This Esc With That Motor

[crazifunguy]

Once I fugure out how these things work the possibilities are endless. Heres my question.
Will this esc
10 amp ESC (http://www.webx.dk/rc/ecs2b.htm)
Drive these little motors
1.2V 10 Ohm
Ø 7x 17 mm 2.78 g
shaft 1.00mm
Didel (http://www.didel.com/Frames.html?MainFrame=microkit/)

What it seems to me is that the motor is connected to the + on the ESC that the battery connects to. If I have 10ish volts comming in is the motor seeing that 10 volts also? If the motor is rated at 1.2v i would think that it would fry.

[slipstick]

No that's a complete mismatch. Your link is to a 40A ESC which would be ridiculous overkill for a pager motor like the 7mm Didel motors (they take about 0.3A). The ESC alone would weigh about 10 times as much as a complete plane should for that motor. Even a 10A ESC would be silly.

Also these motors are normally used on a single lipo cell (3.7V) or 2 NiMH cells (2.4V). That ESC needs more than 5V just to drive the internal electronics.

Steve

[Gary Warner]

Yes, the motor will see 10 volt spikes. I'm not sure what if any damage would be done, but I'm leaning towards yes, it could hurt it.

I'm going to expand on this a bit - maybe something useful will come of it.

When a magnetic field grows, it's not instantaneous. It takes time to grow. And so long as the field is actively growing there is a significant amount of resistance, limiting the current. This growing period is very fast and the magnetic field will max out most likely much faster then the average chopper speed used in the PWM. The smaller the motor Q (inductive resistance) the faster the chopper speed needs to be to prevent magnetic saturation, when trying to control a motor not rated for the applied source voltage.

Two things need to be met when controlling a motor as you have described. One, the maximum ON time of the PWM should be limited (never saturate the PWM to anything close to full ON). Second, the chopper rate must be kept at a very fast speed to avoid staying in magnetic saturation too long.

All in all, it's poor form to control a 1.2 volt motor with a 10 volt source WITH a chopper ESC. Considering the low wattage demands of a motor this size, you might be better off looking at linear style regulator/ESC.

Hope this helps.

Gary
--

[crazifunguy]

That is some good info. Let me explain what Im doing. Im making a proxflyer clone with dual 360mm rotors pulley driven. I want to build my own esc for all 3 motors on 1 tiny board. Im looking for schematics and trying to go from there. It seems that pic's all need 5v to operate. If theres some low voltage alternatives or an easy way to update that circuit please inform me.

[Gary Warner]

That is some good info. Let me explain what Im doing. Im making a proxflyer clone with dual 360mm rotors pulley driven. I want to build my own esc for all 3 motors on 1 tiny board. Im looking for schematics and trying to go from there. It seems that pic's all need 5v to operate. If theres some low voltage alternatives or an easy way to update that circuit please inform me.

Many (most common) PICs can run down to 2.5 volts at 4mhz or less. But I don't see what this have to do with the motor voltage. The PICs don't directly run the motors. They drive FET's that connect full B+ to the motors. What will be a problem at 2.5 volts driving the FETs is that 2.5 volts won't be enough voltage to saturate the FETs - they won't fully turn on. At least none that I've seen.

Gary
--

[vintage1]

Many (most common) PICs can run down to 2.5 volts at 4mhz or less. But I don't see what this have to do with the motor voltage. The PICs don't directly run the motors. They drive FET's that connect full B+ to the motors. What will be a problem at 2.5 volts driving the FETs is that 2.5 volts won't be enough voltage to saturate the FETs - they won't fully turn on. At least none that I've seen.

Gary
--

At these power levels why not use a good saturating transistor? A bipolar.

Heck, if you want low ON resistance whats wrong with a germanium transitor !!!!

Seriously, most mosfets will turn on ENOUGH not to be embarrassing with a motor running at less than an amp.

