Novak XRS reverse issue

[GSMnow]

I recently rebuilt one of my old trucks for my 4 year old son to learn how to drive RC. I fitted a XRS so he could reverse it, I have no ither reversing ESC's except for my Mamba Max brushless setup I race with. I have a very mild motor and slow gearing for the beginner. Current draw should not be an issue, it runs for 30 minutes on a 4200 pack.

Here is what is happening.
Forward drive is flawless, it responds great with no apparent glitching at all. The motor has the 3 caps on it, and we are at short range. When we try to back up, it does any one of 3 things.
1)some of the time it runs fine and will even spin the tires in reverse.
2)It barely moves at all then stops and the green LED just flashes.
3) it will pull backwards for a big, reach some speed, then stop very hard, like full on brakes. The green LED is flashing at this point as well.

In any case, if I let off of reverse trigger and try again, I can usually get it to go, and if it reaches any speed, it usually will keep going, but every once in a while it will lock up the brakes again.

I have a theory. I think a radio glitch may be causing the ESC to see a forward throttle setting for an instant, and the ESC is going into the reveres lockout mode until I go back to neutral again.

Has anyone seen this happen before?
.

[InspGadgt]

Have you tried resetting the ESC?

[rccardude04]

What kind of motor?
Did you check to see that the brushes aren't hanging and the effect being magnified by the negative timing in reverse?
-Eric

[timie1]

I have a futaba mc330 and it does this, ever so slightly differently, but it sounds like the same exact problem. In my instance, it's not glitching. I've tried every set of radio gear I have and also in every car I have with every different battery and motor I have, and it does it all the time. On some motors it doesn't do it as much. In my touring car it doesn't do it as much as it does in my B4 or 4wd buggy. Also, if I am in grass, or on a flat but then am reversing and it starts to approach a hill, it'll jam full brakes on just like yours.
I don't know what it is that causes it, but I do know what it isn't, and that's radio glitching. I THINK it's something to do with the current the motor pulls in reverse is too high and the esc stops. My esc only has half the amps for reverse as it does forward, but if that is the case, that's annoying cos I'm running a 19t motor on a 13t esc, so it should be able to handle it.

When it was new it did the exact same thing, so I sent it in to Futaba. They replaced it, but the new one still did it, just not quite as much. I've reset it many times to try some makeshift fix, but it's never really solved it. I've learned to live with it, but I will never ever buy a futaba ESC again because of it.

[rccardude04]

In reverse, motors pull a bit more current than they do in forwards. Another thing to remember is that your ESC probably has 4 or 5, maybe more forward drive FETs, and most likely 1-2 reverse drive FETs. They're not designed to drive around in reverse. They're designed to back away from obstacles and that's it.
The Futabas do that. Every single one does it, and there's no way around it. They're just not designed to drive in reverse. Would you rather sacrifice forward drive capability so it does a little better backwards?
-Eric

[GSMnow]

If it is a current limit issue, does the LED show anything different? Mine shows the exact same indication when it is braking from forward, Backing normally, or locking up from backing. In each case the green LED is a stead flash. It won't go steady green in reverse like it does in forward, I think due to the trigger having more forward than reverse travel. I re-did the 1 button cal, and it is the same. It is very possible a current limit as it seems to do it worse with a better battery pack. I stuck in an old crap battery and it never locked up inreverse. Dropping in an IB4200 and I could not back up, at all.

I am geared SLOW with a 30+ turn closed can Jonson electric cordless drill motor. The timing is basically zero as it pulls under 2 amps no load in forward or reverse. Wheels off the ground never acts up either, and once it is rolling good ni reverse, it seems to stay rolling just fine. It is starting backwards, which would be the highest current.

I don't want to lose forward performance, but another pair of FETS would not be THAT expensive. This thing is tiny, and has no external heat sink. It barely gets warm, even abusing it for 20 minutes (how long it took to kill an RC2400 NiCd pack) I have done the fly backwards and yank forward, and it either slips the slipper clutch or spins the tires. That drill motor has some serious torque, but it only turns 12,000 rpm. I am running 19 to 86 with a 2.55 trans, but on Masher 2000 tires. What can I say, my son likes driving in the grass.

Thanks for the suggestions. I will try to monitor current and see if it is hitting some form of limiter.

[kschauwe]

Another thing to remember is that your ESC probably has 4 or 5, maybe more forward drive FETs, and most likely 1-2 reverse drive FETs.
-Eric

Novak XRS is rated the same FWD/REV.

