Drive motor and gearing

[SteveD 2]

Hi 

I am very new to this hobby, so please don't make any assumptions I know much about this.  I have recently bought and built the Tamiya VQS (2020) off road car.  I tested the motor and the steering servo and all seemed great. I added the wheels and tested again.  The buggy steers correctly and moves forward, however it moves very slow (walking pace).  The motor seems to be working correctly.  Am I right in thinking the problem is with the differential gearing?  Can I please ask for advice on how to fault find the problem and does it require me stripping the vehicle back down?

Thanks in advance of any recommendations.

 

[Mrowka 493]

What motor and Electronic Speed Control do you have? Does the motor get hot when you run the buggy?

What pinion gear do you have in it? (The pinion gear is the gear that is attached to the motor shaft.) Assuming everything is working, you may try a numerically larger pinion gear. 

[SteveD 2]

Hi 

Thanks for your reply...

All the parts are the standard parts that came with the new "VQS" (2020 edition)

The motor is a Type 540. The ESC is a Tamiya Brushless ESC 02S TBLE-02S.

The motor doesn't get hot, but due to the current problem with speed, I haven't really run it much. Just a few straights up and down the drive.

The pinion gear came with the kit a BA26 (21T pinion gear) connected to the shaft of the motor.

The problem I have is getting to the motor to take the motor out. There is a significant number of screws and kit to strip away.  I wish they made access to the important areas a little easier.

 

[Mrowka 493]

Further assuming that your gear mesh is okay (which is probably the case if your motor isn't hot), try a taller pinion gear (assuming it will fit) and see how it works.

After you start doing it a few times, swapping out pinion gears will seem like no big deal.

[87lc2 2659]

Something is wrong if it's only moving at walking pace, stock 540 motor and gearing should be good for at least 15-20mph.  Assuming there are no odd noises coming from the gearbox or motor, what type of battery are you running?  Is it fully charged?  Sounds stupid, but it really sounds like you're just not getting sufficient voltage from the battery assuming the car was assembled properly. 

Also, on that ESC there should be three motor wires for a brushless motor.  Since you are using a brushed motor you will noyl be using 2 leads, make sure they are plugged into the proper leads as stated in the ESC manual.  

These are mostly just guesses, but there's really not much to go wrong here.  I tend to think the ESC is hooked up incorrectly or the battery is not supplying enough voltage for some reason.  The buggy should move at a pretty good pace even with the stock electronics.  

[Toad16v 282]

Have you set up the throttle points on the esc?

 

https://www.wonderlandmodels.com/blog/article/tamiya-electronic-speed-controller-setup/

[SteveD 2]

Hi

 

I haven't setup anything on the ESC. I wasn't aware that would be necessary.  The only thing I can say is the motor seems to be spinning at a very high velocity but there doesn't seem to be enough frictions between the gears to get the motor fully engaged.

 

 

[87lc2 2659]

2 minutes ago, SteveD said:

Hi

 

I haven't setup anything on the ESC. I wasn't aware that would be necessary.  The only thing I can say is the motor seems to be spinning at a very high velocity but there doesn't seem to be enough frictions between the gears to get the motor fully engaged.

 

 

Time to take the gearbox apart, something is definitely wrong or was assembled incorrectly.  I would recommend taking it apart, double checking everything per the manual and bench testing before putting it back together.  I'm not familiar with that gearbox so give any opinion on what could have been assembled wrong, but will most likely be obvious when torn down.  Good luck.

[SteveD 2]

Thanks.  Sounds like a big job.  lots of parts to take off before getting to the centre of the gear box. I thought it might come to that ;-)

 

[87lc2 2659]

Yea, it's unfortunate but hopefully it can be fixed and no damage was done.  Since you weren't hearing any grinding inside the gearbox most likely everything is OK and something was just missed or installed incorrectly.  It will be worth it once fixed, the buggy should move pretty good even with the stock motor.  

[Mad Ax 9306]

Does this buggy have ball differentials?  They are easy to assemble incorrectly if you're new to them.  They need to be fairly tight and shouldn't slip if you hold the car down and spin one wheel.  If they are set too loose, the outer gear will spin around the inner balls and wear the pressure plates.  It may be possible to tighten the ball diffs without disassembling everything - normally you remove the drive shafts from the cups,  insert a hex wrench into one side and something flat into the other to lock it up, then screw in the hex wrench to increase the pressure on the balls.

I'm assuming it doesn't have a slipper clutch, being an older model?  This is a set of springs and pressure plates around the main spur gear (the big one that the motor pinion engages with).

Also check the motor pinion itself - they easily come loose until you're used to tightening them up properly.

[MadInventor 3884]

Sounds like it might be the centre diff slipping. This is a ball diff. The other 2 are gear diffs (Assuming T haven't changed it from the original). It would explain the motor spinning at high revs but no grinding noises and the slow speed. Alternatively it might be a loose grub screw in the pinion, everything meshed ok but the motor is barely spinning the pinion. This can happen quite easily if you don't ensure the pinion grub screw is tightened down onto the flat on the motor output shaft.

 

 

[SteveD 2]

Thanks for all your help.  Managed to get the thing going.  FYI - I hadn't tightened the center differential tight enough, so it was slipping. Great to find it ;-)