Motor Controller for RC Car

[kl22]

UPDATE: Thread re-opened!

Hi

I've been reworking my RC car (bought chassis only). What I'm trying to understand is that the guys over at the RC hobby shopes are telling me that an RC car motor can sometimes require up to 200A!! Does seems right to me so I looked up some RC motor drivers and indeed they are rated at 200A.

I bought myself a Pololu High-Power Simple Motor Controller tahts is 18V-15A continuous. Which means it is not power full enough to get the full power out of the motor. Anyone have any suggestions on a high current motor controller I can buy for. brushed (give me ones for brushless as well) DC motor that I can interface with arduinos and Axon2.


Thanks in advance.

[Soeren]

Hi,

What I'm trying to understand is that the guys over at the RC hobby shopes are telling me that an RC car motor can sometimes require up to 200A!!

Only the wildest and I really thought they were only used in model planes.

I bought myself a Pololu High-Power Simple Motor Controller tahts is 18V-15A continuous. Which means it is not power full enough to get the full power out of the motor. Anyone have any suggestions on a high current motor controller I can buy for. brushed (give me ones for brushless as well) DC motor that I can interface with arduinos and Axon2.

Isn't 15A enough for your purpose?
Assuming 12V, you can draw up to 180W with the one you have.

Are you planning to use a motor burning more than 1kW?

[kl22]

Hey Soeren,

I don't think that I will be, but pretty much I'm just trying to make a really fast car. I'm currently using a stock 540 motor, I would, as you said, assumed at 15A was more than enough.

I want it travel at around 30mph.

If I were to buy an RC motor controller, how would I interface that with the axonon arduino? I would assume PWM, but how do control forward and reserve?

[rbtying]

You'd treat the RC ESC as a servo - more than 1.5ms pulse would be forwards, less would be backwards. 

30mph usually means ~20A+ current draw, in my experience - check the resistance of the windings on the motor, it'll give you an idea of the stall current.  Most RC car ESCs I've used go to around 40A max, which makes sense.  RC plane ESCs are easily 100A =).

Realize that you're going to run out of battery power in about five minutes of runtime though - massive current draw invalidates whatever battery life you might have had before. 

[Soeren]

Hi,

I don't think that I will be, but pretty much I'm just trying to make a really fast car. I'm currently using a stock 540 motor, I would, as you said, assumed at 15A was more than enough.

I want it travel at around 30mph.

Ah, I thought you're building a 'bot
The current it takes depends on its number of turns - do you know the T on your motor?

Something like this?
27T Stock 540 Motor with 3S Lipo RC18T

If I were to buy an RC motor controller, how would I interface that with the axonon arduino? I would assume PWM, but how do control forward and reserve?

Same way as a servo is the common possibility and some ESC's have an option for other kinds of input signals as well.
If your motor has a stall of around 42A like some I've found, you either need the ESC to cope, or you need to sense the current and shut down or chop the current if it gets too high (unless the ESC has that functionality already).

If you've got too much cash, take a look at the Sabretooth ESCs.
If you've got too little, consider making one yourself.

[kl22]

Thanks Soeren & rbtying.

I've looked into the Sabertooth ESCs, well mainly the 2x25A version and still I'm a little confused on that vs a Tazer 10t (http://www.dynamiterc.com/Products/Default.aspx?ProdID=DYN4928)

I'll test it with what I have, if something fries then I guess I'll learn something

[marto]

I guess the distinction between the two is that one is a "robot" controller and the other is a "car" controller. 

First difference is that the 2x25A is 2 channel mostly because robots all use tank style steering. The sabertooth also accepts a variety of inputs (RC, serial, analogue voltage) where as the car controller will only work with an RC style signal.

The main functional differences are that the Sabertooth controller  will allow instantaneous (relative) reversal where as the car ESC will go into braking mode until you re-center the stick then it will go into reverse. The sabertooth also has current limiting which is usually only found in high end car controller, which helps save your batteries, motors and speed controller when things fail.

If its an RC car... go buy a RC car controller. If its an RC car that you want to use as a robot then maybe look into something different.

And also in relation to the pololu one you bought I would say it would be fairly underrated for RC car style motors and I wouldn't use it. It also states pretty clearly on the site it has no current protection so you are pretty likely to fry it if you use it on a motor which is too large.

