Vintage Kyosho Rocky - NiCad to NiMH conversion

[Makers]

I have a question regarding replacing NiCad battery packs with NiMH on my 80s-vintage Kyosho Rocky. I assume the speed controller and motor were spec'd at the time to be able to dissipate the heat over the runtime of a NiCad battery pack. Since it appears that modern day NiMH can offer runtimes at least 3x as long, do I have to worry that the original motor and speed controller might boil over if I run the car continuously over a full charge?

[Dadio]

I have a question regarding replacing NiCad battery packs with NiMH on my 80s-vintage Kyosho Rocky. I assume the speed controller and motor were spec'd at the time to be able to dissipate the heat over the runtime of a NiCad battery pack. Since it appears that modern day NiMH can offer runtimes at least 3x as long, do I have to worry that the original motor and speed controller might boil over if I run the car continuously over a full charge?

Yes you do , you have hit the nail on the head , you have to keep an eye on temperatures ! It's the biggest mistake people make thinking " I can now run it for 15 min nonstop " closely followed by " my motor has burnt out , where can I get a new one ?" Followed yet again by " my new motor didn't last long ! They don't make them like they used too ! "

[Makers]

Thanks! I figured as much, but thought I'd ask just to be sure. Are newer motors of the same form factor built to handle longer running times?

[Frankentruck]

If you get a battery with a similar mah rating to what NiCd batteries had (1200 to 1500 mah), then there should be less risk of overheating. They would also be lighter weight than the old NiCd pack which is always good. But same run time, not longer.

Traxxas has a cooling fan integrated into their Titan 12T (550 sized) brushed motor so it can run longer without overheating. I'm not familiar enough with the Rocky to know if you could fit a Traxxas 550 motor (also has larger bushing on pinion end).

[Dadio]

The other option is to fit a modern brushless motor and speed controller , they run much cooler and typically with modern Lipo batteries you can drive them for over 30 min but you have to remember to be kind the the old school transmition as well , modern brushless motors can be astonishingly powerful ! For a vintage car a 17.5 turn brushless is akin to a good 27 turn brushed motor and a 13.5 turn brushless is more like a 19-21 turn brushed motor , lower turn brushless motors are not going to be kind to old gearboxes unless you have a slipper clutch .

[radioactivity]

The motor's heat questions can be partially addressed by gearing.
I inexpensively modified 3 items on my Rocky.

1. I cleaned and polished the MSC printed circuit board with McGuire's polish.

2. I replaced the contacts on the MSC wiper arm.

3. I replaced the old broken ceramic resistors with higher wattage (10watt) aluminum resistors. Mounting tabs were removed.
I did use small pieces of heat sink thermal pads on top and bottom of resistors, any heat sink grease will work too.
The fit of the resistors was almost perfect, much better than the original ceramic resistors.

resistor.png (95.63 KiB) Viewed 164 times

resistor.png (95.63 KiB) Viewed 164 times

Chuck

[Makers]

If you get a battery with a similar mah rating to what NiCd batteries had (1200 to 1500 mah), then there should be less risk of overheating. They would also be lighter weight than the old NiCd pack which is always good. But same run time, not longer.

Traxxas has a cooling fan integrated into their Titan 12T (550 sized) brushed motor so it can run longer without overheating. I'm not familiar enough with the Rocky to know if you could fit a Traxxas 550 motor (also has larger bushing on pinion end).

Thanks!

[Makers]

The other option is to fit a modern brushless motor and speed controller , they run much cooler and typically with modern Lipo batteries you can drive them for over 30 min but you have to remember to be kind the the old school transmition as well , modern brushless motors can be astonishingly powerful ! For a vintage car a 17.5 turn brushless is akin to a good 27 turn brushed motor and a 13.5 turn brushless is more like a 19-21 turn brushed motor , lower turn brushless motors are not going to be kind to old gearboxes unless you have a slipper clutch .

Are you saying the brushless motors have more torque thus may damage older gear gearboxes?

[Makers]

The motor's heat questions can be partially addressed by gearing.
I inexpensively modified 3 items on my Rocky.

....
Chuck

Nice! Thanks! And thanks for the pics!

[Dadio]

The other option is to fit a modern brushless motor and speed controller , they run much cooler and typically with modern Lipo batteries you can drive them for over 30 min but you have to remember to be kind the the old school transmition as well , modern brushless motors can be astonishingly powerful ! For a vintage car a 17.5 turn brushless is akin to a good 27 turn brushed motor and a 13.5 turn brushless is more like a 19-21 turn brushed motor , lower turn brushless motors are not going to be kind to old gearboxes unless you have a slipper clutch .

Are you saying the brushless motors have more torque thus may damage older gear gearboxes?

Well it depends on the motor but yes they can be a different ball game to brushed motors in terms of torque/power for the same size motor and can easily strip vintage gears in many cases or at least reduce their life greatly , most modern cars have a slipper clutch to reduce not only wheel spin but excessive torque on the gears .

[Makers]

Makes sense. Thanks.

[Coelacanth]

Also, current ESC's will let you dial down the "punch" or torque of the brushless motor. Basically acting like a slipper gear.

[Makers]

Thanks, @Coelacanth . Do the speed controllers you're referring to incorporate variable gearing? I think the only way you can reduce torque (without also reducing speed) is by changing the gearing. Let me know!

[Dadio]

Thanks, @Coelacanth . Do the speed controllers you're referring to incorporate variable gearing? I think the only way you can reduce torque (without also reducing speed) is by changing the gearing. Let me know!

The punch setting on the speed control is more of a soft start so if you nail the throttle it feeds it in more gradually stopping shock loading the transmission and reducing wheel spin .

[1911Colt]

Thanks, @Coelacanth . Do the speed controllers you're referring to incorporate variable gearing? I think the only way you can reduce torque (without also reducing speed) is by changing the gearing. Let me know!

No, not gearing, just "computer magic". The ESC can be programmed to deliver power in a non-linear fashion.

I pilfered this chart from the interweb. It was made for a different purpose, but will work as an example. The red line is linear throttle input with no signal shaping from the ESC. Moving the throttle trigger any amount from 0-100% results in 0-100% of battery power being applied to the motor. The blue line is "softer", meaning the ESC doesn't apply power as quickly as you move the trigger. Full throttle is still full throttle, but less power is delivered initially to avoid spinning or damaging the transmission. Conversely, the green line has a more aggressive curve, giving you power even faster than you move the trigger, to launch you out of a turn.

The blue line is good for loose surfaces and also reduces driveline stress. In your case, this is what you want.

The green line is better suited for 2WD on a high bite surface or a 4WD buggy.