Interfacing with ESC's « LeafLabs Garden

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Interfacing with ESC's

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Started 3 years ago by Schillie
Latest reply from xchg.ca

Schillie
Member

I need to control motors:

http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=2105&aff=588847
KD A22-15M Brushless Outrunner Motor
Kv (rpm/v) 1050
Max Current (A) 20
Max Voltage (V) 11

using my Maple for a project I'm currently working on. Most of the RC community uses ESCs such as the following:

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=4312
TURNIGY Plush 18amp Speed Controller
Cont Current: 18A
Burst Current: 22A
BEC Mode: Linear
BEC : 5v / 2A
Lipo Cells: 2-4

however, these units are built to be used with a standard RF controller and have a number of built in features that I don't need (since I can easily implement them using the Maple). They are also (from what I've heard) a bit finniky to control via a micro controller. Sadly, I cannot find a solution for controlling ~20A motors that doesn't involve one of these ESCs.

I was curious if anyone had done this before/has any ideas?

Thanks

Posted 3 years ago #
blackswords
Member

It's quite complicated to build such ESCs, especially the sensorless ones. The code is complicate for having good results. I'm not saying that's impossible, I saw some realizations on the web but none with Maple or an STM32. Most of them are written in assembly because they use small MCU but still need some performance.

If you can find anything helpful, post it, I am very interested in that subject too

Posted 3 years ago #
gbulmer
Moderator

you might get some inspiration from:
http://www.robotpower.com/products/osmc_info.html
That is a 160A design.

Toshiba do quite a lot of motor control, and have specific Cortex-M3 parts for motor control:
http://www.toshiba-components.com/microcontroller/TMPM370.html
so they may have some application notes (I thought I saw an application note a few weeks ago, but can't see it now)

How smart do you need it? How small do you need it? How cheap do you need it? How much time and effort can you afford?

Do you have test equipment (oscilloscope, storage scope)?

You should be able to measure the motor-current using a high-side current shunt, so you can have feedback from the motor without external (e.g. Hall) sensors.

Posted 3 years ago #
crenn
Moderator

For that speed controller, set the period of the timer to be 20-22ms, and the channel values should be between 1.0ms-2.0ms. If the controller doesn't like that, look at using a values between 1.25ms and 1.75ms. Usually for ESCs you need to start at a value other than your lowest point, stay there for about 500ms and then set the signal to have the lowest value (so either 1.0ms or 1.25ms depending on the speed controller) for about 1-2 seconds to allow the speed controller to 'arm'.

I have done the above method before for several speed controllers (unfortunately, I don't have any speed controllers and motors that aren't in aircraft, so I can't give you a demonstration via youtube) and it's worked well. There is also another method for controlling the ESCs, but it requires a bit of work to do. Usually you need to rewire the internals of the speed controller (cutting traces and also removing the BEC) to free up the TWI/I2C interface pins on the microcontroller (majority of the speed controllers are based around the Atmel ATMEGA8 or ATMEGA88, there are a few other non-atmel microcontroller based ones floating around) to allow you to interface with the ESC via I2C. I personally haven't done the conversions myself, however the person I was working with on my final year project did the conversions (and only broke 2 pins out of about 10 speed controllers, it's quite fiddly work) which allowed us to communicate 'faster' with the speed controllers (we had some other problems which I believe was the speed controllers crashing the I2C interface by holding it low. The problem was never verified.) with either an Arduino or a Maple/Maple Mini. We also used level converters with the speed controllers to protect the Maple/Maple Mini from the higher voltages on the I2C bus.

As for which ones you can use, I'd recommend searching around the rcgroups forum for conversion threads, but here are a couple:
The TowerPro 25A ESC (HobbyKing no longer sells these last I checked)
http://www.rcgroups.com/forums/showthread.php?t=766589
http://ng.uavp.ch/moin/Documentation/HOWTO/BL-Ctrl/HK-TypeH-rev1.1
http://www.mikrokopter.de/ucwiki/en/TowerPro25A2Regler
The HobbyKing BlueSeries 30A ESC
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=13429
http://www.rcgroups.com/forums/showthread.php?t=1401408

Those should get you started.

Posted 3 years ago #
Schillie
Member

Thanks for the responses!

