Hi!

I have got a "new Traxxas Rustler VXL." It runs pretty good. But I have minor issues.

#1. When I give just a little bit of throttle to move the car very slowly, it does not move smoothly. The motor and the gears sputter. But if I give a little more throttle, it does not sputter any more and goes smoothly and faster. Sputtering occurs only when the minimal input of the throttle is applied. (In addition, at this moment, I am running the car with 6-cell (7.2V) Ni-Mh batteries.) Is this normal or not?

#2. When lifting up the car from the ground, over the half throttle, vibration occurs. When taking off the rear wheels, above the half throttle, there is no vibration. But with putting the rear wheels on the car back, over the half throttle, vibration occurs.

Does this mean that the rear wheel are out of the balance? Or is there anything wrong on the drive train? I ran this car only twice for a test run. No jumpings or abuse yet.

If the wheels are out of balance, what is the best way to do balancing? After balancing the wheel, does balancing stay or not?

Your advices will be greatly appreciated!

Thank you very much for your attention!

James

#1 is common with sensorless BL systems. It's called cogging. That is the rotor passing through each magnetic field in the motor.

#2 is tire balance, stick on weights will cure this. Nothing sounds "wrong" with the truck. Balancing the tires is something you want to do.

-JB

Hi, JB!

Thank you very much for your response!

This is first time for me to run a brushless powered car. So is cogging normal?

And where can I get stick-on-weights?

Once again, thank you very much!

James

agreed with jailbird
cogging -> don't go slow (cogging is very normal for sensorless brushless systems)
tire balance -> take off the rear wheels and slid them onto a free spinning thing, then let the heavy side go down, and add a little weight to the top side till there is no heavy side.

If your tires aren't out of balance, they might have ripped from the bead on the rim (unglued). If you can peel the tire off the rim in any place just use some CA glue (cyanoacrylic (kinda like super glue)) to glue the tires back to the rims. My stock slash tires weren't glued very well to the rim.

as for balancing weight, you can use none drying clay, you can buy specific balancing putty, or get creative....I've used that poster sticky tack before to balance tires. It's worked for 5 dirt runs so far....lol

Brainanator, good call on the unglued tires! That is certainly something to check on any RTR.

-JB

Hi, guys!

Thank you very much for your good advices!

This is out of the topic, but because you guys are knowliedgeable, can I ask one more question, please?

I have a HPI Spirint 2 Sport. It a fairly new, too. It runs good, but when pushing the trigger of the transmitter all the way down to break, the car does not stop. It has almost no break power.

I adjusted the throttle trim, but it is still same. In this case, is the ESC wrong or is the way it is?

Once again, thank you very much!

you may need to re calibrate your ESC. I know how to do it with the XL5 and the Mamba Max, but probably not with your HPI one. Take a look in the manual and see what it says about calibrating it to your transmitter. If you don't have the manual check HPI's website, they'll have an electronic version you can look at.

I doubt it, but it is possible that the ESC has been programed to a very a low braking strength, see if that is an option for your ESC while you're looking at the manual, you might be able to increase it and get better results.

Which HPI ESC is in the Sprint 2? I had the EN1 for a while and it had very poor braking power as well.

Hi, guys!

Thank you for your answers!

The ESC in my HPI Sprint 2 is the stock one, "SC-15." It does not have any button on it for reprograming. Also the manual does not mention about programing or reprograming either. I checked the HPI web-site, but I couldn't find.

Any ideas?

Thank you again!

hmmm, I looked at manual on the website and I would say it leaves something to be desired. I did read that the ESC auto calibrates everytime you turn it on, and you need to make sure that you pull the trigger (make the car go forward) before you push on the trigger.

But that's all I got, if the braking seems weak, maybe they just want you to keep going fast! lol

Cogging is not the norm with brushless sensorless motors.. Its a side effect of underpowered batteries.The batteries cannot supply the amps or voltage required by the motor.. ..Lipo's will cure the issue and so will reprogramming the esc to run on Nimh batteries.. I've had that issue with my Mamba until I reprogrammed the esc to know it was running Nimh batteries and it worked much better.. still a little cogging if I really feathered the trigger.. I only run lipo's now and there is no more cogging.. You will still feel the motor stutter a bit, thats how the sensorless work, but nothing that I would call cogging...

Tire weights are a must with the high speeds of the brushless system.. You won't realize them till you add more voltage, but it will be much more obvious when you do.. stick on weights are the way to go..

my mamba max cogs at low speeds (very low) with 2s 30C lipos....

all brushless (sensorless) will cog at very low speeds.... barely moving.. but it shouldn't cog when throttle is applied off the line when accelerating... I think that what he meant.... Mine makes more of a humming noise and a brief stutter but only when barely moving.. Off the line its all power....

This is what he said...:
The words "little bit of throttle" and, "very slowly" make me think he only using a little bit of throttle, and making the car move very slowly. I can also reasonably assume when he said "if I give it a little more throttle, it does not sputter any more and goes smoothly" he means that when he give it some more throttle the car stops sputtering, and moves smoothly.

Both of those are pretty much the definition of sensorless brushless cogging. Stuttering at very low speeds, with very little throttle input.

So I guess I'm not seeing the part that makes you think he talking about off the line acceleration.

I read the thread at work and I guess I misread what he wrote... what he is saying is exactly what happens.. You are correct Brain in what you are saying....

Thanks cenracer1, much respect goes to you. Sorry if I came off as a jerk.

Well, thank you very much for your inputs! I really appreciate that!

I have been running nitro and brushed cars, but this is first time for me to run a brushless. Anyway, your inputs are very helpful for me.

Thank you again!

James