RMZ250 (hard)enduro build

[Balgaroth]

Hi guys,

Since the thread I posted few months ago I found a pretty good deal on a RMZ250 from 2008 nearby. Even thought I haven't figured out everything yet I decided to pull the trigger, start building it and to learn as I go. So far the bike will remain as it is, I am not willing to put a lot of time and effort if I don't like it in the end (I am also rebuilding my 2 stroke at the same time, which has the priority finance wise). If I end-up enjoying the e-RMZ I will take everything appart and give the chassis a full clean-up/makeover.

So far I got the motor mounts from Lithium-king, sadly I messed up the measurement and I will need to grind the forward hole a little bit on the mount and will probably do so on the frame too. Probably 3-4mm off the mark, I knew that the measurement would be tricky but I didn't think I'd be this far off the mark. I installed my controller in the airbox, in place of the airfilter/filter mount (you can see it in some of the pictures). This seems like a good position to me as it allows some airflow to reach the controller's radiator. I also did most of the wiring, using waterproof connectors instead of the ones provided with the controller. Now the the motor is in place I need to figure out a way to make a battery holder and the final dimensions for my battery. One of the old motor mount located near the top of the rear shocks is in the way, I might cut it off in order to keep the battery as rearward as possible. Another point that was interesting it the brake pedal situation. I'd like to keep the rear brake at the foot in order to keep muscle memory for when I transition back and forth with my 2 stroke. I picked the motor as it is supposed to allow for the use of a brake pedal but the tip of the pedal is touching the hall-sensor cover. I will see if I can space it out to run it properly, otherwise I will need to run it super low which isn't ideal.
So far here are the specs of the bike:
- Bike: RMZ 250 2008
- Motor: QS138v3 70h
- Controller: Fardriver ND96680
- 13t front sprocket (lithium king), 48t rear sprocket (came with the bike)
- Throttle: CCXT e-throttle, sold as a Surron throttle.

I have a few questions that came up along the way, hopefully some of you can enlighten me.
- My goal is 25kw in my normal map and 30kw for a "MX" map. I picked the ND96680 thinking that it would be well able to it, but looking back at the specs the line max Amp is limited to 250A and phase amp is limited to 680A . So is it possible to reach 30kw or not ? Going by the line amp my max should be around 24kw, but if I go by phase amp I would be able to reach my 30kw comfortably. I find this confusing, like how is it possible to have more phase amps than the max provided by the battery ?

- In some builds I saw some master switch of fuse between the battery and the controller, but many (most) builds don't seem to include one. Is it necessary ?

- As for the battery I got in touch with Amorge asking for a battery around 5kw. With the budget that I am willing to put in this it could either be a 26s10p with Samsung 50s, or a 26s12p using EVE 40P or 40PL. Which one seems best in your opinion ? If I did my research correctly, the EVE pack would be slightly heavier (~1kg) but it might be cheaper and would have better performance with less V sag.

I might try the bike with a 72v Talaria battery from a friend, just to get a first idea of how this can turn out. Some rachet straps would do to install it and ride the thing on green lanes

 

[bananu7]

max Amp is limited to 250A

On paper or during actual programming? Phase amps aren't indicative of the system power, as they are calculated after controller PWM at lower voltage. The easiest way to is to get the power draw on battery - 250A times nominal 96V gives 24kW, or 27.3kW on the fully charged battery. Remember that there's going to be some losses on the controller - most report efficiency around 93-94%. For enduro purposes it likely won't be the issue - the 680pA limit is far more important as it will dominate at low RPMs. For MX use, you indeed want outright top end power, but I wouldn't worry too much until you test ride the bike. If you get a fitting battery, replacing the controller with a more powerful one is perhaps the easiest upgrade path.

Another thing to keep in mind is the gearing. 2.35 * 48/13 = 8.68, which is on the faster end I'd say; RPM-wise it should be good to around... 110km/h? ish? something like that. Again, for an offroad bike I would say torque is often more important, so gearing down for lower top speed will have huge impact on the wheel torque. If you've read my thread, you know that that was one of the reasons why I went for the shorter-link 428 chain and 54T rear sprocket.

If you want some more info about phase amps vs battery amps, we had a longish discussion on that recently - feel free to join that thread if needed: Phase Amps to Motor Math

Looking at the battery, firstly make sure you're within current specs. Samsung 50S has 35A max discharge, EVE has 40 or 70. and you're saying that you'd have 12p then. That would be absolutely huge 480 or even 840A batteries - assuming Amorge can even build it for such high current. The cell connections, busbars and external terminals all need to be absolutely top notch to sustain such use. Regardless, any of those 3 choices would be comfortably above the stated controller limit.

Capacity-wise 5kWh (not kW) is a bit above average. The actual amount of riding time is hugely dependent on your riding style and conditions so, common sense applies.

At least one fuse should be placed between the battery and the controller. Votol controllers have provision to put them right on the controller enclosure. I'm planning on another one inside the battery if I can fit one; this one is I would say not strictly necessary and would only come in use if the BMS failed in an open state.

