Brushless Maxx hesitates
 

I have a supermaxx with a 9920/1940 7 turn hi amp, running a UBEC, spektrum, and 14 ib3800 cells with deans. The motor is wired to the controller using 3.5mm plugs. Motor has a heat sink, ESC has a fan.

The problem is hesitation in mid acceleration. Its almost like cogging yet its after the truck is well under way. Its hard to describe, but it looks like the hesitation you might see if a truck were shifting from low to high. Just a momentary pause and then its off. Of course, my truck is a single speed so thats not it. This has happended with gearing 14 to 16 on the pinion/51 spur.

Any thoughts on what might be the issue?

hmmm..for some reason..i had this same exactly problem, but on stock titans w/14 cells ib3800s.

I solved it by using a receiver pack.

You have a UBEC, so that's probably not the problem. But perhaps you should try a regular (nimh) pack, just to eliminate the chances of that being it...

is your e-maxx running hot. because there are some chances of the cut of to that?
but most of the time its at full?

it actually might be your ubec. sometimes they cause weird problems. try moving it somewhere else.

Yeah, i would try a receiver pack to start with.

Mine does the same thing at full throttle. i tried redoing my batts and adding a ubec, droping the receiver pack, and will test tomorrow and let you know if it cured it. my ib's were done in a stick pack...

What about gearing? Have you tried gearing a bit lower?

That would reduce the current draw - a 7 turn 1940 must pull a sick ammount of current at the best of times - if it's over geared, i shudder to think lol

Check things are nice and cool - packs, heatsinks etc

Try a receiver pack to start with first.

I am running 16 GP3700's on my e-maxx and a 8xl and ubec and it runs great. If your motor draws alot of amps you might try bigger batteries ( more cells or lipo's)
Good luck

Its not his batteries. Chances are its the ubec. sometimes they cause interferance issues.

Is there a way to test to find out. No matter where I mount my ubec it works fine. Oh yea, You have to mount the ubec backward, Point the flat side toward the electronics. Are you doing that Steve?? Here is a pic.

Guys - thanks for all the responses. I have not had time to test this yet. I am not running the UBEC like mmdooley (I have it flat on the chassis towards the rear) so I will try that first. Then, if necessary, I'll give a spare receiver pack a try.

I'll post an update this weekend.

Steve

For me, I dropped the receiver pack and and redid the batts from stick to side by side...tested, no probs at all. I do have a very short receiver wire though which i think is my problem when i get too much distance. Does it happen far away from you and near you? Or just far away?

UBECs are awful. Never had any luck with them.

This is not true, just because you didnt have any luck with them doesnt mean you can say they are awful, lots of forum members including me have glitch free running with a UBEC...

I finally broke down and purchased a UBEC.....it runs so smooth now.....before I was running a 5 cell 1400 mah rx pack....now with this I have zero cogging even @ slow speeds.......it just added more wires to the mess... but not much....

Hey guys - I'm resurrecting this thread again...

I tried the receiver pack finally tonight and it does the exact same thing - hesitates to respond to throttle input under all sorts of distance and speeds. Actually, I think it ran worse with the receiver pack but I could be wrong.

So back to the UBEC - should I try it mounted in some different positions?

Is there anything else I should consider testing out? I think I'm going to try a different radio just for kicks. I run spektrum (for now) so I wouldn't think that would be the issue but you never know.

Thanks again,

Steve

Id try mounting in different positions, i run a spektrum too and no problems. You run a switch right? What is your bracket made of? aluminum? That could also cause an interference.

Did you try mounting the ubec with the flat side toward the electronics? The board is the shield, That's what the directions told me.

It's hard to tell from the picture; but is your receiver right behind the controller? can you get a more detailed picture?

Did you tried re programming your controller? and you did removed the BEC jumper from the 9920?

I use sponge foam to seperate the reciever away from the metal and the UBEC. Stopped the interference I was having. So they sit on foam, instead of aluminium. ;)

Was an opinion. :024:

Well if you have tried rx pack and ubec. You went thru and checked all your connectors and made sure they got good connection. I would check with different batteries as well to see how they would do. If all this don't help and moving the rx don't help. If you can would or could you try another esc?

I don't have a switch. I probably should, but I thought it would just add more wiring to the confusion.

One of my initial thoughts regarding the ubec was the quality of my soldering on those tiny wires. I had a less than a fun time getting them soldered on to the deans tabs with the other, fatter wires. But since I have the same problem without the UBEC in place, I'm assuming that wasn't the issue.

The controller and the motor connection is what I'm starting to think is problematic. The controller sits on the chassis, attached with industrial velcro, right behind the front shock tower and perpendicular to the drive line. Its just barely out from underneath the motor. I will experiment with some alternative locations on the controller.

The other area I'm not sure about is the motor to controller. If you've ever seen an uninstalled 1940 7 turn hi amp, the back of the motor has three separate solid strands of copper winding coming out of it about a half inch or so. No preinstalled plugs. For flexibilty, I soldered on some 3.5mm plugs onto the ends of these wires and heat shrinked the plug and the exposed wire. Then I soldered plugs onto the controller and made the connections. I found over time that one or two of the 3.5mm plugs seemed a little loose, so I used some electrical tape to try better hold the plugs together.

I guess this was a long way of saying I think this motor was designed to be direct wired. Do you guys think, given my problem, that it might be worth undoing my motor connections and direct soldering?

