Another GasGas trials bike conversion

General Discussion about large electric scooters and motorcycles and other things with no pedals.
rynhardt   1 W

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Another GasGas trials bike conversion

Post by rynhardt » Sep 18 2019 8:43am

Hi everyone.
Total noob here with regard to building EV's, but I've been lurking long enough to understand that I do indeed know next to buggerall and will need some help..

I've been riding an OSET 20 recreationally the last year or so, but it's time to get something bigger. Recently got hold of a 2001 GasGas 249 TXT (pic below), which I hope to convert it to electric.

There is an existing topic on a very similar build over here: viewtopic.php?f=10&t=89073

But since this is a new build, this is a new topic. Moderators, please advise/move to the correct forum if this not in the right place.
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PaulM   100 W

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Re: Another GasGas trials bike conversion

Post by PaulM » Sep 18 2019 12:32pm

I just picked up an OSET 20R myself; it's an amazingly fun little bike!!

Did you consider an OSET 24 at all? I'd like to find one but no used ones even remotely close to me and new is pretty expensive.

Best of luck with your conversion!

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Re: Another GasGas trials bike conversion

Post by rynhardt » Sep 19 2019 1:02am

I got an OSET 12.5 for my son when he turned 4. Not long after that I got an OSET 20 for myself to ride with him. And then of course the missus wanted to join in so I got another OSET 20 for her. And another OSET 12.5 for visiting kids to ride with my son. He's outgrown the 12.5 so I got an OSET 16 for him when he turned 6. And an extra one for when his friends visit.
All of these I bought used fairly cheaply, did a minor service on the moving parts, replaced a few SLA batteries and they were good as new.

I did consider getting an OSET 24, but it's still not quite a full-size bike with full-size wheels, and I'm right on the limit of 90kg. It also still has the motor mounted on the swingarm, which may or may not be a problem. I have managed to dislodge a magnet from my OSET 20's motor on a hard landing (which I subsequently reglued), so I think having the motor as part of the unsprung mass will result in reliability issues if you ride aggressively. And I have been steadily riding more aggressively to the point where I'm worried I'm going to break my OSET 20; that being said, it's quite a robust little devil.

Add to that the fact that the OSET 24 is expensive and there is no apparent market for it here (South Africa). One guy has been trying to sell one on Gumtree for the last year and he's still trying to sell it. The OSET 20,16 and 12.5 are a lot cheaper and there is a much more active market for them here.
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rynhardt   1 W

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Re: Another GasGas trials bike conversion

Post by rynhardt » Sep 19 2019 3:54am

When I bought this GasGas donor bike I thought I'd ride it with its existing 2-stroke engine for a bit.
But having ridden the OSET for some time now, I have really become spoiled with its torque delivery characteristics and ease of use. No clutch, no gears, no noise.
Needless to say, I took one ride on the 2-stroke and that was the last time. That engine has now been ripped out and might be turned into a wakeskate winch (pic below).

For the record, here are the specs for the original 2-stroke bike (at least as much as I could find):
Wet weight: 75kg
Max power: 15kw (20hp) @6000rpm
Max torque: 25Nm - 45Nm (varying specs on the net, let's split the difference and make it 35Nm)
Gearbox 1st gear: 2.9:1 (first gear is crazy low, good for rock crawling)
Gearbox 2nd gear: 2.5:1 (most guys use 2nd gear for power actions)
Rear/front sprockets: 42:11 (3.8:1)
Rear wheel dia: 0.67m

The trials guys tend to use the clutch a fair amount, essentially storing energy in the flywheel for actions requiring short bursts of more power.
On my OSET I found that you can achieve the same result without a clutch, because all the power is available on-demand and it doesn't drop off when the flywheel has expended its energy.
However, the technique is different. Same end-result though.

I am fairly impressed by how much torque the OSET 20 puts down. I normally run it at the 50% power setting, which means it ramps up to full power over a period of about 1 second.
I almost never run it wide open (or should I rather say full-scale, seeing as the throttle is not actually opening an airway :-)).
Full power is frankly rather intimidating. I have in fact mounted a cut-off switch on the rear brake because it's too easy to go full whiskey throttle standing up. And this is on a 1200W motor, 48V SLA 9AH battery pack.
Generally I potter around at about 10km/h, with occasional bursts up to 30 km/h. High power actions (wheelies/splats) are few and far between, probably 10% of riding time.

