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Old 12-01-2012, 07:02 AM   #1
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Default Newbie with HPI Sprint 2 Flux problem

Hi all

I have a problem with my new HPI sprint 2 flux, i've had it less then 3days, was running perfectly, and then it started SCREECHING when moving forward.
I've checked over the main culprits.
Can't pin point where the sound is coming from.

Video here : Unfortunately forum rules have stopped me posting video urls. ALAS

it's the sounds like two pieces of wrapping plastic being rubbed against each other.

Any help would be appreciated.
Thanks
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Old 12-01-2012, 07:10 AM   #2
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Is one of the pulleys rubbing the chassis anywhere? Maybe a bad ball bearing.
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Old 12-01-2012, 01:32 PM   #3
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Probably a bad bearing or more likely one of the belts is rubbing something. The belts don't have a whole lot of clearance, even when it's out of the box.

Make sure your belts don't have too much flex. Also, the belts when static may not look like they are hitting anything, but they move and expand when you are under power. Look for rub spots, particularly on the ESC and Servo and radio box.
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Old 12-02-2012, 09:04 AM   #4
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Quote:
Originally Posted by atmosphere View Post
Hi all

I have a problem with my new HPI sprint 2 flux, i've had it less then 3days, was running perfectly, and then it started SCREECHING when moving forward.
I've checked over the main culprits.
Can't pin point where the sound is coming from.

Video here : Unfortunately forum rules have stopped me posting video urls. ALAS

it's the sounds like two pieces of wrapping plastic being rubbed against each other.

Any help would be appreciated.
Thanks

Type out the url for the video just don't link it in the typing window.

If that doesn't work Type out the url but leave off the www and leave a space instead of a . for the .com


Have you tried putting the car on a stand - this way the drive train is not under load - run the car at various speeds and see if you can localize it to the front or rear.

Does it do it only under load = driving?

Does it do it on a car stand = not under load?

Is it a steady sound or does it lope = like come & go depending on revolutions and speed?

Could be a dry or seized bearing and/or spinning in the plastic carrier... Check the main shaft eccentric bearings - They do not fit tight and are not rubber sealed...

*Could be dry bushings on the OEM front belt tensioner...

Could be a diff rubbing the bulkhead...

Could be a rim rubbing on a control arm...


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Old 12-02-2012, 09:28 AM   #5
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or motor bearings,used to happen to my older brushed motors if they sat for a while, make sure their is no grinding or rough feeling in drive train (turn wheels by hand and check differentials by turning them back and forth in opposite directions) clean and oil all bearings and check belt tensioner bearing
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Old 12-02-2012, 11:32 AM   #6
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One or more of the bullet connectors on the 3 motor wires may not be making a good connection. Check where they plug into the ESC. Give each one just a little bit of a twist on the ESC post. Tricky to do this while giving it a little throttle, but then you'll see right away if it's the problem. I had one of these cars briefly, a few years ago. Did the same thing. I had some similar trouble later on with a speedpassion motor that used bullets on the endbell. It's far more noticeable with sensorless systems though.
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Old 12-02-2012, 12:18 PM   #7
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When it makes the noise, do the wheels at least spin? Could be a few things, the Pinion gear striped the Spur from a bad crash? Stripped belt, or the belt jumpped off a diff or pulley?
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Old 12-02-2012, 10:26 PM   #8
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Thanks for all the suggestions.

I have posted this question on several forums and this is by far the most replies i have gotten.

Great community, i think i will make this one my home .

After more inspection i believe that it is the grub screw on the pinion gear that has come slightly loose. I have thread locked it and tightened it again however as per usual with HPI's RTR quality a few other screws have gone missing in one of my runs.

Once again thank you all for the helpful suggestions.

I shall be posting my finding on this unit when i get her back up and running

just so you guys ca hear what i was talking about : youtube.com/watch?v=ulMavrbc3j8

Last edited by atmosphere; 12-02-2012 at 11:15 PM.
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Old 12-03-2012, 09:52 AM   #9
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oh, okay, it's not the issue with the bullets I was thinking of. That sounds like you might have something jammed under or behind the rear diff pulley.

If you loosen the motor screws and move the motor so the pinion doesn't make contact with the spur, if you spin the wheels by hand, does it feel like there's some extra resistance somewhere in the drivetrain? Is the sound still there?
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Old 12-03-2012, 11:02 AM   #10
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Happy to hear you found the culprit.

Quote:
Originally Posted by atmosphere View Post
After more inspection i believe that it is the grub screw on the pinion gear that has come slightly loose.

Loose grub screw...
Whoda thunk it...


...a few other screws have gone missing in one of my runs.

Yeah, they disappear like a candy at a kid's party...

Wait til ya toss a dog bone...

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Old 12-04-2012, 02:27 AM   #11
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Quote:
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Happy to hear you found the culprit.




Wait til ya toss a dog bone...

they have popped out many times, but thankfully i have always found it again. Though saying that i should probably buy some spares.
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Old 12-04-2012, 10:59 AM   #12
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How come the dog bones pop out??

On my Diffs, i put ball bearings that are 5x8x2.5mm, and i had to put 4 shims on each side of 0.2mm thick to remove the slop/loose.

In the front i put the springs, but i didn't use springs from a pen, but springs from the front suspenion of a Tamiya F103! These ones, part number 50509

In the rear i put 1 red o-ring on the diff cup, more to just hold it, since the wheel isn't used for steering it won't use out as fast as the fronts.
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Old 12-04-2012, 11:40 AM   #13
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Quote:
Originally Posted by atmosphere View Post
they have popped out many times, but thankfully i have always found it again. Though saying that i should probably buy some spares.
Doesn't hurt to have hot spares for the stuff that flies, bounces, disappears or breaks when you least expect it.

Of course if you're smacking into stuff - expect it...

Axle pins fly, bounce & disappear, but usually only when you pull the hex nut off and the pin is pointing anywhere except 9 & 3 o'clock - HPIZ264

Main shaft pins fly, bounce & disappear as well / when you go to change belts - HPIZ262

Someone on here has a sig that says something like:
The difference between a basher and a racer is when a basher has a crash he's astonished when something breaks.
Whereas the racer, when he has a crash, he's astonished that something didn't break.

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Old 12-05-2012, 08:20 AM   #14
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Alas i believe it maybe a bearing problem or the motor as the sound is back again but everything looks in tip top shape.

Belts are in good form. And the diff's act correctly

Bearings are good as far as i can tell no noise is made unless that amount of load is put on the car. once it hits top speed (whilst in my hand) it makes no sound but when placed on the ground and accelerating (so with the load of the car and traction of the ground) it makes that sound ALL the time.
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Old 12-05-2012, 10:55 AM   #15
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Best fix for the dog bones are to replace with CVDs. Replacing the ball cups with RPM is also a great idea as slop is taken up and the camber links don't dislodge as easily, hence dropping the bone.
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