Twin motored PK Ripper--A little over the top!
- Thread starter recumpence
- Start date
liveforphysics
100 TW
My rotor is also blue'd. I don't think you need to worry though, as it seems to have blued right away from the repeated high speed stops, and hasn't seemed to show any further signs of problems for the 2 months of abuse after it turned blue. It's never had brake fade.
To the folks talking about powering the front wheel... Umm... A front wheel in the air, spinning or not spinning, doesn't add any traction.
Once something can accelerate hard enough to shift it's weight completely to the back tires, powering the front tires is useless. This is why all the AWD drag cars that get tuned to be insanely powerful enough to wheelie always are converted to just RWD, as powering the front wheels just adds more weight and drag for no reason.
Also, with a bike/motorcycle, having anything that borrows from the available traction of the front wheel on a bike that is able to lighten that front wheel up a lot (or even wheelie) is a terrible hazard to ride through corners.
To find how rapidly something can accelerate that isn't power or traction limited, it's a simple relationship between the location that rear tire contacts, and the location (height and distance forward from the rear contact patch) of the COG (center of gravity). You draw a little triangle from those points, and the slope of the line represents the amount of acceleration possible. For example, a COG at the same height as the contact patch has an infinate slope, and would be capable of infinate acceleration when no traction or power limited. A COG right above the contact patch would mean the device is just balancing on it's rear wheel, and even infinately small acceleration will cause it to wheelie.
So, quicky solutions, move the seat forward a few inches, lean the bars forward a few more inches (to encourage more forward centric body positioning), lower the seat (and/or tuck down and forward). Not as quicky solutions would be extending the rear wheel outward a bit. A bike made for precision cornering often completely has the performance and turning ability ruined by this (perticularly with street bikes). A short wheelie bar is something awful to ride, and really damaging to the drivetrain, as everytime the bike starts to wheelie, it unloads weight of the tire, the tire spins, the acceleration decreases as soon as the tire spins, causing the bike to plant back down on the tire, getting traction again and shocking the piss out of the drivetrain, along with making a herky-jerky jumping riding experience.
A super long wheelie bar works fantastic. It would make and otherwise very elegant beautiful bike seem pretty awkward though.
What's the best solution? Train that wrist to work with the rider's ability to lean forward and low during acceleration, and ride a low wheelie during the accleration phase. It truely becomes a pleasure learning to ride power wheelies, and I find riding things that don't power-wheelie to be quite dull at this point.
Embrace the wheelie! It requires no solution!
Fantastic work as always Matt!
To the folks talking about powering the front wheel... Umm... A front wheel in the air, spinning or not spinning, doesn't add any traction.
Once something can accelerate hard enough to shift it's weight completely to the back tires, powering the front tires is useless. This is why all the AWD drag cars that get tuned to be insanely powerful enough to wheelie always are converted to just RWD, as powering the front wheels just adds more weight and drag for no reason.
Also, with a bike/motorcycle, having anything that borrows from the available traction of the front wheel on a bike that is able to lighten that front wheel up a lot (or even wheelie) is a terrible hazard to ride through corners.
To find how rapidly something can accelerate that isn't power or traction limited, it's a simple relationship between the location that rear tire contacts, and the location (height and distance forward from the rear contact patch) of the COG (center of gravity). You draw a little triangle from those points, and the slope of the line represents the amount of acceleration possible. For example, a COG at the same height as the contact patch has an infinate slope, and would be capable of infinate acceleration when no traction or power limited. A COG right above the contact patch would mean the device is just balancing on it's rear wheel, and even infinately small acceleration will cause it to wheelie.
So, quicky solutions, move the seat forward a few inches, lean the bars forward a few more inches (to encourage more forward centric body positioning), lower the seat (and/or tuck down and forward). Not as quicky solutions would be extending the rear wheel outward a bit. A bike made for precision cornering often completely has the performance and turning ability ruined by this (perticularly with street bikes). A short wheelie bar is something awful to ride, and really damaging to the drivetrain, as everytime the bike starts to wheelie, it unloads weight of the tire, the tire spins, the acceleration decreases as soon as the tire spins, causing the bike to plant back down on the tire, getting traction again and shocking the piss out of the drivetrain, along with making a herky-jerky jumping riding experience.
