I am planning on making an electric skateboard and I am one of those people on my team who does everything that doesn’t relate to physically touching the robot and don’t really know much about hardware related stuff. Is a CIM a good motor to use for this stuff or are there better options when you aren’t bound by competition rules. I was originally planning to use 2 CIMs wired up to talon SRXs hooked up to an Arduino with a CAN shield. I was thinking of using a 6s lipo battery to power this but don’t know the best way to lower the voltage from ~22 volts to 12 volts. I’m thinking of using FRC parts because I have seen them work and can borrow them to test before I buy my own. My main 2 questions are:
Are CIMs good for non-FRC use?
If so, what is the best way to do from 22 volts DC to 12 volts DC for this type of application?
Also, I would like to use a computer in my project, unlike most people who just hook up a wireless receiver to a motor controller for their control systems.
That being said, there are many types and sizes of CIMs. I work with a device using a CIM that weighs more than an FRC robot, and can pull a LOT more than 1 FRC robot. The CIM in question is a pretty big one, and definitely NOT FRC-legal.
In this particular case, you’re looking for moderate strength and small packaging. I’d go MiniCIM, and likely more than one.
But there’s a few other considerations: CIMs (and, well, just about all other motors as well) will need to be geared down for this sort of application. I suggest using JVN’s Mechanical Design Calculator (from https://www.vexrobotics.com/vexpro/examples-guides/application-examples-guides --take the “Additional Examples and Guides” button and go to bottom right of the popup) to try to figure out gearing and such like.
As far as control, ask yourself: Do I really need more than just speed control? If you don’t, you can make life really easy on yourself by using something like thisto control speed. (Remember, you’re presumably going to be balancing on this thing holding a controller. Do yourself a favor and make the controller small and easy to hold.)
So a quick google search says something along the lines of using a switching voltage regulator but these things look like tiny chips and I don’t see how it won’t get fried. Also if I am powering multiple things that run if of different voltages like LED strip, arduino, whatever else I add etc. Does it make sense to use multiple voltage regulators? It seems like there is a better way to do this.
If you want to do this JUST for the educational experience (don’t plan on practically riding it around), ignore the following.
To do this right, you really should stick to brushless motors. Specifically outrunners. There’s a lot of commotion in the esk8 community about hub motors (motors inside the wheel) but their lack of torque relative to outrunners make them undesirable if you’re seeking any sort of practical performance in my opinion.
Electronics is a huge area that people typically skimp out on and I really don’t support using a RC car grade ESC to run the motor. Benjamin Vetter started an open source project to develop an affordable and powerful ESC that has gone under many iterations throughout the past couple years. It’s called the VESC. You will find many vendors sell it mainly since its an open source design that works very well (designed specifically for esk8s).
As for batteries, a balance charger is a must and I personally would opt for Samsung 25Rs but I haven’t paid much attention to the 18650 market as of late so it is possible LG or Panasonic have better offerings.
There are plenty of communities that have well established guides for this sort of thing that I suggest you check out. Esk8.builders is the best organized IMO but Endless Sphere is the OG so you might find some good stuff there.
Be mindful that a robust board might end up costing you a pretty penny, but I really believe it’s worth it if you plan on actually using it practically. I personally ride a Boosted Board V2 to class but had I taken the DIY route I would have gone with the exact parts I mentioned earlier. Best of luck!
Most eBoard people use brushless outrunners, as Nikita specified above. I know several people that have gone this route without issues. VESC is ideal, but I know people that used regular brushless car ESCs without issue as well.
18650’s are ok batteries, but even regular hardcase lipo batteries will work fine.
A CIM will be hard to fit under the deck of a skateboard, so brushless is probably the way to go.
Hub motors of the right size are very hard to find, although I do seem to recall one from a random site a few years ago that advertised pretty good power numbers.
Use a motor controller or design your own. Look up “H-bridge”. It uses high power (relatively) MOSFETs to deliver power to the motor. You’ll also want some MOSFET drivers as well. If you’re really interested, you can check out the black Jaguar schematic (http://www.ti.com/lit/ug/spmu130c/spmu130c.pdf), but to be honest, I’d just buy a COTS motor controller.
You shouldn’t need a reversible ESC for a skateboard - this allows you to use a motor controller MUCH cheaper than a Talon SRX for almost the same results.
I think you’re also going to want a physically smaller motor - if you’re insisting on an “FRC” brushed motor, I’d start with 775pros. Packaging CIMs is tough and the weight kills you here.
