldon Brown:

Alfine ratios.JPG

First gear spins the wheel up to (500x0.52=260RPM) 20mph and eighth gear is 61mph (calculated, I need to true the wheels). Controllable wheelies, enough torque for crawling, top speed to keep up with any traffic, this isn't an ebike anymore. The downside of this setup is the battery requirements aren't as convenient since this monster wants about 120A of battery current.

I'll be redoing the mounts in the next couple days and going for a trail ride. Crash cam to follow...


-dave


*edited to clarify torque ratios
 
That is effing sick! Damn it Dave, now I want one. I can't believe the Alfine 8 can take that kind of power without breaking. Also I think your torque figures are understated, a 200 lb rider standing on a pedal will have leverage come in to play depending on how long the cranks are. It just shows that your torque specs are more in line that stated. Plus if I'm actually pushing on the pedal, and/or pulling up on the bars, torque figures are going to be way more than 200 lbs.

EDIT - I have no idea what I'm talking about.


Can we get some chest mount footage? :) :D
 
Hi Dave,

Great work. Can't wait to see some videos.

You say "200lb person standing on the cranks= 200ft-lbs". Are you sure? I remember that the cranks are close to half a foot long which gives half that figure.

Uri
 
You're more correct than I am Uri, 170mm=6.7"

Fastjohnny has a point though about the person probably getting more than 200lbf on the pedal, but that wouldn't be double. Revising the post, thx.
 
How do you even figure this out? I'm 220, and can leg press about 700 lbs, and I'm riding on 175 mm cranks.

Is it my weight 220, plus half my leg press power 350, times 175 mm in feet, or 220 + 350 = 570 * .574' ? If so, than my maximum instant torque is 324 lb/ft.
 
You can't push down more than you weigh, you'll jump off the pedals! You'd have to brace your back against something or pull on the handlebars to put more force down than gravity is pulling with. Take out the 350lbs and your calculations should be correct.
 
tangentdave said:
-------
200lb person standing on the cranks= 200ft-lbs
32t chainring->16t Alfine 8 cog = 110ft-lbs of chain pull
Click to expand...

FYI - sprocket ratios are irrelevant for chain pull. Pedal weight is multiplied by crank arm length / ffront sprocket radius. Rear sprocket does not come into play (other than generating torque at the rear wheel), and assume a locked rear wheel for maximum force. i.e. for a 4" diameter sprocket and a 175mm crank, 200 pounds of pedal weight generates ~115 ft-lbs of crank torque and ~690 pounds of chain pull.

Typical bike chain tensile strengths appear to be on the order of 1800-2000 pounds (though specifications are hard to come by).
 
A ft-lb isn't the right unit for chain pull, gotta take the foot out. What I mean here is a person turns a 4" sprocket with 115ft-lbs and the motor turns a 2" sprocket with about the same, so the forces the bike is seeing from the motor turning the crank are at most twice what an average person does when the pedal is perfectly horizontal. However the motor applies this power smoothly and holds the loading constant, not like a persons jerky cadence.

These are the same numbers with the 40:1 3210 and 60A also. The difference is the max RPM of the drive is half (250 vs 500) and you only need 20Ah to last all afternoon on the trail.

Thanks for keeping us honest, let's make sure I'm not missing something.

-dave
 
Curious about pricing here? Is the kit available yet?
 
Ok cool, been looking at vids, it seems kind of loud, is there any way to quiet it down? Would be PERFECT if just a bit more silent, I think MTB trail riders might complain. Out here, you're sharing the trails with several bikes at any time..
 
dave done what he can too make a nice sound from the new gearbox , with new rubber mounts. i Really don't see the sound that bad You the right frame , is the Key for quiet sound middrive , take note i have not use new 20.1 gearbox yet.

thank you
 
Are you saying to build a box around it possibly? I was thinking something like that could help with an open bottom so it can still breathe but sound is deflected downward... ??
 
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