[rccardude04]

Well that's good to know then.
Have you bugged the novak guy who visits the forums? NovakTwo I think is his s/n?
-Eric

[InspGadgt]

Mine runs fine in reverse with a 19T...given the motor you are using it doesn't sound like there should be any issue there. How is your reciever placed in relation to the ESC? Do any of the power wires come close to the antenna wire? You might want to try hooking the motor up backwards to a battery to see if maybe it is an internal problem with the motor.

[rccardude04]

or, even better, swap the motor lead wires and see if it does well car backwards (esc forwards) and horrible forwards (esc reverse).
-Eric

[Miedin]

Slightly off topic but my XRS just caught on fire! the lights worked but forward and reversed stopped. I reset it and when I gave it throttle it lit up like a christmas tree. Now my house stinks like burnt plastic lol. oh well I got almost a year out of it.

[GSMnow]

Wow Miedin, that sucks. I have several Novak forward only ESCs that are 15 to 20 years old, and never had anything like that happen. The XRS in the ony reversing ESC I ever bought, well besides my Mamba Max which is set for forward only for racing. The only ESC failures I have had was a blown brake FET and then my 410M1c started acting odd and running hot after my stock motor threw a wind, shorted internally, and locked solid. Hard to blame that on the ESC.

[CharlieS]

The reverse isn't working consistently more then likely because of the trigger pot on the radio. I could be mistaken, but from what you have described, the revers doesn't work each and everytime.

The XRS must see the neutral for the reverse to work, if it doesn't then it won't. Often times, radios trigger pot simply doesn't return consistently, so the reverese also doesn't work consistently.

How do you fix this, simply move the trim on the TX until the LED on the ESC stays red. Flick the trigger a few times and make sure it keeps staying red.

There is no current limiter in any Novak ESCs.

Now, onto the other problems noted, Its possible that the ESC has for some reason lost a few Mosfets, so when you pass power through them, sometimes they work then they get hot and stop working. An intermittent problem based on a partial failure. If that's the case I'd simply recommend returning the ESC for service.

Thanks
Charlie@teamnovak.com

[GSMnow]

The reverse isn't working consistently more then likely because of the trigger pot on the radio. I could be mistaken, but from what you have described, the revers doesn't work each and everytime.

The XRS must see the neutral for the reverse to work, if it doesn't then it won't. Often times, radios trigger pot simply doesn't return consistently, so the reverese also doesn't work consistently.

How do you fix this, simply move the trim on the TX until the LED on the ESC stays red. Flick the trigger a few times and make sure it keeps staying red.

There is no current limiter in any Novak ESCs.

The trigger pot does not seem to be my problem. Whenever I let go fo the trigger, I get a solid red led, no problem. From stopped, when I push towards reverse, it will ALWAYS start to go backwards, but then it will stop and it seems to go to brakes. It is not consistnet and with a weaker old NiCd pack it is not a real problem and it backs up pretty much every time with no issue. When I put in my good IB4200 NiMh packs, it varies from being able to back up, without a glitch, going a foot or two then braking, or barely turning the tires a 1/4 turn and braking. Somketimes advancing the trigger to reverse slowly seems to overcome it and I can them back it out. It seems pretty consistent that my packs that put out more current are causing more trouble. The motor is a 550 or so size, but it has alot of turns, probably around 30. It is actually a Johnson closed end bell motor with an internal fan that was meant for cordless drills. The rating on it was 6 to 12 volt, 12,000 rpm at 6 volts at 1.2 amps no load. Certainly very mild, even compared to a stocker. I only have it geared to go about 10 mph too. This setup is for my 4 year old son to learn on. This is why I bought a reversing ESC so he can back it off the walls, posts, house, legs, swing set.... You get the idea. I also have the slipper clutch set so it only draws about 10 amps if you block it and rev the motor slipping the clutch. It runs about 30 minutes on the IB4200's. If it was some form of glitching from the radio, it is odd that it does not seem to do it at all in forward, only in reverse.

And this is why I am thinking, MAYBE, if the radio is getting a tiny glitch, could it be giving a single false pulse from the RX that tells the ESC forward (even a tiny amount of throttle) and then when it gets the good reverse pulse again, it is now in BRAKES from the previous forward signal???? Would just a single pulse do that?

I know my RX is not great, and I am planning on getting a new one, the range is pretty short now. TX is fine, I swap crystal with another system and this TX run the other car fine, and the other TX has the same short range on this truck. It is a very old Novak micro receiver (NER 1s I think). The Futaba one has much better range.

Gary M.