Dani's mid drive (GNG motor) - CAD heavy pics!

[Dani]

Hi everyone,

my name is Dani, I'm 25 and I love riding bikes / anything that moves without (or close to no) effort. I come across the GNG kit and it sucked, except for the motor. Then I saw LR's kit, which is pretty awesome, but too expensive to me. Also I wanted something lighter, smaller, better and selfmade. I love being in the workshop. I know being better is pretty hard but I don't mind

I will update the development from time to time. As a student I shouldn't even have time left for this.. but I'll manage. somehow.

goals:
very light build
as small as possible
easy to build (little to no special tools)
cheap! Any penny counts
sturdy! So I can put 2kW+ on this thing

advantages over the LR/GNG Kit:
less parts (less sheets, less screws, less everything)
lighter (lasercut and bent aluminum, designed for light weight)
Easy available parts (like a bottom bracket instead of a custom made jackshaft/housing/bearing)
Let's find out if this can be done any cheaper

Sheets:
I want one sheet, one piece, which saves me costs on the Laser Cutting factory. They are pretty cheap and based in germany. The whole box (1 sheet, without any extensions/screws/..) will cost me less than 20€, more like 15€ or so.
After lasercutting I'll bend it on my yet to be built DIY-20ton-hydraulic-press like this one
Any source for cheap metal carrier within germany would be golden.

Bearing (jackshaft):
A bottom bracket should do the job. The problem is the ISIS shaft, which I can't machine a fitting sprocket/tube onto. So I looked at BBs with JSI shafts. I could make a sprocket to fit the square with my drill press and a file. Also they cost less than 15€ (FAG). I couldn't find much reviews about the one linked, but they are FAG/schaeffler made (german, high quality bearing producer) and are said to be long-lasting. We'll see. A truvativ DH isn't that much more expensive (<35€).
15€ sounds better than machining my own jackshaft/housing/bearing.

gearing:
I like to use the same setup like LR does. It has a nice gearing reduction, it is silent on the primary drive and is to some degree proven. I don't need to reinvent the wheel here. I'll buy the 90T GT2 pulley from him directly (can't find any good source), it's made of plastic, which is light and strong enough. No worries here. I also have in mind to just lasercut 3 pieces with the wanted tooth profile and screw them together.. printings will follow. Also aluminum, very light.
same gearing on the secondary side. I'll make my own big sprocket, let's see. Not sure which freewheel I'll end up with. Need to find a good source for a heavy duty freewheel that is affordable. Otherwise I'll end up with a cheap freewheel that will have a very hard time

tensioning:
first tension the secondary (right side) by turning the top screws on both sides evenly. Once the chain has enough tension, tighten the BB (top). Now use the primary tensions screw (front, single screw) to push the motor away from the jackshaft. Once tension on the belt is good, simply screw the motor to the sheets, relax the primary tension screw a little: et voila, it's done.

Disclaimer: I don't think I will go commercial with this. As of now this is a hobby for me. If you need CAD drawings or think this is suitable for you, just contact me, no problem ,

First try:

Second try:

Third try:

this is the summary of the first few posts. For development continue reading here

I still need the correct dimensions of the GNG motor. Anyone care to help out?

 

[SolarRay]

Couldn't find it on taobao

http://item.taobao.com/item.htm?id=18826436986
motor: http://item.taobao.com/item.htm?id=16174853904

 

[Dani]

Couldn't find it on taobao

http://item.taobao.com/item.htm?id=18826436986
motor: http://item.taobao.com/item.htm?id=16174853904

You sure about the motor? Seems off: 160 Yuan ~ $25.

 

[SolarRay]

If this is too cheap, then I can find more expensive.

 

[SolarRay]

http://item.taobao.com/item.htm?id=7018010465
http://item.taobao.com/item.htm?id=14596906173
http://item.taobao.com/item.htm?id=35779626136
Some motors are wider and powerful.

 

[Dani]

Haha, it's fine, ordered the first one. Let's see if it arrives before winter is coming.. 8)

 

[ebike11]

How are you guys ordering from the site? Assuming you cant read chinese

 

[SolarRay]

Through an intermediary.
And http://translate.google.com/m/translate

 

[ebike11]

But even if you can translate it...you must need to talk to the chinese seller for shipping quote etc.
And what payments do they accept??

