Advice needed - RC car making grinding noise (with video)

[RegiMental]

Hi all,

 

My RC car is making what can only be described as a 'grinding' noise when it changes from going reverse to forward (does not happen the other way round). I have attached a video with this post to show this.  I was wondering if any of you know what may be causing this.  I have a suspicion that it the differential, but cannot be certain.  Would appreciate any expert opinion.  The car is the Subaru Impreza that was the DeAgostini subscription from back in the 00's.

 

Appreciate any help offered.  Thanks!

[Gampla]

It's locked have you got a 2wd or 4wd

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[RegiMental]

Thanks for the reply.

 

It is a 2WD car.  when I built it initially all those years ago it made this noise and I boxed it and left it as I did not have the time to strip it and fix at the time.  However, I had it apart last week and put it back together and the noise stopped.  I have had it out for about three runs since and towards the end of the last run, the noise just started up again.  Before that, going from reverse to forward, would change the direction of the wheels instantly on the ground and it would brake/skid (as would be expected) depending on how long the stick was held forward.  Now; no skids and just the grinding noise.

 

 

Edited July 22, 2020 by RegiMental

[rob foster]

Looking at the pics it looks like the spur and pinion are not dead on..  Also the teeth look, well very small have you made sure they mesh up properly?  Does the car have a slipper clutch? 

Can you take a better pic of the rear end

[Stormbringer]

the motor also looks a bit squint as if the motor mounts bent 

[Gampla]

Take motor out turn both back wheels see if you get grinding

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[Garry]

Its a Bycmo which was a partworks magazine build in the late 90s, it was notoriously poor quality in that it came with a soft plastic pinion gear which helped in shredded everything in sight. You've done well for it to last as long as it has, some were reported to be dead after a couple of test runs. I'd put money on the mesh and/or teeth quality being the root of the sound.

[rob foster]

9 minutes ago, Garry said:

Its a Bycmo which was a partworks magazine build in the late 90s, it was notoriously poor quality in that it came with a soft plastic pinion gear which helped in shredded everything in sight. You've done well for it to last as long as it has, some were reported to be dead after a couple of test runs. I'd put money on the mesh and/or teeth quality being the root of the sound.

I would second this.   It looks to me as if there is just enough pressure to get the thing moving, but there's a definite delay which sounds like gears spinning on each other

[RegiMental]

Thanks for the replies.  I will get some more pictures together of the rear of the product and may even take the gear box (correct name?) apart to show.  However are you saying that all of the gears will be borderline useless?  If so would be good to get a spare parts recommendation if possible.  Looking at the the cogs in the diff the other day, they looked like they had been battered with a small hammer, will also try and get pics of them.  Thanks so far.

 

You are right about the motor sitting skewed, but I cannot seem to remedy that, but the motor plate sits flat when on its own.  I think that the motor sits to close to the rest of the gear box and so could trim that down I guess.

 

Edited July 22, 2020 by RegiMental

[Gampla]

Maybe look for aluminium upgrade

 

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http://sbcgb.com/Bycmo/Spare-parts?page=4

[RegiMental]

Gampla: thanks for the link

 

Thanks all for replying so far.  I managed to get time yesterday to take things apart and get some more photos which are below.  I think that all the gears seem to be seated well; would welcome opinion of others.  However please see the pictures showing the gears in the differential: They seem to be completely worn down.  I have included a picture from the instructions to show what they should look like.  With that in mind; could this be causing the problem experienced? even if not should these be replaced? further: Is this common in Diff gears?  is it a sign of my initial poor construction skill all those years ago or a sign of shoddy components?  

 

Thanks in advance!

 

Edited July 24, 2020 by RegiMental

[Stormbringer]

those diff gears are more than likely the problem

[Raul]

translated with Google translator from:  https://reparar-cochesrc.blogspot.com/2021/01/mejoras-el-bycmo-subaru-impreza-110.html

Improve  Bycmo Subaru Impreza 1/10

 

The Bycmo Subaru Impreza 1/10 is a rear-wheel drive car that was sold for the first time  from the Altaya-De Agostini publishing house in 2002; It is still sold on the Bycmo website ready to use for around 80 euros. It is a low cost and simple car that has many problems with the differential, gaps between parts, poor quality plastic, tires with little grip...

