My Quanum QRF400 Modifications

After quite intensive testing with the Quanum QRF400 Bike I would like to let the other bike owners to participate on my experiences.

First of all I would like to make a statement for this bike, for those guys who don't read the whole thread.

The Quanum QRF Bike definitely is worth it's money. You'll have to invest some further bucks and some good portion of time to make this bike tough. Still the bike will be much cheaper than other similar bikes.

I already started another thread with some other useful information:
http://hobbyking.com/hobbyking/forum/forum_posts.asp?TID=12114

Here is my config:
Motor: KD36-60-08L 3000kv Brushless Inrunner
Pinion: 13T/5mm M1Steel Pinion Gear
ESC: Hobby King Brushless Car ESC 100A w/ Reverse (Upgrade version)
Prog Card: Hobby King Programming Card for Car ESC
Servo: MG959 Alloy Digital Metal Gear Servo 15kg / 75g / 0.2sec
Transmitter/Receiver: Hobby King GT-2 2.4Ghz 2Ch Tx & Rx
Lipo: Turnigy 4000mAh 3S 20C Lipo pack (Perfect for QRF400)

Where do we start?

The motor:
Like I already wrote in the other thread, the stock motor is crap. Don't even bother installing it. It fails after a few minutes. Really really bad quality. Go directly with the above mentioned motor or a similar one. It's a tight fit, but it fits. You'll have to experiment a little bit.

The puppy:
Looks absolutely identical to the HPI Driver used by AR Racing but the material for sure is different (not so flexible an stable) => result => the puppy brakes after a few crashes. On the picture you can see how I fixed the broken parts. Working very good so far. Of course not a nice look, but what the heck :-)
If you don't wan't to put screws in your puppy go with the original HPI puppy which is a lot more expensive then this one. Those a becoming hard to get. That's why AR Racing build their own Rider => this thing really is ugly. It is very flexible and won't break tough.











Before I did the first ride I of course checked all screws and the gyro => you should to. Tighten all screws with thread lock since most screws go into metal an because of the gyro and of road riding the bike experiences a lot of vibrations. Although I checked the gyro it failed after a few runs (do it better). The planetary gears were scrubbing the plastic disk an the plastic melted => the gyro stopped working. I had to put shims on 2 places (between clutch/flywheel and between the plastic disk/planetary gears). After this problem was fixed, the next one came right behind. The planetary gear mount (which is fixed by one grub screw on the axle (without any flat spot at this place)) became loose. I fixed it several times and it always came loose again => I flattened the axle, so that the grub screw has a better bite => worked better but the mount still came loose due to the force and vibrations => next I drilled a new whole in the planetary gear mount collar where another grub screw (5mm, the other is 4mm) is holding the assembly additionally. I also replace the original little 4mm screw with a longer one. So the thread-lock has more surface to work. So now the mount is being fixed with 2 grub screws and the axle has 2 flat spots (sorry, no picture of the flattened axle, but hope you can imagine what I mean). With this mod I've made about 10 runs, and everything still is working fine and running very smooth. Although the flywheel is not perfectly balanced. I've seen some guys who tried to balance the flywheel better. For sure this is even better for the smoothness of the gyro, but in my opinion not worth the work. The original AR Racing flywheel also wasn't 100% perfectly balanced and worked for several hours. You'll have to replace the bearings if you're experiencing to much play of the flywheel.





On the following pictures you can see where and how i placed the ESC. I replaced the front screw (holding those silver protectors) with a longer one, so that the ESC can fit the easily. Oh yeah, and i removed the fan which is useless. The ESC becomes enough air flow in this position and further the ESC isn't working at it limits all the time. Works really well this peace.





The sidebars are crap, most of you should know this matter of fact by now. I widened the sidebar holder holes to 4mm I think a put new sidebars made of "perlon" on it. Those things are also used for 1/5 onroad RC bikes. Works very good on tarmac and offroad (if the offroad surface is not to soft, on sand most sidebars will fail I guess).



