Motor cut out on accelerating, tt02b, neo scorcher

[Reliver]

I hope you guys  dont mind me asking you more questions.

Recently bought a neoscorcher and managed to trash my esc as a part broke off the motor.

Bought a new esc and motor and the car cuts out on accelerating.

Not sure what the issue is but I read a post about disabling the low voltage protection if you are using a Nimh battery. @Hobbimaster

Disabling the low voltage protect seems to work. 

I wonder if anyone could supply more detail here?  Will it be ok to do this?  

Should I have had to do this or is there likely another issue?

[checked all connections etc.. and all seems ok]

[TurnipJF]

There are three main battery chemistries in use these days - LiPo, NiMH and LiFe.

Most of us in the Western world are familiar with the first two, but Tamiya for some reason have decided to standardise their ESC low voltage cutoffs (LVCs) on LiFe - the least common one.

Each chemistry has a different minimum safe voltage. LiPo is the highest, then comes LiFe, then comes NiMH.

So, a standard Tamiya ESC's LVC is too low for LiPo, hence the recomendation to use an external LiPo alarm with them.

However the LVC is also too high for NiMH. This won't do any harm, as the ESC cuts out before the battery is in any danger. However it also sometimes has the frustrating side effect that you are experiencing, with the LVC activating prematurely. The solution, as you are already aware, is to turn it off. Either that, or alter your gearing and/or motor choice so that the current draw is not as close to the borderline. This will give you greater runtime but less performance.

Hope this helps!

[Reliver]

15 minutes ago, TurnipJF said:

There are three main battery chemistries in use these days - LiPo, NiMH and LiFe.

Most of use in the Western world are familiar with the first two, but Tamiya for some reason have decided to standardise their low voltage cutoffs (LVCs) on LiFe - the least common one.

Each chemistry has a different minimum safe voltage. LiPo is the highest, then comes LiFe, then comes NiMH.

So, a standard Tamiya ESC's LVC is too low for LiPo, hence the recomendation to use an external LiPo alarm with them.

However the LVC is also too high for NiMH. This won't do any harm, as the ESC cuts out before the battery is in any danger. However it also sometimes has the frustrating side effect that you are experiencing, with the LVC activating prematurely. The solution, as you are already aware, is to turn it off. Either that, or alter your gearing and/or motor choice so that the current draw is not as close to the borderline. This will give you greater runtime but less performance.

Hope this helps!

 

Thanks Turnip. That makes a lot of sense. 

When you say the other solution is to alter the gearing, do you mean a lower gearing {high ratio}?

How is the LVC related to the current?

Thanks

Alun

 

[Juggular]

I thought of the capacitor banks @Nicadraus posted the other day. If the ESC cuts off on acceleration, the motor might be drawing more than what ESC is holding?  Capacitors store, so wouldn't that help, I wonder?  (Then again, it just dawned on me that when the motor draws more than it's holding, LVC might activate too? Which means this is just another side of the same coin?)   Of course, lowering gear ratio means the motor wouldn't have to draw so much amp.  So ESC could supply steady current.   

[Reliver]

Thanks Juggular! Not sure I fully understand the above though.

Just to clarify what I experienced.  The car is stock build neo scorcher and was working fine.  Then after 15 mins it would accelerate for a few seconds then cut cut out before max speed reached .  If I accelerated gradually, it seems to get to top speed. Although after 5 more mins it wouldn't even do that. Does that sound like LVC?

[Rb4276]

Check the brushes they may not be laying right. I had the same issue with both a superstock bz and rz. I thought it was the esc to god knows what. Someone told me to check the brushes and i took them out. After that no issues. Supposedly it happens after from crashes or just banging around 

[TurnipJF]

1 hour ago, Reliver said:

 

Thanks Turnip. That makes a lot of sense. 

When you say the other solution is to alter the gearing, do you mean a lower gearing {high ratio}?

How is the LVC related to the current?

Thanks

Alun

 

To alter the gearing so that the motor has an easier time of it and draws less current, you would increase the spur size or decrease the pinion size, the latter of which is the easier option.

Current draw causes voltage drop, voltage is measured by the LVC. Hence when the motor draws enough current to drop the voltage below the LVC threshold, the car cuts out.

[TurnipJF]

50 minutes ago, Reliver said:

Thanks Juggular! Not sure I fully understand the above though.

Just to clarify what I experienced.  The car is stock build neo scorcher and was working fine.  Then after 15 mins it would accelerate for a few seconds then cut cut out before max speed reached .  If I accelerated gradually, it seems to get to top speed. Although after 5 more mins it wouldn't even do that. Does that sound like LVC?

