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Gebbly

GF-01 Somethings wrong?

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Hi all, I need some advice. I have finally completed the chassis build for my GF01 but I notice something which may be an issue. It may be expected behaviour but being my first build I couldnt say. If I hold the car aloft and spin one of the front wheels and let go the front wheel on the opposite side spins on the opposite direction and both wheels spin freely. This seems fine to me.

However if I spin one of the rear wheels I can feel some faint resistance. The rear wheel on the opposite side spins in the other direction correctly but I am concerned about this resistence.

As I gently rotate either of the back wheels there is a faint feeling of gearing stepping through notches, a kind of tick, tick, tick sensation as I rotate the wheel. This means the wheels dont spin as freely as the front wheels and they will stop their spin in one of these "notches" for lack of a better word. Is this normal for the rear wheels of a GF-01 or should the rear wheels spin just as freely as the fronts?

I think I may have to completely take the car apart again to look inside the gear case. :(

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It seems when I remove the motor the rear wheels spin freely and the problem goes away. Is the motor causing this? Am I mounting the motor incorrectly? I have used the Tamiya motor guard, perhaps that is causing an issue? This is odd.

Removing the motor (a Tamiya torque tuned which came with the kit) and holding it in my hand and rotating the pinion it has the same tick, tick feel as I rotate it rather than a smooth rotation is this correct or is the motor faulty? And why would I feel the motors quirk in the rear wheels and not the front given that it is 4wd?

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Hi Gebbly

I don't think it's the gearbox.

 Does the tick tick tick sensation happen when one of the dogbones moves past/rubs the notches of the drive cups?  If so it could be that your suspension is too low and so the angle of the dogbone is too tight. This causes the dogbone to rub against the edge of the drive cup and clip the notch every 180 degrees.

For fixes did you use o-rings? I can't remember if mine has them or not. Try them in or take them out and see what happens. And try holding up the car but lifting up the rear arms a little, to reduce the angle and then spin. It may be the clicking goes away. You might need to shorten the shocks to reduce the  angle of the dogbones to they don't rub on the edge.

For my modified GF01 I extended the rear wheelbase, so the dog bone angle is more extreme (as the dog bones are pushed down and backwards) and I get gentle tick or click. When I spin the front it's smooth, but on the rear I hear the clicking. The good news is that it works fine, and when driving sound and works well, it just just when held up I notice it! 

 

 

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With the motor out I held the rear up, held one of the rear wheels in place and slowly rotated the other rear wheel. During a single 360 degree rotation of the wheel it feels like something bobbles over a notch 10 times.

Holding the suspension so that the dogbones are horizontal rather than at an angle still gives the notchy feeling.

During the build I placed a single o ring in each of the gear box joint cups as described in the instructions.

7 minutes ago, Nikko85 said:

When I spin the front it's smooth, but on the rear I hear the clicking

Well at least that is consistant with what I am seeing.

Does anyone notice a notchy feeling as they rotate a motors pinion by hand? During a single 360 degree rotation of the motors pinion it feels like it goes past a notch about 6 times.

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Trying to think of a better way to explain the feeling its like when I rotate the middle wheel of my mouse, it sort of bobbles over notches as I rotate the mouse.

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I also notice that, with the motor out, if I hold the car aloft and gently rotate one of the rear wheels WITHOUT holding the other rear wheel stationary both rear wheels rotate in the same direction perfectly smoothly. Could it be some limited slip diff thing going on?

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https://www.msuk-forum.co.uk/forums/topic/223537-smooth-or-notchy/

"The more poles and slots a motor has, the more resistance ( notchy ) feeling a motor will have, since every time a pole on the magnet crosses over a slot it creates resistance.

So a 4 pole 18 slot motor will have more resistance than a 2 pole 10 slot, as more magnets pass over more slots in one rotation of the motor"

Sounds like a reasonable explanation for the notchy feeling of the motor. Strange that, when installed, I only feel it in the rear wheels and not front though.