The next thing was the puppy mounts. You'll break your fingers if you try to push the stock puppy legs on this things. The same pain in the ass if you try to remove the driver. It's just to tight. I first widened the puppy wholes (under the boots) with a reamer, worked better but still was a pain in the ass removing the puppy. While trying I broke one of the mounts. However I found i quite useful to just cut a line through the mounts with a dremel. This makes them softer and mounting/dismounting of the puppy now is very easy and the driver still is holding perfect during the rides. I also replaced the mount screws with longer ones and put m4 nuts as spacer between the chassis and the mount. The reason was that the mount know are better accessible and the puppy leg isn't pushed against the chassis. A carbon or alloy pipe would work either I guess and looks better but I you can see I'm not that much into that => has to be functional ;-)



Steering Servo:
This is an optional mod. The stock servo is working quite good, has meta gears and enough force. With the 15kg low budget turnigy servo you'll get a quicker steering and you can run tighter turns on higher speeds. I would recommend it. It's just about $20.
The stock servo linkage is working fine also.



The Shock:
The stock shock is not that bad but it's leaking at the bottom O-ring. There must be a way this can be fixed, but I didn't try because I had an original ARx540 shock here which ever since worked well. By the way, this is a Traxxas Revo shock I think. I'm using 5000 mugen diff oil which works best for me.



Wheelie bar (very important):
With this motor the bike will wheelie all the time and the power sometime is hard to control => the front wheel goes up an sometimes to much => crash!
With a wheelie bar crashes of this type will be avoided most times. I've build one myself from a 2mm fiber glass plate, a plane wheel, some alloy pipes and long screws. Meanwhile you can buy RTR wheelie bars in some shops, but this was quickly made and works perfect. Used it on my ARx540 Nitro bike for several hours and it's really strong.





Chain tensioner:
Is a pain in the ass. Also was with the original ARx bikes because the grub screw is hard to reach and only works with a ball end 2mm allen wrench. If you put much thread lock on them you can't get them loose if you put to less the screw will get loose and the chain tension also. So I made my own chain tensioner. I made one side of a 1mm thick steel plate and on the other side of 2mm fiber class. Both materials work well for this purpose. The pictures should tell the rest of this construction.

Chain:
Replaced it with the original AR Racing part. The Quanum chain is not so strong and the segments have pretty much play. The stock chains works, but the AR Racing chain works better ;)

Rear wheel:
I've removed the foam which is put around the rim. The reason was I had open the rim several times. While riding without the foam on the rim, I found that the driving is very good. It's just like the wheel is working like a additional mini suspension in the rear ;-)





Front fork spring:
Are to soft. After wheelies the front fork was being compressed completely and the tire is scrubbing the mud guard => I've added an additional spring in each fork pipe. The fork still works smoothly, is much tighter know and in my option the front fork works perfect with this configuration. No wobbling and no oil needed.



Rear tire:
Should be glued with CA on the rim, because with this power the rim spins inside the wheel.



Ohh, I forgot the main axle. Just like with the sidebars everybody should know by now that the stock shaft is pretty soft => to soft. Quanum shortly delivers a hardened tuning axle or you can take the original from AR Racing which I did. No problem from here anymore.

Last but not least here a some charts which I measured with my Eagle Tree eLogger V3.
Todda measured just 75A with his wattsup unit. Don't know why there are so big differences since i run the same setup. The wheel and spur gears run very smoothly on my bike. I also changed the ESC time to high (like Todda) but this hasn't changed anything.

You can see that the are current peaks of about 115 Amps. The Volts don't drop under 10,5 Volts in the first minutes, but after 6-7 minutes sometimes it will. I first hat the cutoff voltage set to 10,5V => if the voltage drops below this mark the ESC will deactivate the motor => the ESC needs to be reinitialized. After I changed the cut off voltage to 10 Volts everything worked fine. I get about 9-10 minutes drive time with this combo (in this scenario I was accelerating hard, braking hard, again accelerating hard, braking hard, and so on). So this is the worst case scenario. When driving on a track the race time is about 15 Minutes.

The ESC and Lipo get hand warm after a run. The motor has about 45-50°C i guess.

Further I deactivated the reverse function with the prog card and the set the brake value to 75%. Standard is 100% => to hard and with 50% the rear wheel doesn't block anymore.

