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Replica101

Gravel Hound problem

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Hi all. I have a Tamiya Gravel Hound DF-02 that has been packed away for a while. I recently had a bit of spare time and after eagerly charging all the batteries and getting excited about racing it around the park, I switched it on and realized that it had a problem. I’m sort of a newbie to RC cars from a technical perspective (although I bought my first Tamiya more than 20 years ago!) so I’m hoping someone here might be able to diagnose it for me. Also, that high pitched whiny noise - what’s that all about?? It’s always been there but it bugs the badword out of me! Here’s a video of the car, lurching:

Appreciate any help you can offer!

Cheers

 

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That high pitched whining sound is what brushless motors do at minimum throttle. Not sure why, but it's normal.

What throttle position is it in when it's lurching?

If it's less throttle input than when it's whining (and moving), could be a sensor wire issue.

 

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Only when I do full throttle. I can squeeze it really gently and it’ll go without surging, albeit really slowly of course. 

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Do you have any kind of low voltage protection on it?

What batteries are you running?

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I’m not aware of any low voltage protection. Here’s a shot of the inside - the battery is pretty basic, but it’s been in the for a long time now. 

F8D604C9-57CC-4BFC-B55A-9203CE51D544.jpeg

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Hmm, you're running a brushed motor, NiMH battery and AM radio.

Forget everything I just said :lol:

I had the same issue a long while ago with an old Kyosho ZX5 with analogue radio.

Not sure exactly what the problem was, but had something to do with the radio or the receiver.

Changed it out with 2.4GHz and problem solved.

Do you have another radio set, or can borrow one to check if that is the problem?

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Looks like a Tamiya TEU-101BK speedo.  Very common and usually run well (I've had dozens and never broken one but I know others haven't been so lucky).  That whining noise is quite normal - to adjust the speed electronically, the speed controller 'pulses' the current to the motor very rapidly.  This creates the whining sound.  Learn to ignore it, it's not going to go away.

Now as for what's wrong with it - could be a variety of things, but the phrase "packed away for a while" and "eagerly charged all the batteries" throw up some warnings - how old are those batteries?  Did you fast-charge them or trickle them?  If they've been sat for a while then they might have got badly out of balance.  Your fast charger may well detect a peak in a single cell before the others are charged, which means you'll have one charged cell but not enough voltage to operate the motor.  When you try to go full throttle, the voltage drops and the ESC cuts off.  I don't recall exactly what the 101 does when the voltage drops (it doesn't have a safety cut-off like later LiPo-safe ESCs) but at some point it won't have enough current to operate.

So - first thing, if you have another battery or five, try them and see if you get better results.  Also try running it with the wheels off the ground and see if it will run longer / faster.  Less load on the wheels = less current draw = should run longer and/or faster before shutting off, if it's a battery issue.

Try slow charging your batteries or looking up some advice on reviving old NiMHs.  In my experience once NiMH batteries are past their best they don't recover well, but some people have better results.

Check the terminals in the battery and ESC - those Tamiya connectors are quite bad, they overheat and burn, leading to bad connections and poor performance.

Having said that, your steering servo seems to have plenty of speed, so it might not be a battery issue.

Another thing you could try (ideally with the car propped on a tub or something so the wheels aren't on the ground) is to swap the steering and ESC plugs in the receiver.  This won't 'fix' anything, but it lets you test the throttle lever by watching the servo move.  If the servo doesn't move smoothly when you operate the throttle lever then you have a radio problem.  If the servo moves fine but the ESC doesn't respond correctly to the steering channel then you have an ESC/battery problem.

Another thing to try - IIRC the 101 needs to be calibrated to your radio.  It could operate incorrectly if it's not calibrated.  Follow the setup instructions here:

https://www.tamiyausa.com/media/files/45029ml-955-8787.pdf

Let us know if that gets you anywhere :)

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I did replace the stock motor a long time ago with this one - if you have suggestions for a better (faster) one that would work for this car, then I am all ears! I don’t have access to another radio set, unfortunately. I’m willing to start replacing parts in order to fix it - I just don’t know which I should replace first. Maybe the battery? 

