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JeremyC
2009.12.06, 08:19 PM
UPDATE: I verified that the problem was that the comm was out of round.

Hey guys,

This may be a long and convoluted post, so please bear with me.

Yesterday I bought the front portion of an ASF MR-02 from one of the fast drivers at NYRC. All I did was to move my T-plate, Motor mount, and DDS from my AM car to the new ASF car. Before I had it, the ASF car looked very fast down the straight. Also my old AM car was very fast down the straight as I had 2x2 8858 FETs in there.

For some reason the ASF chassis with my old motor is considerably slower than either of the old cars. It is also noticeably slower than most other cars down the straight. It isn't ridiculously slow, but I know that something isn't right. Also, this isn't because of speed carried through the previous turn. I'll be going full speed down the straight pulling away from a car and they will be on top of me before the end. This happened in both the B and A mains at NYRC last night.

I immediately suspected that my batteries were the issue, but I tried two brand new sets of Orion 900's, and all three of my older Orion 900 sets. I am pretty convinced that it is *not* my batteries, and I even borrowed a set of batteries from a very fast car with the same result.

I then started to think that it was my KT-18, not going to full throttle. I read and re-read the manual, and I played around with the throttle endpoints a lot. I also adjusted the neutral position several times. I even put my car on my oscilloscope to look at the waveform to see if full power was being given. I'm pretty sure that the KT-18 isn't the problem either.

So, that is where I'm at. I'm kind of at a loss of what to check next.. The potential problems that I can think of are:


Motor is worn out - It could be, the car has felt slower over time, and I didn't drive my AM car for nearly 3 weeks before this change. It is an Atomic Standard BB that I have had for about 2 months, racing every other week or so.
Gear mesh problem - I have a 3Racing ball diff, and I noticed that the spur gear is slightly out of round. As I turn the spur the mesh gets tighter and loser. I just set it up so that it spins freely, and this hasn't been touched since it was 'fast' on the AM car.
excessive drag somewhere on the car - My bearings do need to be cleaned, but the car as no tweak and is running perfectly otherwise. I don't think this is the problem either.


So, please. help.

JeremyC
2009.12.06, 09:58 PM
Update...

So I took the motor out of the car and looked at the brushes.

One of the brushes is virtually gone, but more disturbing is that when I spin the armature by hand I can see the brushes go in and out. Meaning that the comm is no longer round, and the brushes are continually moving on the springs. I'd say that the brushes are flexing a quarter of a millimeter, guessing by eye. At 20k RPM I can see why the motor doesn't have power, as the spring of the brush probably isn't rebounding fast enough to keep in contact with the comm.

Anyone out there do cheap comm lathing?

-Jer

JeremyC
2009.12.06, 11:33 PM
Update 2...

I just put a new Speedy 05 in the car and gave it a little gas. It certainly appears that the wheels are spinning a lot quicker. I don't know when I'll be able to get to a track next, but I think the problem was the motor.

Felix2010
2009.12.07, 12:05 AM
Hello,

Even though it seems you found the big reason for the speed discrepancy, if you just bought the car, check the ICS settings for the board using the MR02 ASF ICS program menu. The "DRIVE FREQ" is what you re looking for. If you want max torque/speed, make sure this setting is set to 1.2khz.

Hope this helps:)

JeremyC
2009.12.07, 12:58 AM
What are the other frequency settings? What is the default?

Thanks for the thoughts Felix I'll be sure to look into that as soon as I can find someone with an ICS interface. :)

-Jer

Hello,

Even though it seems you found the big reason for the speed discrepancy, if you just bought the car, check the ICS settings for the board using the MR02 ASF ICS program menu. The "DRIVE FREQ" is what you re looking for. If you want max torque/speed, make sure this setting is set to 1.2khz.

Hope this helps:)

LED
2009.12.07, 01:49 AM
What are the other frequency settings? What is the default?

Thanks for the thoughts Felix I'll be sure to look into that as soon as I can find someone with an ICS interface. :)

-Jer

Take a look at this before you start changing stuff with the ics.

http://mini-z-guide.com/ASF.htm

You also want to read this if you dont want to spend 80$ on the usb dongle.
http://mini-zracer.com/forums/showthread.php?t=31464

As for the driving freq. Mine is on 5 khz, you need to work out for yourself whatsbest for you.

JeremyC
2009.12.07, 01:56 PM
LED; thanks for the links. I would love to tinker with those settings! I wasn't aware that you could make all those changes to the ASF cars.

So as a 'conclusion' to this story I lathed the comm on the motor. Check this thread (http://mini-zracer.com/forums/showthread.php?p=369013#post369013) out for how I made my own comm lathe. :)