25 replies to this topic

[Uncle Fred]

Recently, at the "Texas Two Step" at Dallas Slot Cars I had a very poor performing Can Am.  It had poor straightaway speed and no punch through the corners. We run PS4002FK motors with mandated 8 tooth pinions.  I had replaced the springs with Champion lights (Red) and radiused Mura Big Foot brushes and broke it in accordingly.  My car weighed in at 114 Grams and everything was in good order, bearings good, gear mesh good....  The day after I tore the car down looking for a motor problem.  I found that I had inadvertantly installed a 7 Tooth Pinion on the motor!  Coupled with a 30 tooth crown for an insane gear ratio!  But why wouldn't the car accelerate? Was the 7/30 .810 tire combo too much for such a low torque motor to handle? Especially on a flat track?  What do you guys think?   

[MSwiss]

I wouldn't call a 4002FK a low torque motor.

Did you have any push start issues?

If so, possibly you lost a pole, and the motor is flat because of it.

[Uncle Fred]

No push start issues.  The motor sounds good and runs cool...…..

[swodem]

Gearing just too low

Actually gearing isn’t that low given your large tyres

Must just be a dud motor


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[MSwiss]

I thought of the same thing, but with a racer as experienced as Fred, it seems like he would feel a touch of acceleration.

Did the car have massive brakes?

Regardless, you'll find out more when you try the motor again, geared correctly.

[Pablo]

I think you should give the motor an 8T and foggettaboutit.

Don't overthink why a wrong gear ratio does the opposite of what you'd think.

They do that sometimes. Been there done that got the tshirt

[Uncle Fred]

No the brakes seemed about the same but the motor was so cool after 7 heats you could touch it with your tongue...……...NOT     that I would suggest that.   I'm just thinking that an FK type motor in a heavy car just can't pull that kind of gear coming off a slow corner.

[gotboostedvr6]

Take A pic of the brush faces.

If they look like this you need to true the comm.

[Uncle Fred]

Sealed motor.  

[tonyp]

Sounds just like the gearing was out of the power band of the motor.


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[gotboostedvr6]

I never said you had to take off the seal. It can be done pretty easily without touching the seal

[MSwiss]

It can be done pretty easily without touching the seal

Yes, Fred.

Every slot racer has a comm lathe set up to true comms inside a sealed motor.

It should be in your box, in the drawer next to the Allen wrench and bottle of oil. Lol

[Uncle Fred]

Next  you'll be telling me you can rewind the arm without taking it out! LOL You can't, ……..can you?   

[gotboostedvr6]

Need videos?

[gotboostedvr6]

Here is a pic or 2

This job takes a few min to complete.

[Uncle Fred]

And the rewinding?  Just kidding.  Thanks for posting those photos Dave, but the comm on my motor was fine. I'm thinking more along what Tony said, the ratio fell so far out of the power band it just didn't work at all.

[Eddie Fleming]

Truing the com on cheep sealed motors

 

Is it legal--- sometimes? but probably not.

 

Is it one of the reasons cheep sealed motors of this type are a farce?--- Yes

[Richard G With]

8/29 is generally standard at DSC. I'm surprised that a 30 tooth crown got past tech due to clearance.

I've had PSFK motors at DSC that liked 8/28 if the bite is low enough.

[Uncle Fred]

Your right Richard, thats what I usaually run as well.  

[idare2bdul]

Before changing the pinion consider racing it on a very short track. Or do what I am doing, hand the car to a grandkid so it is too slow to crash.

[Richard G With]

One of the points about this is that DSC uses RETRO rules which mandates 8t pinion for the ProSlot motor. Apparently it's not a problem if a 7 slips through tech as it will be sort of a self enforcing rule due to the performance hit at DSC.

The rear clearance, under both RETRO and IRRA rules is 050 minimum. With fresh 8125 tires, a Parma 29 is barely legal With some sanding. A 30 tooth Parma crown would not give legal clearance. Go fast and Koford gears are a bit smaller diameter but not enough to allow 30 teeth.

So I contend Fred's car should have failed tech on both pinion and gear clearance.

[Uncle Fred]

Yes!  I intend to rib Ken Stevens about it. 

[Ramcatlarry]

How far off was the ratio? ---8/28 is 3.5/1;  with a 7T, you would need a 24 or 25 spur.  Even an 26 would not run that good.    Tech should  have caught it.

[Uncle Fred]

7/30= 4.285

[swodem]

7 or 8 tooth what’s best?

It’s just a matter of a pinion        


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