Electric Racing Chainsaw Build, Help Please

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Sarcassidy   1 µW

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Electric Racing Chainsaw Build, Help Please

Post by Sarcassidy » Feb 27 2020 2:52pm

Hi Everyone - I compete at the top level in Stihl Timbersports/Lumberjack Sports competitions. One of our events is the hot saw where we are using 330cc Rotax or Honda CR motors tuned for racing. Here is a video https://youtu.be/G9DiMPGsH9U?t=12037

For a while now I've thought that going electric could be a game changer for a few reasons. There would be no warm-up or starting issues, there should be less vibration making for smoother operation, and the motor would reach top speed faster. Maintenance and reliability should be easier/better as well.

I'd like some guidance on electric motors and battery/power pack/supercapacitor configurations that would meet my needs.

Our 2 stroke motors crank out 50-60 horsepower, 50 lb of torque, and generate chain speed of 290 feet per second. The motor and exhaust weigh about 30 lbs. Are there any elecrtic motors out there that would have similar power and weight profiles?

A typical "racing cut" is 3 cuts on 16-20" softwood. Times are usually 5-9 seconds. Max run time would be 12 seconds on hard wood. What sort of battery/power pack/supercapacitor configuration would meet these power needs above and last 20 seconds or so? The less weight the better if i were to mount the power supply onto the saw, but I would also have the option of keeping the power supply separate from the motor/frame/bar unit and connecting it via cables. If I were to go this route, what sort of connections and cables would I need?

Any info you can relay me would be a good start. Thanks!

flat tire   1 MW

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Re: Electric Racing Chainsaw Build, Help Please

Post by flat tire » Feb 27 2020 6:40pm

You can easily do this the main issue will be not paying an arm and a leg for everything. You probably want a battery not supercaps, because you would need to construct a very big supercap bank and it will end up being more complicated and expensive than high discharge Rc Lipo.

You will probably spend 170-200 Wh energy with the battery outputting 50kw (reasonable approximation for 50-60 hp after losses) for 12 seconds. If you want more power, scale the energy consumption proportionately. Any pack you build will be large enough due to discharge constraints that you will have enough energy for several runs.

How much do you want to spend on the motor? If weight is important check https://emrax.com they can do "as much power as you want" if we're talking chainsaws, and with weight about as low as it gets.

For the RC LiPo you want to divide the power figure in Kw by the C-rate you can ACTUALLY expect for 12 seconds (found by googling tests of batteries) plus some overhead, to determine you pack size. This is definitely a place you want to get a respectable brand even though it will be more expensive. Turnigy Graphene high discharge is one brand that can meet your needs, but there are others.

This will not be CLOSE to a cheap project at all, unless you want your chainsaw to weigh 100+ lbs. Expect to spend a few thousand.

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Re: Electric Racing Chainsaw Build, Help Please

Post by Hillhater » Feb 27 2020 7:17pm

Where are you located ?
For professional , high performance , electric racing advice and components ( especially batteries), there are few better positioned than John Metric at Amaholic racing. http://www.ampahaulic.com/
Whilst not specifically focussed on chainsaws, they have performance electric drive systems from 40hp upwards.
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flat tire   1 MW

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Re: Electric Racing Chainsaw Build, Help Please

Post by flat tire » Feb 27 2020 7:28pm

Those guys may (or may not) have good batteries but the motor technology is last-century and nothing anyone wants in a chainsaw good lord.

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Re: Electric Racing Chainsaw Build, Help Please

Post by Ianhill » Feb 28 2020 1:09am

:shock: why so much KW to beat the hp power.

Torque is what's making the cut that's how makita got a 36v jobby with no where near the power of a 39cc saw but can keep up on the cut.

Damn 20kw on a torque heavy low kv motor and oak tree would tap out, key is to getting the chainspeed matching the motor rpm and get rid of the heavy ratio gears there's a good 15% in power no longer needed in gearbox and clutch losses the 2 stroke revs like crazy to get enough overall power through the system start to end to make the cut where as electric can much closer match the chainspeed straight from the rotor.

Thing I like about the 36v electric chainsaws is kickback detection and chainspeed ramp up detects as the load of a log is applied and the thing chews harder.

Thing I miss blipping the throttle soon as I let off the thing won't start again till its stopped and had a second bit of a pain and I'd program that out if I could.

