Enduro with a Clutch and Transmission

[ecstatic_subjectivity]

Thought this forum might appreciate my build.

I've got KTM dirtbike that I'm converting to electric, retaining the clutch, transmission, and original crank. I've been through a few iterations in different frames, but the right call here ended up being my 2011 KTM 300 XC. Today I finally had the time and motivation to tear down the dirtbike:


And drop the bottom end into the bike:


I've got the rough mounting locations figured out:


Awhile back, I spent some time on the forums discussing the value of a clutch and flywheel on these bikes, and the transmission is also critical to maximizing acceleration and drive/slide at low speed while also maintaining a reasonable top speed.

Next steps: Split the cases, remove the conrod, weld up the crank so it can't rotate around itself, balance it to minimize vibration, weld a sprocket mount to the rotor (or just lazyweb and weld the sprocket directly), build the motor mounts and battery box. Then find a location for the controller, wire everything up, and it should be ready to go.

As to why I'm going through all this work, well:
1. The Brammo Empulse R taught me that a transmission on electrics bike actually rules. Having quick acceleration at low speeds and a high top speed is good! You don't need as many gears on an electric - a 3 speed would probably be fine, maybe 4, but a gearbox gives back much more in usable acceleration than it costs you. This goes double when you can run the motor in higher efficiency ranges because RPM isn't strictly linked to road speed. In the early days of cars, we compensated for a lack of transmission gears and quality with bigger motors, but packaging and motor availability is a problem on bikes.
2. A clutch and flywheel is critical for managing rapidly variable traction and aggressive power delivery. If you're on a motocross track that is groomed and has relatively consistent traction, you don't give up much. But for hard enduro, trials, and getting the most power to the ground when you need it, you can't ride the same way if you don't have a clutch/flywheel to store and deliver bursts of power to the ground. It also means you can modulate a much more aggressive power delivery, because when you need to reduce power you can just slip the clutch a bit.

There are a few transmission / clutch motors out there, but none with the flywheel mass I want or the power level I want, so here we are.

With 2.5kw of battery, I should be able to do about 20 miles with this, which is fine for our shorter days. There's space for plenty more battery. Weight should be equivalent to stock, but much lower CoG.

 

[GaryDe]

Good to see someone going down a different route.

Good luck with the build.

 

[ecstatic_subjectivity]

Thank you! No time to work on it tonight, but tomorrow I'll hopefully have some time to split the cases and do the welding needed.

 

[MorbidlyObeseKoala]

First of all, good luck and good for you trying something different. The parts are there, might as well try it and see if it matches the vision in your head. I can't really offer much on a full sized dirt bike build but cheerleading so go team.

Are you concerned with your gear ratios being set for the ICE engine power band? IDK how difficult or pricey it is to change out the gears or if people even do that.

There was a lot of discussion on here a while ago about the need for a clutch in slippery situations to manage the power more precisely, probably still ongoing in the moto trials thread. I kind of thought a cool idea for doing that electronically would be having the clutch lever change the throttle curve to either be more linear or maybe decrease sensitivity (limit the total voltage through the throttle) to simulate that sensation of slipping the clutch. You wouldn't have the momentum of the internals spinning when you release it but with all the torque in the electric motor available at very low rpm, I would think you would still get good oomph from a stand still.

 

[ecstatic_subjectivity]

Thanks, it's really nice to hear the support for a different approach!

I'm not broadly concerned about gearing. The QS138 does about 4k RPM without flux weakening, and up to 6.5k or so (iirc) with flux weakening, and the rev range the 2 stroke uses is about 2-5k under normal usage, so it should be just fine. I've also got the option to adjust the motor to crank ratio by changing the sprockets on the crank/electric motor. It's common on dirtbikes to change final drive sprockets(stock countershaft to rear sprocket) for different conditions, so there's also a pretty wide range of potential final drive options available. You wouldn't typically change out the transmission gears (although KTM makes multiple versions of the transmission for motocross/hare scrambles/street legal dual sports), but final drive changes are commonplace.

The issue with electronic clutch modulation is it's a single variable control, whereas the flywheel inertia combined with a clutch is a 2 variable control - you can slip the clutch to increase or decrease engine braking, momentarily interrupt power to the ground, or to dump a bunch of power to the rear wheel, depending on what the motor and chassis is doing when you pull the clutch in or release it. The torque of an electric motor is marginal compared to the point in time burst power you can get out of a flywheel dumping a massive amount of stored rotational mass to the ground - even if your electric motor is powerful enough to give that output, the throttle only power delivery needed to match a bike doing a clutch up wheelie at 40mph would be basically unrideable under normal offroad conditions.