A super long wheelie bar works fantastic. It would make and otherwise very elegant beautiful bike seem pretty awkward though.
What's the best solution? Train that wrist to work with the rider's ability to lean forward and low during acceleration, and ride a low wheelie during the accleration phase. It truely becomes a pleasure learning to ride power wheelies, and I find riding things that don't power-wheelie to be quite dull at this point.
Embrace the wheelie! It requires no solution!
Fantastic work as always Matt!
gwhy!
100 kW
liveforphysics said:
Never a truer word spoken
Lucky_Hoodlum
10 W
- Joined
- Apr 11, 2009
- Messages
- 66
liveforphysics said:
I guess Yamaha disagree they produced a two wheel drive road and trail bike in 2003
KTM also have a two wheel drive in development
I think it would be ridiculous to do two wheel BMX setup no ponit, a
mountain bike used almost exclusively off road climbing would be advantageous in my own opinion.
Control on launch, mastering the power wheelie is the only way to go also i believe.
two wheel drive solution wouldn't stop the wheelie just proved more traction when the front wheel is in contact with the ground i think.
johnrobholmes
10 MW
I don't think that Matt is having any problem with getting traction :lol:
For an offroad bike 2wd is a pretty good idea. I want to build one actually.
For an offroad bike 2wd is a pretty good idea. I want to build one actually.
recumpence
1 GW
Yesterday I began experimenting with accelleration. I have gotten at least a little used to the power-wheelies. I had one good solid 100 foot power-wheelie that was the front tire about 3 inches off the road and I was laying on the bars. That was the best accelleration I have ever had. That wheelie took me from about 10mph to somewhere around 30mph in that short distance.
Matt
Matt
liveforphysics
100 TW
Outstanding Matt! That's the hot ticket!
That Yamaha was made for the loose sands of baha, where a paddle tire doesn't hold up at those speeds, and the bike had adquate power to spin the tire at most speeds.
On pavement, grass, woods, even most wet trails, I can always lift the wheel at will with a crack of the throttle, and/or an adjustment in body position. This means powering the front wheel isn't going to be helping me any. For a loose sand run, or a wet clay/mud run up hill, it might be of some help. I would hate the idea of my rear tire being coupled to my front though! You MUST have the ability to lock the rear tire, and/or power slip the rear tire at will to help rotate the bike. If your front wheel tried to be doing the same activies... ouch!
For something on pavement at these power levels and short wheelbase, traction will never be a concern, and powering the front wheel would be of no advantage.
Matt is doing exactly the right thing here. Learning the mannors of the bike, and training himself to have the control needed to maintain optimal acceleration, which means the front wheel is just a bit off the ground with the body as far foward and low as possible.
Great work Matt!
That Yamaha was made for the loose sands of baha, where a paddle tire doesn't hold up at those speeds, and the bike had adquate power to spin the tire at most speeds.
On pavement, grass, woods, even most wet trails, I can always lift the wheel at will with a crack of the throttle, and/or an adjustment in body position. This means powering the front wheel isn't going to be helping me any. For a loose sand run, or a wet clay/mud run up hill, it might be of some help. I would hate the idea of my rear tire being coupled to my front though! You MUST have the ability to lock the rear tire, and/or power slip the rear tire at will to help rotate the bike. If your front wheel tried to be doing the same activies... ouch!
For something on pavement at these power levels and short wheelbase, traction will never be a concern, and powering the front wheel would be of no advantage.
Matt is doing exactly the right thing here. Learning the mannors of the bike, and training himself to have the control needed to maintain optimal acceleration, which means the front wheel is just a bit off the ground with the body as far foward and low as possible.
Great work Matt!
recumpence
1 GW
Admittedly it is work riding this bike, though. But, so are certain interpersonal encounters. :wink: Effort required to achieve a large return of joy is no real sacrifice at all. 
Other than my chain coming off, I cannot believe how reliable this thing is. It just keeps running without complaints. So, I know I am not asking all I could from this drive.
Matt
Other than my chain coming off, I cannot believe how reliable this thing is. It just keeps running without complaints. So, I know I am not asking all I could from this drive.