Edit
Just done a quick search on the makita 36v and it's 1.1kw max and a 20m/sec chain rate, off the cuff to the ear it sounds around 5krpm and runs 10s/36v that would be around 150kv or so and proberly a 6374 motor like a skateboard unit.
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Re: Electric Racing Chainsaw Build, Help Please

Post by Hillhater » Feb 28 2020 1:48am

The key to this will be in the battery pack
One that is powerful enough for a very high burst of power, without being too heavy or big.
3 of those 6S 100C “sleeper” cell packs would give 72v and 400+amps, or 30 kW, for 30 secs or so!
2.5 kg and $400 .. :bigthumb:
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Re: Electric Racing Chainsaw Build, Help Please

Post by Ianhill » Feb 28 2020 2:14am

Are you talking of something powerful enough to win this vid?

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Re: Electric Racing Chainsaw Build, Help Please

Post by Hillhater » Feb 28 2020 3:02am

The other little issue will be chain speed....which i suspect is a critical factor ?
290 feet /sec is fast !..17,000+ feet/min.
So for a typical 6000 rpm motor speed (Emrax ?) , that would need a 12” drive sprocket if no gearing is used
Even with a 4” dia drive sprocket you would need a 18,000 rpm motor speed !
Do we know of any compact , 30kW, motors that can spin at those speeds ?
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Re: Electric Racing Chainsaw Build, Help Please

Post by Ianhill » Feb 28 2020 4:14am

18krpm sound like an f1 chainsaw you have greenpeace chewing your arse.

20m/sec works out to 45mph chainspeed/66 feet per second or 3960 feet per min.
Don't think you need such high rpm to go there not even the 2 stroke will get that high they top out round 13kprm at best, looking in them they are geared heavily so there's tons of rpm to be lost and pure grunt to be added, any diesel turbos out there that chew the arse off a log.

Watching the vid I see high speed cuts are effective but the 2 strokes can't hold the torque needed so they using 4 stroke car engines lmao and just blitzing the thing NAZI style engineering.

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Re: Electric Racing Chainsaw Build, Help Please

Post by Hillhater » Feb 28 2020 6:21am

Ian,... read the OP.
I trust he knows what he is talking about..
Our 2 stroke motors crank out 50-60 horsepower, 50 lb of torque, and generate chain speed of 290 feet per second. The motor and exhaust weigh about 30 lbs.....
I would guess chain speed is directly proportional to cutting rate
Your 20m/sec just wouldnt “cut it” in a comp like those.
.... And, there are plenty of 2 strokes that turn 20+k rpm !
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Re: Electric Racing Chainsaw Build, Help Please

Post by Ianhill » Feb 28 2020 6:56am

:roll: didn't take in the 290ft per second, damn that's alot more than the makita :lol: That's chain speeds approaching 200mph not quite super sonic yet mind plenty room for improvement :D

20krpm 2strokes are competion spec no doubt but trying to swap that into electric and compact is going to need some cutting edge stuff to go direct drive so yeah got to bow down and agree gearing is needed to get there.

I can see means off getting it 1/2 of the way there and keeping it around the 30lbs weight with mild gearing of less than 2-1 and that would use water cooled hydrofoil motor they got a round 14krpm in them 10kw burst current for the 12secs or so and might get the chain upto 100 m/sec with some decent torque 14lbs to back it up but not competion spec.

Any 2 stroke that does 20krpm in a chainsaw with 60hp while remains mobile by one man is the F1 of the chainsaw world, formula E just won't compete yet in my eyes and keep the weight low at half the power, I think it can be done specially with a slotless motor custom controller and high spec cells but £€$£€$ no doubt and it would be just be keeping up at best with the one man 2 stroke 20krpm tuned saws.

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dogman dan   100 GW

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Re: Electric Racing Chainsaw Build, Help Please

Post by dogman dan » Feb 28 2020 7:53am

I would look at motors first, and see what has the most rpm. Honestly have no clue what rpm drag strip car electric motors run at, but I would safely guess you need more than a golf cart motor, even on double the normal voltage.

it comes to mind you might look at heavy starter motors, like take offs from a big airplane engine. Look in Tucson maybe, for something not able to be used again on an aircraft. Designed for short duration, but very high torque use. Same things that make them so so for your electric VW bug might make a starter motor of some kind perfect for a hot saw.

And of course, whatever you get, run it on much more voltage than the designer intended. But not 10x volts, because that is more likely to just make heat and melt the motor. But nearly all motors can easily handle 2x volts.

Battery will be pretty simple, RC type lipo packs are light and cheap. For racing, figure on new or near new for any main event. Main thing you will need is the highest C rate you can get, because you will be running a huge amps compared to a typical RC drone.