 

[Dani]

But even if you can translate it...you must need to talk to the chinese seller for shipping quote etc.
And what payments do they accept??

Well, I don't know, but the ordering went kinda smooth (if you know what to click and what not - just try until you get through). You fill in where you live, they should manage to do the rest. Of course, if you have to pay duties, your local duty office (or whatev its called) will contact you (likely by mail or phone) if you need to pay taxes/duties. I paid via credit card. I'll update once i receive them

 

[Dman12]

But even if you can translate it...you must need to talk to the chinese seller for shipping quote etc.
And what payments do they accept??

Well, I don't know, but the ordering went kinda smooth (if you know what to click and what not - just try until you get through). You fill in where you live, they should manage to do the rest. Of course, if you have to pay duties, your local duty office (or whatev its called) will contact you (likely by mail or phone) if you need to pay taxes/duties. I paid via credit card. I'll update *if i receive them

:lol:

---
also there are taobao agents that take commission, but give you final price + shipping, and they speak some kind of english.

 

[Dani]

8)

me again. Motor not received yet, I'm not a very patient person. Can someone give the the exact dimensions of the motor? Width, diameter and the thickness of the motor cover for each side?

Could I easily replace one of the two covers (the plane one, right in the picture) with my own mounting sheet without any problems (except for a new seal)? I'm designing my own mounting system for a while now, similar to Lightningrods design and I want to get rid off that as it makes my build unnecessarily wide.

 

[Samd]

Hey Dani,
I spent yesterday looking on Mr Tao also for a similar reason. I am trying to go down a similar but different road.

I think it is significant that these guys found a bigblock motor with half the kV rating of a regular GNG or BigBlock.
http://endless-sphere.com/forums/viewtopic.php?f=28&t=57483
Or at least the half kV bit is significant. But I do not think the extra width and weight is possibly justified on a bigblock. Plenty of good riding to be had on the GNG 1.1 normal width at 3kW if the audible (high) meshing frequency of the primary side is dealt with, and the chain slack on both sides is improved.

Rather than take the road that LR has done with adding width and weight in the drivetrain via a higher kV motor, I would like to find a BLDC similar or identical with GNG 1.1 in size but half the kV.

This would ideally allow the larger reduction wheel on the primary side to be a lot smaller and tuck it up better into an integrated tank on one of my light offroad builds and leave room for lipo still. Ideally the shorter drive length would allow me to keep it in line with the chainstay without sacrificing ground clearance. Using a smaller primary reduction and half the kV does have other likely hurdles to overcome.



If I can do all of that I could avoid also buying a GNG 1.1 only to throw most of it in the bin, and avoid 1/2 to 3/4 of the cost.

I did find these guys yesterday. Output shaft an issue but bloody cheap.
http://www.aliexpress.com/store/product/BM1418HQF-500w-Dc-48v-brushless-motor-electric-bicycle-motor-BLDC-without-differential-gear/1209624_1799750463.html
Unite seem to be the motor maker on all of these.

There is a good company site for Unite Motor manufacturers, just a matter of finding a wholesaler who can offer good freight and reliable rpm-per-volt info.

 

[Dani]

Hey samd,

nice bike setup . What yoU're doing now is the 2nd stage in my plan. I first like to transform my regular Voitl MX III bike to an ebike.

Mid drive is the way to go. The easiest way to achieve this is a similar setup to Lightningrod, I don't mind about that ground clearance, still plenty left

Why would you buy the GNG1.1 kit? You can find the motor only, as well. 25$ + shipping.

I saw the other motor as well, but I highly dislike the size and weight. I want something light.

I found the motor you suggested as well, but without too much info around, so I discarded it. I'm very interestd in more detailed info about rpm per volt etc.

*edit* *forget the link that was here before, never mind.*

 

[Samd]

Nice one.

What's your plan with the shaft on the motor - cut it and reduce the diameter?

 

[Dani]

Yep. Afterwards make a keyway and mount the rest. I was thinking of a pulley that fits tightly on the redurced diameter of the shaft, and then simply drill 2, 3 or 4 holes in it and hammer some pins in there. Similar to this (the lower left one):

Et voila - Strong connection without any expensive tools. Just a drill press.