The 2-stroke, in 2nd gear, with the standard sprockets, at max engine torque, should deliver 35Nm x 2.5 x 3.8 = 332.5Nm at the rear wheel.
With the standard rear wheel, that equates to 332.5Nm / 0.67m = 496N of forward thrust (provided we have lotsa grip).
If me and the bike weigh 165kg together, that thrust provides 496N / 165kg = 3m/s^2 of accelleration, which means a 0-100 time of approximately 9.2s.

Going electric, I would prefer similar or better torque performance. Top speed is somewhat academic, but let's say 40km/h is sufficient.
The rear wheel stays the same, so let's start with rear wheel torque, i.e. 333Nm.
I can use a gearbox or I can use a direct drive from the electric motor. Direct drive is easier to build and has less frictional losses, but sprocket size can be an issue.
Let's say I use #35 chain, I can go 10T front and 100T on the rear with a sprocket size of 0.308m
(https://www.rollerchain4less.com/Sprock ... _88-1.html)
#35 chain has got a max allowable load of 2kN and up, which is at 5 times my requirement.
(https://www.did-coltd.com/english/produ ... /sr_35.pdf)

On a 0.67m wheel I can run a 0.308m sprocket, giving me a 10:1 ratio. I think this is fine, given that my OSET 20 has a large rear sprocket and I've not had any issues fouling rocks or terrain with it.
I can also drop down to #25 chain if I need even higher ratio.
(https://www.did-coltd.com/english/produ ... 02-103.pdf)

With a 10:1 ratio, I can get away with a motor that provides 333/10 = 33Nm shaft torque.
For 40km/h (666m/min), and a wheel size of 0.67m dia (circumference = PI x 0.67 = 2.1m), that gives 666m/min / 2.1m = 317rpm.

So. Motor.
Minimum: 33Nm, 317rpm.
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Grantmac   10 kW

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Re: Another GasGas trials bike conversion

Post by Grantmac » Sep 19 2019 12:15pm

I'm considering a motorcycle conversation with similar power requirements (just 3x the speed with less torque) and I'm looking REALLY hard at the QS3000 mid drive. They happily peak at 15kw.

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Re: Another GasGas trials bike conversion

Post by rynhardt » Sep 20 2019 9:05am

This one: QS Motor 3000W 138 70H Mid Drive Motor

Yeah I'm looking at exactly the same one. They now come with a few different housing styles and you can also get them with a sprocket on the output shaft.

I have in fact sent an email to QS regarding the differences between the 7T and 4T windings. Will post here once I get some feedback.

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PaulM   100 W

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Re: Another GasGas trials bike conversion

Post by PaulM » Sep 21 2019 7:58am

rynhardt wrote:
Sep 19 2019 1:02am
I got an OSET 12.5 for my son when he turned 4. Not long after that I got an OSET 20 for myself to ride with him. And then of course the missus wanted to join in so I got another OSET 20 for her. And another OSET 12.5 for visiting kids to ride with my son. He's outgrown the 12.5 so I got an OSET 16 for him when he turned 6. And an extra one for when his friends visit.
All of these I bought used fairly cheaply, did a minor service on the moving parts, replaced a few SLA batteries and they were good as new.
I like the fleet of OSET's! My boys are 4 and 6 so I don't think just one is going to cut it here either!

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Re: Another GasGas trials bike conversion

Post by rynhardt » Oct 07 2019 1:53pm

I've been doing a fair amount of research the last two weeks. In between family and work and everything else as usual. :roll:

After evaluating various motors and controllers, I'll most likely be using a brushed, air-cooled, series wound DC motor and a non-regen controller. In particular, the Motenergy ME0909 motor and the Alltrax SR 48300 controller.

The brush life on the ME0909 is apparently 1500 hours, which is a lifetime in trials hours. The series wound motor is very robust and simple to control. There are no hall sensors, for example.

I'm not particularly concerned with high speed or even continuous medium speed. The motor will most likely spend most of its time in a low torque and low rpm state, with occasional bursts of power. I don't foresee heat buildup being an issue either.

From what I've read, regenerative braking needs to be managed and can have variable results depending on the system state. The last thing I need when doing technical riding is another variable to manage, and since I'm not too bothered with range I believe a non-regen system will work for this use case.

The Alltrax controller seems to have good track record and support available in English. The programming software is free and runs off a Windows PC with a USB cable.
Most importantly for me the the SR range has two throttle response maps (user switchable) where you can dial in torque and speed response.