This combo eats approx. 1250watts. This is quite a lot, but the bike with this combo is a power beast.







I hope you enjoyed my modifications and you'll adapt the one or other mod.

If you have some further improvements, let me know.

I also made a list of my costs:
QRF400 Brushless 1:4 Scale RC Dirt Bike ARR: $119
QRF400 High-Strength Upgrade Swing-Arm Shaft: $2.99
Another pair of springs for the front fork: $10
AR Racing chain: $15
KD36-60-08L 3000kv Brushless Inrunner: $28.95
13T/5mm M1Steel Pinion Gear: $3.38
Hobby King Brushless Car ESC 100A w/ Reverse (Upgrade version):      $37.99
Hobby King Programming Card for Car ESC: $5.98
MG959 Alloy Digital Metal Gear Servo 15kg / 75g / 0.2sec: $22.26
Hobby King GT-2 2.4Ghz 2Ch Tx & Rx: $15.99
Turnigy 4000mAh 3S 20C Lipo pack (Perfect for QRF400): $24.70
---------------------------------------------------------------
Let's see what we get:                    $286,24

So you'll get a durable, well working RTR 1:4 scale dirt bike with 3s lipo setup, lot's of power, transmitter and receiver, fast and strong steering servo for under $300.

Well that's quite deal ;-)

With shipping I paid about about 260€ (~$335) for everything. The AR Racing ARx540 base kit costs 299€ (that's just the bike and this bike has less alloy parts).

So I'm pretty happy with this deal.


Edited by sebdel - 09/Sep/2010 at 3:15pm

Yes it is, but you have to drill those two holes (each side) for my custom chain tensioner.

No, just updated the thread right now (added some info and corrected my bad spelling :-) )

I've replaced the stock one with the original part of AR Racing. The stock one bent after about 20 minutes ride time (just like the others).

MODIFICATION UPDATE:

First of all I broke my steering arm yesterday. Was quite a crash but not that bad that the steering arm should brake (with my other ARx Bike),





Compared the original steering arm with the QRF400 steering arm => almost no flexibility in the QRF400 steering arm. That's one reason why it's braking faster. The other point is that for some reason the steering arms have to much play on those front fork pipes. I had to place some further shims to eliminate the play. If there is to much play, the force on the steering arms will hit harder because they have space to move and then will be stopped instantly. Hope you understand what I mean.



The next problem is/was that the bearing on the steering swiper are mounted incorrectly. Due to the wrong mounting the steering swiper bent when the steering arms broke (see picture 2). The bearing on the fork side needs to be inverted. In this way the fork simply can fall of when the steering arms break and won't bend the steering swiper.



Don't forget to thread lock the fork parts as well .... :)



And here is another problem. Really don't know how I managed to do this. As you can see on the picture the rear axle dislocated itself on the swing arm. This must be the result of the aluminum quality of the swing arm. Had to press the back end together a little bit and know it works again. Hope this won't happen again otherwise I'll have to think of a solution or just take the ARx swing arm.



You should consider that I'm really abusing this thing :)
I believe with normal use this won't happen.

I'll post some driving videos soon.

Here are some temperature facts of my trust combo after 10 minutes full throttle ride.
Lipo: 44°C
ESC: 57°C
Motor: 67°C







Everything looks pretty fine. I believe I won't change the motor pinion anymore since the current seems to be fine for those components and the high end speed really is incredible. Plan to go on a onroad race track someday. BTW: HK please offer some supermoto tires :D
With a smaller pinion the bike would wheelie all the time i guess which would be pretty annoying.


Edited by sebdel - 11/Sep/2010 at 2:29pm

Well TEK.

The steering arms are supposed to brake when the force is getting to big. It's to protect the more expensive front fork!

With those alloy things you'll brake your front for for sure, e.g. frontal crash or bad highsiders.

I mean what do those pastic steering arms cost? Something about $3 or $4 i believe. And how much does the fork costs => much more.

I'll definetely stick with this plastic one. Just was telling that the quality of the original steering arms is better and they won't brake as fast as the Quanum ones.


Edited by sebdel - 12/Sep/2010 at 11:27am