 

[azeus17]

- In some builds I saw some master switch of fuse between the battery and the controller, but many (most) builds don't seem to include one. Is it necessary ?

Are you referring to the contactor? It is basically a high current relay. Some builds use them, some don't. I don't think many builds leave out a fuse. I used a contactor on my build and have it wired to a kill switch as an e-stop. If something goes wrong, I can hit the button and cut power to the controller.

 

[thebes]

but looking back at the specs the line max Amp is limited to 250A and phase amp is limited to 680A . So is it possible to reach 30kw or not ?

Depends on where you look, the one I bought says 330a on the tin but Ive had it up higher around ~350, dont remember exactly what the software limits you to though, was able to hit ~35kws with a 33s9p pack of a123 26650s and a 138 70h mounted on a db27 frame.

 

[Balgaroth]

On paper or during actual programming? Phase amps aren't indicative of the system power, as they are calculated after controller PWM at lower voltage. The easiest way to is to get the power draw on battery - 250A times nominal 96V gives 24kW, or 27.3kW on the fully charged battery. Remember that there's going to be some losses on the controller - most report efficiency around 93-94%. For enduro purposes it likely won't be the issue - the 680pA limit is far more important as it will dominate at low RPMs. For MX use, you indeed want outright top end power, but I wouldn't worry too much until you test ride the bike. If you get a fitting battery, replacing the controller with a more powerful one is perhaps the easiest upgrade path.

Another thing to keep in mind is the gearing. 2.35 * 48/13 = 8.68, which is on the faster end I'd say; RPM-wise it should be good to around... 110km/h? ish? something like that. Again, for an offroad bike I would say torque is often more important, so gearing down for lower top speed will have huge impact on the wheel torque. If you've read my thread, you know that that was one of the reasons why I went for the shorter-link 428 chain and 54T rear sprocket.

If you want some more info about phase amps vs battery amps, we had a longish discussion on that recently - feel free to join that thread if needed: Phase Amps to Motor Math

Looking at the battery, firstly make sure you're within current specs. Samsung 50S has 35A max discharge, EVE has 40 or 70. and you're saying that you'd have 12p then. That would be absolutely huge 480 or even 840A batteries - assuming Amorge can even build it for such high current. The cell connections, busbars and external terminals all need to be absolutely top notch to sustain such use. Regardless, any of those 3 choices would be comfortably above the stated controller limit.

Capacity-wise 5kWh (not kW) is a bit above average. The actual amount of riding time is hugely dependent on your riding style and conditions so, common sense applies.

At least one fuse should be placed between the battery and the controller. Votol controllers have provision to put them right on the controller enclosure. I'm planning on another one inside the battery if I can fit one; this one is I would say not strictly necessary and would only come in use if the BMS failed in an open state.

Thanks for your feeback ! I agree with the fact that going with a good battery for my goal is probably the best option as going up one or two size of controller is definitely cheaper and easier to manage. As for transmission ratio, I am using the sprocket that's on the bike right now just to get a feel for it, I definitely don't need 110kmh with this bike, the plan is more to have 90 to 100kmh so I will probably end up with a 52t sprocket in the long run, this is what Electro&Co is using on their YZF conversion so I guess it should be good for me too. I am also worried that having too much of gear reduction will make the low speed hard to control which would be problematic for the planned use of this bike.

I will read the thread, I also end up reading another good thread (easier to understand) about it yesterday which helped me understand the relation between phase and line app, especially thanks to @E-HP who shared a graph about different phase amp for identical line amp.

I definitely want a battery as close to 5kwh as the run time for such a battery in a full size bike seem to be within what I need (according to E&Co conversion et range tests from different bikes). As for the capacity of Amorge to build such battery, they offered a 26s10p battery using Molicell P50B with 420ampC and 550ampP, I doubt that a 26s12p with EVE40P will have higher numbers than this, either way I won't need such number so they could simply tune the BMS in order to have something reliable i guess ?

As for the fuse, I imagine this is the type of fuse I need to use on the red lead to the controller ? With a capacity slightly above max peak Amp rating ?

 

[Balgaroth]

Depends on where you look, the one I bought says 330a on the tin but Ive had it up higher around ~350, dont remember exactly what the software limits you to though, was able to hit ~35kws with a 33s9p pack of a123 26650s and a 138 70h mounted on a db27 frame.

So far I never plugged the thing with a battery (since I don't have one) so the 250Amp value is the spec sheet value. If it is possible to go higher than the advertised value I might just to than indeed, especially if this is for a MX map that I will most likely rarely use.

This leads me to another question, I saw that you can setup different maps which are determined using a % of the primary map. The YT tutorials I saw always used lower values for their maps (like a 50% "eco" map and a 80% "easy" map). As I understand this, your default map is setup for when the map switch is in a neutral position, so, would it be possible to have one of the maps setup as "hard" with 120% of the normal map ? I guess it is a detail but it seems more logical to me to have my normal map un the middle of the switch and eco/hard on either side.

 

[bananu7]

As for the fuse, I imagine this is the type of fuse I need to use on the red lead to the controller ?