Matt
recumpence
1 GW
Hey Guys,
I want to thank you all for the PMs and your thoughts and prayers regarding my wife's brother's cancer.
I just wanted you all to know he just passed away at 12:55 PM today.
Thanks again.
Matt
I want to thank you all for the PMs and your thoughts and prayers regarding my wife's brother's cancer.
I just wanted you all to know he just passed away at 12:55 PM today.
Thanks again.
Matt
Terrible news, Matt. Very sorry to hear that.
It's hard to make it through such times.. I think my dad gave me the best advice when we lost my aunt and uncle to the C several years back. Just remember their smile and all the good times, and know they are somewhere better now, away from the pain.
Very sorry to hear that.It's hard to make it through such times.. I think my dad gave me the best advice when we lost my aunt and uncle to the C several years back. Just remember their smile and all the good times, and know they are somewhere better now, away from the pain.
northernmike
10 kW
Sorry Matt. I hope he got to see, or at least hear about the PK before his passing.
One can only try to live life to the fullest.
My condolences to you and yours.
What was his name?
One can only try to live life to the fullest.
My condolences to you and yours.
What was his name?
recumpence
1 GW
Thanks Guys.
His name is Rick. He was only 42.
Anyway, I did not want to make this a pity party. What is done is done. We miss him dearly.
Oofnik,
We will probably be out of state middle of the week through the weekend. But, I would love to get together and hang out.
What is your schedule?
Oh, also, I replaced the chain on the PK with the masterlink clips on the inside. It works without that clicking sound now.
I may need to add some more cells to reduce the voltage drop under load. I have the LV cutoff set for 40 volts right now. If the pack is freshly charged, it runs REALLY strong! But, once 1 or 2 amphours is taken out of the pack, the LV cutoff starts kicking in. I will reset it for 38 volts. But, on 12S, that means I am really pulling the voltage down under hard accelleration. If I add another 4.4ah (50% more cells), I would only gain about 3 pounds and reduce my voltage drop significantly while upping my output (like I really need more power :wink: ).
Anyway, I am trying to keep my mind of Rick.
It is hard when my wide is so stressed.
This is her forth sibling to die.
Matt
His name is Rick. He was only 42.
Anyway, I did not want to make this a pity party. What is done is done. We miss him dearly.
Oofnik,
We will probably be out of state middle of the week through the weekend. But, I would love to get together and hang out.
What is your schedule?
Oh, also, I replaced the chain on the PK with the masterlink clips on the inside. It works without that clicking sound now.
I may need to add some more cells to reduce the voltage drop under load. I have the LV cutoff set for 40 volts right now. If the pack is freshly charged, it runs REALLY strong! But, once 1 or 2 amphours is taken out of the pack, the LV cutoff starts kicking in. I will reset it for 38 volts. But, on 12S, that means I am really pulling the voltage down under hard accelleration. If I add another 4.4ah (50% more cells), I would only gain about 3 pounds and reduce my voltage drop significantly while upping my output (like I really need more power :wink: ).
Anyway, I am trying to keep my mind of Rick.
It is hard when my wide is so stressed.
This is her forth sibling to die.
Matt
biohazardman
100 kW
It's always sad when we loose someone as we miss them but remember that it's just another step in life in the grand scale of things. It's so much better on the other side. I can honestly say this as I've been there. http://www.nderf.org/Duane's%20NDE.htm
johnrobholmes
10 MW
How many cycles do you have on the pack? It will take about 5 for them to break in.
recumpence
1 GW
I have a couple 2ah cycles in them. No biggie.
So, I just set my LV cutoff to 38 volts instead of the 40 it was set for.
Matt
So, I just set my LV cutoff to 38 volts instead of the 40 it was set for.
Matt
recumpence
1 GW
I set the LV cutoff to 38 volts instead of 40. That helped the accelleration at top end. However, I noticed something; I never, before, really let it wind out. I was waiting untill the violent accelleration ceased and assumed it was wound out. However, this time I went for a longer ride with a very long straight street. What I found is the bike accellerates like a bat out of hell up to about 38 or 40mph. Then it gently accellerates (gentle for this beast) about 5 mph further. So, the pack voltage is dropping. I must be pulling a couple hundred amps to be encountering this. Also, yes, the cells are running exactly like my MaxAmps cells in my recumbent. They have that slightly "Flat" feeling to them. So, I think John is right. They need to wake up for a few runs.
