I’ll copy the text here though, because I assume people here might be interested:
I’ve got a project in my head about taking a 1/10th scale OpenRC truggy and replacing the 1/10th scale motor with four smaller motors, one for each wheel, to allow me to do torque vectoring with computer control.
My question is, I’m looking at 1/18th scale motors, 1/14th scale motors, looking at kV, wattage, etc, and I have no idea if they will be a good replacement. One of the difficulties is that the 1/18th scale motors that I would like to use (https://hobbyking.com/en_us/trackstar-1-18th-scale-14t-brushless-power-system-4300kv.html) - because they’re pretty cheap - don’t list a wattage.
I’m also not certain how important wattage is as a metric for this task. For instance, if you compare this 1/10th motor (https://hobbyking.com/en_us/turnigy-trackstar-4-0t-sensored-brushless-motor-8240kv-roar-approved.html) with this 1/10th motor (https://hobbyking.com/en_us/turnigy-trackstar-21-5t-sensored-brushless-motor-1855kv-roar-approved.html), they are essentially identical but with different windings and thus different kV values. The 1855kV motor says it can put out 150w, and the 8240kV motor says it can put out 620w. I’ve checked, they have very similar ratios between kV and wattage. However, the lower kV motor would have better torque, so it would be better suited to a larger vehicle, although it would be slower. If you geared the faster motor down to match the speed of the slower motor, you would have a similar effective output, I assume.
So what metrics should I be looking at to determine whether the motors are up to the task? And if they’re not listed on the product page, how can I calculate them? My intuition tells me that the four 1/18th scale motors should be able to provide enough power to replace a single 1/10th scale motor, but I don’t know, and I don’t want to waste $200 buying them only to discover they can’t do it.
Doing an individual all wheel drive system is obviously a little more involved and there are a few aspects to consider in this approach. I think really the biggest concern you should be having is, how practical is adding 4 motors to the car? I’d try answer that one first.
Will you be using brushed or brushless? You may as well use brushed to save cost, and only have a forward direction by using one mosfet per motor (saves having to buy, and fit 4x ESC’s or using an H bridge circuit). The downside is they don’t have very long life and aren’t as efficient (85-90% efficient vs 75-80%) but they are cheap and should work fine for your project? You can do more research and decided which type to choose. If in doubt hit me up here or google if you need general info.
What I’d do is pick a low kv motor that will fit in your vehicle and weight limits, then play with the gearing and number of cells connected to it to get the right RPM range. You may not find a suitable brushed motor and will have to look for a brushless one. If you can get this done you’re sorted!
@Jotham_B Yeah, my main issue is figuring out which motor to use that won’t overheat. I think if I can get four low kV outrunners like you’ve got there I might be sweet. Especially because aerial motors and their ESCs have a small, lightweight design they might work very well. My other concern is whether they will suffer from the high impact loads that you get in cars. I also need to make sure I have ESCs with 3D mode so I can reverse them. I don’t want to go one-way because one of the cool things a system like this can do is turn like a skid-steer, and I don’t want to sacrifice that!
Practically, the other main consideration is where to fit them. One of the great things about the idea is that it greatly reduces the number of moving parts in the drivetrain by completely obviating the need for diffs. My idea is to have pinions on the motors with belts to drive spur gears attached to the CV joints, straight out to the wheels. Using low kV motors should reduce the size of the spur gears, which should help them fit in where the diffs would go.
As for command & control, that’s the fun part, it’s the whole reason I’m doing it! I’m also considering how I can get feedback to the computer for how fast the motors are turning. For that I might need to use hall effect sensors or something, I’ll figure it out as I go. I could use crawling sensored brushless motors, but they would be bigger, so I’d need to go for a bigger chassis and everything would get more expensive. I’m trying to keep this as cheap as I can.
What vehicle are you fitting this on to? Not the F1 car? It’s quiet small for this.
I wouldn’t be too worried about power levels. Say that motor there that I’m using… 315 Watts x4 = 1260watts is not bad at all. I’ve got a 3670 1900kv, 1800watt and it is absolutely overkill. It gets nowhere near warm and neither does the ESC or batteries powering it. It’s setup in 3s mode but I’m going to try it with 6s later. Completely 3d printed btw: https://www.youtube.com/watch?v=N3IDdorSQlc
But if you’re aiming for overkill … Hehehe it is fun : ) try asking in the RCgroups forums. There’s a really big knowledge base there and they were very helpful with my project.
Going for the truggy. For a start I have no idea how I’d fit all that gear inside the F1. The truggy has a nice big open pan design, and it should be pretty easy to change the base plate design to fit all the hardware I need.
For now I’m planning on using my existing 6000mAh 2S batteries that power my Glamis Uno. I’ll talk to RCGroups, but I suppose overpowered might not be the way to go for the first design. I think “reasonably fast” about describes what I want. I’ll hold out on “extremely fast” till V2.
Also, love the jetboat! Did I see a 720 in there? Also, you sound like an Aussie from the accent? I’m Aussie myself, NSW Newcastle area.
EDIT: Just heard the end of the video. Definitely Kiwi
The truggy seems like a good choice. Sounds like a good approach. Do link to the thread or build thread if you end up making one. Mine is linked somewhere on here a few posts down. In the group
Yeah, I’ll definitely link it here. Not sure if I’ll build it in the near future or not - I have to prioritise my spending fairly judiciously at the moment. I like the motor you linked - it’ll end up being almost half the cost of the other motors I’m looking at, and the low kV is a big plus, not to mention being able to upgrade the batteries up to double the cell count for an easy power boost if I need it. I’ll look around and see if there’s anything better suited, but aerial outrunners are back on my radar now, it looks like there’s more selection there than I realised.
Nice. You can get that motor in 3 sizes 1100kv to 1400 I think. There is a fair bit of variation out there. Yep the outrunners tend to have lower KV ratings than the inrunners.
