Twin motored PK Ripper--A little over the top!

He is going to turn the throttle and all the spokes are going to snap...

Hope he makes a video :)

Matt that is a completely insane setup. I remember when I saw your first setup with 4kw and it was off the charts, can't wait to see this thing in action. With all the testing and design you did on your bent and that awesome clutch addition I was blown away. Heck my mnt bike is 35lbs with all the crap on it and it only has 100 watts (me).

I think your going to compete with 250cc dirt bikes or even more but one test will be worth... well you know :)
 
Yeah, so do I. I'd prefer if he turned on the camera before the spokes break. :lol:

Anyways, I found the "50cc class" at wikipedia's page and it appears they can get upto 10 hp, so a 12 hp 60 cc engine is believable. It just seems like it's an engineering feat to extract that much power out of a small volume that "common" 50 cc setups typically are less than 5 hp. The ones for bike kits only seem to be about 2 hp, possibly 2.5.
 
12hp from 50cc is in fact possible :)
 
But remember, those dirt bikes have five gears. :?

On the other hand, Matt's bike should have super smooth power delivery without having to pause between shifts. It would be interesting to see a race on a small tight track between The Ripper and a decent pit bike. Now that would be fun, spanking gassers on a track, and then taking their money. :mrgreen:
 
Be interesting yes, i think a decent pitbike would spank the BMX though, it would handle alot better i think than a zero suspension BMX bike, I have ridden a few myself they are alot of fun. Also they have 125cc petrol motors ;) Recumpence bike would have power to weight advantage yes but i can't imagine being able to even half open the throttle on this BMX bike without flipping it while accelerating it will be quite unrideable at speed from take off i imagine, but good advertisement for these recumpence drives :) The wheel base is far to short for any decent kind of handling though in my opinion, it will be very sensitive (dangerous) at higher speed to. It is very much overkill for power on light bike which i think is not always the best if it sacrifices the bikes handling, time will tell i eagerly also await this video of the BMX with reumpence making wheelstands. I would like to see this setup twin rc in a pitbike chassis that would be fun on a tight circuit ;)
 
One interesting thing about this build is the fork/head tube angle relationship.

I am running trials forks. Those forks are about 2 or 2and 1/2 inches longer than stock BMX forks. That accomplishes numerous things;

#1 It slackens the head tube angle.
#2 It brings the bottom bracket up a bit higher.
#3 It creates more clearance for the motors.

#1 Is the important thing. The steering should slow down quite a bit because of that. Also, this is an XL frame. The longer wheelbase will help too. Lastly, the added 15 pounds of weight inside the frame will slow the handling down a touch.

I am not worried about it handling 35mph.

I do think I will really have to lean over the bars to use anywhere near its capacity for accelleration, though.

Matt
 
I know it can't really race bikes on a dirt track since it has no suspension but it would be fun to try. OTOH that is going to be fun to run around everywhere on the back wheel since you can't keep the front down. I wonder if you will be able to do burnouts with out destroying things but it won't matter since you will beef up anything that gives.
 
recumpence said:
I am running trials forks.

#1 It slackens the head tube angle.
Click to expand...

Matt,

I found those forks very interesting looking when I first saw them. I raced BMX for around 20 years and spotted the unusual front geometry right off. I'm looking forward to hearing how they change the handling. I think I would kill myself on a normal 20" bmx bike going 35 miles per hour. They just turn too fast. Heck, it takes me a bit to get used to a 24" cruiser when I jump on one from time to time.

I recently thought about getting an SE OM Flyer http://www.sebikes.com/Retro/OM-Flyer-Blue.aspx. Mountain bike size with BMX flavor. I (like most old BMXers) have a special place in my heart for SE even though it's not what it used to be. I just wish the OM Flyer was made from chrome alloy instead of aluminum.

Btw, is that an old Taig motor I see on the floor in one of those pictures? I really need to send you a pm about what kind of power supply you use to power an outrunner on a mill.
 
Yup, that's an old Taig motor lying there. I am using my CNC motor on my manual mill so I could run the outrunner on the CNC.