Steve

[kl22]

Thanks for the info marto.

I ended up buying a RC controller because I fried the pololu one as you mentioned.

[kl22]

So can someone compare these two for me

Sabertooth 2x25
http://www.dimensionengineering.com/sabertooth2x25.htm

vs

Team Tekin RX8
http://www.teamtekin.com/rx8.html


From the specs it seems like the Tekin is alot better than the Sabertooth.

25A continuous, 50A peak per channel, 6-24V nominal, 30V absolute maximum for Sabertooth. Versus Input Voltage: up to 6S Lipo, Continuous Current: 210 Amps* for the RX8. Does this mean I could essentially use the RX8 to drive, for example, a windshield motor if I really wanted to? Just seems like why go for the Sabertooth when RC hobby ESCs seem to be rated much better for less.

I realize that the RX8 is about $80 more but for the same price as the Sabertooth I can probably find at least an RC Motor Controller rated at 100A continuous.

[hopslink]

Yes, but it depends how you rate your controller. See the little * after 210 Amps. Follow it to the matching part where they say 'this is the biggest number we found in the spec sheet for this device'. Try actually running 210Amps from a 6S continuously through that driver and it's lifetime will be measured in seconds...

Now compare to Dimension who have been around for a long time and have a solid reputation. Their 25A will be a current that the components in their controller can handle all day at the maximum input voltage, with enough to spare so the device will run on and on... Then don't forget the Dimension device has 2 channels, is designed as a brushed motor controller, and offers lots of flexibility as to the control method.

You have to compare like for like - so over to Dimension Engineering:

Sabertooth 2X25 uses 1.3 milliohm MOSFETs in its bridge. Going by our competitor's ridiculous rating schemes this would make it a dual 190A motor driver!

A dual 190A motor driver for $80 less than a 210A single channel driver is a bargain surely...

Note: I am not saying that Dimension's products are the best value you can get, but you need to compare carefully. Personally I would far sooner buy from a company that gives me real world figures, not 'big numbers BS'.
 
 

[kl22]

Thanks for the info hopslink. I was very skeptical about the "210Amps*" as well.

So will for example the RX8 be able to drive things that the sabertooth can? The big motors?

Just wondering because the RX8 seems better suited to me since I want to build an RC car and also use it for my bots. And it supports brushed, brushless and sensored brushless motors.

[kl22]

What you all think about this?

http://www.talkingelectronics.com/projects/Xenon/Xenon.html

[marto]

Unfortuantely you can't really have a controller for you car and for you bots.

Q1? Does you car have a brushed or brushless motor?
If its brushless or you want to upgrade to brushless then go to hobbyking and buy a motor and controller for ~$70.

Q2? Do you need one or two wheels driven for you robot?
By that I mean will it be ackerman or tank style steering. If its tank style well you are going to need 2 RC controllers anyway.
If its only one then you may be able to get away with a RC controller the main disadvantage of RC controller is that they have a reverse delay which is a problem for robots. You have to brake.... center the stick then it enters reverse mode probably with a lower speed. This really makes it difficult to do tank style steering with them but if you are doing ackerman type then you might get away with it.

The sabertooth 2x25A will work well for your robot controller and will work OK for your car but might be a little interesting to setup and will limit the current to your motor and hence the performance of your car.

Long story short you will probably need a separate controller for each as they are designed for completely different purposes.

Steve

[kl22]

Thanks marto! That's what I was leaning towards as well just needed someone to say so

Thanks.

BTW, some RC controllers can be programmed to remove the delay and either instant reverse or have it set up for a "crawler" style where all it needs to do is automatically go to neutral->brake then it starts reversing.

[marto]

I am sure some can but I would also put money on it not being any of the cheaper ones. I have been reprogramming brushless ESCs to do what I need them to anyway.

I would also be a little wary of the Sabertooth 2x25A. I have two and they work great but some other people I know have bought them and just not been able to get them to work at all. Possibly dodgy units or problems trying to run things off the 100ma BEC circuit. I think they have a newer version now which has a 1A BEC so that has solved a lot of peoples issues. I would make sure you get that one if possible.

Steve

[kl22]

Thanks marto.

I'm actually looking into a ESC that mgm makes it is their X-series model.