Brushless Stuttering / Hesitating in One Car but Not Another – Please Help?

[mrki]

Hi Everyone,

I am new to these forums so please be gentle. After getting back into RC recently after several years away, I thought I would try brushless.

I picked up a Nosram Evil Power / Dragon 10.5T combo (sensored) a while ago to run in my Tamiya Blackfoot Xtreme and it has run flawlessly with no heat, cogging or stuttering issues. The ESC is an A.I. set up so no settings to play with.

I built up an Ansmann Macnum, ball raced it and transferred the Nosram Brushless combo into it and I get really bad hesitating when accelerating. I swapped the whole system over from my BFE (27mhz radio gear and all) so I know it all works fine in at least one car. I have swapped it between them a couple of times and it will run with no problems in the BFE but not in the Macnum.

I am using a new Vapextech 3700nimh pack but this performs brilliantly in the BFE, leading me to believe it is not the battery problem. It is using a standard Tamiya connector but nothing is getting that hot.

The symptoms in the Macnum are that when accelerating on 3/4 to full throttle, the car will slow / hesitate for a second almost like it was a nitro car changing gear and you can hear the motor revs drop. It does this through the acceleration not just at one point. I have tried it with 23T down to 16T pinions and it is exactly the same symptoms. The motor and ESC are not getting hot, so as far as I can tell it is not over geared.

I don’t think it is cogging and at low speed or part throttle its fine. It has no problem getting moving or driving around at low speeds.

I tried a brushed motor (Peak Racing 13T) with the Nosram ESC last night and got the same problem. So it is not exclusive to the Nosram Dragon motor.

I was wondering whether it could be the slipper clutch or something out of true in the gear box that is causing problems with the ESC / motor loading. Alternatively, could the drive train be slipping? I have tightened up the slipper and ball diff, loosened them and everything in between.

If you rotate the spur gear it doesn’t run in a true arc and you can see a slight bit of wobble, essentially a rise and fall or 0.5mm over the whole rotation as well as a small amount of back and forth play despite the ball racers.

As this works in my Blackfoot (ball raced and the gears run silky smooth), I know there is something in the Macnum set up causing it. Could it be the ESC responding to the loading on the motor and cutting out?

I would really appreciate some help on this.

[blue_pinky]

Not really sure, but, maybe electrical interference?

Maybe the position of everthing in that particular car is causing some receiver intereference? 27mhz is more susceptable to probs with that I think...

Try moving things around, separating the recevier from other things better?

Also, you say the spur is not concentric...how well meshed is the pinion?

You'll need to adjust the motor/pinion position so that there is a tiny amount of play between the teeth at the closest/highest point on the spur...not sure if the amount of meshing would cause the stuttering you've described, but adjusting that will help the general running of it. It's a prob with some spur gears, best fix for that though is to buy a new one and hope it's got better concentricity. Be careful though...give it too much play and it'll start shreading teeth at the low point on the spur!

[mrki]

Thanks for the response. Would a 2.4ghz system help assuming that is the problem?

The pinion is meshing ok with just the right clearance.

Now you have mentioned it, I am thinking this could be an emf issue with shielding on the ESC and cables hence the same issue with the brushed motor. The blackfoot layout is very different, notably the location of the motor to the radio and antenna.

[sparrow.2]

You could try installing the reciever standing on its side with the crystal as far away from the chasis as possible.

2.4GHz might help but would be silly to throw money at the problem if it isn't that.

[mrki]

Good Stuff!! keep the suggestions coming.

Now I have been looking at the possibility of electrical interference, I have been googling hard under a number of different search parameters.

This has turned up some interesting results. It seems some people have had experience of my symptoms after they have had to change their steering servo and they have been suggesting servo compatibility issues with the ESC or transmitter.

Now the only thing different in the electrics system is the servo. I have a Hitec in my Blackfoot Xtreme and an Acoms in my Macnum. Never had a problem with the Acoms before in other cars but then I have used brushed ESCs with it. I will swap out the servo tonight to test this.

[Battle_axe]

Originally Posted by mrki

Good Stuff!! keep the suggestions coming.

Now I have been looking at the possibility of electrical interference, I have been googling hard under a number of different search parameters.

This has turned up some interesting results. It seems some people have had experience of my symptoms after they have had to change their steering servo and they have been suggesting servo compatibility issues with the ESC or transmitter.

Now the only thing different in the electrics system is the servo. I have a Hitec in my Blackfoot Xtreme and an Acoms in my Macnum. Never had a problem with the Acoms before in other cars but then I have used brushed ESCs with it. I will swap out the servo tonight to test this.

the ansmann spurr is miles from round but i have never really had any problem with it what servo are you runing? could it be than you need a cap in the reciver? is it spectrum? what reciver are you useing? also i knnow this sounds silly but i did it have you put the green spacer inside the gearbox on the topshaft? also if you lock the slipper fully and try it does it work ok as the spring is a bit naff to start with? pm me if you want any help as i run the madrat week in week out and it is the same as the madcum truck

thanks
carl