Downhill project motorcycle transmission

motorcycle transmissions are so heavy, better save the weight of the gearbox and use a bigger motor, this way you need only one ratio. Minimum power for a single speed that goes 50kph is around 4kW, to get up the steepest hills.

The KX gearbox weighs just under 3kg cases and all, with the motor this will be about 5 kg on the knocker. If there is a motor than can outlay up to 9kw that is happy in a 20 - 90 kph range weighing 5 kg then I'd go down that road. Not trying to be argumentative but to say motorcycle trans are so heavy is a bit of a generalisation. Harley Davidson- sure, the current crop of two stroke small bores. Not so much.

1 Shifting gears keeps me snug and familiar, takes me back to days when I was young and frisky, about 6 months ago
2 Recycling existing wares
3 Solid, easy and compact engine mounting
4 Good potential for water cooling
5 Very reliable and shifts well

Honestly all suggestions are welcome don't get me wrong. But I am to a degree set on this idea and kind of committed to it. What is the motor, reduction and controller set up you have in mind?

Ecobogan said:

AussieJester said:

I have extended a steel Isis works a treat, insert tube inside after cutting then weld it up..

Cool, could you post a pic of that? Might end up going that way and is your set up an off roader or more street pedal?

Am going to run the KX gearbox as I already have it, we'll see how it goes.

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yes there's pictures in my working somewhere, on TAB to frustrating searching sorry... it's in the "hobo powered 2 speed cruiser" thread IIRC

KiM

Ok, if you ´wanna go that fast than at least 2-3 speeds make a lot of sense. You could get a motor with 9kW like the 150cc Rotomax and CA120-70, but it's hard to drive these beast (suitable controller...) Also hard to cool them properly/reliable

Maybe you can make a custom shifter cam on a 4-axis mill, so you only shift gears 1-3-5. You could throw out gears 2 and 4.


Running outrunners in an oil bath is not a good idea, it lends to do so in such a drive, but that induces a lot of drag/loss even with thin oils. Watercooling the stator would be best, or go for an inrunner like the Astro or the 8pole chinese made motor (also used in the GNG V1 drive). They are not the most powerful, nor the most lightweight, but they have proven to be quite reliable and are simple to cool, and are available in different sizes, they work great with cheap controllers.


I think is I was you i'd go for the astro since it can be a simple drop in for your setup. Just fill the box with oil, it will be enough cooling for the Astro. Also it fits the speed your gearbox was designed for. A 80-100 terminated in WYE is also drivable by most controllers, at least if you stay below 90V. But here again you have the cooling issue

I run Turnigy CA120 have no extra cooling and Kelley controller, hasn't missed a beat..
very easy if you use the right controller and gearing...

KiM

Thanks guys for the responses and cool build on the cruiser aussiejester, do love some hardcore pipe notching myself, I also was more grind and shape prone than the cad print. Sometimes to the detriment!
Right, I sure could have a new shifter drum machined on a 4 axis mill to select 1st 3rd and 6th gear but that I'd much rather spend that effort and expense elsewhere. It's funny I stared at that exact item for a hours on end trying to nut out a way of reconfiguring the shift pattern and in the end gave in and left it as is.
This was in part due to the nature of the gear dogs and sliding spline set up in 2nd 4th and 5th, they transmit the drive to the gears either side of them and to redesign this would mean basically redesigning the whole trans. The gear clusters fit in the palm of the hand and the weight savings from omitting these gears would be negligible.

The Astro flight 3220, at the moment, is the motor I'll most likely use. The main conundrum is whether to go for a 4 or higher turn motor. Probably the 4 turn as it seems to be able to handle a few more amps in the low end speeds. Also whether the housing can could be watercooled effectively sealing wise.

AAAAAAnd what about a wye/delta switch for even more silly speeds? Surely I could gear this sucker right down to get full throttle at 20 kph in wye which would still get well over 100kph flat out in 6th in delta. All this with 44v 25c li po (that being with a 4 tun). Am I just being greedy, wrong calcs or is this the way forward?
I'm itching to cut this Trek up and get wriggling with it

Thanks lads and keep it coming

Just my opinion, but I'd say leave the delta/wye switching! With the gearing you have available I just don't think it's necessary. It will accelerate so fast as it is, any more will just make it difficult to ride?

I agree. Simpy use enough voltage to run in in WYE properly /fast enough for your needs. Then you'll need no Delta.

I run Turnigy CA120 have no extra cooling and Kelley controller, hasn't missed a beat..

