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KidsWheels
Need new motors? Grind a gearbox? Adding teeth to a pinion?
User avatar
By LeeHene
#146451
Hey guys, I need some input.
My son is going through Banebot 18v 775 motors every few months. I'm using all heavy wiring, Gruber 18aH batteries and a Kelly KDS 200 amp controller. Accel and decel curves are set as slow as possible, and output to the motors is restricted to under 18v. No traction bands or anything on the wheels. Total combined weight of the buggy and my son is about 140lbs (70lbs each).

Is there a better type of motor that will hold up? He's about to outgrow it. =(
User avatar
By toycrusher
#146453
LeeHene wrote:Hey guys, I need some input.
My son is going through Banebot 18v 775 motors every few months. I'm using all heavy wiring, Gruber 18aH batteries and a Kelly KDS 200 amp controller. Accel and decel curves are set as slow as possible, and output to the motors is restricted to under 18v. No traction bands or anything on the wheels. Total combined weight of the buggy and my son is about 140lbs (70lbs each).

Is there a better type of motor that will hold up? He's about to outgrow it. =(


What vehicle is it installed in? What kind of failures are you experiencing? Is it getting so hot that it melts the fan on the end of the can?
User avatar
By Hammer-fm
#146459
I agree that a better description of the failure mode would be helpful. Do the brushes wear out? Does it overheat (wiring insulator melted/fan damaged/etc.).

I haven't used the controller you mentioned, but the configuration program demo shows a number of settings. You mentioned that you'd set the accel/decel ramp to its lowest setting (this is the "throttle Up/Down Rate" in the configuration program?). Is the 18V limit done via the "Motor Top Speed" setting?

Have you set a limit on the Max Armature Current? The soft start would reduce how of ten a high current draw is seen since it will be ramping up the PWM relatively slowly, but in a high-drag situation (uphill, in grass), you could still end up seeing 150+ amps, and that much current dumps a lot of heat into the motor.

Also note that the worst case conditions for heat generation is 'just enough throttle to keep the motor stalled' -- in this scenario there's no cooling. Do you see this happening quite a bit or does your son stomp on it and start it rolling pretty immediately?
User avatar
By LeeHene
#146462
This is the current setup. (Copied from my build thread)

-Banebot 775 18v motors
-Axial 16t 32p pinions
-Kelly 200amp 24-36v drive
-Two Gruber Power 18ah batteries wired in series. (6 AWG wire)
-40amp main OL
-60amp main contactor
-Dual 30 amp DPDT reverse and brake contactors (one set for each motor)
-Two control relays for brake/throttle interrupt
-When braking, throttle input to the drive is switched to 0v before engaging the brake.
-Shifter high/low/rev is fully functional. Top speed for low and rev is calibrated by sending the throttle signal through a resistor chain via the orignal switches in the shifter.

It's been working well for over a month.
Battery life is great (2+ hours WOT off-road) and there is no visible wear on gears!
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User avatar
By LeeHene
#146463
On the previous motor failure, things got so hot that it melted the brush bar. This last failure, the armature got hot enough the discolor it some and it lost continuity, resulting in the opposite gearbox to shred teeth off the second and third gears.
User avatar
By LeeHene
#146464
Its a Power Wheels Dune Racer. The controller is set to limit output voltage to 60%. In the real world it tests at 17.5VDC when batteries are at 26VDC.
Output current is limited to 50% of max, 200/2=100amps, shared between two motors, each with a stall current of 120amps.
None of the wiring is stock. 6AWG main to the drive, then splits to 10AWG for each motor group. All connectors were soldered to the wires at 800° F.

The compartment housing the motors and controller has fans forcing air in and out. The only damage to the motors has been in the area where the brushes contact the commutator.

My son is 6, so he never drivers slow (which is why I restricted drive output so heavily). Our land is really hilly, so I tried to set this thing up for torque, not speed.