 

[Samd]

Sounds like its worth a try.
I was thinking about the adjustable length needed to get the primary and secondary chain tensions right a few months back. One design idea was to copy a car alternator bracket config so it swings down to get the tension right.

I also started thinking about sourcing a bottom bracket shell to space the two side plates apart as per your CAD drawing. The idea of using an eccentric BB shell to get the chain adjustment came to me also - just gotta find an inexpensive one.
http://www.ebay.com/itm/like/260696847297?lpid=82

 

[Dani]

Update: I did not receive my motor yet. 4 weeks passed, the merchant site still says it's not shipped and the seller won't reply. Also I figured the postal code was wrong, though I did check carefully on the checkout. I tried to correct it, but the system is bugged. Germany has a 5 digits postal code, but taobao will only accept 6 digits. Support can't help either. Oh well :|
Edit: Refund processed. Nothing yet on my creditcard, but I guess it will show up this week. Oh well..

 

[Dani]

So this is what I came up with . It is similar to Lightningrods build, which I think is already very good. I think the way I will tensions this will work better, as I need less material. Also I'll make it out of 6mm Aluminium, which saves weigth.
I can adjust tension two ways: by sliding the motor within the sheets and by adjusting the screws for the upper jackshaft. By sliding the motor you can tension the belt drive (left) and by screwing with the screws you will tension the chain (right).

I will bend the case out of one sheet, but the part which holds the left and right sheet together will be on the upper part instead on the lower bottom, as LR did. Why? To not let the momentum of the left and especially right side of the jackshaft twist the sheets. I reduce leverage by placing this closer to the jackshaft. Simulations showed the same result: less twisting, less tension.

Finally I chose to use a standard, off the shelf Bottom bracket with JIS as a jackshaft for the big 90T pulley and 18T sprocket. It is cheap and easily replaceable. I'll put a tube between the two sheets so the BB can be screwed into. Maybe I'll weld the tube to the sheets, should be really stiff then. I wonder if one can buy an adapter from ISIS BBs to something more usefull (keyway?). This way so I could fit a freewheel on the ISIS with just one part I can buy instead of make. Saves time, saves money. I chose JIS because I can "easily" get any freewheel/pulley on it with my drill press. I lack a lathe and I can't make any keyway with my equipment :? .

The sheet and top tensioners will be laser cut and bent. Should be able to bent this on my own (yes, a hydraulic 20T man-made-press-of-madness is not that far! )

So I played a lot with CAD and simulation lately and I figured this should work. I assumed under 2000W I would have 6,3Nm output at the motor axle and after gearing it up with a beltdrive it is 31,5Nm on the upper jackshaft.
My guts tell me this case should survive 4000W offroad until I break the frame of my bike or something else fails miserably. Maybe it will fall apart after day 1. Who knows.

This is what my simulations came to. I simplified many things, but overall I'm pleased. Tension seems to be lower than 100Mpa except for two hotspots. Rp0,2 for AlMg3 (5754) is 80Mpa+ (I find anything from 80 to 160.. so I'm not sure). If 80 is the case, this will break at some point. maybe only after a few hundred stress cycles, maybe after many thousands, when my bike is already trashed.

I have two hotspots, one which is there because of my weak CAD skills (150Mpa @the hole: Made it so I could assemble/allign the motor correctly, too lazy to make a correct assembly)
the other one is the part where I need to bend the whole thing with a rather sharp edge @125Mpa. Nothing much I can do here, should be sufficient though.

What do you guys think?

 

[Samd]

Seems like an opportunity to box it up at the top as well and increase the torsional rigidity.

It's been a while for me and FEA but do you think your hotspots are real, or just local effects due to the mesh quality?

Any sign of your motor?

I still want to try a motor with half the kV and halve the size of the large wheel on the primary side.

 

[Dani]

I could and should box it up. I think the hotspot for the hole is not true, but this makes me think my other sliding holes might be stressed more as the real diameter/area of contact is smaller in reality.