Anyway, I am loving this thing. I am also getting used to the explosiveness. I may, indeed, add more cells though. I never pull my recumbent pack under 43 volts with a fresh pack. Being able to pull this pack down to 38 volts means I am pushing it REALLY hard! I have room under the bolltom bracket for more cells. I think I will add 5 or 10 more AH down there.
Matt
Anyway, I am loving this thing. I am also getting used to the explosiveness. I may, indeed, add more cells though. I never pull my recumbent pack under 43 volts with a fresh pack. Being able to pull this pack down to 38 volts means I am pushing it REALLY hard! I have room under the bolltom bracket for more cells. I think I will add 5 or 10 more AH down there.
Matt
liveforphysics
100 TW
Matt, if you have something you can load test your pack with, it might be good to check to see your Ri is roughly what it should be for your cells. I don't think they should be falling that far so soon off the charger.
If you can find something to use as a load bank, I use this cheesy 4x 500w halogen work light I got wally-world for $20. I just tapped into the power cable and threw a deans connector on it, so I can still use it as a work light, but I can also plug my pack into it for load banking.
Drain pack to somewhere near nominal cell voltage (3.7v), plug in load bank, measure the current it's pulling along with the voltage of the pack, I leave it running for about 30 seconds. Then unplug it, and see what voltage the cells jump back up to. You can change the order of events, and try testing at different states of charge, but once you know the voltage drop and the current, it's simply V(delta)=IRi to find the Ri of the pack.
And it should be said that this isn't the professional fancy pants 1khz switching way of measureing pack Ri, however, I think for our types of pack loading, it may be more useful data than the fancy pants way of doing it.
You could also get an estimation from taking a mental snap-shot off your cycle analist for current/voltage under load, verses the resting voltage right after the pull. Then do the same calculation, and see what you are getting for an Ri on the pack. Typical healthy 20C LiPo should be about 25-35mOhms/Ah/cell.
So, your 9Ah cell groups should be looking at 2.8-3.9mOhm per 9Ah cell group, and times 12 cells would be 34-46.8mOhm for total pack Ri.
So, when resting at nominal voltage, 44.4v, and a 200amp load is applied, the pack should drop 6.8-9.4v, or you should be seeing around 37.6v-35v when you make a full 200amp pull with the pack starting from nominal voltage.
It's important to remember that the underload cell voltage is only is a concern for heat in the cells (resistive heating power = Ri(I^2)). It's not chemically dangerous to the cells at all. Your only worry for hurting the cells is if the resting cell voltage gets down too low.
So, IMHO, I would adjust the low voltage cut-off down quite a bit, or disable it, and just keep an eye on resting cell voltage to make sure it doesn't fall below ~3.3v/cell (39.6v for your 12s pack).
If you can find something to use as a load bank, I use this cheesy 4x 500w halogen work light I got wally-world for $20. I just tapped into the power cable and threw a deans connector on it, so I can still use it as a work light, but I can also plug my pack into it for load banking.
Drain pack to somewhere near nominal cell voltage (3.7v), plug in load bank, measure the current it's pulling along with the voltage of the pack, I leave it running for about 30 seconds. Then unplug it, and see what voltage the cells jump back up to. You can change the order of events, and try testing at different states of charge, but once you know the voltage drop and the current, it's simply V(delta)=IRi to find the Ri of the pack.
And it should be said that this isn't the professional fancy pants 1khz switching way of measureing pack Ri, however, I think for our types of pack loading, it may be more useful data than the fancy pants way of doing it.
You could also get an estimation from taking a mental snap-shot off your cycle analist for current/voltage under load, verses the resting voltage right after the pull. Then do the same calculation, and see what you are getting for an Ri on the pack. Typical healthy 20C LiPo should be about 25-35mOhms/Ah/cell.
So, your 9Ah cell groups should be looking at 2.8-3.9mOhm per 9Ah cell group, and times 12 cells would be 34-46.8mOhm for total pack Ri.