More info: My pictures didn't transfer over with the copied text in my last post. Here's my build thread: viewtopic.php?f=9&t=18982
User avatar
By Hammer-fm
#146469
I looked at the build thread and it looks like you've definitely covered the bases well. The primary comment would be that all of these types of motors are "intermittent" rated. If you are running them below their maximum efficiency point very much they will likely wear out fairly quickly even with good ventilation. That said, It looks like (from your other post) that these are only lasting 2-3 months? (Feb->Apr->now), and that does seem pretty short. I haven't taken mine out to inspect them since I've had them in (~4 months, 50A total limit, 22.5V max, no additional cooling), but hadn't seen anything from any other users that reported such short liftetimes. Mine get run almost exclusively on hilly pavement, and most of the time with "slicks", so overall they get pretty easy treatment. (That said, the same treatment at similar speeds torched the stock motors).

One question:

Do you have any datalogging or indication of how often it's pulling at or near the 100A limit while already moving (eg. hillclimb/etc.)? If it's often hitting that limiter then that would suggest that lower gearing may improve the situation. The thermal strain is related to the current being drawn, not the applied voltage, which varies because of back-EMF in the motor. You could reduce the gearing and raise the max voltage to make up for the speed loss. An 8514 motor should have ~140mohms of resistance, so 50A is only ~7V plus whatever back EMF the motor is already making. The motor is most efficient at 20A according the the datasheet, so even if you needed to up the max voltage you'd probably get better life overall.

Unfortunately the only stock lower gearing is an older Hurricane gearbox combined with 14T pinions (a 12% reduction). You could combine this with a correspondingly lower current limit (44A) and higher voltage (20.5V) and get the exact same max torque and max speed that you have now -- but with 20-25% lower thermal loss under high-load condition and some amount of accelerated wear due to higher RPM under lighter loads. Power loss in the windings is I^2*R, so reducing the current by 12% will reduce the thermal loss by about 25%. This would reduce brush temperatures as well as the overall current density, which I'd think this would reduce brush wear substantially if it's often running 40-50A today for any extended period of time (>5 second duration). It's just a really small motor to be sinking 300+ watts into on for any extended period of time (300W is how much it burns in the windings at 50A).

Reducing the current by itself (without changing the gearing) likely won't improve the situation as it will just sit on the limiter that much more often (running slower, for longer duration).

I'm not sure whether that would end up being a good tradeoff or not without having some sort of datalogging of the current being used during regular driving now.


You probably won't have room to do what i did on my son's F150 truck -- which is to install two 775-series motors in each gearbox (posted under "quad damage") to help spread the thermal load.

I haven't see anyone install a CIM motor in the stock gearbox -- that would be an interesting build. That's an example of a motor with substantially more heatsinking (in the form of mass, mostly) -- shows up very clearly in the extended power tests. I'll post it here since they also test the Banebots 18V / 8514 motor. Vex motor comparison
User avatar
By LeeHene
#146479
Thank you for such an in-depth response!
One quick point, I'm running my main power through a 40amp overload that is not tripping. (Of course that doesn't rule out burst current)
Unfortunately, no data logging.

One test I did before starting installation of the drive and related gear was to test how much current the motors pulled going up a major incline on grass with my son. At 13VDC, current of both motors combined held at 33 amps, tops. The first set of motors ran mainly on 12VDC for a little under a year. Oddly, both went out at the same time, a couple months after incorporating the drive.

This last time, my son had just figured out he could use his brake pedal to skid. Not 45 minutes after warning him to quit, a gearbox was toast.
I made him save up (a month or two) for the anticipated repairs (metal gears). To my surprise, I found a dead motor on one wheel and a stripped gearbox (second and third gears) on the other side when I finally opened it up.

Each motor has a set of two 1 Ohm 10watt resistors in parallel to dissipate power from dynamic braking.

Do you think its possible that current from BRAKING could be what is taking out the motors?