Lastly, my fleet of OSETs all run brushed series wound motors. These have all been put through the wringer, and aside from the one motor's magnets that need to be re-glued, have been 100% reliable. That's plenty of confirmation bias for me right there :lol:

On the battery side, I'll most likely be running 48V, and in fact will be using one of my OSET 20's 48V 9Ah SLA battery packs. Once I'm happy that the performance is dialed in, and my budget allows, I'll upgrade to LiFePo4.

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Re: Another GasGas trials bike conversion

Post by Xtr6 » Oct 07 2019 3:08pm

Woudn't go for the LIFEPO4. Much too heavy. Put in 14s lipo with 16.000 mah and you wil have ridding time enough.
Basicly trail riders like to have as les weight as possible. My Gasgas TXTe weight 63 kg compleet.

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Re: Another GasGas trials bike conversion

Post by thoroughbred » Oct 07 2019 4:14pm

rynhardt wrote:
Oct 07 2019 1:53pm
I've been doing a fair amount of research the last two weeks. In between family and work and everything else as usual. :roll:

After evaluating various motors and controllers, I'll most likely be using a brushed, air-cooled, series wound DC motor and a non-regen controller. In particular, the Motenergy ME0909 motor and the Alltrax SR 48300 controller.

The brush life on the ME0909 is apparently 1500 hours, which is a lifetime in trials hours. The series wound motor is very robust and simple to control. There are no hall sensors, for example.

I'm not particularly concerned with high speed or even continuous medium speed. The motor will most likely spend most of its time in a low torque and low rpm state, with occasional bursts of power. I don't foresee heat buildup being an issue either.

From what I've read, regenerative braking needs to be managed and can have variable results depending on the system state. The last thing I need when doing technical riding is another variable to manage, and since I'm not too bothered with range I believe a non-regen system will work for this use case.

The Alltrax controller seems to have good track record and support available in English. The programming software is free and runs off a Windows PC with a USB cable.
Most importantly for me the the SR range has two throttle response maps (user switchable) where you can dial in torque and speed response.

Lastly, my fleet of OSETs all run brushed series wound motors. These have all been put through the wringer, and aside from the one motor's magnets that need to be re-glued, have been 100% reliable. That's plenty of confirmation bias for me right there :lol:

On the battery side, I'll most likely be running 48V, and in fact will be using one of my OSET 20's 48V 9Ah SLA battery packs. Once I'm happy that the performance is dialed in, and my budget allows, I'll upgrade to LiFePo4.
This is essentially just like a Zero X bike as far as the drivetrain you describe. I have a couple but with sr48400 and lithium batteries. Still working on the throttle response since it is pretty crude for trail riding and will be even more tricky for trials bike use. They will wheelie but not great.

One of them needed disassembly not because the brushes were worn out but because the brushes were stuck in their slots by corrosion.

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Re: Another GasGas trials bike conversion

Post by rynhardt » Oct 08 2019 1:39am

thoroughbred wrote:
Oct 07 2019 4:14pm
This is essentially just like a Zero X bike as far as the drivetrain you describe. I have a couple but with sr48400 and lithium batteries. Still working on the throttle response since it is pretty crude for trail riding and will be even more tricky for trials bike use. They will wheelie but not great.

One of them needed disassembly not because the brushes were worn out but because the brushes were stuck in their slots by corrosion.
Would you mind elaborating on the throttle response issues?
I'm hoping to get the throttle response dialled in using the Alltrax throttle curves.
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Re: Another GasGas trials bike conversion

Post by thoroughbred » Oct 09 2019 6:26am

I need to play with the tuning more but so far I have a pretty abrupt engagement at 0 mph/0 % throttle. The SR controller is smoother than the older AXE controller in this regard. I have a domino and a magura throttle but I need to compare them more to say if one is better than the other. Domino is a quicker twist, though.

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Re: Another GasGas trials bike conversion

Post by rynhardt » Oct 10 2019 4:14am

Xtr6 wrote:
Oct 07 2019 3:08pm
Woudn't go for the LIFEPO4. Much too heavy. Put in 14s lipo with 16.000 mah and you wil have ridding time enough.
Basicly trail riders like to have as les weight as possible. My Gasgas TXTe weight 63 kg compleet.
Thanks for the heads-up. I might just go for LiPo instead, as I see their C rating is generally much higher.
Did you put two 7s LiPo packs in series?

