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new to electric rc need a little help

new to electric rc need a little help

Old 09-06-2015, 11:28 AM
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let me first say hi this is my first post on this site .... OK so i have recently got into the wonderful world of rc bashing just so much fun and have found many hidden tracks around my area . i started out with a 16th scale e revo love this little guy . soon after getting that little guy my girlfriend showed interest in going out bashing with me (win win i get a hot chick to look at and a bashing buddy) so i found a 2002 traxxas stampede that i bought for her i replaced all the electrics all metal internal steering servo esc (xp digital sc500bl) with a reedy 3300kv and run 7.4 lipo 2s i figured it would be a good tough truck and that it has been we have both been out many times and im always the one that has to take some time to fix my car while she is still jumping stuff but the last couple of time going out her truck would not take off smoothly it reminds me of a real car out of time ..... anyways it stutters then goes fine and i did some research and found out that maybe some dirt or small rocks got into the motor so i took apart and cleaned it out but that just seemed to make it worse with the motor out of the truck its shaking violently before starting to spin with it in the truck it only shakes horribly did i under size the motor i dont know the gearing (tooth count on pinion or spur) at all i used some gears that i got when i bought the truck from any craigslist any help would be much appreciated and thank you for any help you can offer
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Old 09-06-2015, 03:15 PM
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Welcome to the forums. Your esc is sensorless meaning it doesn't use a sensor in the motor to determine motor position. Instead it uses the EMF coming back through the motor wires. The stuttering you're seeing is referred to as cogging and is similar to an engine that has incorrect ignition timing. It occurs when the EMF signal is not strong enough for the esc to read and/or is not what the esc is expecting so the esc stays in its startup algorithm longer than it should. Cogging is usually the result of gearing for too high a top speed and the startup algorithm not being powerful enough to overcome the gearing. However it's strange the cogging just appeared as it will usually be constant right from the start. This leads me to believe there's a loose motor wire connection or something wrong with the esc. Check the bullet connectors and make sure they're tight. Also make sure the drivetrain isn't binding anywhere, dirt buildup can cause binding as well as bearings.

For the sake of curiousity, check the gearing for us. Both the spur gear and pinion should have the tooth counts on them and measure the fire fire diameter as well.
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Old 09-06-2015, 03:59 PM
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just took the truck apart again found an 81 on the spur and no markings on the pinion but marked a tooth and counted it 3 times coming up with 28 all 3 times as for the fire fire ? i can onlt think you meant tire the tires are 2 inch wide and 2.8 inches tall
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Old 09-06-2015, 04:02 PM
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the esc did come unstuck on one outing and shortly after that the problem started do you think that maybe on of the wires coming out of the motor was damaged from this happening ?
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Old 09-06-2015, 08:13 PM
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Originally Posted by Rooster696 View Post
the esc did come unstuck on one outing and shortly after that the problem started do you think that maybe on of the wires coming out of the motor was damaged from this happening ?
It's possible. One of the wires coming out of the esc, motor, or at one of the bullet connectors could be damaged. That's kind of hard to diagnose other than to resolder them, possibly cutting them back or replacing them entirely.

Have you ever checked temps? If I just put together your combination I'd start with gearing for a lower speed, maybe 28/90 instead of your 28/81. It may be worth a shot trying the larger spur gear, they're cheap around $5. It may help with the cogging and if your temps are high it'll lower them.
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Old 09-06-2015, 09:44 PM
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found out that my problem is coming from the esc put the motor in my e revo and it was doing the same thing so i though but when i went to run my e revo i noticed the rear left axle was binding so i hooked the motor up one more time and it runs wonderfully so im trying to figure out how to replace the wires in the esc but im kinda lost because the eletronics are sealed into the case ..... guessing thats how they water proof?
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Old 09-06-2015, 11:38 PM
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Sounds like bad ESC capacitors possibly.

Also, I was just wondering how placing a larger spur gear in place of a smaller spur gear would reduce cogging? This would mean more initial load on the startup of the motor would decrease cogging. I noticed the opposite. However, my cogging is fairly faint and goes away relatively right away.
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Old 09-07-2015, 12:45 AM
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Glad you narrowed down the issue. The wires are only a possibility, there could be something internal from when the esc got rattled loose. I looked at pics of your esc, you really can't replace esc wires without opening up the esc and unless you're good at soldering you might make things worse.

Originally Posted by COP4 View Post
Sounds like bad ESC capacitors possibly.

Also, I was just wondering how placing a larger spur gear in place of a smaller spur gear would reduce cogging? This would mean more initial load on the startup of the motor would decrease cogging. I noticed the opposite. However, my cogging is fairly faint and goes away relatively right away.
It's actually the opposite, Larger spur = slower top speed and quicker acceleration due to decreased load. Larger pinion = increased top speed and slower acceleration due to increased load. The gearing calculator says 28/81, 3300kv on 2s with 2.8 Talons (stock Stampede tire, 4.6" tall) is 43mph before tire ballooning, 28/90 is 37mph. Btw I'd definitely check temps, in my experience a combo similar to this would rather be 40mph or lower depending on terrain.

Now when I first mentioned the wires being a possible cause Rooster hadn't yet mentioned the esc came loose during a run. Wires are still a possibility but less likely now. Could be a cap, as that would cause less power to be delivered to the motor which wouldn't help it to spin fast enough to get the esc out of startup. Could be another damaged component inside the esc. I may be familiar with the basic operating principals of an esc but an electronics tech I am not. I'd pop it open, look for anything obvious and inspect the wires carefully at the bullets and esc side but beyond that it's your call what to do next. Sorry I can't help more.
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Old 09-07-2015, 08:17 AM
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I have done alot of soldering in my days ..... what's the worst that happens my truck continues to not work? Sorry that just made me sound like an ass ..... anyways I have ordered a 60a sensor less ecs for 27 bucks I'll get a more expensive one once she gets a little more serious about bashing again thank you for all your much appreciated
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Old 09-07-2015, 09:03 AM
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Ussually is a cap goes bad, it will bulge slightly on top. I would say one of the mosfets is going south. Time for a new esc imo. Watch you're gearing on this, and the temps, it seems pretty tall and running through grass or restrictive surfaces will heat the motor up quickly.
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Old 09-07-2015, 09:07 AM
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i live in so cal so most of what i run it through is dirt or sand
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Old 09-07-2015, 09:51 AM
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28/81 is pretty insane gearing on 3300 in a pede. Need to be in high teens. Maybe 19/81.a new pinion is cheap. Sand creates a much load add grass btw.stock gearing would be 19/90 or 19/86i believe
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Old 09-07-2015, 09:54 AM
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Thank you for the help I just ordered a new esc ..... tomorrow I will go get some new gears and hopefully save me from future problems
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