So, when resting at nominal voltage, 44.4v, and a 200amp load is applied, the pack should drop 6.8-9.4v, or you should be seeing around 37.6v-35v when you make a full 200amp pull with the pack starting from nominal voltage.
It's important to remember that the underload cell voltage is only is a concern for heat in the cells (resistive heating power = Ri(I^2)). It's not chemically dangerous to the cells at all. Your only worry for hurting the cells is if the resting cell voltage gets down too low.
So, IMHO, I would adjust the low voltage cut-off down quite a bit, or disable it, and just keep an eye on resting cell voltage to make sure it doesn't fall below ~3.3v/cell (39.6v for your 12s pack).
johnrobholmes
10 MW
pack temperature also plays a big part in the performance. If you are running them at 70f they won't be as good as spec. Of course you fly helis and are most likely keen on this already.
liveforphysics
100 TW
Yep, temp is a huge factor. Good point John. Cold LiPo doesn't perform anywhere near what hot LiPo does. I'm looking for a way to setup some resistive heating pads between my packs to keep them toasty while riding. I'm absolutely certian that the better voltage and lower Ri would more than compensate for the minor energy drain of the resistive heater. Nothing performs like a high C LiPo that's hot. I've thrown heli-packs in my exhaust while I'm idleing to pre-warm them before a flight. The voltage raises quite a bit! and the performance and capacity is boosted a lot! Not something I do with my good packs though... Lol
recumpence
1 GW
Good info, Guys.
Here is a question, then;
When I was running top speed RC cars, I used to pull my 30C Flight Power 2100 12S lipo down to 26 volts under load (3 seconds bursts). I would go two runs that way before recharging. That pack only gave me a good 40 runs before it went bad.
So, if load voltage is not a problem, why did that pack go bad? Was I pulling it WAY too far down?
At any rate, I am used to seeing packs wake up after a few good cycles.
Also, with the LV cutoff set for 38 volts, I have to really push the crap out of that pack to get the LV cutoff to activate.
The IR may be off a touch. But, also, the pack is still brand new, and it was 50 degrees yesterday.
I know about the cold lipo thing. But, I wasn't considering that yesterday.
Anyway, the pack runs good. I just want as much advice as I can get.
Matt
Here is a question, then;
When I was running top speed RC cars, I used to pull my 30C Flight Power 2100 12S lipo down to 26 volts under load (3 seconds bursts). I would go two runs that way before recharging. That pack only gave me a good 40 runs before it went bad.
So, if load voltage is not a problem, why did that pack go bad? Was I pulling it WAY too far down?
At any rate, I am used to seeing packs wake up after a few good cycles.
Also, with the LV cutoff set for 38 volts, I have to really push the crap out of that pack to get the LV cutoff to activate.
The IR may be off a touch. But, also, the pack is still brand new, and it was 50 degrees yesterday.
I know about the cold lipo thing. But, I wasn't considering that yesterday.
Anyway, the pack runs good. I just want as much advice as I can get.
Matt
etard
100 kW
My advise to you Matt, is to take a damn video of that 100 foot power wheelie!!! :wink: :lol:
Man, I can only imagine the feeling of not being able to lean over the bars far enough, for fear of TOO MUCH POWER!!
Man, I can only imagine the feeling of not being able to lean over the bars far enough, for fear of TOO MUCH POWER!!
recumpence
1 GW
I agree. I will have a friend take a video soon.
I am getting used to riding the beast. I have found leaning forward and being very careful with the throttle gives me nice strong accelleration. I also have gotten used to using the voltage drop of the pack bumping into the soft LV cutoff as a poor mans wheelie control. Basically, if I snap the throttle, no matter how hard I lean forward, it wheelies. However, if I lean forward and roll on the throttle, the current draw lowers the pack voltage untill the LV cutoff begins taking affect at 38 volts. Then I can get harder on the throttle and let it accellerate. Once the drastic accelleration is over, the pack begins regaining voltage which makes it accellerate the rest of the way smoothly. Once I add cells, the voltage drop will not be enough to kick the LV cutoff. At that point, it will be much more violent (as it is now if the throttle is snapped). So, what it boils down to is, if the throttle is snapped, the voltage takes a touch of time to drop. So, while the voltage is still up (1/2 second or so) it will wheelie pretty much no matter how hard I lean forward. But, if I let the voltage settle down a bit under load, it become more docile for that particular run. Basically, I am learning how to exploit the shortcomings of a power system that is more than the pack can cope with.