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stan.distortion   100 W

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Re: Electric Racing Chainsaw Build, Help Please

Post by stan.distortion » Feb 28 2020 8:49am

Start small, I've prototyped one for day to day use and it worked out really well but there where a few issues that could have meant a total re-design. Temperature was the main one and if you're looking for peak performance then it's going to be a top priority, getting high power output will be fairly easy but keeping things cool when you're pushing the limits wont. Water cooling would help, it's unnecessary complication for my application but with yours it could be worth considering from the start.

I'd suggest looking into electric skateboard drivetrains, pretty much everything you need for up to 5kw peak is available off the shelf for relatively low prices and for competition it could be worth considering a belt primary drive, I'm using one for prototyping and it allowed me to dial things in easily. I can go to direct drive now I know what to expect but being able to go up or down a tooth will likely come in very useful for yours. Consider flywheel mass too, it shouldn't be an issue at higher power levels but I need to add some here to prevent stalling on minor snags.
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speedmd   100 MW

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Re: Electric Racing Chainsaw Build, Help Please

Post by speedmd » Feb 28 2020 9:13am

The Plettenberg nova 30 looks to be in the ball park, size / weight / power wise in near stock form. RPM is questionable. https://plettenberg-motoren.net/en/prod ... ons/motors

How much raker is left on the chain you could remove.

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Re: Electric Racing Chainsaw Build, Help Please

Post by Hillhater » Feb 28 2020 9:50am

There is nothing in the Pletenberg range that has the kw and rpm to match the requirements here.
Maybe a special fast wind on a Nova, but then yo lose the torque and have to run crazy voltage.
And a jackshaft could be used to boost the rpm x3 , you then lose 2/3 of the torque again !
As for water cooling :roll: ....get real, this thing is going to run for 10 secs... the water wouldnt have time to even get warm !
This is the chainsaw version of a top fuel drag racer !
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stan.distortion   100 W

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Re: Electric Racing Chainsaw Build, Help Please

Post by stan.distortion » Feb 28 2020 10:11am

Hillhater wrote:
Feb 28 2020 9:50am
There is nothing in the Pletenberg range that has the kw and rpm to match the requirements here.
Maybe a special fast wind on a Nova, but then yo lose the torque and have to run crazy voltage.
As for water cooling :roll: ....get real, this thing is going to run for 10 secs... the water wouldnt have time to even get warm !
This is the chainsaw version of a top fuel drag racer !
Yep, and when you're tuning an engine for performance you have to break them. A big chunk of the crazy prices paid for top fuel engines goes on top quality parts thrown on the scrap heap before they ever get near the track, the only way of knowing how much something can take is pushing it past its breaking point. This is experience talking btw, I've been performance tuning for most of my life and a good chunk of that professionally.

The same applies to electric motors, he's going to have to push them past their limits before he knows for sure what they can take and that's going to mean a hell of a lot of heat. Tbh, I've very little confidence in the cooling systems used on any motors I've seen so far, oil immersion would be a far better option until they're better developed for peak outputs but efficiency takes a back seat here, he's going to need every bit of cooling he can get.

DC might be the better option too, brushless seems the obvious way to go but DC is still on top with electric drag racing and it doesn't look like that's going to change any time soon.
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speedmd   100 MW

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Re: Electric Racing Chainsaw Build, Help Please

Post by speedmd » Feb 28 2020 10:25am

Have you any dyno data on the existing setup. While in the wood? Just watching the vid tells me that it is no way turning 20k rpms. Fast for certain, but how much of that is just to squeeze out the last bit of available power and stay far away from the torque cliff you fall off once the revs drop a bit. Not finding any dyno charts on Rotax or CR's suggesting anything close to the RPM estimates.

Hill, are there any voltage limits to this dragster? :lol:

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stan.distortion   100 W

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Re: Electric Racing Chainsaw Build, Help Please

Post by stan.distortion » Feb 28 2020 10:31am

Hehe, I think I see where this thread is going. Before it goes any further and the horsepower daemon takes over, is Endless Sphere going to get some sponsorship out of this? ;)

EDIT: I hadn't really considered DC much but this could be one of the very few applications where starter motors are a good option, something cheap and plentiful that can take lots of amps. Geared starter motors could have an added advantage, torque reaction usually pushes away from the cut but a geared motor would do the opposite, push harder as revs pick up. Not sure how many truck starters are geared though, they're probably out there but might not be easy to find.
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speedmd   100 MW

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Re: Electric Racing Chainsaw Build, Help Please

Post by speedmd » Feb 28 2020 12:07pm

Not sure the starter motor is the way to go long term. Short term, it may be a simpler setup, but I hope for all of us here that some thought gets run into a more wide spread beneficial platform. BTW, I remember a small motor project the shop was working on that designed-used a sub minute run dc motor roughly the size - weight of the nova 30 that was tested at 200+ HP. It was water cooled. Price was insane.