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Thanks everyone for the in-depth answers and advice. I took the ESC apart and checked that all the connections looks good, and went through the calibration per the manual, as suggested. Interestingly, it does run better when the wheels aren’t touching the ground, perhaps pointing towards a battery that’s not holding its charge fully? I think I might start by purchasing a new 7.2V and see if that fixes the issue (I really should get myself one anyway!). Any recommendations on a good battery? 

Thanks again. 

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Also, there was a question about what charger I use. I have this one, which I seem to remember was pretty much the cheapest option when I bought my car :-) 

351CFFA4-8703-4DF4-8050-9672E0A91D3B.jpeg

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I remember the time when the noise was bugging the living daylights out of me.  

Getting old took care of it.  lol... :D  Now that I'm in the middle of my 40's, I cannot hear above 15,000hz.  If your ears are newer model than mine, you'd hear higher pitch too.  But the trigger whine is normal.  

I figure it's something like transformer making noise.  Just like @Mad Ax said, ESCs chop electricity down.  At slow speed, it could be like 20 hz (20 squirts of electricity).  Your motor gets more hits of electricity like 30, 40, 50, 60 times per second, as it gets faster.  Until the power is continuously supplied at maximum speed.  I am wondering that it could be the motor that's making the noise.  Not at the powered time, but at the lull between power.  Because when it's full power, you don't hear the whine.  (or is it because of the motor and gear noise?)  But it could be ESC too.  

<Bearings> IF you haven't done it, I would recommend full ball bearings.  Full bearings can add 15% to everything.  15% faster acceleration, 15% faster top speed, 15% longer battery run time. (roughly speaking. In reality, it's anywhere between 12-18%)   5x11x4m bearings are like $3 for ten.   I think Gravel Hound comes with few 1280 bearings and 1150 bearings?  Maybe ten more bearings would cover the rest.  There is no other $3 upgrade that can get you 15% improvement across the board.  

https://www.ebay.com/itm/10pcs-685-5x11x4mm-Open-Miniature-Bearings-ball-Mini-Hand-Bearing-Spinner/132141882994?hash=item1ec4451e72:g:iZQAAOSwTM5Y22J~

<Radio>  AM radios are fine.  They are old, but quite reliable.  

<Motor> Your ESC's max is Sport Tuned.  Super Stock motors are faster, but your ESC will blow up.  You need to upgrade your ESC.  If you are going to upgrade the ESC, you may just go for a brushless for the same price.  About $40 for a brushless motor and another $40 for an ESC. 

There are 2 kinds of brushlesses: sensored and sensorless.  Sensored is a refined version.  Smoother lower RPM, no "cogging" hesitation at lower RPM.  Sensorless is a rougher version, where the ESC does not get any feedback from the motor.  If you just gun it without hovering at lower RPM, sensorless would be better, as they tend to be waterproof. You don't always get the cogging problem either.  Many ESCs have loud fans, and I found them a lot more annoying than brushed ESC's whine.  

Personally, though, most of mine mount Sport Tuned.  It's not that I haven't tried faster motors, just that to me, Sport Tuned has the best balance of speed/control for my ability. (Also I never liked my buggies ramming into things at 60kmh)  Also, beyond Sport Tuned, some soldering would be required.  But everybody has to try a faster motor to know their limits.  Your limit might be 5.5t, who knows.  

<Battery>  NiMH is fine, but I would cycle it.  Full charge, discharge, cooling in between, repeat that 4-5 times. The battery will be as good as it can get.  Don't discharge to 0v.  That's not good.  Noticeably weak would do.  

 

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As others have already said, the whining noise is caused by the way that the electronic speed controller modulates the car's speed at partial throttle. Although the signal is generated by the speed controller, the noise is actually coming from the motor.

Interestingly, the beeps that the speed controller makes when powering on are also created via the motor, which acts as a speaker in a way. For a long time I thought that there was some sort of buzzer built into the speed controller itself, but no, it makes beeping noises by sending high frequency low power signals to the motor, making the armature vibrate at a a pitch that we hear as a beeping sound.