Also, these 8 pole motors are a little "Bucky" at low throttle settings. The HV110 is a great ESC. But, with low pole count motors, and high power drive systems, they can sort of glitch and buck a little at very low throttle settings. With two motors, this trait is aggrivated. Plus, the throttle spring really needs to be tighter. So, between the occasional minor ESC burp (tiny surge forward) and my thumb bumping the throttle, it is a little challenging to ride slow and smooth. That being said, so is driving a blown big block car.
Matt
I am getting used to riding the beast. I have found leaning forward and being very careful with the throttle gives me nice strong accelleration. I also have gotten used to using the voltage drop of the pack bumping into the soft LV cutoff as a poor mans wheelie control. Basically, if I snap the throttle, no matter how hard I lean forward, it wheelies. However, if I lean forward and roll on the throttle, the current draw lowers the pack voltage untill the LV cutoff begins taking affect at 38 volts. Then I can get harder on the throttle and let it accellerate. Once the drastic accelleration is over, the pack begins regaining voltage which makes it accellerate the rest of the way smoothly. Once I add cells, the voltage drop will not be enough to kick the LV cutoff. At that point, it will be much more violent (as it is now if the throttle is snapped). So, what it boils down to is, if the throttle is snapped, the voltage takes a touch of time to drop. So, while the voltage is still up (1/2 second or so) it will wheelie pretty much no matter how hard I lean forward. But, if I let the voltage settle down a bit under load, it become more docile for that particular run. Basically, I am learning how to exploit the shortcomings of a power system that is more than the pack can cope with.
Also, these 8 pole motors are a little "Bucky" at low throttle settings. The HV110 is a great ESC. But, with low pole count motors, and high power drive systems, they can sort of glitch and buck a little at very low throttle settings. With two motors, this trait is aggrivated. Plus, the throttle spring really needs to be tighter. So, between the occasional minor ESC burp (tiny surge forward) and my thumb bumping the throttle, it is a little challenging to ride slow and smooth. That being said, so is driving a blown big block car.
Matt
recumpence
1 GW
I am learning more and more.
Ok, I am getting very used to the PK. I found that (earlier in my testing), though I was leaning forward, I was still not getting as much weight over the front wheel as possible. I was bracing myself against the seat and pedals using my torso to hold up my body weight. The times I was truely puting my weight on the bars (leaning on them), the bike would wheelie only if I opened the throttle hard below 20mph. I found myself leaning on the bars hard with it wanting to wheelie up to about 20mph, at which point the handling gets weird with so much weight on the front end. So, I would naturally transfer more weight onto the seat for better handling. But, leaning forward still (yet back on the seat), the bike would still wheelie for another 15mph or so, at which point, the voltage sag became apparent and the road is fast reaching its end. So, I would let off.
With more testing, I am much more confident on the bike, though it is still pretty hairy.
Now, I want more cells to see just how hard this thing can run!
Matt
Ok, I am getting very used to the PK. I found that (earlier in my testing), though I was leaning forward, I was still not getting as much weight over the front wheel as possible. I was bracing myself against the seat and pedals using my torso to hold up my body weight. The times I was truely puting my weight on the bars (leaning on them), the bike would wheelie only if I opened the throttle hard below 20mph. I found myself leaning on the bars hard with it wanting to wheelie up to about 20mph, at which point the handling gets weird with so much weight on the front end. So, I would naturally transfer more weight onto the seat for better handling. But, leaning forward still (yet back on the seat), the bike would still wheelie for another 15mph or so, at which point, the voltage sag became apparent and the road is fast reaching its end. So, I would let off.
With more testing, I am much more confident on the bike, though it is still pretty hairy.
Now, I want more cells to see just how hard this thing can run!
Matt
Ypedal
100 TW
Video !!!!!
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