...I knew I should've gone brushless!
User avatar
By taz11
#146485
Glorydays wrote:WOW! This post really make me feel stuppid. I shudda staid in scool :(


LOL! :lol: :lol: :lol: :lol:

I ran those motors for years. The failures that I did have were usually related to a full throttle stall condition. Not sure that helps at all.......you've documented it way more than I ever did.
User avatar
By Hammer-fm
#146505
I wouldn't expect the braking to be a big problem here, although it's obviously more stressful than having a real mechanical brake. Two 1-ohm resistors in parallel should never be pulling more than 35A out of each motor -- and that would only happen if it was at full speed (going directly from throttle to brake). Realistically it's going to be quite a bit less than that, and that's going to be a short transient. Relative to the amount of heat/power used for acceleration I think it's probably only a very small contribution.

With 33A @ 12V, It sounds like we'd expect up to 50-60A at the full 18V for both motors, depending on how much the grass/terrain drag coefficient goes up as a function of speed. The motor wiring loss for 30A (one motor's current) is going to be somewhere around 110W in the 8514 motor (130mohm resistance, i^2*R = 900 * 0.13). At 25A this would be ~80W. That's great, except that the problem is that I have no idea whether that's too much with the cooling that you have, or if it should be fine -- I don't have a good way of estimating the rate of heat transfer out of the motor. We can look at the rate of heat rise (it's around 0.8 C/second @ 110W input power, with NO cooling) -- but without knowing how much is being dissipated it's hard to tell what the steady-state temperature is.

BTW the 12V corresponding # (33A total) is much lower for power loss in windings, due to the square function (16.5A => 35W). Given that they lasted for a long time @ 12V, you may indeed be running into just an overtemp case due to the higher speed and related power use. It would be nice if there was a way to have a "short term" current limit of 100A and a long-term limit of something like 30-35A -- the limit would mean slower speeds going up hills (similar to how it was at 12V) but you could keep the higher speed you get from 18V when going on flat terrain. It's just that you can't get the thing moving from a stop with only 35A if you're in any sort of high-drag terrain.

Hopefully there's someone else on the board that has more engineering background in motors. It would be good to have some commentary from someone that does more instrumented testing.
User avatar
By wesleyb82
#146529
6AWG wire!! Pretty sure that's not the problem!

The only thing that jumped out at me are the additional motor cooling fans. I once added motor cooling fans to one of my first 550 setups which I later discovered after a motor failure were blowing against the internal motor fans more or less canceling out airflow and causing the motors to overheat and fail. Also, it has been my experience in the 5kW+ brushed motor world that mfr's and pro's have told me not to waste my time with external cooling since heat build up occurs internally and cannot be relieved externally. I have not done any testing myself to see what effects if any external fans/heatsinks have on 550/775 motor temperature or longevity but any thermal measurements would be on the external motor case anyway which again may have a relationship to the internal temperature but is not a true representation of the internal temp so I'm not sure how useful that test would be anyway.

Ultimately the proof is in the pudding, we use 18v 775 Banebots (Mabuchi RS-775WC-8514 https://product.mabuchi-motor.com/detail.html?id=129) at 24v with no cooling and have only had one failure over the years so based on that and others experience I am pretty confident cooling fans are not needed and in this case may actually be causing a problem.

Also btw I use a Eagletree eLogger which logs voltage, amp and thermal information and has been tremendously valuable for understanding and troubleshooting issues http://www.eagletreesystems.com/index.p ... duct_id=54
User avatar
By Shambosley
#146934
taz11 wrote:What vehicle is it installed in? What kind of failures are you experiencing? Is it getting so hot that it melts the fan on the end of the can?


My son toasted a banebot 775 motor in less than 10 minutes. Its on a dune racer with a 24v 1000w ESC setup. And yes one motor got so hot it melted the fan on the end of the can. And are the motors supposed to connected in parallel, i believe thats how I have them, pos to pos, neg to neg. I need help! Lol please
User avatar
By Hammer-fm
#146937
Connectivity shouldn't have been any different than with the stock motors -- one side needs to be wired reverse from the other. But if you did connect them both the same way, one wheel would have turned the opposite direction and your vehicle wouldn't have moved very fast; if one side had more traction then it would "win" and move the car forward but it would have been pretty slow, and you'd definitely overheat the motors quickly.