Since I'm doing this project on the side, I don't think I'll have the time required to build a custom brush-less controller from scratch (however, it definitely will be something to keep in mind as another project to pursue, so thanks for the links).

That being said, I think I'll go with buying a market ESC. Has anyone found a good "bare-bones" ESC for controlling ~20A motors that works reliably but doesn't include all the various RF communication features?

Thanks for the arming tips crenn, I'll probably go that route as well; using I2C sounds like a bit too much work for me at the moment.

Thanks again!

Posted 3 years ago #
blackswords
Member

What is the application for this motor? It's a good start to choose the right ESC.

Posted 3 years ago #
Schillie
Member

Im planning on putting together a quadcopter using the following frame: http://www.hoverthings.com/frame-sets/ht450bk.html. It lists a recommended motor in the 750-1050kv range; i put the motor above within the post as an example. If you had a motor + esc recommendation, that would be great.

Posted 3 years ago #
crenn
Moderator

It's not so much a motor/esc recommendation but a motor/esc/propeller recommendation that you want. They recommend 2 prop sizes, and some motors, so take a look at that. It's possibly a good idea to look into a program called MotoCalc to calculate the draw of the motor versus the thrust of it. You want to balance the weight of the quad with the thrust produced, it's not going to be very good if you need to have all the engines at full to get off the ground and for it to only last a short time.

Look at a getting the props at full thrust to be doing 2-3 times the weight of the quad if you can. This way the engines will not be working hard and it will also help with moving around rapidly. As for ESCs, just go for one of the hobby king ESCs which aren't card programmable. That should allow for easy interfacing.

Posted 3 years ago #
blackswords
Member

if you want to make a quad, you need special ESC. Standard ESCs accept a new command every 20ms (like servos) so 50 times per second but for stabilizing your quad, you need to update the outputs at least 200 times per second. So you have different possibilities. If you have some money, you can buy the ESCs from microkopter, they are especially made for this application. You can also seach for RapidESC and TuboPWM on google, you will find some interesting things. (I flashed some ESCs with the RapidESC firmware and it works fine)

Posted 3 years ago #
crenn
Moderator

I disagree, while you can only update it at 50Hz, you can program to ensure the stability is available. In fact, a few hobby quadcopter controllers use off the shelf Hobby ESCs.

Posted 3 years ago #
gbulmer
Moderator

My ESC guru tells me that many off-the-shelf brushless DC motor ESCs 'largely ignore the frame rate', 'mostly use the pulse width', and 'will run up to almost 400Hz'.

I have no doubt that someone who understands the control problem could make a quadcopter with a 50Hz control rate, but ...
A brushless DC motor could make more the a rev in 1/50th of a second, so there were several instants when motor speed could be adjusted.
To put it in context, an object would free-fall about 2mm, and a powerful quadcopter could climb 10mm or more.

Run at almost 400Hz and the free-fall is 1/64th that, and their are many more signals to control motor speed.
I'd try to make it easier for myself by having an ESC that could run at several hundred Hz.

Posted 3 years ago #
Schillie
Member

I believe I've collected a good list of parts, the motor I now plan on using is:
NTM Prop Drive series 28
http://www.hobbyking.com/hobbyking/store/__17345__NTM_Prop_Drive_Series_28_26A_1200kv_250w.html

along with 9x4.7 GemFans
http://www.innov8tivedesigns.com/product_info.php?cPath=46_132&products_id=975&osCsid=8e43faedf9e47719bb0eb6d513793787

I've only looked into the low-end ESC solution, namely:
HobbyKing Red Brick 30A ESC
http://www.hobbyking.com/hobbyking/store/__18004__HobbyKing_Red_Brick_30A_ESC.html#

The motor and the fans were both approved by the creator of the frame, so i feel set on those. However, the main issue is still the ESC. I feel like getting a basic, reliable one like I have listed above would be a good route, but i can see where greater update rates would help things out quite a bit.

Has anyone used a ~200-400Hz ESC that they would recommend for this type of situation (ie, controlling it with a Maple)?

Thanks!

Posted 3 years ago #
xchg.ca
Member

I have done the above method before for several speed controllers

Crenn, can you share some code which illustrates how to control ESC specifically on Maple (STM32) ?

Thank you.

Posted 2 years ago #

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