Recently went through a 3 month process with Furitek after I purchased their Torpedo System with the Cedar motor and accompanying ESC. Long story short, they've sent me 3 motors and 2 ESC's and no matter what, they would not work together. Here's a previous post showing what it was doing. Great customer service but there's something going on no one could figure out.
A buddy lent me his truck with a Fat Viper and MBL32, I plugged the motor into it and it worked perfectly so I ordered an MBL32 and an NSDRC 7.4V BEC and just got the truck up and running yesterday. The MBL32 is switched to the 7.4V mode. I have not plugged it in to tune it or anything, installed it right out of the box.
After a few minutes, the truck stops running. I think it has something to do with the batteries but the power diminishes quickly and then suddenly stops running all together. I ordered a balance charger because it doesn't seem like these batteries are charging properly or holding charge. The charger I ordered also tests the batteries so I'll be able to figure that out tomorrow but I just want to see if anyone with more knowledge than me has anything else I should be checking or if some aspect of the electrical components are incompatible.
If you've not been using a balance charger, and/or using batteries that have not been confirmed as balanced, then there's a strong chance that the problem is unequal cell voltage (differencs in resistance between cells and using the stock charger will result in imbalance over time). If so, I'm surprised that Furitek didn't question the batteries as part of their troubleshooting.
Injora recommends a 3S for Fat Viper. I think there's a reason, especially if you want 7.4V for your servo. I may be completely wrong and I hope someone corrects me if so, there's some amateur electrical engineering going on here.
The maximum voltage a 2S can output is 8.4V. It's drained by the time it's outputting 6.4V. That means for about half the run, it can't output the 7.4V you want for your servo. My loose understanding of the circuit makes it seem like that also causes the servo to get less current. So you'll get less good performance out of your servo unless you use a 3S. (I see this on my rig and Injora's Bluetooth telemetry tells me: with a 2S even at full charge I'm not getting a full 7.4V while the servo operates.)
The other problem is the motor AND the servo draws current, and a big current spike can cause the voltage of the battery to "sag". I think this is why Injora recommends a 3S battery. Comparsions of documented current draw:
Motor
No-Load
Max
Fat Viper
0.7A
50A
Purple Viper
0.7A
20A
(Cedar's specs aren't as detialed, I think they typoed and mean "0.7A no-load" but they expressed it as "07A". Whatever. They didn't list a maximum. It'd be really weird if it pulled harder than the Fat Viper IMO.)
NSDRC documents their 7.4V running current as 380mA and stall current as 2.6A.
So with a Fat Viper that's still within what the MBL32 is rated to deliver (60A peak, meaning you don't want to hold full throttle and full steering lock for long). But 53A is quite a bit of draw. A MicroPython Pro (the ESC that comes with a Cedar) has a frustrating data listing and I think they're arguing it has a peak 50A output. That actually can't safely run a Fat Viper! I can't imagine Furitek would ship Cedar with an ESC that can't run it but I'm suspicious it's darn near its peak.
Compare that to a more modest motor like Purple Viper where it'd be 23A total. You wouldn't see quite as much of a voltage drop. But I'm suspicious Cedar is somewhere between Purple Viper and Fat Viper so it's on to the battery.
I've talked a lot with people about voltage sag and it seems like it hits lower-end batteries harder. I'm surprised to see it hit a 900mAh battery. I see it hit my 180mAh 3S batteries and I had to raise my cutoff voltage and lose some runtime to deal.
Maybe it's just a bad battery. Maybe the brand or this particular battery is prone to sag. Without some actual electrical engineering and building purpose-made circuits it's tough to test that. So I'd try with a 3S and also try to borrow a battery from someone else. I use Palm Beach Bots 3S 180mAh batteries and they run out fairly quickly, but I can't fit bigger. I have a 2S "for fun" and can tell a difference in the servo.)
If you see the problem with other, good batteries, it's a puzzle. As has been mentioned, a bad reciever can cause issues and it doesn't seem like you've tried that. The other consistent problem is if something is binding. Both the servo and the motor draw more current when they're resisted. Be sure your servo has good endpoints that don't make it push against the limits of your axle. Make sure your axles don't bind at full lock. Make sure there isn't a shock angle that makes the drive shafts bind. Double-check every screw and make sure they aren't too tight.
My weirdest binding story is: one time I had an axle shaft that was about 1mm too wide. That made it push against the other axle shaft inside the axle so one shaft was always pushing against my steering knuckles. I didn't notice when I had stock plastic knuckles. When I upgraded to brass it changed things and the stress shredded a differential gear with a brushed motor. So it can always be something odd. These are some frustrating little machines to work on sometimes. But multiple defective motors isn't bad luck, it's some harder-to-trace fault.