This isn't a huge concern for most, but if you're riding quickly offroad, there are times when you want to burst power to the ground to go over something, and the combo of clutch and throttle gives you the ability to immediately deliver that power to the ground exactly when you need it. A "torque reduction" lever can't really do that, and you'd have to run a massive motor to get to the point where you could have that sort of performance off the throttle alone.

 

[MorbidlyObeseKoala]

I've also got the option to adjust the motor to crank ratio by changing the sprockets on the crank/electric motor.

Lol oh right, duh, even shown in the photos. Pretty simple to change rotation before or after the transmission.

Point taken on the precision of lifting the front wheel with the mechanical clutch. I am still stubbornly thinking there is a way to do it electronically with regen braking or a turbo power level button/lever for that explosive torque situation but you would need the motor and battery to handle those bursts. I suppose if the Stark vaarg guys didn't do it, it must be far more complicated or little benefit than I am imagining. Plus you would probably have to re-learn to ride with that feature instead of the clutch feel.

Anyways, interested to see how your build comes along.

 

[ecstatic_subjectivity]

Managed to make some good progress after work today!

Split the cases:

This Motion Pro crankcase splitter is very expensive but also a wonderful forever tool.

No conrods allowed:

If you don't want to retrue the crank, just angle grinder the conrod off.

Welded the crank up, as a 2 stroke crank really is not designed to be driven off the rotor side:

And the bottom end back in the frame and ready for me to start on building the motor mount, battery box, and controller mount.

Not so far away now...

 

[ecstatic_subjectivity]

Things slowed down a bit, but still making forward progress. I did temporarily get the motor running just to make sure everything works, so a short clip of that is available on my Instagram if you'd like to see it.

This build is a bit more slapped together / rough, but I'm not entirely sure the concept is going to work, so it feels like investing time in doing proper fabrication work is wasted. If this works out, I'm going to want the next one to be a new model chassis anyways, so the goal is finished as quickly as possible, so I can start testing and see how I feel about the overall setup. Could ride it and have it be awful, after all.

With all the parts, it looks like it'll weigh around 245 pounds, which isn't too bad with a full tank of electrons. I've got a very basic battery retainer bent up:

Need to similarly bend up some guards for the battery itself, and then it's wiring, a chain guard, mounting the controller in what once was the airbox, and reinstalling all the parts. Hopefully I'll have it finished up tomorrow, but we'll just have to see!

 

[bayodome]

Interesting concept. Can't help but think of how much weight this is adding to your bike. But I suppose the net weight is probably similar to what it would be if you only used the electric motor and took the rest of the space up with a larger battery.

I'm all about MX/XC builds so best of luck! Will be curious to see the results.

 

[ecstatic_subjectivity]

I got the cases sealed up, and the upper motor mount fabbed up:

Following that, I discovered something pretty disappointing - the placement of the electric motor + crank sprocket is such that I'm perfectly between the link sizes on the chain.

Need a half link in 428, because I welded on the lower sprocket, the upper sprockets for my particular QS138 configuration only seem to be available in 520. Don't have enough space to significantly move the motor, or have enough space to fill the slack of a longer chain with a tensioner assembly. Half links that don't use a cotter pin assembly seem to be pretty exclusively available from overseas dealers. So it goes!

I'll probably get impatient and just fit the QS120 I have instead. I designed everything to be pretty modular, so it's just 3 parts (upper and left / right side brackets) to swap motors. That'll drop me to about 50% of the power I had intended, but it will be a bit more power than my electric motion trials bike with the option for much shorter gearing, so maybe it'll all work out.

bayodome, I've weighed the cases and they're about 25 pounds with all the extra bits stripped out - yeah, I'm definitely giving up a bit on weight, but I think I'm going to more than get it back in acceleration in lower gears while still being able to keep up on transition roads. I wear 25 pounds of gear when I'm dirtbiking anyways (3 liters of water, tools, full protective gear + helmet, etc), and the 20 pounds is pretty low in the bike, so it shouldn't be too bad. All in, I think the bike is going to land at right around the stock weight - ~245 pounds, even with my very heavy / slapped together brackets.