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did you enclose it/ protect it from dirt?

Edit: OK you didnt since it's ina cruiser. In an offroad verhicle you have more probs with dirt on/between the magnets. I have bad experience in that direction with air cooled outrunners

You're probably right on the wye/delta. I'm thinking out loud and wanting the max. I'll get it running first then see what it needs. What prompted me to look into wye/delta switching was the HV 160 controller being limited to 44v and also being able to gear the bike right down for hill climb crawling and still have 100 kph+ up the old sleeves.
What's happening here is that I don't really know what I'm talking about and just need to get the bastard going, it's about thrills after all not max speed or whatever.
On that, I've bought a 4 turn 3220, controller and throttle set up which is on its way. I'm getting the drive sprockets made up out of 35 pitch kart sprocket blanks in 13, 14 and 15 tooth to fit the countershaft of the KX motor and got my young self 10 ft of EK chain.
The machinist and I worked out a way of neatening up the internal gears that run directly off the electric motor by way of pressed splined sleeves and keyed spacer bushes rather than the dodgey way I was going to do it. All takes money.
I'll have all the machine work back in the next week or so which means I can set up the drive/gearbox end of things and get fabricating,the electrics will be a bit longer, a month or so.

the motors i tested all did run smoother and cooler in WYE. I have tested EMP N6354, EMP/ Turnigy 80-100, Clyte HS-3540, Bafang BPM2 in both WYE and Delta, that is why i recommend higher voltage in combination with WYE termination. All of these motors run fine in WYE @ 74V.

44V is not enough to get serious power out of these in WYE. The HV160 may burn from high peak current at low speed if you use no centrifugal clutch. Something you have may want to try yourself I testet sensorless Infineons vs the HV160, the Infineons accelerate faster/have crisper throttle response. I tested the EB312 vs the EDGE HV 160

Still I wouldnt recommend either of these. sensorless Infineons have sync issues at higher power >2000W with all motors i was able to test with In Delta even at lower Power. The sensored Infineons dont have these issues. Sensorless suxx for high power IMO, for lower it's fine.

I now try sensored Kellys, maybe i have more luck with these.

The higher quality 3220 may run in Delta as Good as in WYE,i have no experience with them..dont know, maybe they come in WYE already..
you can get a sensor adapter/kit for this motor somewhere here in the sphere

Thanks for your thoughts on all this mate. Due to my utter noobness I'm kind of going with what others have proven to work ie. Matt's 44v set up in his trike. That being 9kw peak at 44v pulling 200+ amps. If pushing 72+ volts is the way forward (so to speak) then I'll have to change controllers and re configure the battery pack. The heat produced by big amps in my case will controlled to a degree by the water cooling jacket.
As I mentioned it seems that one advantage of a wye/delta switch is being able to run high rpm on lower voltage whilst maintaining a decent mah. Could and probably do have this all horribly wrong.
This is the de noobing build and when she's all up and running I'll know what I want and more so how to do it.
Keep it coming bro, do need all the help I can get!!!!!!!

If I can chime in here. It was said that you really only need 3 gears. Having ridden dirt bikes for over 40 years and sportbikes for over 30 (even before there were any "real" sport bikes, and getting my children their first bikes at 3 years old, I have some little bit of experience. A good three speed transmission would be the one on the crf50 or the pw50. I know it is only a 50cc bike but they are very durable. I converted one to 125cc with a big bore kit for my son and he thrashed it and so did I.

It is also very compact. Just a thought.

Yeah no doubt there are a few different ways to do the gearbox. I certainly didn't want to spend too much coin on a more modern set up, got this one for $150. It's pretty tiny and the smaller motors have a smaller crankcase diameter where the crank sits. This area is critical size wise to house the motor. The KX crank area is only just big enough to take the astro, a 50 might be too small.
I'm sure if I checked out EVERY small bore motor something better may have presented itself but this one with its 6 gears will be fine.
Cheers

Subscribed - I'm pretty fascinated to see how this works out. Good luck Eco.

before you get too far into this motorcycle tranny thing, do you realize they are constant mesh?. that means all gears in the gear box are always meshed and turning. that means the tranny will consume a good deal of power that is not going to get to your drive wheel.

do a test set-up. drive the tranny with an electric motor and measure the amp load it takes to spin it at the rpm's you will need to ride the bike.

I would love to find a efficient 3 speed light weight tranny to use on a e-bike. but no luck so far.

