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M.L. Toys
KidsWheels
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Gruber
KidsWheels
I want to go faster.
User avatar
By alan cook
#149567
HI team I really need your help and plenty of different opinions. I am looking for a slight increase of speed by only 3 or 4 Mph. I need strong reliability. I want to increase the speed of a 12V DC RS550 15000 RPM motor with something very similar 12V RS550 DC no load 20,000 RPM motor. I don't want to change the battery so keep it as a 12Volt battery no upgrade to 18 or 24V. Will I get slightly more speed? Will there be any problems? I really need it to be reliable.. do you think it will be and work?


User avatar
By M.L.Toys
#149568
The no load rpm of a motor means nothing, especially with the heavy load the vehicle puts on these motors. The higher rpm motor may actually be slower if it doesn't have enough torque to reach it's rpm. Best way to know what works is to use a motor that's already been proven.
User avatar
By Hammer-fm
#149573
Agree with MlToys. Having datasheets helps, and most ebay/amazon motors don't.

However, some do. Here's my preferred motor for your situation -- a ~40% speed boost at 12V: viewtopic.php?f=9&t=7832#p146887

As you can see, the torque is similar to stock (but pulls more current).

Manufacturer: Nichibo
Model: KC3SFN-8021F
Voltage: 12V
RPM/V: 1920
No-load RPM: 23000 (+45% vs stock)
Stall current: 86 A (+40% vs. stock)
Stall torque: 4.4 Kg*cm (~0.43N*m) (+8% vs stock)
Max power: 256 W

The data sheet seems to be reasonably accurate. It's much faster than the stock motors, and it has noticeably more torque than the Corvette motors (which are about 20% faster than the stock PW motors).

They're still available on ebay - $9 for a pair shipped to your door (assuming you're in the US):
https://www.ebay.com/itm/Nichibo-Taiwan ... 8021F.TRS0

You need to be able to swap the gear off the stock one (vice + punch, then rough up the new motor's shaft end to give the gear some bite; it's a press fit but not an extremely tight press fit so I usually put a drop of red loctite on as well). Or buy the appropriate new 32dp gears that uses a set screw and file a flat into the new motor's shaft.

I've used these on two vehicles for ~1 year with no problems even on stock batteries -- one Jeep with stock gearing (19T box) and one with 23T gears for extra speed. However, they're mostly pavement runners -- it's possible that they'll pull too much current on tall grass and pop the thermal breaker. That would be true of ANY 550 motor that offers higher speed.
User avatar
By Hammer-fm
#149615
Ah, hadn't noticed that :( .

It looks like Jameco will ship it if you order through their web store. Hopefully shipping is reasonable.

https://www.jameco.com/webapp/wcs/store ... ernational

Here's the page for that product:
https://www.jameco.com/z/KC3SFN-8021F-7 ... 58540.html


Another option is this motor (from a company in Canada :) . It's only a ~20% speed increase (~1mph) though
https://www.robotshop.com/en/rs-550-mot ... oz-in.html

The Nichibo is faster by about twice as much -- should be about a 2-2.5mph increase:
Stock: ~15700
Robotshop: 19300 (+22%)
Nichibo: 23000 (+46%)

There are several motors listed on Ebay, but as MlToys had pointed out, it's hard to know how many of them will live up to the few specs that are listed. A real datasheet for those (like the one Jameco has for the Nichbo) would be nice... If Jameco doesn't charge an arm and a leg for shipping, I'd still recommend that as the first choice.
User avatar
By spencergs
#149618
One more question for you sir...how would you recommend protecting the motors while getting the maximum torque from them? I'm using an aftermarket 12V 12AH SLA battery.
User avatar
By Hammer-fm
#149619
Beyond just a standard fuse (30-40A) for protecting against wiring problems? Your main problem is going to be overheating of the motor.

There's a limited amount you can do: A temperature monitor combined with a smart motor controller would be the best solution -- so it could shut off or reduce power if it's getting too hot. That's $$$...

You can get larger motors: A higher-torque 775-case size motor at lower RPM could be coupled with a lower gear ratio (eg. use a 22T gearbox, which would be a 45% speed increase over a 15T gearbox) -- that can be useful if you're running on a Dune Racer / Hurricane/ etc. that uses the small gearbox. It will be less likely to overheat, but it doesn't prevent it.

I'd install the faster motors and then monitor it. Let the kids drive it, then check the external motor temps. People run stock motors at 18V with some degree of success and that will run quite a bit hotter than the Nichibo 23k RPM motor would at 12V.
User avatar
By spencergs
#149620
Actually I was thinking instead of a fuse. Admittedly I don't know a lot about DC motors, but judging by the stall current specs it seems like the fuse would blow well before we risk damaging the motor in a high torque scenario approaching stall.

I currently have a 30A inline fuse but it blew while my wife was trying to take the Escalade up a slight incline...lol. I'd like this not to happen unless there's risk of damaging the motor or other parts.

I am running everything with a microcontroller so I could add a couple motor temp sensors easily enough and forget the fuse?
User avatar
By Hammer-fm
#149623
I had generally considered the fuse as protecting against wiring problems -- wires being damaged / pinched, etc., or the motors shorting (motors often fail open, but also often fail by shorting together part of the coil, resulting in a much lower resistance and potentially a fire hazard). You're right that they can protect the motors from excessive loads as well.