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43 minutes ago, Replica101 said:

Also, there was a question about what charger I use. I have this one, which I seem to remember was pretty much the cheapest option when I bought my car :-) 

351CFFA4-8703-4DF4-8050-9672E0A91D3B.jpeg

Ouch! Those chargers are notorious for killing batteries, as they have no way of telling how full the battery is, and just carry on jamming power into it until the timer runs down even if the battery is full to bursting already.

Pretty much any charger with a peak detect function will be better than the one you have. If there is any chance of upgrading to lipo in the future, a multi chemistry battery charger would be a good idea, as it can charge many different kinds of batteries including nickel metal hydride and lithium polymer.

Personally I like Overlander chargers. This is the one I use:

https://www.modelsport.co.uk/overlander-rc6-vsr-80watt-7a-output-ac-dc-lipo-balance-charger/rc-car-products/408440

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So based on the advice from the forum, I think the first thing I’ll try is to buy a couple of new batteries and a lipo charger. Thankfully parts for this car are pretty cheap! It now looks as though another problem has appeared - the ESC is flashing constantly and not responding to anything that I do. So I may just buy a new ESC while I’m at it. Would it be best to buy the same exact model, or is there a better version? 

@Juggular is that seriously all I need to replace all of the bearings in my car? Just $2 worth of bearings?? That’s awesome!

Thanks again, this is the best forum!

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4 minutes ago, Replica101 said:

The ESC is flashing constantly and not responding to anything that I do. So I may just buy a new ESC while I’m at it. Would it be best to buy the same exact model, or is there a better version? 

Chances are that it is a radio issue rather than an ESC issue as the TEU-101BK is pretty reliable, but if you do need to replace it, the Quicrun 1060 is the current ESC of choice for brushed motors.

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17 minutes ago, TurnipJF said:

Chances are that it is a radio issue rather than an ESC issue as the TEU-101BK is pretty reliable, but if you do need to replace it, the Quicrun 1060 is the current ESC of choice for brushed motors.

Thanks @TurnipJF  - wonder why this radio issue has suddenly appeared?! 

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21 minutes ago, Replica101 said:

Thanks @TurnipJF  - wonder why this radio issue has suddenly appeared?! 

Receiver connections are often to blame. With the openings for the plugs and crystal pointing upwards, dust and debris can enter and settle in the casing.

Unplugging everything, unclipping and opening the receiver casing, giving the PCB a good cleaning and then putting it all back together again is not a bad idea.

Also check that the crystals in your receiver and transmitter are plugged in securely, and that the "legs" are not loose in the crystals casing. 

 

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1 hour ago, Replica101 said:

@Juggular is that seriously all I need to replace all of the bearings in my car? Just $2 worth of bearings?? That’s awesome!

That's up to you.  Adding bearings is a good starting point.  

If you go with LiPo, spend $3 and get yourself a Lipo fireproof bag.  It doesn't happen often, but it could catch fire.  Modern chargers are kinder on the batteries.  Most are Lipo, LiFe, Li-ion, NiMH, NiCd capable too. (Still, fireproof bag is a good idea)  "iMax B6" is popular, but the charger Turnip linked has 7A.  That would charge faster than iMax B6 with an internal power supply of 5A.   

<Flashing lights>  You could reset the ESC.  You can follow the instruction below.  Most ESCs do it automatically:  you plug it, pull and push.  Voila, you are done.   But not TEU-101BK.  It asks you to actively push the button long at neutral, once at full throttle and one last time at full reverse.  https://www.tamiyausa.com/media/files/45029ml-955-8787.pdf  At least, it's not that hard. 

 

If you get bored with Sport Tuned, all 3 options below should give you similar speeds.    

[Option 1]  As mentioned, Hobbywing Quicrun 1060 is like the standard ESC for brushed motors.  You can get one for about $20.  It will allow you to use faster motors like Super Stock BZ, TZ, RZ.  I don't think there is big difference between different Zs, but I don't own any to compare.  Super Stock motors can be found for about $45, which is just as expensive as brushless motors.  Super Stock are good motors, but they are brushed motors.  5-10 hours later, you have to replace brushes.  Less efficient in terms of power consumption.  