I realise they are constant mesh, I've been into motorcycles for years, was a bike mechanic once what a cruddy job. You're right there will be some power losses how much exactly is hard to tell.
Without pouring big bucks into designing a trans with lightweight exotic materials, the alternatives were either light and weak or heavy and strong.
The gear clusters are physically very small. Both clusters will fit into the palm of your hand and the box does 'spin' very easily but there will be some drag for sure. I'm going to use the lightest oil possible also. I'm going for longevity and reliability and plan on doing a lot of k's on this old girl. This is an experiment really and the only way to know if it's a good idea is to have a crack.

I like this attitude rather than pages of CAD drawings and discussions on if it will work etc... Get in and have a go I say!

KiM

Cheers mate and to be honest if it is too draggy in the power sucking I'll just add another 3220 and extend the wheel base. If this thing ends up stupid then that's ok too. Even adding a hub motor to the front wheel is on the menu. I'd rather bomb proof than broken bits. May end up with a thud two speed but the KX is it for now.

Go Eco Go!
I too am excited to see how she runs... I'm guessing well.

Curious as to whether the clutch could be retained?
I can't visualize it perfectly and am unsure of the weight gain.
Mainly thinking of the low speed dependability on a sensorless
set-up. Perhaps a bit of "feathering" could be helpful to get it
spooled up a bit and add that "gasser" feel as well?
Could even ditch the rear brakes for the clutch lever and some
"compression" regen? (not that you don't already have that).
And set-up a right-handed front brake lever?

Just food for thought :lol:

Glad to see you carrying on...
Cheers!

Thanks K-ray I'm hoping it all goes to plan also! Won't be to sad if it doesn't. These kind of capers rarely go uber smooth first up. On the weight, she comes in at 5kg, motor, box, cases, the lot ,which I think isn't too bad. I've managed to shave a lot of lard in unused shafts and gears. One of which was the clutch, it would be beneficial to have one in some instances but it would have added at least another kg and the bulk would have widened the whole set up to the point where crank clearance would have been a major issue. So clutchless it is. The brakes will remain as is right front left rear
I really need to post some more pics and will do when I return home, currently in Alice Springs 2500k out of Melbourne. The utter centre of Australia.
Am just going to wing it sensorless for now to see what it's like. I can fit them afterwards easily enough if need be?

View attachment 2
So yesterday the butchering commenced. The temporary brace in 40mm shs was welded on first and after much revisiting the cutting path, I whooped into it with the 5'' grinder.
Next will be plating over the open sections and fitting the gearbox mounts.
Also, finally a splined boss I was having machined up for the clutch shaft is done and ready. Some sort of coupling boss is still needed to attach the drive gear to the motor shaft but I'll wait for the motor to arrive before tackling that (hopefully soon)
In my typical camera retardation I took stacks more progress pics in too high a resolution, so this it for the minute.
There seems to be better crank clearance than thought and it sits well in the frame with decent chain alignment.
The 8mm top plate will be welded to the frame with the gearbox fixing to it via the four existing barrel studs. This plate will be shaped and reduced after all mount fixings are resolved and will also serve as the liquid cooling capping plate.
More to come

Got stuck into the disc sprocket plate the other night and went forth to dissect the swingarm as well. This allowing some idea of what the driveline situation is. Fitted up there's a respectable amount of chain play at ride height which will need some decent spring tension roller sprocket attention, probably beef up a single speed tensioner for the time being.
The sprocket plate is just a plasma cut and drilled 6mm 6061 disc offsetting the sprocket outwards by that amount. The swingarm took quite some tweaking and re tweaking then re postioning another 6 times to get it right for best structural design and full travel clearance.
Also resolving any flex issues around the case mounts and then bracing speculated failure points gave us all a grand old giggle. More 6061 gussets and shaping. On the rear brake I was thinking of getting an oversized 250 odd mil brake rotor made and offset it inwards as there is a fair bit of room there, and mounting the caliper between the swinarm spars.
I've got this old Lincoln 250 AC/DC tig at work the size of a tractor that needs a good run, time to fire it up again.

If you remove any of the gears from the box you do need to be careful, I have done this before to create a 5 up box for easier neutral selection on an engine I raced a long time ago. At first I just removed the unwanted gear and substituted them with spacers but it did cause shifting problems because that gear was responcible for rotating the shafts to ensure correct dog alignment. if both of the gears are splined they cant be removed, if one free wheels and locks to a splined engagement dog you will be fine removing them.
I have often wondered about doing this myself.

Yes this I realise and there'll absolutely no changing any gears anywhere