 

[ecstatic_subjectivity]

If I were to swap the QS120 in with an EM-100 controller, how high could I reasonably turn up the controller Busbar current without worrying about frying the controller / motor? My use case is different from most, cause I have a clutch, so I'll tend to slip the clutch at lower RPM to bring motor and flywheel mass up and allow controlled drive off the line, which I understand will create less phase amperage draw.

I'm also going to be running significantly shorter gearing (I think first will top out at something absurd like 12mph, 5th will be good for roughly 70mph), and I can keep the motor in a higher RPM range as needed, so that also creates some change, because it's unlikely I'll spend an extended period of time at high throttle openings at low RPM because the motor will simply accelerate faster.

I really wish I could set up an idle/auto-tick over, like I have on my Electric Motion, where the controller would "hang" at 500 RPM or so, just keeping the flywheel mass moving, but it doesn't look like there's a way to cause that behavior on the controller.

Any thoughts welcome!

 

[ecstatic_subjectivity]

I've got a fully enclosed chainrun with delrin sliders now - swapped the QS120 on, remade motor mounts. Might need to go to a 520 instead of the 428 that it came with. That'd also open up some other options for gearing. I can adapt the delrin setup to have a spring loaded tensioner on it, although given that there's no major movement in the assembly, I'm inclined to just let it run as is loose. Very short run, after all.

Unfortunately, I didn't have a 520 chain floating around that was long enough to fit, so have to wait until that shows up.

Starting to come together though - I'll need to hack up the gas tank to make space for the battery, and still need to bend up a battery box and I want some rubber inside that box to make sure there's a little extra flex should I pitch the thing into a rock. Also need to seal the battery box so that the battery doesn't get exposed to water in the rainy PNW.

Weight as it sits with the smaller motor and controller was 238 pounds. It'd be lighter still if I made proper engine mounts and brackets, but that'll come with time. Probably can sneak under 250 pounds for v1, and maybe a bit lighter for V2.

 

[ecstatic_subjectivity]

Drive chain showed up today, and I did a quick spin on it. The electric motor configuration is too soft off the bottom when you have a clutch, it doesn't feel very responsive. Also probably want to turn down the regen. It needs the bigger motor for sure, although aggressive clutch use works okay at low speed. The shifter is also sticking slightly, despite everything moving cleanly when the cases were originally assembled - I think something is binding in the clutch cover. I need to more carefully balance the crank, install the larger motor. It's also loud, kinda thinking about running a belt rather than a sprocket. But it's an initial success, so can't complain! Pictures and video to come when it's assembled.

 

[Dui ni shuo de dui]

Great job mate.
That looks like a very interesting build, I always wanted to make a bike with a flywheel and gearbox to get some more thrills. Can't wait to see it finished!
I hope you will manage to get it working soon.

Keep up the great work!

 

[ecstatic_subjectivity]

If you'd like to see the E-moto in (very light) action:
Conan Dooley on Instagram: "First ride on the E-moto, need to finish up armoring, battery mount, and get all the plastics and such on it. Chain might have stretched enough to fit the qs 138, will just have to see. So much mechanical noise!"

I'm feeling a bit tired of working on the E-moto and I have some parts I'd like to have arrive before I make more progress, so will probably spend the next few days instead focusing on cleaning up ECU maps and getting my ECU flashing process all sorted. I've got a stack of other projects of the more gas-oriented variety that are capturing my interests right now, so probably be a week or two before I get the e-moto into the woods.

 

[ecstatic_subjectivity]

Alright, well, wasn't super happy with how the old project was going, so did some work and got the EM ePure Race motor in the 300, at least enough to pop around the yard a bit:

Things remaining to do are:
Weld on lower rear motor mounts
Get the lower mounts done in aluminum
Design some armor for the battery so I don't dent the battery in a drop
Better secure the controller
Fit up the rest of the plastics
Fit some lever guards

I'll need to do a bit more experimenting, think I might want to drop the gearing a bit more, but as it sits, it's got a good amount of grunt and it drives nicely off the bottom. It's on a 11 tooth front sprocket from the factory so can't really go any smaller, any changes will require going up in the rear.

Weight is 217 pounds with a full battery, so a full +50 pounds over the EM. But I gained a much better chassis, suspension, brakes, and seating position. In the long run I'll build a bigger battery pack for it - My target max weight is around 240 pounds so should be able to do pretty decent with another 23 pounds work of cells - I think it'd make for a delightful woods bike in that configuration.

I'll also probably eventually want to throw the QS138 at the other dirtbike frame I have just to have the comparison between the two bikes.