I agree a BMX bike will be twitchy at high speed. However, the head tube geometry is not the only thing that will slow it down. The longer wheelbase (this is an XL frame) and the added weigh of the E-quipment will help too.

I have not wired it up yet (been out of town alot). But I have pedalled it at 20mph and it handled nice and predictable. No twitchyness at all.

We shall see, though.

Matt
 
I do know that BMX has changed a lot the past few years and with it frame geometry so a 20" xl frame probably handles a LOT different from what I remember anyway. There are so many insane almost downhill races (like the Beijing Olympics track) that they're designing frames for more and more speed.

And I hope I didn't sound negative about the frame choice. I think it looks like a blast. I can't wait to see it in action.
 
When I chose this frame, it was primarrily because it was long. But, also, it uses a Euro bottom bracket and an integral headset.

This frame is super light and crazy strong, too. Also, the oval tubing assures no drive system twist on the frame from all the torque.

Matt
 
OK, I got the wiring done and I rode it.

The pack was not charged. That being the case, I am assuming I was bumping into the LV soft cutoff. I set both controllers for 40volt soft cutoff. I can hammer the throttle and it just smoothly accellerates up to speed (about 35mph or so). It pulls fine, but feels like about 3kw or so right now. I do not have the explosive power I was expecting. That is why I am assuming the 40 volt LV cutoff was kicking in, especially considering the fact that I did not charge the pack yet. They come with a 40% or so charge from the factory. So, it was safe to ride, but again, it was very low.

So, I will charge the pack (I need to make a charging harness for it), set the LV cutoff for 36 volts, then go back out and run it. I am sure it will rip!

A couple things I noticed;

#1 It handles the speed fine. No problems at all. It rides with much the same feel as a motorcycle. Also, the lack of suspension is not a problem with basic road imperfections.

#2 The front motor gets hot while the rear motor gets just luke warm. I think I have a setting different from one ESC to the other. Or, the LV cutoff was kicking in harder or sooner on the rear motor than the front causing the difference in temperature.

Oh, it does make some whining sound when I ride, but not terribly.

All in all, it was a good maiden voyage. I plan on doing some more testing and experimentation with ESC settings over the next couple days. I have a full day of work tomorrow. So, I doubt I will get more testing done before Wednesday.

Matt
 
If your motor Kv's are a bit different, one motor will run hotter than the other. That is what I would suspect. The castles ability to limit current is perplexing. If they can limit current based on pack voltage...they should be able to implement current limiting during normal use...that combined with an HV-200 would be awesome!!
 
I did some more testing. I let the drive run with the bike up-side-down. The motors ran the same temp that way. Hmm, I really think the LV cutoff is limiting the rear motor before the front motor so, under heavy load accellerating, the front motor is doing pretty much all the work.

That would be my guess at this point. I cannot be too sure untill I charge the pack fully and reset the LV cutoff.

I also need to set the throttle response to "High" rather than medium. Startup is set for low. That feels about right.

At any rate, twin motor systems really come into their own under heavy load. Just tooling around will be kind of a waste on this thing. But, heck, so is tooling around in a blown streetrod. :wink:

So, it will be a couple more days of waiting to get it really running.

Matt
 
recumpence said:
I need to get a decent scale. I would say the bike feels about 45 to 48 pounds with all equipment mounted including the pack. I have to figure a way to weigh it properly.

I will be taking the bike home from the shop soon to begin all the wiring.

It is getting close, my friends. Very close! :mrgreen:

Matt
Click to expand...

Try this, its cheap, I use it to way my freon cylinders...
http://www.berkley-fishing.com/prod.php?k=79557&sk=79557&u=CFS50MT

Roy
 
Is the motor that is getting hot the one that drives the reduction? I think the issue maybe that it is working harder than the other one, which just drives the belt drive. I think you may need to run the #25 chain around dual motor sprockets, and maybe lose the belt drive between the motors. The chain drive has a bit of play built-in, so slight controller differences may not matter. Even if you have identical settings in both controllers, they are never going to be completely synchronized. I think it is easier to do with sensored controllers.

