I've recently purchased a Turnigy 1/16 Rally Extreme Edition but am having various problems with it, first problem was that a screw connecting a gear inside the front gearbox to the drive shaft would come loose after only a few minutes of use, so fixed that by gluing it in - will replace with thread lock when I get some.

Now I'm having another problem where the car really struggles to move off, I thought it was related to the previous problem but it doesn't appear to be, I've taken the gearboxes apart a few times now and they both seem fine with no metal shavings, they seem to mesh properly, and are not stiff to turn.

I have uploaded a video to YouTube to show the problem.

Problem with Turnigy 1/16 Rally Extreme Edition (0 min 19 sec)

What is shown in the video occurs randomly when trying to move off, and as shown in the video, once actually moving the car appears to run fine, but once stopped, and when trying to move off again the issue usually reoccurs. The wheels appear to turn in the video, but in real life they are actually stuttering.

Please note that the car is sat on a stand in the video, so there is nothing touching the wheels.

Also to add to the video, as well as making the clunking sort of sound, it may instead just give off a high pitch noise (not very loud) and there will be no movement what so ever.

This occurs no matter what position the transmitter trigger is pulled to, a small amount, or all the way.

If any one has any ideas what is wrong please let me know! I've contacted Hobby King but their support has been quite awful, their final response was "i am not sure what is the cause of that".

I've taken a slightly better video with the shell off if that helps.

Problem with Turnigy 1/16 Rally Extreme Edition (No Shell) (0 min 44 sec)

It is what is called cogging. I have found that this is common with non-censored brush less motors. I've had the same issue with a couple of cars.
Tighten all the gears to spec & run it til your ready to upgrade.

Is it possible that this particular motor is the problem? There are other people with exactly the same stock setup who do not appear to have this issue at all?

You shouldn't hear cogging with the wheels in the air, it sounds like you have a stripped gear, or something rattling around in the drivetrain too.

I did suspect a stripped gear or problem with one of the differentials, but as I mentioned, I've opened up the gearboxes a few times and there is no sign of wear at all, there is a small amount of wear on the main gear that meshes with the motor pinion, but that is to be expected as that is plastic, but it certainly isn't stripped. Also, if there was a stripped gear, would it not be making an awful noise when the motor was spinning full throttle? As it sounds perfectly fine once going, it is only when the motor has slowed down and then tries to move off again that it makes the clunking noise.

It is cogging. My Turnigy Monster Beetle(same platform) does the same thing. The noise is the collective clunking of all the free play in the driveline as the motor stutters. It's common to all non-sensored brushless motors and it's more a function of the ESC than the motor. Some ESCs start smoother than others, these particular ESCs seem to cog a lot. I wouldn't worry about it to much.

I've NEVER seen a motor cog that badly with the wheels in the air, that's brutal! Even my cheap leopard combo doesn't cog that badly with the wheels on the ground!

The slipper and center driveshaft on these things make a lot of noise as they rattle back and forth. The more I think about it, the more I think the ESC is at fault. I think it's programmable, but I've never tried to do it. I bet the timing got off somehow. He says in the original post "Also to add to the video, as well as making the clunking sort of sound, it may instead just give off a high pitch noise (not very loud) and there will be no movement what so ever. This occurs no matter what position the transmitter trigger is pulled to, a small amount, or all the way." This describes exactly what a few of my hand wound very high KV outrunners do when I use a cheap ESC and don't adjust the timing.

The problem is getting weirder now, I had the car in bits checking all the differentials and parts for anything loose or broken - which nothing appears to be. I had another ESC, so before testing it I decided to give the car a good thrashing, no cogging whatsoever, even at slow speed on grass, completely smooth, apart from the odd bit in reverse but for whatever reason the reverse speed seems to be extremely limited anyway, I assume a "feature" of the ESC. Ran through a whole 2200mAh pack until it got into "slow mode" or whatever it is called where the cells are getting low, and cogging was awful in reverse but going forward was fine (this is on concrete), on grass it wouldn't run, but this is to be expected.

I don't understand what the problem could be, or how it could be like that for ages, and suddenly go away, if it was a loose connection I think the thrashing should have found that. Or even if it is a temperamental issue, it should have happened at least once during the run.

I had another run which started off okay, but it now seems to be back to the same problem, not quite as bad, but certainly nowhere near as smooth as my earlier run.

I tested another ESC and the problem is about the same, not as bad as originally shown in the video but still noticeable, I really need to get hold of another motor to try that too.

What happens if you try it with the motor removed from the car?

Basically same thing, but obviously not as loud.

I have noticed the motor appears to be turning one way, then the other when this is happening, rather than stuttering in one direction, it goes back and forth.

If your motor is like mine, the magnets are very strong and you can feel very distinct magnetic notches between them? If that's the case, it stutters back and forth because at low speed it doesn't have enough power to jump over the magnetic "hump," it gets part way and the power cycles off and the magnets push the rotor back down. I wonder if the magnets in your motor are misaligned a little, they are pretty cheaply made motors after all. It might not be enough to have much effect at higher speed, but it could be enough to affect low speed operation.

Originally Posted by Bugman Jeff

If your motor is like mine, the magnets are very strong and you can feel very distinct magnetic notches between them? If that's the case, it stutters back and forth because at low speed it doesn't have enough power to jump over the magnetic "hump," it gets part way and the power cycles off and the magnets push the rotor back down. I wonder if the magnets in your motor are misaligned a little, they are pretty cheaply made motors after all. It might not be enough to have much effect at higher speed, but it could be enough to affect low speed operation.

It seems to feel as if there are two magnets in there, wouldn't say they are overly strong, but noticeable.

I realise what you are saying about slow speeds, but it will sit there and stutter for a good few minutes even if I have the trigger pulled all the way, then after what seems like forever, maybe 3 minutes or more, the car may suddenly shoot off. Other times I have to give it a push, or wait a few minutes and try it again. Almost without fail it will stutter after trying to move off from a light impact, say with a curb.

A broken motor wire or a poorly soldered bullet connector will cause a stutter too, especially a random one like you're describing. Check your ESC to motor connections and wires. While it's stuttering, wiggle all the wires around and see what happens. Maybe one of them is broken and only contacts sometimes, or contacting just enough that it works sometimes.

Originally Posted by Bugman Jeff

A broken motor wire or a poorly soldered bullet connector will cause a stutter too, especially a random one like you're describing. Check your ESC to motor connections and wires. While it's stuttering, wiggle all the wires around and see what happens. Maybe one of them is broken and only contacts sometimes, or contacting just enough that it works sometimes.

I had a look previously and thought one of the bullet connectors was bad, so connected the ESC wire to the motor wire directly, which seemed to make no difference, I've tried wiggling the wires but doesn't appear to do anything.