Terra Scorcher not moving on ground

[bubblewrap 1]

Hello! I had just begun building my absolute first Tamiya RC - the 2020 Terra Scorcher. There were frustrating newbie moments for sure: plugging the ESC to the wrong CH ports on the receiver and thereby being unable to do the high point setup etc.

Anyway the first time i managed to get it running i tested it, had a blast, got a few knocks, and then the wheels didn't spin even though you could hear the motor working. Took everything apart and i think it was a loose pinion gear on the motor shaft flat. After tightening the grub screw the wheels now spin properly when the car is upside down on my work table.

Unfortunately the moment i set it on the ground it emits a whine and doesn't move when i throttle. The moment i pick it up of course it works. Can anyone help please? 

I googled it and some sources talk of a slipper clutch problem? Does my car even have a slipper clutch? The manual makes no mention of it.

Any and all advice would be very much appreciated.

[catman79 346]

have you used the correct motor mounting holes in the metal motor mount for the pinion you are using?

 

[Mad Ax 9306]

A loose pinion on the motor shaft will definitely cause the problem you describe in the first instance.  But you say you fixed that?

Is the new problem different, or the same?

Or in other words - is the "whine" you describe the same as it was when the pinion was loose, or is it a different whine now?  If it's the same then it's likely the pinion is still loose or not properly engaging.  The fact your wheels turn when in the air suggests the pinion is making contact with the spur; if it wasn't properly seated (i.e. motor mounted in an incorrect hole) I would expect a grinding or buzzing sound, i.e. not good.  Anyway, it's worth popping the motor out again and double-checking the pinion is properly tightened down and in the right place.  Sometimes if you tighten the pinion while it's very slightly off the flat, it will feel tight when assembling but pop loose the moment you apply torque to the motor.

I don't think the Terra Scorcher has a slipper clutch, so don't worry about that.  Also I don't think it has ball differentials - these can also slip if not assembled properly.

When you run the car with the wheels in the air, do all four wheels turn, and do they all turn in the same direction?  It's possible you have popped a dogbone (driveshaft) or even lost a drive cup.  Make sure the driveshafts are properly installed on all four corners.

Also make sure the wheels are properly installed and the hexes are engaged on the drive pins.  It's not uncommon for a wheel nut to back off and let out a drive pin.  You'll lose drive to that wheel, and through differential action, you'll lose drive to the opposite wheel too.

As your car is 4 wheel drive, it makes more sense that this is an issue in the main transmission rather than on any particular corner, as there is no centre diff in the Terra Scorcher, so even if you lost a dogbone or drive pin on one axle, you should still get drive to the other axle, but it's worth checking every part of the transmission just in case.

Finally, if you have been running in the wet, it's worth checking if the tyres a slipping in the wheels.  The instructions normally say to glue the tyres to the rims but lots of people skip this step and have drive problems when the wheels get wet.

The ESC can emit a whining sound at partial throttle.  This is the ESC's way of varying the voltage that goes to the motor.  When you apply full throttle, there should be no whine from the ESC.  If you only apply a very small amount of throttle on the ground, the motor might not have enough torque to move the car, although it will be able to spin the unloaded wheels when the car is in the air.  If you weren't trying full throttle, you might want to ease the throttle on a bit more to see if the car moves or tries to move.  Only do this once you're sure the rest of the drivetrain is OK as you don't want to damage anything.

I hope that gets you started

[EvilSpike 294]

9 minutes ago, Mad Ax said:

I don't think the Terra Scorcher has a slipper clutch, so don't worry about that.  Also I don't think it has ball differentials - these can also slip if not assembled properly.

Correctamundo! The 2020 Terra Scorcher does not have a slipper clutch or ball diffs.

My guess is that you've tightened the grub screw up but not on the flat of the motor shaft. When you take the aluminium gear off the motor you should see the shaft has a flat part and a rounded part, the grub screw should be pushing against the flat part. I'd suggest thread-locking the grub screw in place too or else you'll be tigtening it up again soon.

If it's not that then I suspect it'll be you've mounted the motor in the wrong pair of holes on the aluminium motor mount and the motor gear and gearbox gear are only just meshing by the tiniest fraction. Check which holes it should be mounted in.

Good luck!

[bubblewrap 1]

27 minutes ago, Mad Ax said:

A loose pinion on the motor shaft will definitely cause the problem you describe in the first instance.  But you say you fixed that?

Is the new problem different, or the same?

Or in other words - is the "whine" you describe the same as it was when the pinion was loose, or is it a different whine now?  If it's the same then it's likely the pinion is still loose or not properly engaging.  The fact your wheels turn when in the air suggests the pinion is making contact with the spur; if it wasn't properly seated (i.e. motor mounted in an incorrect hole) I would expect a grinding or buzzing sound, i.e. not good.  Anyway, it's worth popping the motor out again and double-checking the pinion is properly tightened down and in the right place.  Sometimes if you tighten the pinion while it's very slightly off the flat, it will feel tight when assembling but pop loose the moment you apply torque to the motor.

Different whine. This is more of a high-pitched whine that makes me afraid to apply more throttle for fear of breaking some internal.

27 minutes ago, Mad Ax said:

I don't think the Terra Scorcher has a slipper clutch, so don't worry about that.  Also I don't think it has ball differentials - these can also slip if not assembled properly.