I would get the meter out and check the resistance of all solder connections to make sure they are good.

Nl - alright, I'm showing my electric ignorance. What do I need to do this (specific name of tool?), how do I do the test, and what is the expected result?

Thanks for the help!

I have the same problems with mine. 9920, hmmm, i would also like to do this test!

Okay, now that I thought about it for a second I believe nl12 is referring to getting out an ohm meter.

Anyone care to describe how to use an ohm meter to test soldered rc connections (motor plugs, deans plugs, etc...)?

here are my questions again.
 

and again..

A normal meter isn't capable of measuring contact resistance bytheway.

Serum - I'll take some detailed pics tonight. The receiver (and the receiver pack or ubec) is at the opposite end of the truck from the controller, near the rear shock tower. The controller is at the front. Both are mounted using velcro to try and isolate them from the aluminum chassis. I have removed (and have always had it removed) the black bec jumper on the underside of the controller (near the programming jumper).

I have not tried re-programming but I should be able to try that tonight as well.

So is there no way to test the quality of a solder join as nl12 suggests?

A bad solder joint wouldn't result in the problem that you have. It would show under hard acceleration.

This is exactly how i have my truck too, but my controller sits on a plastic plate up front, my receiver sits in the back with foam underneath with adhesive, then the ubec on top sitting on a mount plate as well. I have the same exact problem steve080773, I have tried everything...redoing my batts, new receiver, rx pack, putting in a swith, everything. let me know what happens. I'm gonna try a new chassis and redo my whole truck again! but thinking maybe my controller to motor wires are not good? hmmm, not sure, but would like to test all my connections somehow. Sorry to hijack the thread, but we are having exact probs. When did you get your controller?

Serum - maybe it is the solder joins. The problem really is evident when the truck is rolling (maybe 1/8-1/4th throttle) and I try to make a stab at the throttle. It also seems to be worse when there is more rolling resistance, ie dense summer grass vs pavement or dirt.

Any thoughts?

Newe - my controller is probably only a few months old bought from Mike. Very odd that we are having similar problems...

Mine is just as old, of couple of months maybe. allso from Mike. Although, i had less of a problem when i ran the plastic stock chassis. what chassis are you using?

I have a UE lightning chassis (aluminum). I haven't thought about trying a plastic chassis - makes me ill to think about running plastic with this much power.

Here are some closer pics of the layout.

http://i19.photobucket.com/albums/b1...3/IMG_4778.jpg
http://i19.photobucket.com/albums/b1...3/IMG_4779.jpg

I'm really beginning to think its the controller to motor wiring. Spent a lot of time just tooling around in the drive way and the hesitation really only occurs when I ask for more than 1/8th or so of throttle. Consistently, and the hesitation is worse if I try to go full throttle. I find it hard to believe that its interference because it was so predictable. I did reprogram the controller and no change occurred; I also tried a different radio/receiver and no change.

Here's what the motor and controller wires originally looked like:

http://i19.photobucket.com/albums/b1...3/IMG_3965.jpg

Do you think I should try and direct wire them or use some 4mm plugs instead of 3.5mm? Or do you think I'm just on the wrong path all together?

It could possible be a motor, esc, or even battery connection. Check em all and maybe consider 5.5mm plugs if you have problems soldering the wires into the small connectors. For temperary I would just direct solder.

It's hard to tell what your problem is. Did you tried another receiver/transmiter? Or another set of batteries?

This must be frustrating for you.

I didn't catch if you were running it fine for a while and it just starting doing this, or if it was doing it from the start?

I don't know what a 7 turn high-amp motor will pull for current, but maybe the 9920 just isn't up to the task? I know I've seen over 100A bursts from my BK Wanderer 8XL when I punch it from a standstill. Or if it's not that, maybe the ESC was overheated quite a bit burning out a few FETs and now is running on fewer FETs? I don't know of any type of current limiting capability in these ESC, but that's exactly what it sounds like.

One way to tell a bad connection would be heat. A bad connection creates a voltage drop, which in turn dissipates power as heat when high current flows. Wire and connectors should not be warm at all to the touch, or VERY little.

As far as direct soldering goes; it will be a better connection providing it is done correctly (no cold solder joints), but less convenient than connectors if you need to replace something. Just make sure the connectors are soldered well and they fit snugly together. The 5.5mm ones Mike has are quite beefy.

They are beefy, untill you crash them once. then you need to reposition the pins on the male plugs. you need to feel a rather firm resistance when plugging/unplugging them.

Brian - its been doing this from the start, and it does it irregardless of the battery pack I use.

I'm hoping for now that its not the battery wiring from the esc as I have little excess wire to mess with. I don't have a switch, so I have to unplug that batteries to shut the truck off and I have never noticed any warmth to the plugs/wires.

I am going to try the esc to motor connections next - probably over the next few days. I always felt a little uncomfortable with that connection because the 3.5mm plugs didn't fit all that well with those large wires (especially the copper windings coming from the motor). If the 4mm doesn't look like it will improve things, I will direct solder.

Unfortunately, I don't have another ESC to experiment with. I bought the 7 turn hi amp and 9920 from Mike after much collaboration with him, so I would hope its not the problem. I will add that to the list though, and if redoing the motor connections doesn't help, I will look into buying a 12020 or perhaps the new quark.

Thanks for the feedback guys! I'll update later this week.

Steve