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Re: Electric Racing Chainsaw Build, Help Please

Post by stan.distortion » Feb 28 2020 12:25pm

speedmd wrote:
Feb 28 2020 12:07pm
Not sure the starter motor is the way to go long term. Short term, it may be a simpler setup, but I hope for all of us here that some thought gets run into a more wide spread beneficial platform. BTW, I remember a small motor project the shop was working on that designed-used a sub minute run dc motor roughly the size - weight of the nova 30 that was tested at 200+ HP. It was water cooled. Price was insane.
For general use there's nothing much to do, something can be built using tried and tested electric skateboard setups for very low cost that beats infernal combustion in every aspect other than cutting logs (I get enough runtime from a 5ah 6s Lipo to fell and trim pretty much anything up to 24" but cut logs that size and I'll be changing packs after just 5 or 6).

RC parts work very well for it because standing starts don't really matter, overspec the motor and limit current on the ESC and temperature wont be an issue or open it up and use thermal limiting for a "balls out" power level, something the size of an MS180 can have double the power of an MS660 with that option ;)

Batteries are the only thing that needs development for general use, Lipo's open up the crazy high performance possibilities but Li-Ion limits things to sane power levels, enough to match regular saws but not enough to beat them by a good margin while keeping things reliable.
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Re: Electric Racing Chainsaw Build, Help Please

Post by Sarcassidy » Feb 28 2020 2:15pm

I appreciate everyone's input so far. I've worked a bit with the data on the emrax motor specs and it appears that while the raw power on these electric motors is sufficient, the lower rpm will be an issue in regards to creating competitive chain speed.

I've reached out to the most knowledgeable people in the current 2 stroke hot saw game and while they can't give me real dyno numbers, they can give me their best estimates. Here are the numbers that get tossed around a lot.

9000-11000 max rpm
290 feet per second chain speed
50-60 hp
torque ???

Here's a bit of info on some of the other 2 stroke components that affect performance.

Chain - We are using a specialty chain made by stihl called 404 high tooth. It is a .404" pitch that has a higher tooth than regular 404. It was specially made by Stihl for the purpose of racing and the mold wore out last year, so it is currently discontinued. When it was in production we would pay $250 US for an 88 driver loop. We now pay $500-$600 for a loop on the secondary market, and then another $200-$300 to a guy who puts a racing grind on it. These "grind recipes" are closely held secrets, and are hard to replicate even when a top grinder gets his hands on someone else's top chain. Some of the more knowledgeable hot saw builders and racers consider the chain design to be one of the greatest limiting factors for hot saw performance. When you watch a top speed cut, chips are getting cleared from both ends of the scarf, which means that the teeth are cutting more wood than the rakers can clear.

Sprocket - The sprockets we are running are 16-18 tooth. Beginner racers run a 16 tooth. Most top guys use a 17 tooth. A few expert operators use an 18. The bigger sprockets result in higher chain speeds, but lower torque. The most decorated hot saw racer (and top chain grinder) of all time Mel Lentz runs an 18 tooth sprocket, but he stalls out his saw nearly as often as he has a clean run. When he has a clean run he usually wins. This is where the knowledge and skill of the operator comes into play. Managing rpm and pressure through the top, middle, and bottom of the cut is very important. Larger sprockets and higher chain speeds can also result in a thrown chain.

When I lay the 404 high tooth chain tight against the smaller 16 tooth sprocket I end up with a 5 inch radius.

A 5" radius at 11000 rpm gives me a chain speed of 239 feet per second. I'm unsure what the radius on the 17 and 18 tooth sprockets are as I don't have one on hand at the moment. A 6" radius at 11000 rpm gives a chain speed of 287 fps, which gets close to that 290 fps number that has been tossed around. I don't know what the torque is as I haven't found a conversion formula I can fully figure out.

The Emrax 208 motor is quoted as maxing out 6000 rpm. With the chain speed formula I've been using it would take an 11" sprocket and chain radius to get in the high 200s fps for chain speed. Again, I'm unsure where this would put the torque. A sprocket this large would require a giant bar and giant chain, which would require a redesign of the frame and add a lot of weight. This doesn't seem practical.

The battery part of the equation seems workable in terms of cost, size, and capacity.