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@Gebbly What you describe seems normal to me (given I understood what you posted).  

These motors have a clicking sensation when manually turned due to the magnets working against and for for the heavy metal on the rotor.  

The slight resistance you are feeling while the motor is installed, rear wheels off the ground spinning in opposite directions is also normal especially if you used any kind of thick grease or diff putty.   

Also note that things will loosen up after some break in.    

Have fun with your new car!  :D 

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14 hours ago, Gebbly said:

I also notice that, with the motor out, if I hold the car aloft and gently rotate one of the rear wheels WITHOUT holding the other rear wheel stationary both rear wheels rotate in the same direction perfectly smoothly. Could it be some limited slip diff thing going on?

That's very common. Without the motor there is zero resistance against the gears so they free spin. Adding a motor increases resistance  so the diff engages instead. 

 

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It is just the motor magnets. This "problem" is even more pronounced with my Thunder Dragon (not known for smooth quiet transmission) and a TZ (in fact any Zs) motor. 

Also, being brand new, the gears need a little time to "bed in". 

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2 hours ago, Gebbly said:

With the motor out I held the rear up, held one of the rear wheels in place and slowly rotated the other rear wheel. During a single 360 degree rotation of the wheel it feels like something bobbles over a notch 10 times.

With no motor installed, 10 notches in a complete rotation rules out dogbone issues, as they would result in 4 notches in a complete rotation. 10 notches indicates an issue inside the rear differential, where the small spider gears rotate significantly faster than the wheels when the diff is in action.

You will probably find that a small piece of moulding flash on one of the spider gears is causing the issue. A careful check followed by removal of the offending imperfection with a small file should set you right. 

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I guess tomorrow I'm taking the whole chassis apart again to get into the rear diff and see if I can track down the fault. Darn.

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1 hour ago, Gebbly said:

I guess tomorrow I'm taking the whole chassis apart again to get into the rear diff and see if I can track down the fault. Darn.

Frustrating I know, but once it is sorted, you shouldn't need to do anything like that again for a long time to come. I have Tamiya gear diffs of that design that have had literally years of use and are still functioning just as well as the day they were assembled. 

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3 hours ago, TurnipJF said:

Frustrating I know, but once it is sorted, you shouldn't need to do anything like that again for a long time to come. I have Tamiya gear diffs of that design that have had literally years of use and are still functioning just as well as the day they were assembled. 

I'll second that - I run multiple cars with these diffs and I've broken one (out of 6) in 5+ years. I run 2S plus a 12T motor so they get pushed.

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Sounds like a diff issue with that many clicks. Apologies, it sounded very much like my drive up issue! 

If you are spinning one rear wheel and the other is going to other way the motor won't be in play, other than to provide enough resistance to engage the diff so I doubt it's the motor. If the motor was going the front wheels would be moving too.

Open it up and have a look I think @TurnipJF is spot on. When you do open up also ensure that the bearings that the diff cups sit in are pushed firmly into the chassis, I had that error on my GF01 and I really needed to push them in hard, as they were sitting 0.2 mm proud, causing diff issues too.

Once you get it going it's a very very tough chassis, and runs pretty trouble free. I've got two of them, and they are great little cars! 

 

 

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Right then, stage one complete. I have stripped everything off the chassis box and whilst holding one gear box joint cup stationary and turning the other side there is a real notchy feeling. Having dogbones/o rings/wheels and tires connected if anything muted the notchy feeling to some extent.

Next step, open the chassis box and try with just the wheel diff and 2 gear box joints removed.

....

Removing the gear diff from the chassis all of a sudden the gear joints are lovely and smooth. Putting it back in the chassis I notice thatas I slowly put the chassis screws in, after just a few turns of each of the 3 rear most screws the diff is still smooth. Once I have tightened the 3 rear most chassis screws the diff becomes very notchy. Somehow when the chassis is tightly closed it is causing the diff to become unpleasantly grindy/notchy. Loosen the chassis screws and the diff once more becomes smooth.