When you run the car with the wheels in the air, do all four wheels turn, and do they all turn in the same direction?  It's possible you have popped a dogbone (driveshaft) or even lost a drive cup.  Make sure the driveshafts are properly installed on all four corners.

All four wheels turn in the same direction! I did the simple test as well rolling just two wheels against a surface whilst power is off and can confirm all wheels are turning in the same direction.

27 minutes ago, Mad Ax said:

Also make sure the wheels are properly installed and the hexes are engaged on the drive pins.  It's not uncommon for a wheel nut to back off and let out a drive pin.  You'll lose drive to that wheel, and through differential action, you'll lose drive to the opposite wheel too.

As your car is 4 wheel drive, it makes more sense that this is an issue in the main transmission rather than on any particular corner, as there is no centre diff in the Terra Scorcher, so even if you lost a dogbone or drive pin on one axle, you should still get drive to the other axle, but it's worth checking every part of the transmission just in case.

Ok will check next!

27 minutes ago, Mad Ax said:

Finally, if you have been running in the wet, it's worth checking if the tyres a slipping in the wheels.  The instructions normally say to glue the tyres to the rims but lots of people skip this step and have drive problems when the wheels get wet.

No have not been running in the wet so far been indoors only.

27 minutes ago, Mad Ax said:

The ESC can emit a whining sound at partial throttle.  This is the ESC's way of varying the voltage that goes to the motor.  When you apply full throttle, there should be no whine from the ESC.  If you only apply a very small amount of throttle on the ground, the motor might not have enough torque to move the car, although it will be able to spin the unloaded wheels when the car is in the air.  If you weren't trying full throttle, you might want to ease the throttle on a bit more to see if the car moves or tries to move.  Only do this once you're sure the rest of the drivetrain is OK as you don't want to damage anything.

I hope that gets you started

I tried increasing the throttle although not full. The car does seem to want to move it makes some small movement now and again amongst the whining sound but it almost feels like something is not catching on properly?

[bubblewrap 1]

I checked that i have indeed attached the motor using the correct holes. I am using the kit provided 15T Pinion gear and this is the position per the manual.

[catman79 346]

is there a space between the pinion and the body of the motor, or is the pinion tight against it?

[bubblewrap 1]

2 minutes ago, catman79 said:

is there a space between the pinion and the body of the motor, or is the pinion tight against it?

There is a bit of a gap. Should i be pushing it all the way in? Will there be a snap/ click sound?

[catman79 346]

8 minutes ago, bubblewrap said:

There is a bit of a gap. Should i be pushing it all the way in? Will there be a snap/ click sound?

no, looks fine as it is.. 

dont suppose you can post a video of what its doing can you? will probably be easier to help if you can

[Silver-Can 402]

2 hours ago, bubblewrap said:

Took everything apart...

Daft question but are you sure you put it all back together again correctly? As others have said, definitely sounds like a main drive issue (ie something between either the motor/pinion and or rear gearbox). 

[mud4fun 1696]

It must be either missing pins from axles or motor pinion issue (either loose or not engaged - there is literally nothing else that would stop a terra scorcher from driving at least one of its wheels under power (short of catastrophic damage) if the motor is spinning because there are no centre or ball diffs. The diffs are massively strong and can take huge power hikes so unlikely to be them.

I never glue my tyres and not had an issue with tyres spinning on rims with the sort of tyres and wheels I run, even with 13T motors and 9.6v.

My money is on pinion.

I always use a tiny spot of threadlock on my pinions to ensure the grubs don't work loose. I also use higher quality allen keys to make sure they don't easily round off like the cheaper allen keys.  I really do not like the new alloy motor mount. The old steel mount was far superior and combine that with the old pinion setting tool I never had pinion issues with them.

First thing I would do is slacken the motor mount screws right off and wiggle the motor a bit to ensure the mount is properly engaged in the shaped area of the gearbox - it could (long shot) be that you've not had the mount seated properly before tightening the screws so the pinion will not be engaged on the spur. (also make sure there is not a bit of grit or gravel stuck on the gearbox where the motor mount would sit)

EDIT: A VERY LONG SHOT - you have charged the battery fully? once the battery drops charge, the ESC may allow it power the wheels when in the air but on the ground it will require more power than the ESC will allow and the ESC may whine but you'll get no drive (however in that case your motor would not spin) - is the whine coming from the transmission or the ESC?

 

[bubblewrap 1]

Thank you all for the help this has been a very pleasant introduction to the community!

@catman79 you inadvertently led me to the problem. I realised that, when i put my car back together the first time, i hadn't placed the pinion gear the required 14.5mm distance away from the motor mount.

All of you were right in that it was indeed a pinion issue. Once i fixed that the car started working on the ground again. Excuse my not having the shell on i just couldn't wait.

After about 15 mins of bashing the car stopped moving again even though the motor was spinning. I hope it's just the battery running out or some failsafe when the motor overheats? @mud4fun i will have to take your suggestion on the threadlock now i think i've solved the issue.

Thank you all again very much.

[catman79 346]

glad you got it sorted.. sounds like the pinion has come loose again though!! 

with pinions you have to cram them up as tight as you can, if your just nipping it, it'll work loose in no time, looking good though, i do love a scorcher!