The temp sensor would provide you feedback, but there are limits to what it can protect against. The biggest issue is that on these brushed motors you really can't mount it anywhere that is directly connected to the heat source (coil inside the motor). You can connect it to the case but it's basically heating up from a combination of heat transmitted through the front & rear bearings, and the air movement through the case. If you get a true stall or very low-speed high-current-draw scenario, the case will heat up many seconds after the winding assembly has burned up. Where it is really helpful is for extended use -- like the scenario that burned up one of my Banebots motors, even with a 40A limited step-down converter, which was a full (125+) lb load, run for an extended period of time.

In that type of situation a temperature sensor on the case is perfect and would be able to shut down the motor before the internals got too hot.

You *could* use the microcontroller to monitor current and shut down under certain circumstances. It could even monitor current and attempt to approximate the temperature inside the motor. Power lost in the windings is just I^2 * motor resistance - if you assume half of the current goes to each motor on average, then it becomes fairly easy to estimate the wasted power in each motor. You can approximate the mass of the armature and the heat capacity, though you'll have a harder time estimating the rate of dissipation. I tried to build some amount of that modeling into my Power Wheels Motor/Gearing calculator XLS. I had done it two ways -- one where I calculated the theoretical net power (based on the motor specs - torque & RPM) and subtracted that from the delivered power (current * voltage after wiring losses). That was a bust, because most of the motor specs are not that accurate. I moved to the I^2*R method (plus bearing losses -- that will be harder to calculate in the system without an encoder).

Otherwise, for overload protection, I'd recommend a thermal breaker (slower to trip than fuses), or continue to use a fuse. I don't think stepping up to a 40A fuse is a problem.



For an interesting visual picture of how quickly these types of motors fail when fully-stalled or under heavy load, take a look at the "Locked Rotor Stall Tests" on Vex Robotics' page, eg this one for the Banebots 18V motor (run at only 12V):
http://motors.vex.com/other-motors/bb-775

Even at just 8V, stalled, the motor fails after about 12 seconds (you have to download the CSV file to really see it - the current decreases from ~66A to 47A as the motor heats up, then suddenly jumps around 13 seconds when the wiring shorts out, then goes to 0 at 21 seconds when the short finally blows out).

The 'Banebots 550' motor is the most similar to the stock Power Wheels ones, and it lasts just 3 seconds at 12V. (pulling ~70A). They do their testing with larger-capacity wire and a strong power supply -- the typical SLA batteries will sag to 7-8V if you try to pull 80A out of them, so the "stall" rating on the motor is never actually seen in ride-on cars. At '30-35A' (6V), they go about 30seconds before smoking -- but that's from a "cold" starting point.

These little fan-cooled motors pack a lot of power into a small size, but they just don't have much thermal mass. Ccompare that to the CIM motor listed on their page,which is a sealed larger motor with ~350W of output -- basically like 2x the stock Power Wheels motors. It can handle 12V locked for ~37seconds before failing, and that's pulling 80-90A for most of that duration.

http://motors.vex.com/vexpro-motors/cim-motor
User avatar
By spencergs
#149624
That's all really great info. Thank you for the well thought out post. I spent some time looking at the "locked rotor stall test" data and datasheets for some thermal breakers. My conclusion is that I'm over-thinking it. I tried choosing a breaker that would give me a second or two at stall current but there are too many variables. I'm going to go with this thermal breaker to replace my fuse: https://www.digikey.ca/product-detail/e ... -ND/509841

If that trips prematurely by my standard after upgrading to the Nichibo and 10ga wiring then I can up it to 40A. If I want to get fancy then I can monitor the current with this badboy and shutdown the ESC based on the behavior I want: https://www.digikey.ca/product-detail/e ... ND/2042746

And worst case...the motors are 1/4 the price of the breaker! :)
User avatar
By Hammer-fm
#149628
Yeah, that looks a good model. Actually, I'd say an even better fit than the one I got (a Carling CLB-30) -- at 4x the rated current (120A), the one you showed is guaranteed to trip in 2.5s (range is 0.4-2.5s) , vs a range of 0.4-5s for the Carling one.

I haven't tripped mine, even with me or the wife driving it (although I did drive it for only a short time). The meter I have installed was showing >60A @ 36V once I hit full throttle (which was at about 35% max speed -- I'm not certain the gearbox will handle full load from a start with my already over-weight rear end on it), but it rapidly drops as the vehicle speeds up.

I would definitely recommend monitoring temperatures. If the vehicle is heavily loaded (thick grass, lots of standing-starts on hills, etc.), you may end up needing to upgrade to a larger motor (RS-775) and adjusting gearing to make up speed. Unfortunately, ones that run high RPM at 12V are harder to come by -- but if you get to that point, post a query and I'll see if I can help find something that isn't quite as crazy as what I put in mine :lol: . In an Escalade (stock = 17T), you can swap a 21-22-23T gearbox in (you can buy empty gearboxes for fairly cheap - the gears all swap), but you still need a faster-than-stock motor to keep the ~45% speed increase you get with the 8021F Jameco motor.

Good luck -- am interested in hearing your experience with the motors once they are installed.

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