The improvements do not try to turn the car into a racing car (that would be impossible), but rather the car is more reliable and has better handling, but spending little money.
 

 

 

The chassis of the car is a 2mm rectangular aluminum panel, it has a RS540SH motor and a mechanical Speed controller. The body is very nice. I only bought the car and the transmitter, very cheap from a second hand ad.

Measurements (with bodywork): Length 450mm, Width 185mm, Height 150mm, Wheelbase 257mm
Weight (without battery) 1120 gr. Transmission ratio 8.57 Wheel diameter 63mm, Width 24mm


 

 

 

 

Assembly is easy, although some maintenance operations are more complicated than in other cars: for example, removing a front wheel and accessing the servo saver. This picture is the exploded diagram:

 

 

Chassis and exploded view                     Upper part and electronics

 

 

 

A picture of the  disassembled car:

 

 

 

 

TRANSMISSION

 

The  car I have had a problem with the pinion: it was slipping on the motor shaft because the captive screw did not thread into the plastic. I changed the pinion and put another metal one with 25 teeth and a 0.6M module

 

The rubber is to achieve the perfect pinion-crown fit

 

 

 

Another problem I had is that sometimes I lost traction because of the differential fault. To disassemble the gearbox, two screws are removed from the motor support and two other screws from the box itself below the chassis. Also removed are two bolts holding the shock tower to the box.
 

 

 

Once the spur held by an E-clip has been removed, the motor support with a screw, the transmission cups and two screws that join the two parts of the case, it looks like this:
 

 

 

A fairly easy upgrade is to replace the stock nylon bushings with ball bearings; Measurements are shown in the photo.

 

 

 

The stock gear ratio is 72/24 * 40/14 = 8.57

The RS540 motor has about 22,000 no-load rpm at 7.2V (1.9A). At a top efficiency speed of around 19,000rpm and with 64mm diameter wheels, the car's top speed would be around 28km/h.

 

 

 

The problem with the differential is that it has clearance between the parts (it does not have a good quality), sometimes the two cover screws do not tighten well and the satellites and planetary gears do not engage.
I solved it with washers on the axles of the differential, between the covers and satellites (in red in the picture).
Other times the opposite could happen and a washer would have to be placed between the axes to move them further out (in green in the picture). This could happen if the diff locks instead of slipping.

 

 

 

This is how it looks with the washers on the axles:
 

 

 

With the washers placed on the planetary shaft from the inside and well greased, the differential works well and no longer slips or noticeable gaps.

 

 

 

As a curious fact, in other countries where it was sold in installments with the De Agostini publishing house, it came with these gears:
 

 

 

 

Sometimes the car loses traction due to the captive screw in the diff tumbler coming loose. You have to put fixing screws.

 

WHEELS

Another "problem" is that the wheels have a 10mm hex instead of the usual 12mm; if you want to change wheels, you have to change hexagon.
The tire has very little grip, serious on a rear-wheel drive; It can be improved a bit if you put sponge in. Plastic bearings, it is better to replace them with 5x10 bearings.

 

 

 

To remove the front wheel, you have to insert a Phillips screwdriver to lock the axle, otherwise the axle slips when you turn the wheel nut. Adjusting the wheel is difficult because either you have it braked or it is loose.

 

 

 

This picture is the steering knuckle and the front axle:
 

 

 

 

 

WHEEL CHANGE

To replace the rear wheel with another 12mm hexagon, we simply change the hexagon for another 12mm  size and made from metal with a  5mm hole. The new pin may be thicker and we need to drill the hole in the shaft to make it a bit larger.

 

 

 

This is how it would look in the picture; it may be necessary to put thin washers between the pin and the bearing.

 

 

 

To replace the front wheel  with another one with a 12mm hexagon, it is a little more complicated given the shape and dimensions of the screw-axle and that it does not have a hole for a pin. Originally, the parts of the wheels are like this:
 

* First way : you have to file the original shaft a little to reduce the diameter from 4.1mm to 4mm. Then, we put a spacer with a 4mm hole and about 5mm in length and a 12x4mm bearing (5mm wide). It is convenient to change the plastic bearings for 10x5mm bearings (4mm or 3mm width). It may be necessary to put some washer.
 