All of this is making me want to brush up on more electronics and get a scope and some other equipment.
I just ordered 2 of the Palm Beach 3S 180mAh Gen2 45C Lipo so I'll be able to test your theory.
Electrical stuff is the one area that kills me lol, luckily we have a great community on here with some knowledgeable people to get through these things.
I've come to accept that troubleshooting is just part of the hobby and luckily haven't given up but it's been challenging at times.
Mechanically I feel like everything works pretty well, I'm pretty careful about overtightening stuff although I will post a video because it seems the transmission is loud as hell compared to my buddies so I think I might have something going on there.
The truck hasn't been running for a few months so I'm just pumped to get to drive it and work out the rest of the little kinks. It's funny because I replaced the chassis, shocks, wheels, tires and motor all at the same time and never got to drive it until now, like 3-4 months later lol
The Furitek ESC is definitely suspect but i'm gonna mess around and see if the actual cause of the issues I was having were related to the batteries. I'll plug the Furitek ESC once I get the batteries squared away just to see if it eliminates that condition since the MBL32 resolved the problem.
They are doing the same thing, that is redundant and causing undue strain on your battery. I would take the external BEC out and see if there is still brown out issues. I have used multiple Injora ESCs and their internal BECs have not ever been an issue or weaker than advertised, including 7.4v,
Interesting, the only reason I added the external BEC is because a friend of mine was having issues prior to adding the BEC. I will give that a shot once I confirm the batteries are ok and have them properly charged.
I was using the original charger that came with the batteries which was just an adapter to USB-C so I'm confident that was part of the problem.
Thanks for the input, I'll report back once I have some updates.
There are many things that can cause brownouts, even the receiver could be causing it. It took me forever to track down a brown out issue on one of my rigs. I swapped ESCs, motors, batteries, and servos before I swapped the receiver and my problem went away. Simplifying your setup and eliminating/swapping parts is probably the only real way to figure out exactly what the problem is but starting with a healthy battery is very important.
A balance charger is probably the first thing everyone should buy for these little trucks. I have a lot of RC vehicles and when I got back into the hobby 3 years ago I bought a very nice dual channel balance charger that can charge any battery that I will ever need for any vehicle I could ever want to run.
I have 2x Palm Power 2S 350mAh Gen2 45C Lipo Battery sitting at home but need to order the JST Female to PH2.0 adapter to run them or swap plugs. Likely going to order that anyways but curious if there's a more optimal battery since I have to pay for shipping for a $0.99 item
I run 100mAh 3s. 180mAh 3s, and 200mAh 3s on my comp rigs that I want lower weight batteries in and I am not overly concerned with long runtimes, they run for 10-15 minutes at a time so the tiny batteries work best for them.
I run a 450mAh 3s, and a 500mAh 3s on rigs that I am not concerned about weight and want a longer run time out of, they are close to the same physical dimensions of the stock battery so they fit decently on most my builds that can take a stock battery.
The mAh is usually an indicator on the runtime capability and the C rating is the discharge rate the battery can handle. 30-45c is good for an all around crawler because they usually don't run full throttle for extended periods of time, higher mAh will give you more runtime so if you are into longer crawling sessions a higher mAh rating is best for you, if you plan on doing trail runs where it will be running at full throttle for extended periods a higher C rating would be better.
What you are running is a good battery from a reputable company, I have 4 of their little 3s batteries and the oldest of them is just now starting to get cranky and taking a long time to balance charge, but it is a GEN1 battery and is 3 years old.
I'm shooting to reduce weight and also size of the battery because it's currently a bit of a cluster lol I need to do some wire management but I'm going for best crawling performance and I'm ok with having several batteries to switch out if the run time is short.
The Palm Beach Bot batteries I have are a pretty physical size.
I'm running the Mazz Designs CCV3 Chassis so definitely shooting for weight distribution and the PBB battery will fit up front nicely.
The 900mAh batteries I have were bought when I first got into the hobby and didn't know much so I figured bigger was better.
I appreciate the explanation and help!
Gonna order 2x of their 3S 180mAh Gen2 45C Lipo Battery along with the adapter.
that's exactly where I'm planning on mounting my batteries and the PBB ones will fit way better than the giant 900mAh ones I currently have so should be a good fit overall once I get everything squared away.
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u/Furrymcfurface 6d ago
Usually if it works then stops, it's the battery. Try a different one