You definitely don’t need a reversible ESC, but that doesn’t mean that you can’t use old FRC parts. Most teams which have been around a while have old Victors which are perfect for this application, just keep an eye on the max voltage for the controller you are using if you are planning to run over-volt the motors, you will need either a Talon SR, Spark or SRX if you want to do this.
In regards to converting a 6S(24v) battery to 3S(12v), it definitely isn’t happening in the form factor and size that you need, a single CIM running a skateboard will draw a lot of current.
Why not just get a 3S battery or even split your 6S pack into 2 3S packs?
The issue with something like a 775pro is that you end up needing a significant amount of reduction to keep it within a safe level of current draw. Like even with GT2 belts you would need more than one stage of reduction as the pulley would be larger than the wheel otherwise.
I also agree with Nikita, you will get a much better end product going brushless.
Medium sized Outrunners about 2" in diameter are common for boards and have plenty of power( probably more than you will ever be able to use).
In regards to ESC and batteries, if you choose to use an RC grade ESC make sure you get one with a much higher current rating than you require. On the topic of batteries, you probably want something reasonably low-profile 18650 Cells could be a good option for this if your happy to weld the tabs yourself. Otherwise just have a look on HobbyKing for some low profile packs you might need to run packs in parallel and in series to get the capacity and voltage that you require.
Before you deal with LiPos make sure you read up on safe handling/charging/use procedures as they get upset easily.
Any number of COTS planetary gearboxes (not even just VPs) interface with the 775Pro and make it into a functional gearmotor that’s still smaller and lighter than a CIM. This shouldn’t be too difficult to accomplish, and the packaging benefits make it easily worth it I think.
As someone who is building an electric skateboard, don’t use a cim. You won’t get the speed and power you need and it is very bulky for the application. Ideally you would use something like a 150-250kv outrunner brushless motor which is smaller and more powerful. Go on electric-skateboard.builders
It is a forum for people who make their own electric skateboards and there are tons of suggestions from experts in the subject. There are also a few websites that sell electric skateboard parts.
The skateboard I am building uses 2 6s lipos paired in parallel so I get a bigger range, it has 1 brushless motor and is gears for 18mph and should have tons of torque for going up hills. Higher end builds use the same motor but have larger batteries and different gearing to reach upwards of 30-40mph which is pretty overkill for high school students
When you use parts like these, if you stay within the specifications it won’t get fried because engineers designed it not to get fried. Sometimes (especially for high power parts) you’ll need to add a heat sink.
That said, don’t use a voltage regulator to control voltage going to the drive motors.
Motors are pretty tolerant of voltages that would destroy most components.
Motors can also act as generators, adding a (possibly uncontrolled) voltage source on the regulated side can destroy digital components spec’d for a lower voltage.
Figure out the voltages you need (sounds like 5V and 3.3V), then find the power supply that fits your need. Typically people use switching regulators instead of linear regulators for projects like yours. Then a standard practice is to daisy chain the regulators (e.g. raw 22V powers 5V regulator, 5V regulator powers 3.3V regulator). This is for increased efficiency and decreased load on the lower voltage regulator.
So it seems that if I want a good board, I should go with non FRC hobby parts. I have seen that many people are using a motor controller hooked up to a receiver. Is it practical to integrate some sort of computer like a raspberry pie of arduino that can control everything. Looks like I should move over to the skateboard forums to do my research.
Agreed. A brushless system is always going to have a higher power/weight ratio, with the trade-off of complexity. You will find a wealth of resources of how to do it the brushless route, but you could absolutely pull it off with CIMs.
Honestly I don’t really know at this point other than rgb LEDs, I just wanted to make something smart that I could add on to later. I am pretty set on doing this unless it becomes really impractical do do this
Honestly I don’t really know at this point other than rgb LEDs, I just wanted to make something smart that I could add on to later. I am pretty set on doing this unless it becomes really impractical do do this
Arduino has a function called pulseIn() that can be used to read the length of signals. You can use that to transfer data from a controller to the Arduino.
Servo.write() can be used to communicate between Arduino and ESC.
A cheap way to do this is to use a wheel from one of those self balancing hover board things. For a motor controller, use a chinese ebike controller off ebay. It’ll be less than $40 total for the motor and controller.
I’ve seen a few scooters and longboards built like this that work pretty well. Weatherproofing a motor is really hard, but the hover board wheels are already pretty well sealed