That sounds like a flat battery!

When the battery charge is getting low, the voltage drops off too, and when the car is asked to accelerate hard, the current draw drops the voltage below the LVC threshold. Accelerating more gently draws less current, hence being able to do so even with a flattish battery. When the battery is getting proper flat, even gentle acceleration is enough to trigger the LVC.

If it happens right off the bat with a fresh battery, then perhaps your gear ratios need attention. However if it is only happening after 15 to 20 minutes, maybe all you need to do is charge the battery more often?

[Juggular]

Yes, 15 minutes is a long time.  It could be that the battery is running low.  Do you notice that the speed is not as fast as when fully charged when it cuts off?  

What's the specs on the motor and the battery?  

P.S. Capacitor bank is a temporary storage of energy. Think of it as a mini battery that could supply fraction of a second's worth of current. When there is a sudden drop in the current, it gives that tiny bit of extra energy, so the ESC would not cut off.  It's like a little snack when the dinner is going to be late, so to speak.  

 

[Reliver]

Thanks All.  Really appreciate the explanations too, that really helps. This forum is literally the best forum I have ever been on by far!

It is a stock neo scorcher.

Motor Tamiya torque Mabuchi RS-540, tble-02s esc, NImh 4600.

Before my last motor bust, it would last about 30 mins. And when the battery went flat wouldnt cut out like this.

I will take out again today and see what happens.  I have taken off the LV protection. Given the lockdown we need to walk a way with my son to get to a good place...hope he'll get some  more run time today.

 

 

[TurnipJF]

5 hours ago, Reliver said:

Thanks All.  Really appreciate the explanations too, that really helps. This forum is literally the best forum I have ever been on by far!

It is a stock neo scorcher.

Motor Tamiya torque Mabuchi RS-540, tble-02s esc, NImh 4600.

Before my last motor bust, it would last about 30 mins. And when the battery went flat wouldnt cut out like this.

I will take out again today and see what happens.  I have taken off the LV protection. Given the lockdown we need to walk a way with my son to get to a good place...hope he'll get some  more run time today.

 

 

While 15 to 20 minutes isn't bad, 30 minutes is better, and there are a few things that could be affecting your runtime which you may want to consider.

So if I understand correctly, something happened to your old motor that required both it and your ESC to be replaced? Could you perhaps go into more detail? If it involved shorting or otherwise overloading the battery in any way, it may have harmed one or more of the cells, reducing its capacity. Does your charger give any indication of how much charge it is putting into the pack?

There is also the possibility that something mechanical may have occurred during the incident that has increased the friction in the drivetrain, causing runtime to decrease. Could whatever damaged your motor also have bent any shafts or have caused any misalignments?

You also mention that it is a stock Neo Scorcher. How stock is "stock"? Does this mean that you are still using the stock bushings? If so, runtime is likely to go down the more you use the car, as the bushings get dirtier and more draggy. This will happen to bearings too eventually, but if you fit ones with rubber seals, it takes far longer.

There are also behavioural issues that may be at play. As whoever is driving the car becomes more confident, they are likely to be accelerating harder and spending more time at full throttle, meaning that even with no mechanical or electronic issues at all, runtimes are likely to be less now than they were at the beginning.

[Reliver]

HI @TurnipJF.  Apologies for the delay in replying, thanks so much for you help.

I took it out yesterday and seemed to work all good and altering the LVC has helped a lot.  I think the issue was a combination of the battery having lost some charge before use and also the LVC cutting in too early

Currently stock for me means, literally with just the original things from the shop. Actually tell a lie, I have upgraded the motor mount for a metal fastrax one as previously the motor was overheating and eventually broke and broke the esc. 

It all seems ok now.  

Thanks for the idea about the bushings.  If you have a sec, can you drop me a link about what ones you mean?

Thanks again.

 

 

[TurnipJF]

1 hour ago, Reliver said:

Thanks for the idea about the bushings.  If you have a sec, can you drop me a link about what ones you mean?

Sure, here you go:

https://www.rcbearings.co.uk/index.php?route=product/product&product_id=1325

At the bottom, you'll see that you can select metal or rubber seals. Metal ones have slightly less friction so are a good choice for indoor racers where performance is paramount and protection is less of a priority. However rubber ones provide better protection, so are preferred for outdoor/off-road use where dirt and dust might otherwise get into the bearings and cause them to seize or wear prematurely. 

[Reliver]

Absolute legend.  Thanks!