Did you check both wheels' rotation with the car off the ground first?
User avatar
By Shambosley
#146942
Well the thing is, one motor has Orange and blue wires and one motor has black and red. So on the Orange and blue side I didnt know which was positive and which was negative to connect with the red and black side, so i guessed and one tire was moving backwards and the other forwards, so I switched it from (blue and black/orange and red),to (Orange and black/blue and red)and they were going the same direction. That was just When I was wiring the stock motors to the relays. When I put the new motors in yesterday i noticed a red mark by the orange stock motor lead so I swapped them back again and one was going backwards and just swapped the leads on that motor and they were both going on the wrong direction so I swapped the motor connections on the relays so both were going in the right direction. It went pretty fast so i seemed like everything was right. But not even 10 minutes of no stalling and the motor fried the plastic fan, and more of course, in the motor. The other motor didn't even seem warm at all. And the capacity is 130lbs and my kid only weighs 35lbs. You are supppsed to wire pos to pos and neg to neg right? That's what it shows in Wesley or whoever's esc schematic. I thought maybe it was the 24v 1000w esc with 24v and them only being 18v motors but my wiring to the motors is really unclear and not professional I just new I got them spinning the same direction in forward and reverse
User avatar
By wesleyb82
#146943
One hot and the other not is a huge red flag. So is burning up a 18v motor on 24v after 10 minutes. I would check for things like: with the wheels off the ground turn each wheel by hand and make sure they have the same amount of resistance, make sure the pinions are the same on both sides, remove the motor from the gearbox and turn the gearbox output by hand and make sure both sides have the same resistance, extract the axle and roll it on the ground to make sure it is true
User avatar
By Shambosley
#146946
I think it's in my wiring somehow. I just had the gearboxes off and they both seemed to be the same( no missing teeth or even wear on the gears). One sounded a bit different but was lacking a little bit of grease between the gears so I used the excess grease to lube them up. The reason I changed the motors was because the stock motors burned up but it was the right side that burned, the new banebot motor burned up on the left side and The shaft looked to be true. The stock motor had a 15t pinion on it but someone recommended 16t 32p pinion so that's what I got for the new motors
Last edited by Shambosley on Thu Aug 24, 2017 10:03 pm, edited 1 time in total.
User avatar
By wesleyb82
#146947
Did you have fans blowing on the motors during this failure?
User avatar
By Shambosley
#146950
wesleyb82 wrote:Did you have fans blowing on the motors during this failure?


No, no fans. Im confused on the motor wiring as the ESC Setup i followed shows Pos-Pos/Neg-Neg>to the relay
BPRO ESC.jpg
BPRO ESC.jpg (41.05 KiB) Viewed 334 times
. A Picture i found on EastCoastPowerUps shows Pos-Neg/Pos-Neg>to relay
Heavy Wire Diagram.jpg


I'd say one is Paralell and one is series. i had it in parallel (pos-pos, neg-neg) when i fried the motor. Im not sure if that makes a huge difference but i know i had it in series(pos-neg, neg-pos) before i put the banebots in. Im only trying to clarify parallel and series so someone can correct me if im wrong


The Axel is warped slightly, not very noticeably.
By Rob222
#146952
Both of the wiring drawings that you are referencing show the motors wired in parallel. If you can take one motor out of the circuit and the other motor is still wired in then the wiring is in parallel. The +/- markings on the motors are pretty meaningless in this case.

series vs parallel.png
Add description
series vs parallel.png (2.24 KiB) Viewed 330 times


You may have found your issue in that axle. Any chance when you put the warped axle back in you switched ends and transferred the problem from the right to left side? I would also confirm if the pinion count change was really ok to do.
User avatar
By Hammer-fm
#146953
The 16T pinion is the correct one to use for the 15-17T spread. Power Wheels has custom-made 15 and 17T pinions that have the same diameter as a standard 16T 32DP pinion. Using a standard 32DP 15T pinion will result in incomplete tooth engagement and the 17T will bind up.