 

* Second way:   drill the original axis to put a 12m hexagon and 4mm hole. You have to do it carefully to center the hole. You have to put two 10x5mm bearings. It may be necessary to put some washer or spacer.
 

 

 

 

* Third way:   use a Bycmo wheel shaft (or any similar size) to put a 12m hexagon with a 5mm hole. You have to put two 10x5mm bearings. It may be necessary to put some washer or spacer.

 

 

 

*  Fourth way:  use a 4mm diameter screw about 30-35mm long, a 4mm hole spacer about 5mm long and a 12x4mm bearing (5mm wide). It is convenient to change the plastic bearings for 10x5mm bearings (4mm or 3mm width). It may be necessary to put some washer.

.

 

 

 

 

 

ELECTRONICS

 

The mechanical Speed controller has 3 forward speeds and one reverse speed; It is the same as the Kyosho models, with an upper part that rotates also moving the motor cables. This can cause a jam or snag and the MSC is blocked and the car is running.

In addition, the resistors get quite hot, even more so if we choose to change to a more powerful motor. 

 

 

It is worth removing the MSC and servo and switch to an electronic Speed controller (ESC) even if it is a cheap model (WP-1040, BDESC-S10E,...): better control of the car, less reliability problems, less weight , more battery saving.
 

 

 

 

The transmitter, receiver and servos are from the Hitec brand. Specifically, it is the Hitec Ranger 2Z model that is included as a private label for some RTR car in addition to the Bycmo Subaru.

 

 

 

 

 

SUSPENSION

 

The friction shock absorber is very simple and has no adjustments; the red spring that it brings is very hard. Another softer spring will improve the car.
 

 

 

In the picture, the car with yellow spring shock absorbers and ESC; basically only toe-in adjustment can be done. The suspension arms are fixed and the wheel camber cannot be adjusted. In the front shock absorbers the angle could be varied taking advantage of the hole in the body support.

 

 

 

 

 

 

The body is very nice but the holes do not match on other Tamiya and Kyosho chassis that I have, in case I want to use it on them without making more holes.

 

 

 

 

 

SUMMARY OF THE "PROBLEMS" OF THE BYCMO SUBARU

 

* The pinion is plastic. Over time, a crack will appear and it will slip on the shaft. Change it to a metallic one.

* It has enough play in the axles of wheels,  arms, steering, etc. Put 5x10x4mm bearings on the wheel axles.

* The drive cup next to the diff tends to loosen (captive bolt) over time. Throw screwlocks.

* The differential also has play and can slip: it is solved with internal washers 

in the axes so that satellites and planetary ones so that they mesh well. The 2 differential cover bolts must be tightened strongly. It may be that the screw threads have been cross-threaded and the cap is coming loose.

If you can, put 5x10x4mm and two 6x12x5mm bearings in the gearbox.

* The tires are bad; They are grab nothing. They improve if you put sponge in the central part so that they support the entire band. You can also change them: tire measures 64x50x24

* The wheels are nice but they have the 10mm hexagon. If you change wheels to other standard ones, you have to change the hexagon for a 12mm one.

* The front wheel axle is a simple screw measuring 5mm in the bearing part and 4.1mm in the wheel part.  

By default, it has a 10mm plastic hexagon that if you press a lot, the wheel stops and if you don't press, it has play.

* The motor support has little adjustment margin to change the size of the pinion, so it would be necessary to change the pinion and crown.

* Do not put a fast speed brushless motor. They won't hold the gears or differential

* The MSC  (kyosho type), sometimes gets stuck because of the cables.

 If it catches you accelerating, it stalls and you can't brake... you have an accident... It's worth putting an ESC

* On the positive side, the transmitter, receiver and servos are Hitec brand. The motor runs a little more than 27 turns.

* If you have the yellow springs they are better for the car (the red ones are very hard).

 

Surely, I have left some other problem out there. This link is the Frequently Asked Questions for the Bycmo Subaru.