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Discussion Starter · #1 ·
So, this morning in anticipation of tonights club night I thought I would have another look at one of my recalitrant SCX Subarus. It's a spare one I bought in a vain quest for some hubs that are mounted properly, you know, ones that won't follow some weird locus as they turn and push the car off into the scenery all the time. They're out there. I know they are because my #6 Solberg car is a beauty. I just ain't found another set yet.

Any road up. Not content with fitting duff wheels to Richard Burn's steed SCX also fitted a duff motor. Well, not completely duff. But the thing is, it appears to run faster backwards than forwards


I've witnessed this before. Motors that sound a lot more up for it when in reverse than when running as intended.

So, mighty tech team. Let's see you earn your spurs here. In terms a thicky such as Scooby Doo would understand:
  • Why does this happen?
  • How do I get it going fast the right way around?
 

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One way of dealing with it rather than worrying about how it happens (timing) is to swap the leads round so that the motor runs in 'reverse'. Now the drive wheels will run in reverse, of course! OK, so, next, switch the drive axle, left to right so the cog is on the other side, thus re-reversing the direction the wheels turn. ie, they rotate in the right direction again.
Job is done - nice and easy!
 

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god damn trop..

could always turn the motor upside down! then the gears to boot..

oh those wheels? swiss sent me some nice white BBS stylee ones


Inte
 

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As stated you could swap the crown over to the other side of the pinion but you may have to cut out the chassis slightly and this could violate your clubs rules. The other option is to take the motor apart(This could definitely violate some club rules, if you get caught) and try to adjust the timing ever so slightly. Most of my SCX motors seem to be timed close to zero (they run pretty much the same speed in both directions) so what you want to do is VERY SLIGHTLY turn the commutator in one direction to change the timing. Don't do this if you're not prepared for the possibility of messing up the motor(broken wire). If you look at the wire connections on the comm you will see a little slack in the 2 wires attached to each segment. This slack is all that you have to work with when turning the commutator unless you want to get into some major work by removing the wires (I won't even get into that). Exceed that slack and a wire breaks. Now I get confused with the whole clockwise - counter clockwise thing on timing so just turn it one way a little and try it. If it's wrong go back and turn it the other way. You can turn the comm by gently grasping the area between the wire attachments with a needle nose pliers and turn. If you want to get cleaver you could take one of your other motors apart and see if there is a difference in timing (where the slots in the comm are in relation to the stack poles [the things the wire is wrapped around.]) between it and the one you're having problems with. Larry S or Rocky or one of the other guys may have a better method than mine so wait a day or so to see other opinions.
Changing the timing can effect the motors torque curve, rpm range and operating temp. Back in the old days guys used to cheat by changing the timing in so called sealed motor races. The evil doers used to be able to change the timing without taking the motor apart. I'm sure no one on this board has ever done this so the method will probably remain a mystery.

Jim

P.S. check the excellent article at: http://www.slick7.com/S7magnets.html for the details on motor timing.
 

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I was hoping Jim would take up the reins on timing - thanks Jim.


The trouble is, that Wankel is so non-technical that he probably thinks a commutator is a dyslexic out of town worker travelling in and out to his city job!


Also, on slightly deeper thought, I realised that there is more to my 'quick fix' than swapping the wires - those things don't actually have any wires to swap do they? Metal traces I think. It could still be done, but with a deal more effort and fiddling around. I'll think about this one again at the weekend.
 

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Discussion Starter · #7 ·
What does non-technical mean and where in the can exactly are these communists?

Thanks for the guidance.

As an aside, the motor in question also needs a big welly full of poke before it contemplates moving: low voltage and it just sits there buzzing. However, after an afternoon of voltage, last night it proved a potent beast and no slouch at all. Just got to get some decent hubs upfront.
 

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Wankel,
If it's running hot sometimes in addition to your other simptoms you might have one pole that the wires are breaking contact. I had this problem on a Teamslot car with a similar type motor. What I did was put a little solder flux on each commutator connection and touch it with a hot soldering iron that had a small bead of solder. This added a small solder joint to each segment conection of the comm and fixed the problem. You can't hold the iron on very long or else you'll dick up the comm. Hold a pair of tweezers on the comm segment you're heating to act as a heat sink and you should be okay.
Jim
 

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Matt Tucker
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This is another world to me - never tinkered with motors only just picked those motors that seemed to give a bit more which I presume is within normal production tolerances. However motor tweaking is interesting just wished I understood it all!!

Matt
 

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Matt. just keep asking questions and there are about six really good motor guys floating around here who will teach us all.
 

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turning the comm with the motor all closed is easy as long as there are a couple of holes.. one of those tiny screwdrivers can be jammed in the gaps in the comm and the arm turned.. ooops!

Inte
 
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