I have a stock 15T (from a Hurricane gearbox) and 16T (F-150). They both measure 0.574" outside diameter, but the teeth have a different profile:
Image

You can look further down in this thread (start at post 28855 or go to 70019 and 70046): http://forum.modifiedpowerwheels.com/viewtopic.php?f=9&t=2773
User avatar
By Shambosley
#146956
Rob222 wrote:You may have found your issue in that axle. Any chance when you put the warped axle back in you switched ends and transferred the problem from the right to left side? I would also confirm if the pinion count change was really ok to do.


I Left one tire on the axle so no it didnt get switched, I did put the gear box that was on one side on the other, but both gearboxes have been inspected and and they are both nearly flawless to my eyes. I can only think it was a defected motor lol

I really dont know what to do or change besides getting a new motor. Should I check the output voltage to each motor or something of that sort
User avatar
By Shambosley
#146986
Well I put on 2 traxxas 775 motors and didn't change anything and they held up all day yesterday for 2 sets of batteries. Hard to believe that the motor would have been defected from all the positive reviews on banebots but I guess it happens.
User avatar
By Hammer-fm
#146989
Yeah, sounds like something was possibly wrong with the motor from the factory (damaged in shipping?) or something got really bound up (in an non-obvious way) during installation. Hopefully the Titans hold up well for you. Did you find it helped with the acceleration at all? Your original post indicated you were interested in improving torque; I have no specs on any of the Titan motors so I'm not sure where they're at in terms of N*m/A.
User avatar
By Shambosley
#146999
Titan775 and banebot775 fall very close, the data provided doesn't correspond exactly with one another but is close enough for comparison. Also Banebot doesnt give all the specs that Titans do, as in the Titan 775 motor being a 10 turn, 3 degree advanced timing motor.

Personal experience so far is that I gained more torque without the lose of top end and if anything maybe a little more top speed.

Banebot
Performance
Model M5-RS775-18
Operating v : 6v - 20v
Nominal v : 18v
No Load RPM : 19500
No Load A : 2.7A
Stall Torque : 166.4 oz-in 1175 mN-m
Stall Current : 130A
Kt : 1.28 oz-in/A 9 mN-m/A
Kv : 1083 rpm/V
Efficiency : 78%
RPM - Peak Eff : 17040
Torque - Peak Eff : 23.99 oz-in/A 169.4 mN-m
Current - Peak Eff : 18.7A


Titan
Performance
Model RS-775WC-8514
Operating v : 6v - 20v
Nominal v : 18v
No Load RPM : 19500
No Load A : 2.7A
Stall Torque : 1216 mN-m
Stall Current : 130A
RPM - Peak Eff : 17040
Torque - Peak Eff : 153 mN-m
Current - Peak Eff : 18.7A
User avatar
By Hammer-fm
#147006
I'm not sure I follow. You're saying the Titan motor is a rebadged Mabuchi RS-775WC-8514? That's a 14-turn motor (85 = 0.85mm wire, 14 = 14 turns -- there's a nice decoder here (or you can find some of the info on Mabuchi's website): http://www.eaelec.com/ea_hobby/tips2.htm. And that's exactly what Banebots ships to you when you order their 18V RS775 motor.

I was pretty sure the Titan was custom wound and if it's 10-turn, should be spinning ~24-25k RPM at 16.8V -- you got the #5675?

For reference, a Nichibo 8510F RS-775 motor (0.85mm wire, 10 turn) specs at 18500 RPM @ 12V (1540 RPM/V) and has a stall torque output of 6.2mN*m/A (slightly LESS per amp than a stock power wheels motor). I would expect the Titan to run similar #s (RPM/v, torque output, etc.).

I'd expect the Titans to be noticeably faster (at the same voltage) than the Banebots or even the stock motors were --though if the one Banebots one was defective it would be hard to compare for sure.
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