Help! Overheating Brushed....

[Catchy 24]

I'm really pickled with my boys Ripmax Jackal overheating... Any ideas what's going on?

Standard silver can and electrics, alloy dogbones, prop shaft and dampers..

He's gone through 3 motors recently, the last one died on it's first run, recorded 130c via an IR thermometer just before it gave in with a puff of smoke accompanied with a right stench!

This latest run was with a 2s 1800mah LiPo, however the last two motors died with standard Nimh, so don't believe it's purely the LiPo, it was only 7-8 mins into the run...

Only other mod is larger wheels from the Ripmax Husky, which from my understanding is exactly the same setup, with these larger wheels and a different shell only..

Pics of the wheels for reference to size change.. Think I'll try the old wheels and check temps, but is there something else I could check? 

Thanks all

 

[Fuijo 880]

Assuming nothing in the drivetrain is binding, it's probably the larger wheels making the gearing too tall. Fit a smaller pinion/larger spur.

[TwistedxSlayer 1290]

As above. The wheels aren't designed for the gear ratios of a buggy

[GregM 1109]

According to the manual, the Ripmax Jackal uses a different pinion than the Ripmax Husky.

 

Manuals found here:

http://www2.ripmax.net/Item.aspx?ItemID=C-RMX0010

http://www.ripmax.com/Item.aspx?ItemID=C-RMX0020/EUR

 

pinions:

http://www2.ripmax.net/Item.aspx?ItemID=Z-RMX736034&Category=900-030-070-010

http://www.ripmax.com/Item.aspx?ItemID=Z-RMX738005&Category=900-030-070-020

 

Main gear seems to be the same for both cars, so I assume the motor mount is adjustable for both pinion positions.

 

 

Using the correct pinion for the wheel size should cure the motor overheating issues.

[nowinaminute 2815]

I've a feeling the gear ratios are the same between the Husky and Jackal so the bigger wheels shouldn't cause such bad overheating.

I would rule out binding in the driveline, wheels, gearbox, shafts etc, does the vehicle come with bearings or bushes as standard?

 

Some vehicles are just geared right on the edge as standard and will run just within limits on nimh but the motor will be able to draw more current from a lipo and overheat but if it happened on NIMH too I don't know.

I would definitely make sure nothing is binding and putting extra stress on the motor. 

[Catchy 24]

Valid points regarding the gearing due to the wheels, I'll do a little research on the husky gearing to see if there is any difference, it's only a tiny 12t pinion on it already thou!

Binding.. It is nowhere near as loose as my TT02B without the motor in it, but still doesn't feel overly tight.. Checked the rear gearbox on the weekend and was spotless.. Will check the front sometime soon also.

Bearings in the wheel hubs, but don't know anywhere else. I'll check later..

Going for a bash in a bit with motor no4 and the smaller original wheels, can't remember if the overheating started before running the big wheels or not...

All the parts on the official Ripmax site state both Husky and Jackal, yet the only pinion available is named for Husky only.. Maybe they are different sized then? I need to look into that also then...

Ta folks.. 👍

[Catchy 24]

Cheers @GregM,somehow totally missed your post earlier!  Yeap that answers part of it, need the smaller pinion to start with..

It still run hot during our bash,  let him take it up to 80c before stopping for breaks.. It's really shifting with the Lipo so maybe that's what's causing this heat.. Plus he's 9, don't grasp the concept of throttle control yet, its just an on and off switch to him!

[TwistedxSlayer 1290]

LiPo won't cause extra heat.

[nowinaminute 2815]

1 hour ago, TwistedxSlayer said:

LiPo won't cause extra heat.

It absolutely will cause more heat, especially in a vehicle where the motor was current limited by the stock battery. More current = More heat.

There's a common misconception that a lipo will somehow send more power through the ESC into the motor but the motor will certainly be able to draw more current and in some circumstances this can lead to overheating. The distinction is that the lipo simply provided the motor with enough rope to hang itself. The end result can be the same, the addition of a lipo can lead to fried motors, just not for the reason many assume.

These little ripmax vehicles have battery packs made from 2/3 size AA cells which are capable of maybe 5-7 amps sustained. I don't know which 1800mah lipo op has but let's assume it's 20c which would mean 36 amps are now available. Even these little RK-370 motors can have a stall current of 20 amps or more so there is potentially a lot more current going through those windings, especially when there's a lot of load put on the motor. 

[TwistedxSlayer 1290]

 No it won't. The motor can only draw as much current as the ESC will allow. You could have the worlds largest LiPo battery, that can give out a million amps, if the ESC can only draw 10amps max, it will only draw 10amps max, after that things are gonna start melting, like wiring and connectors. Not the motor. 

[Backlash 481]

35 minutes ago, TwistedxSlayer said:

 No it won't. The motor can only draw as much current as the ESC will allow. You could have the worlds largest LiPo battery, that can give out a million amps, if the ESC can only draw 10amps max, it will only draw 10amps max, after that things are gonna start melting, like wiring and connectors. Not the motor. 

No, thats not quite right..

The current drawn from the battery is determined by the motor, not the ESC..

The current drawn by the motor is determined by its construction (eg how many turns/windings, magnet strength, airgap etc) and the load being placed on it by the car (eg, gear ratio, tyre size, efficiency of the vehicles driveline, the surface its running on etc)

The ESC can however be a limiting factor on the current flow, by its internal resistance (which causes a voltage drop accross the ESC), and to some extent by the current rating of its FETs, but it is still the Motor that determines the current draw.. Thats the reason why ESC's have current ratings or motor limits, and why the ESC's rating must exceed that of the motor, otherwise the ESC will overheat and go into thermal shutdown, or go up in smoke..

TwistedxSlayer, if what you were saying was true, then there would be no need to put motor limits on ESC's, and I should be able to run a 10 turn modified motor off a Tamiya TEU101BK ESC (that is rated for a Sport Tuned motor) without the ESC going into thermal shutdown... Does that sound right to you?

[nowinaminute 2815]

23 minutes ago, TwistedxSlayer said:

 No it won't. The motor can only draw as much current as the ESC will allow. You could have the worlds largest LiPo battery, that can give out a million amps, if the ESC can only draw 10amps max, it will only draw 10amps max, after that things are gonna start melting, like wiring and connectors. Not the motor. 

That's not how it works, the motor dictates current draw, not the ESC. The current rating of an ESC is the maximum amount of current that should be drawn through it, not the maximum current that it will allow to be drawn through it.

[TwistedxSlayer 1290]

I will happily stand corrected :-) 

[nowinaminute 2815]

A good example is an old 1/10 scale Nikko truck I recently worked on, this was one of the gooduns from yesteryear that had a 540 motor and big fat FETS on the control board, almost a hobby grade in some respects. The truck is very heavy for it's size yet still has a 16T pinion, the same as the F10 buggy (aka traxxas cat) it's based on. This would be like Tamiya putting the lunchbox out with the same pinion as the hornet. The truck was obviously designed and tested around a nicad pack of no more than 1600mah capacity and in those circumstances it will run fine although the motor does get hot. Switch to a lipo though and that heavily worked motor suddenly has access to a lot more current, enough to make the internal cooling fan melt.

[Catchy 24]

Thanks for the comments chaps, totally sure the motor is working harder with the LiPo, the speed and noise it's making is amazing, poor little thing is screaming along! I'll post a video later from the 130c run before it gave out.. 

He also stripped the spur in our run last night so gonna get a new alloy spur and the husky smaller pinion in one go.. Think then we'll try the husky wheels again to see where we are with it.. We're probably just pushing it a little too hard...