Maybe try loosening the belt drive a bit, to see if that makes any difference. These issues sound all too familiar. I remember helping a guy put two big Hacker inrunners on a large RC helicopter that was used for film work. We had all kinds of issues getting the motors to share the load equally. One or the other always ran a bit hotter.

-- Gary
 
Its actually the other motor that is running hotter.

No matter how the motors are linked, they will both be seeing the same load. I considered running the chain around both motors, but that would make a lot more noise and create more drage than the belt does.

I have run twin motors in RC applications, both helis and trucks. There are efficiency issues with it and one normally runs a tiny bit warmer than the other. But, typically it is not hard to sync them.

Again, I know the LV cutoff was kicking in. If that is the case, one motor will do pretty much all the work.

Matt
 
:D :D :D

Great news that you are running on the PK MAtt,
once you get a charge on the bike we expect some vids :), don't worry if it's not running to absolutely max potetial i'm just curios to see it turn a wheel proper now, should be awesome.
Hopefully i'll get some test vid up in the next week or so also :mrgreen:
go rc setups!!!


D
 
I know it will be crazy. :D

There are a few other things I forgot to mention;

The throttle I made works AWESOME! I have the travel of the pot perfect for the controllers. There is no dead spot at the beginning or end of the throttle travel that is normally present with the servo tester (I am not running Rickard's board yet). The feel of the throttle is awesome too.

Also, other than the LV cutoff set way too low, I got everything else spot on first time. I did all that soldering, guessed at the throttle position and everything just powered up and worked fine. That was a relief. This thing is so electrically complicated.

My only concern now is my pack. It is a 48 volt 8.8AH pack that is rated at 25C. That is over 10kw of power. Hopefully it really can deliver that. Otherwise I will need to add cells.

Anyway, I will try to get it charged (I need to make a charging harness for it) and reprogrammed by Wednesday.

Matt
 
top drawer 8)
i'll be watching like a hawk ;)
10kw is going to be silly fast!! i'm only planning on running 4kw on the kona and hoping that will have some beans even at 4kw, i have headroom for 5kw :twisted: but i dont want to stress anything to it's max, i'm hoping running well within each components tolerances will leave me with better reliability.
What i REALLY want to know is Matt, whats happening with your MTB?? :twisted: although i guess it is on hold until the PK is literally ripping?

Cheers mate,

D
 
They could have slightly different KVs. That is possible. What stikes me is the fact that when I run it without load both motors run the same temp. That is why I am assuming the LV cutoff is making one motor run more than the other.

We will know soon enough!

D,

The mountainbike was put on hold to build the PK. But, I have everything here for it, other than the pack. It may have to wait untill next winter, though, because I want to put a drive on my wife's bike.

That being said, the current plan is a super light weight setup running through the pedal chain to make use of the stock cassette. The motor will be about 2.5kw. So, I need multiple ratios to achieve decent performance.

Matt

Oh, I made the charging harness. It is charging now. That will take a couple hours. The pack was down near 20%.

I am expecting the bike to be very powerful, but tractable and very rideable.

We shall see..............
 
Holy COW!!!! INSANE, INSANE, INSANE, INSANE!!!! FREAKING frighteningly VIOLENT! :twisted:

They don't make smileys big or crazy enough!

This thing actually scared me pretty soundly. Holy CRAP!!!!

So, at 75% charge, I couldn't take it anymore. So, I took it off the charger and went for a ride. HOLY ****!! This thing is almost too powerful. I nearly flipped it a bunch of times. It winds out about 40mph. But, at what feels like 35, I hit the throttle while leaning over the bars and it still wheelied! I had no idea it would be this crazy. WAAAAYYYYYYY beyond my wildest expectations!

Oh, also, the motors run the same temp now. :mrgreen:

Man, oh Man, this thing is WICKED!!!!!!

I have to find someone to video me. But, it is hard to get a handle on the power without riding it.

Oh, did I say INSANE?!?!!!

Triple wicked! :twisted: :twisted: :twisted:

Total E-diction!!! :mrgreen:

Matt
 
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