The mesh quality was already pretty good, see pics. I further shrink everything down and made it more compact, this gives smaller leverage. I still miss the real dimensions, though.

I could easily imagine to make a wider motor fit in this, with a little modification of the motor itself. So that my sheets are smaller in terms of width then the motor. Any news on your motor?
PS: I send you a PM.

upper left: it got more compact, smaller I would say.
upper right: mesh quality, also my bad skills of implementing screws.
lower left: Got down the overall tension by over 50%, the hotspot less than 60Mpa. This seems good for more power
lower right: in case you wonder what it would looks like if you amplify the deformation

PPS: I'm no expert on this, I'm still learning how to setup and render these simulations correctly, but this gives a good hint

 

[Dman12]

Update: I did not receive my motor yet. 4 weeks passed, the merchant site still says it's not shipped and the seller won't reply. Also I figured the postal code was wrong, though I did check carefully on the checkout. I tried to correct it, but the system is bugged. Germany has a 5 digits postal code, but taobao will only accept 6 digits. Support can't help either. Oh well :|
Edit: Refund processed. Nothing yet on my creditcard, but I guess it will show up this week. Oh well..

Did you order directly from taobao? because you cant since they dont speak a word in english and just wont ship the item. also the prices is for shipping in china only.
you need some taobao agent (google - there are many) that buy the product for you and ship it to your place for extra $ - but you can at least talk with him.

 

[Dani]

Update: I did not receive my motor yet. 4 weeks passed, the merchant site still says it's not shipped and the seller won't reply. Also I figured the postal code was wrong, though I did check carefully on the checkout. I tried to correct it, but the system is bugged. Germany has a 5 digits postal code, but taobao will only accept 6 digits. Support can't help either. Oh well :|
Edit: Refund processed. Nothing yet on my creditcard, but I guess it will show up this week. Oh well..

Did you order directly from taobao? because you cant since they dont speak a word in english and just wont ship the item. also the prices is for shipping in china only.
you need some taobao agent (google - there are many) that buy the product for you and ship it to your place for extra $ - but you can at least talk with him.

Thanks, I will try that. It looked to me I can order directly, as I was able to set my country to overseas and the shipping cost went up quite a bit. Oh well

Edit: In the end I'll end with 85$+ per motor. Hm..

 

[speedmd]

Nice work Dani

Just some thoughts. On the stress concentrations at the corner of the cross brace sections, you will want to radius that transition some, at least a few mm or better 4- 5 mm. That should get rid of any of the high load sections.

I also don't see how your taking secondary chain loads into the load analysis. They are the major loads on the assembly. I would look at having a cross brace at the lower section vs top section vs none at all. The top section has a cross brace via the jack shaft housing already. With it all made in one part the lower adjustments (at motor) will not act independent and cause some confounding adjustments making it hard to adjust each side separately but it Should work fine as you adjust the secondary side first then the primary. Interesting concept. Look forward to developments.

 

[Dani]

Nice work Dani

Just some thoughts. On the stress concentrations at the corner of the cross brace sections, you will want to radius that transition some, at least a few mm or better 4- 5 mm. That should get rid of any of the high load sections.

Thanks, thats right. stress should be no problem afterwards.

I also don't see how your taking secondary chain loads into the load analysis. They are the major loads on the assembly. I would look at having a cross brace at the lower section vs top section vs none at all. The top section has a cross brace via the jack shaft housing already. With it all made in one part the lower adjustments (at motor) will not act independent and cause some confounding adjustments making it hard to adjust each side separately but it Should work fine as you adjust the secondary side first then the primary. Interesting concept. Look forward to developments.

Yeah, it's not correct applying torque to the analysis. Torque only applys to the jackshaft and where the motor is mounted to the sheets (the motor needs "to be hold in place" with a momentum). The top should only be applied with the force of tensioning the main and secondary. Well, first shot, gotta be wrong somehow . Still, without the (like now, way too high) applied momentum, this thing will be just fine as hell.

Also I looked at having the cross brace at top and bottom. Top seemed to be most effective.
I'll also make the holes for adjusting the motor in an angle that is parallel to the jackshaft and bottom bracket. I need to think about how to include a mounting option to the frame within the sheets.. maybe some more material and another bend.