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Re: Another GasGas trials bike conversion

Post by rynhardt » Oct 10 2019 4:16am

thoroughbred wrote:
Oct 09 2019 6:26am
I need to play with the tuning more but so far I have a pretty abrupt engagement at 0 mph/0 % throttle. The SR controller is smoother than the older AXE controller in this regard. I have a domino and a magura throttle but I need to compare them more to say if one is better than the other. Domino is a quicker twist, though.
I'll probably get a Domino, it looks a bit nicer than the Magura.

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Re: Another GasGas trials bike conversion

Post by Xtr6 » Oct 10 2019 1:19pm

I build my own 14 s lipo with 2 x 4 s and 1 x 6 s and these in serie gives 14 s with no messing with solo cells. Do charge them seperately with lipo balance charger. Simple quit cheap and a lot of power.

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Re: Another GasGas trials bike conversion

Post by rynhardt » Nov 25 2019 1:03am

I got a great deal on a donor bike, the OSET MX-10.
This has the same 1400W motor and 20Ah 48V Li battery as the OSET 24 trials bike. Everything else is also there, controller, throttle, contactor, battery charger, key switch etc., so it's really a just matter of transplanting the electrics to the GasGas frame.

Only problem is my son has called dibs on it, so this project may have to wait until he's too big for the bike :lol:
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Re: Another GasGas trials bike conversion

Post by rynhardt » Dec 01 2019 8:30am

Some more progress..

transferred the MX-10 parts to the GasGas, everything still works :-)

Battery and motor are more-or less where they need to be, still need to make some mounts for them, and get a #219 sprocket for the rear.

The motor is running backwards as expected, since the Oset has the chain on the right side. I should be able to either reverse the polarity on the motor if the timing is zero, or adjust the brushes if not. Will see when we get there.
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Re: Another GasGas trials bike conversion

Post by Xtr6 » Dec 01 2019 1:37pm

Would go for a 2 stage reduction to get a decent Torque. Trail ia al about Torque an low speed.
Wil bring more fun with that smal motor. These 1400 watt needs a lot of Amps. to get you doing a trail track.

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Re: Another GasGas trials bike conversion

Post by rynhardt » Dec 28 2019 7:02am

I've finished the conversion and I consider it to be a resounding success :D
Using the Oset 10 parts were pretty straightforward, so most of the conversion came down to making brackets to mount the motor, battery and rear sprocket.

Performance is fine, basically a bigger version of an Oset 20. Enough to do power wheelies and steep inclines.
Range is still unknown - I'm hoping for 2-3 hours - this will get tested when I've got time.

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Re: Another GasGas trials bike conversion

Post by rynhardt » Jan 31 2020 6:50am

I've completed my first observed trials event with this bike, last weekend. I'm in the clubman class.



With some comments from me over here:


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Re: Another GasGas trials bike conversion

Post by rynhardt » Feb 06 2020 6:59am

I'm adding some more power to the bike.. on the front wheel :lol:

gonna be interesting to see how my brain copes with the secondary throttle.. :shock:
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DanGT86   100 kW

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Re: Another GasGas trials bike conversion

Post by DanGT86 » Feb 06 2020 10:05am

Interesting. Should help a bit with the hook moves. Have you checked to see if 2wd is allowed with the club you compete in?

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Re: Another GasGas trials bike conversion

Post by boars » Feb 06 2020 7:35pm

I don't think my brain couldn't handle 2 throttles :lol:

At the very least it'd take some time to get used to!

Looks pretty cool though.

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Re: Another GasGas trials bike conversion

Post by amberwolf » Feb 06 2020 7:50pm

it's easy to get used to two throttles, one for each wheel. after a while of practice, you learn to use each wheel for the best traction, just like you do with two brake levers for braking.

if you're using throttle controlled motor braking it's even easier.


if you were using a 2wd bike that didn't need independent control of the wheels, you can use just one throttle for both controllers (probably not the goal for this build).

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Re: Another GasGas trials bike conversion

Post by rynhardt » Feb 07 2020 1:49am

DanGT86 wrote:
Feb 06 2020 10:05am
Interesting. Should help a bit with the hook moves. Have you checked to see if 2wd is allowed with the club you compete in?
They're already not sure what to do about the no-stalling rule with e-bikes. :lol:
If push comes to shove I'll just disable it for the event, like remove the chain or something.

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