Yeah. You can buy them in nice enclosures, meant for I believe car audio application, for quite cheap. Take note of mounting hole diameters, as most use 6mm and you need your cabling (I use AWG1 here) to somehow connect to the fuse and then to the controller.

would it be possible to have one of the maps setup as "hard" with 120% of the normal map?

Set the middle map to 83% and you'll get the same effect.

 

[Balgaroth]

Quick update, today I test fitted the battery shape I had in mind and that was validated by Amorge (drawing shows side surface, thickness of the pack should be 15.8mm) It all seems to fit, I will have to build the battery support accordingly. The shape was done with the goal to have a better Front/Back weight balance and to keep the weight as low as possible too. Depending on what Amorge says in term of size/capaci and what they will quote me, I might end up lowering the battery tray by shaving the mount that is on the motor in order to have a bigger battery.

So far the only drawback I see with this design is that it isn't easy to install, which also means that I won't be able to swap the battery. Basically the motor needs to be removed, the swingarm needs to be pulled back a little bit, the the battery is inserted. The battery will need to be placed as high as possible and kept there (rachet straps should work just fine), then you can install the motor and the battery support and then you can lower the battery to its final place. It could be done by one person alone, it should be easy enough with an extra person.

 

[Jim Beagle]

Hello Balga
I like your approach to battery install !

I am building a 2015 RMZ250 and am at the exact same stage as you. Working with Amorge to get a pack to fit this frame. It seems they can build almost any size & shape pack, but their ability to build boxes is limited to very simple cubes.....
Jim

 

[Jim Beagle]

Here is an example, Amorge can build a box in this four sided "custom" shape, but not the extra space below the redline.....

so I loose about 12 x 3 = 36 cells of capacity

 

[thebes]

So far I never plugged the thing with a battery (since I don't have one) so the 250Amp value is the spec sheet value. If it is possible to go higher than the advertised value I might just to than indeed,

Oh just to be clear, its advertised as 330 depending on where you look, the one I have is advertised as 330 battery amps, and 680 phase. The controllers, even with different advertised numbers, appear to be the exact same software and hardware wise!

 

[Balgaroth]

Hello Balga
I like your approach to battery install !

I am building a 2015 RMZ250 and am at the exact same stage as you. Working with Amorge to get a pack to fit this frame. It seems they can build almost any size & shape pack, but their ability to build boxes is limited to very simple cubes.....
Jim

Not sure how the 2015 is but the 2007 is a bit of a pain in the ass as the perimetric upper frame is angled so that you will need to install the battery from underneath, then install the motor. Otherwise you would have to go with something even smaller like with a max length of 20cm most likely.

The design I suggested was accepted by Amorge untill they did their calculations and figured that only 8 cells could be placed in the extra area. So it seems unnecessary to go with the extra complication for so little. Right now we settled on a cube shape of 22x32x15.8cm but I need to make it with wood to make sure it fits and doesn't need to cut the motor. I think Amorge is willing to do shapes that are pretty close to square but yeah your design is a bit complex I imagine. Alternatively you may ask them to build the battery without a box and do the box yourself, maybe they will be more willing to do odd shapes that way.

 

[Balgaroth]

Quick update, today I built a wood battery in order to confirm the shape with a rigid object rather than cardboard that can deform. I used the 22x32x15.8cm shape suggested by Amorge, slightly proud of these dimensions actually in case Amorge isn't perfectly accurate in their sizing. This confirmed that it is impossible to fit the battery top to bottom. Fitting will need to he done bottom to top and the motor needs to be removed too. This is due to the to prongs of the perimetric frame being tilted towards the top of the petrol tank rather than parallel.
Another interesting finding is that I can fit the battery in a very tilted maner, pretty much parallel to the shock. Which means that I can still mitigate the forward bias natural to eMx conversions. I traced the theoretical center of gravity of the battery and it seems that the tilted position shown in the picture shifts the CoG 1.5cm back compared to the more vertical positioning.

Now that still leaves me with one question, which is what battery cradle to build ? Would the motor mount be enough so that I can build a cadle only attached on that single point ? Should the cradle extend to the forward engine mounts, even though the weight bearing will be limited on the forward part of the cradle ? Should I plan a bridge type of cradle with the swingarm pivot, motor mount and forward engine mount ? Let me know what you think.

 

[Jim Beagle]

For me the Battery design is the most difficult part of these builds; many different options for shapes, sizes, install strategies, etc. And they all have compromises....

Are you cutting the bottom of the gas tank ?

 

[Balgaroth]

I agree, especially if you can't do it yourself as it is the most expensive part of the build which means you can't just try again. So far the tank has been cut and I also had tocut the upper engine mount. Mine was located on the back side of the upper shock mount and to keep it would have required to go with even less battery length (probably 19x32x15.8) which would have meant maybe 26s10p, most likely 9p. In fairness I got the bike for cheap, it is 2007 and I could recoup the money spent for the chassis by selling all the parts, aside from the main frame so I didn't have too many remorse cutting it.