Any RC car/truck drivers here?

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gatehealing
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Any RC car/truck drivers here?

Post by gatehealing »

Hey y'all,

I'm now sinking my $$ into an old hobby I had in the early/mid 80's. I just got a new Traxxas Rustler VXL with a 7 cell NiMH battery, but I went ahead and picked up a Venom 5400 20c 3S Lipo battery. It has a brushless motor.

If there are RC folks on here who know these things, I have a question: This thing was running fine with the NiMH battery, and seemed to do ok with the Lipo, except that at about 80% throttle, just as it's about to pop a wheelie, the acceleration goes out, then quickly kicks back in, then out, then in . . . like stuttering. I've seen something called cogging, but that seems to be an issue at low throttle. If I accelerate slower, this does not happen. It also does not happen if I lift the rear wheels off the ground; I can accelerate to 100% immediately, and it goes fine--wheels balloon up etc. Put it back on the ground and it happens again at 80% throttle when I get there too fast.

The other related issue just started happening today: With the NiMH battery, when i accelerate quickly, it does the hesitation thing, but the off period is longer, eventually getting to a total stop (no steering control, no acceleration), including steering. The LED on the receiver blinks red (does not do this with the Lipo as I never lose total power or steering).

I've put my question on a RC groups forum, but am getting some mixed answers. I'm going to my local hobby town tomorrow, but am hoping you folks might be able to steer me in a good direction, maybe some good websites/forums.

Thanks!
Jon
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Re: Any RC car/truck drivers here?

Post by Bahnstormer_vRS »

Hi Jon,

All sounds like great fun although, sadly, I have no idea what the problem is or the solution; other than to suggest that you have a dose of 'kangaroo juice'.

Guy

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Re: Any RC car/truck drivers here?

Post by My Name Is Pete »

I'm no expert here, but I'd guess that the increased torque is causing some flex in the gear cage which is causing the gears to jump.
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Re: Any RC car/truck drivers here?

Post by Ian Mc »

I play around with fast electric rc power boats, with speeds up to nearly 50mph - any faster and they leave the lake!

I think what you are experiencing is that the current draw from the batteries is hitting maximum as you accelerate hard, with the result that the speed controller is cutting it back momentarily to prevent damage to the electronics. The fact that you have no problem with the wheels off the ground seems to support this, as there will be minimum load on the system.

A solution might be to try a controller able to handle a higher peak current.

I dont have this feature on the boat stuff, I guess its something built into your type of esc. In the boats, if the current draw is too high, things go bang and all the magic smoke escapes.

Let us know how you get on.

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Re: Any RC car/truck drivers here?

Post by gatehealing »

Makes sense (esc cutting power). I'll check with Traxxas to see if that rings a bell with them. Shouldn't be an issue though since that truck is supposed to be ready for 3s lipo or nimh without alterations or upgrades. May be a faulty esc tho.

Thanks!
Jon
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Re: Any RC car/truck drivers here?

Post by nigelb001 »

I'd agree with Ian. Lithium batteries are able to supply bigger peak currents than NiMH. That's why lipos can be dangerous in the wrong situations. Slamming the stick up is probably causing the speed controller to limit/overload. Maybe 5400 is too much for the speedo, do Traxxas say 5400 3S is OK?

Seeing this makes me want to dig out my old Associated RC10T2 and slap some modern electronics in it.
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Re: Any RC car/truck drivers here?

Post by gatehealing »

Yeah, the 3s is fine with this model . . . it's said to be designed for it with the VXL system (the ESC and brushless motor, traction stability system, and steering servo). I was wondering if it was a 'clipping' effect on the power though. That might mean a bum motor or ESC.

Sending the whole car back to Traxxas since they are in Texas (like me) and shouldn't take too long to get it back.

We will see.

J