Again, it seems like the electric motor rpm is a problem. 6000 rpm won't cut it. Are there any stock e-motors out there that can crank out an 8000+ rpm yet still come in under 30 lbs? Could one be custom built? A top speed 2 stroke build is $7000 before the bar and chain are added, and over half of that is engine and exhaust work, so $3500 to $5000 is acceptable to spend on an e-motor in theory.

Again, all of this might be futile if the chain not being able to clear wood fast enough and potentially getting thrown at higher speeds is the greatest limiting factor.

Looking forward to more feedback! Thanks!

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Re: Electric Racing Chainsaw Build, Help Please

Post by flat tire » Feb 28 2020 3:24pm

There are certainly motors with that speed and more. I can't recommend any for your application.

To get more chain speed, you can use a CUSTOM larger drive sprocket if not a ratio multiplication. The power is ultimately what's important to make the chain do work at high speeds. A 12000 rpm motor with 60 hp will output half the torque of a 60 hp 6000 horsepower motor with each at max RPM, so the 6000 can have twice as big a drive sprocket for equal torque on the chain at the same high speed. In other words, no problem, if you are serious and have a good budget you can get a new chain drive wheel made easy.

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speedmd   100 MW

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Re: Electric Racing Chainsaw Build, Help Please

Post by speedmd » Feb 28 2020 3:28pm

I think you are over estimating the chain speed. Diameter is where the base of the chain meets the sprocket. The chain (Tooth cutting edges) expands to wrap the drive sprocket. You could only use that figure if you were cutting at the tangent of the drive sprocket. You could make it more simple by just using the tooth count of the sprocket and drive link pitch lengths. 16 tooth sprocket equals 16 drive links distance per rev. Assuming from your figures it is direct drive. RPM on a solidly designed electric should be no big issue matching a 2 stroke.

Now, what is the real rpm you holding in the wood? From the looks of the pipe length, exhaust is tuned for around or under 10000 rpm. Would make it a bit less likely to bog for certain.

Raker is to keep the chain from grabbing too much of a bite to my understanding. How would Stihl take to a aftermarket chain supplier coming in and taking the gold? :lol: Looks to be where significant improvements can be made.

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Re: Electric Racing Chainsaw Build, Help Please

Post by Hillhater » Feb 28 2020 6:47pm

Asuming the same chain and sprockets (16-18T ) are to be used,...so as not to get into unknown chain territory .. then the target must be to retain that same 11,000 rpm , 50-60bhp range with as much torque as possible.
And i guess in this game , more rpm, power , and torque is better than less. !
I dont see this being an “off the shelf” item...but maybe someone out there in EV world is working on a hipo motor that might fit the task,
so i am thinking a straight DC brushed motor, (much over volted and amped) is likely to be be the best bet to simplify the high power inverter that would otherwise be needed, even for a fixed speed drive.
PS, starter motors are normally geared to give a lower output rpm and higher torque.
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Re: Electric Racing Chainsaw Build, Help Please

Post by Ianhill » Feb 28 2020 7:32pm

Having a little think best way I see of delivering massive power condensed around the 5k $ total budget and 50kw burst power is to use a Zero motor bike Zforce motor, not to sure on the controller front there's threads on here about the motors and what people are using to spin them up but they are power houses the chain will not bog down with that it pulls a bike like a 600cc.

Specs
45kw at 100v, 60hp at 4300rpm 80lbf ft claimed torque so there's a fair bit of power there but it will need gearing to get the chainspeed up, but if speedmd is onto something maybe a chain van be adapted to take advantage of a slower cut speed and higher torque form design.

Powering it will be the bitch it will need a 500amp supply so even high discharge Lipo will need dubbling up to get high enough C rate and run 28s for a total of 56 small pouches
18650 can push 30 amp a piece max needing 476 cells to run it, I can't see caps being any benefit for 12seconds they need to be big in themselfs to have any meaningful impact.
Lipo is they way for lightweight but the pack may need to be in a box on the side or a backpack with controller that has the 3 phase wires that run upto the saw to keep it light and mobile, on the other hand the video shows saws with weight that helps pull down so there's some more to digest.

Edit
Just found there new Lipo out 5000mah 100c or 500amp max so if the cells where warmed up like a tyre in a rack before use it would do the 12s it the ultimate max rating by design so touch and go to achieving it in reality, and they weigh about 120grams a cell so the pack wouldn't be to heavy and fairly compact it will contain 0.5kwh and the saw would use 0.9kw per minute so about 40 second blast on a full charge.
Last edited by Ianhill on Feb 28 2020 7:52pm, edited 1 time in total.

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