[Option 2]  There are sensorless brushless combos.  I would recommend at least 60A ESC.  40A won't do you any good.  60A and about 3000-3300kv would give you a step up from Sport Tuned.  Close to Super Stock.  Get one with 3650 sized motor.  Smaller motors don't have the torque, bigger 3660 motors can set smaller 40A ESCs on fire in a second, even 60A (also 3660 may not fit your pinion gears).  The cheap combos should cost you about $45.  So this would be cheaper than Super Stock + Quicrun 1060.  Definitely more efficient and just as powerful, but these are relatively cheaply made.  Robust and waterproof, but ESC fan is loud and there could be cogging issues at low speed.    

[Option 3]  Sensored brushless motors.  Sensored motors have ".5t" at the end.  Like 15.5t, 13.5t, 10.5t, 8.5t.  They are turns, only sensored motors have .5t turns.   Tamiya TBLE02S ESC can handle 17.5t, 15.5t and 13.5t.  But 17.5t is similar to the silver can.  TBLE02S ESC can be found for about $25.  But 13.5t is the limit (about $40).  It cannot run 10.5t, 8.5t which are much faster.  But TBLE02S with 13.5t motor is a popular combination.  I like it because it doesn't come with a loud fan (unlike option #2).  It should be close to 3000kv, and similar to Super Stock.  If you want to leave an option for even stronger motor than 13.5t, you should spend $40 and get Quicrun 10BL120 ESC, instead of Tamiya TBLE02S.  If you get that you can even run a hot motor like 8.5t (5000kv. It can give you about 200% RPM of Sport Tuned -- that's just too fast for myself, which is why I stick with 13.5t).  

 

All this is for later.  Try resetting your ESC.  If you want more speed, sky is the limit.  

 

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To hijack this thread slightly. I got a couple of gravel hounds of Ebay a couple of weeks ago, both had rear tyres perished but other than that in working order. Tyres arrived yesterday and I had new bearings for both so set about getting them running today. 

First car no problem but the second one I'm having trouble with. When I push forward or back I can hear the motor revving however the wheels hardly move, the car jolts forward and backward intermittently.

Took it slightly apart and exposed the motor, if I run the motor on it's own with no other cogs attached it runs freely as it should, however when all the gears are in situ, nothing really driving. 

Didn't get much time to look any further into it as I had an anxious 10 year old waiting to have a go of the other car. Any ideas what to look at before I start pulling it apart again? 

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1 hour ago, enjay said:

To hijack this thread slightly. I got a couple of gravel hounds of Ebay a couple of weeks ago, both had rear tyres perished but other than that in working order. Tyres arrived yesterday and I had new bearings for both so set about getting them running today. 

First car no problem but the second one I'm having trouble with. When I push forward or back I can hear the motor revving however the wheels hardly move, the car jolts forward and backward intermittently.

Took it slightly apart and exposed the motor, if I run the motor on it's own with no other cogs attached it runs freely as it should, however when all the gears are in situ, nothing really driving. 

Didn't get much time to look any further into it as I had an anxious 10 year old waiting to have a go of the other car. Any ideas what to look at before I start pulling it apart again? 

When you say the car jolts, do you mean that when you try to drive forwards or reverse, there is a jolt and then no further progress? Check one of the differentials isn't installed backwards - that would cause the front wheels to try to turn in the opposite direction to the rear wheels, and it won't go anywhere. If you hold it in the air when you press the throttle, wheels should turn.

Otherwise, if you mean that the motor sounds like it is spinning freely (as if it's removed from the car), then either the motor spur/pinion gears aren't meshing properly (motor mounted to wrong holes on the motor mount?), one or more gears have broken teeth, or something in the drivetrain isn't assembled properly. 

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Battery is shot. Not enough voltage for receiver etc so esc cuts power to motor so car doesn't run away out of control

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