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2 hours ago, Nikko85 said:

ensure that the bearings that the diff cups sit in are pushed firmly into the chassis, I had that error on my GF01 and I really needed to push them in hard, as they were sitting 0.2 mm proud,

GOT IT!

I had used the bearings hop up. The 2 rear most bearings inside the chassis were a tiny bit proud (sticking into the chassis cavity about 1mm). I thought I had pushed them all the way in but when I put one thumb against a bearing and the other hand on the outside of the chassis and pushed with all my strength there was a sudden CLICK as the bearing moved a tiny bit more into the chassis casing and now the rear spins really smoothly. If anything its even smoother than the front but I cant get the front bearings to shift any further. I'll have another go at the front bearings as this defintely seems to be the issue.

Thanks for all the brilliant suggestions everyone!

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Just now, Gebbly said:

GOT IT!

I had used the bearings hop up. The 2 rear most bearings inside the chassis were a tiny bit proud (sticking into the chassis cavity about 1mm). I thought I had pushed them all the way in but when I put one thumb against a bearing and the other hand on the outside of the chassis and pushed with all my strength there was a sudden CLICK as the bearing moved a tiny bit more into the chassis casing and now the rear spins really smoothly. If anything its even smoother than the front but I cant get the front bearings to shift any further. I'll have another go at the front bearings as this defintely seems to be the issue.

Thanks for all the brilliant suggestions everyone!

Great news! The reason I thought it might be this (as one of the options) was that it happened to me too. 

 

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Turns out the rear notching is solved but the front fainter notching goes deeper. The bearings are seated correctly and when I remove the front diff and put the 2 bearing joints in directly and turn by hand there is still some resistance and a faint notch. Looks like the front diff has to be opened.

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Well this first "simple" build is certainly proving to be an education.

14 hours ago, TurnipJF said:

probably find that a small piece of moulding flash on one of the spider gears is causing the issue.

So the rear diff was the bearings not seated sufficiently but it turns out inside the front diff one of the spider gears when it rotates has a notch to it. Now I need to clean the grease off and find out where the notch is.

.....

Its not the spider gear itself but the star shaft it sits on. There is a tiny knobbly imperfection in the surface of the hub part that the spider gear rubs against. Not sure how to deal with that. Is the metal soft enough that a craft knife could cut it off or an emery board could file it off?

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45 minutes ago, Gebbly said:

Is the metal soft enough that a craft knife could cut it off or an emery board could file it off?

A metal (steel) hobby file will grind that down. 

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Also found some tiiiiiny imperfections on a couple of the spider gears. Cleaned those off and finally both gear diffs are running smoothly.....now I just have to put everything back together again :)

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7 minutes ago, Gebbly said:

Also found some tiiiiiny imperfections on a couple of the spider gears. Cleaned those off and finally both gear diffs are running smoothly.....now I just have to put everything back together again :)

Glad you got to the bottom of the issue. The good news is that once you've put your first GF01 together each build gets quicker and quicker! really nothing too complex involved so you should be back up and running in no time.

And, like said previously, you should now get plenty of miles of reliable fun out of it! 

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2 hours ago, GeeWings said:

your first GF01 together each build gets quicker

Having put a WR-02CB (kind of half a GF-01?) together recently, I actually find it slightly more tricky compared to regular sized chassis (other than that M-06 mess), probably due to it being so compact and everything squeezed together in a smaller space. Not difficult for sure, just a little trickier. I actually think I seen a review saying the same thing. 

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3 hours ago, Gebbly said:

Also found some tiiiiiny imperfections on a couple of the spider gears. Cleaned those off and finally both gear diffs are running smoothly.....now I just have to put everything back together again :)

You’re going to be a pro real quick!!  :lol:

GL with the rest of your build.  Is this the LandCruiser red body or custom color?  

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