[crazifunguy]

I hope my lack of knowledge isnt annoying. If 2.5 volts is to small to turn on a fet what about a N-type transistor? What are u guys using in your DIY ESC's. Looking into the mosfet issue I found 2 data sheets. 1 for the so-8 type fet used in the 10A and another smt mini fet.
http://www.fairchildsemi.com/ds/FD%2FFDS6690A.pdf
http://www.irf.com/product-info/datasheets/data/irlml2502.pdf

Is the gate to source voltage what turns the fet on and the current how fast it switches?
Seeing things like this little guy is what started this.
http://www.globalhobby.com/public/gallery/443434.asp
5A from the size of a dime from 1 cell.
(What the heck is inside that)
Yes I know I could just buy 1 but then I wouldnt learn anything

My final model will be a 3cell lipo about 500ma each. For learning and testing I have a small 1cell model that I want to run 72mhz and make the ESC for. Just so I'm on the right track. When picking voltage you match to your motors needs? For a 3 cell are they parallel for more current or linear for voltage?

[Zlatko]

crazifunguy,

You are impressed with that GIANT ESC ? :)

If you want to learn, you will have to do a bit of reading in the Indoor Forum and have a look at the earlier links I posted in your other thread.
http://www.rcgroups.com/forums/showthread.php?t=486264

This "thing" will do all that you want out of the box ( if you have a computer TX )
http://www.slowfly.com/store/view.chtml?store=%23735675&view=%23735828
Have a read of the manula thats there. They will soon have a narrow band version if you need it.

Gary and vintage are right, for the 7mm coreless motors you will need a high frequency ESC ( so it doesn't burn out too fast ), there are some out there that go up to 250kHz!!! ( http://www.wes-technik.de/English/controller.htm ) . Didel also have a 7mm 1.9Ohm motor the runs of 1 cell LiPo and can produce 30gm of thrust through a 4:1 gearbox into a GWS5030 prop at about 1A ( for a power system weigth of about 4gm ).
http://home.comcast.net/~gordon-johnson/ss7mm.htm
If you run higher gearing and larger prop than more is possible. With the motor you specified, you won't get much power. You could go even to a 6mm 4.5Ohm motor and still get more power/trust.
http://home.comcast.net/~gordon-johnson/motorconstants.htm

IRLML2502 are commonly used for the indoor flyers, they are good and can work on low voltages . I have a PIC12F683 SOIC that runs perfectly down to 2.2V at 8MHz , this is outside specifications, but its possible. There are FETs out there that are fully switched on at 1.8V as well.
http://www.vishay.com/mosfets/list/product-73518/
Because LiPos dont't like voltages bellow 3V, we don't bother with really low voltage stuff and just settle for what is light and readily available.

What is the weigth of your small model and what does that include?

Cheers

[crazifunguy]

I can honestly say I looked at every threed in the indoor forum. Most of the info there is geared towards brushless and IR. I'll look more but I didint see anything geared at building an ESC.

Here are the specs of the 1 cell heli. Dual 230mm rotors 2 m20 motors 3 ish volts 1.7-1.9 ohm about 45 grams in weight(i guess not that small) 27mhz crappy reciever that cuts out when you sneeze. The ESC has a lm358 on it and some small unmarked smt fets/transistors. It flew well for a cheap toy I paid 1$ for it on ebay. However its in the parts pile with a smoked board. I'll check out those links and the threed some more. I have a feeling something cool is going to come out of this.

[crazifunguy]

Well I found the fets I'm going to make the test circuit with. These dual N-type with a 1.8v min latch.
http://www.vishay.com/docs/71408/71408.pdf
1 will power both rotor motors and if I need more current I can stack them...

[crazifunguy]

Moving on Its time to start looking into RX schematics. Question wide and narrow band can use 72mhz crystals? Looking at this threed
http://www.rcgroups.com/forums/showthread.php?t=358493
is the frequency the broadcast frequency or something else?

[crazifunguy]

Heres the pics if the 1 cell heli...The controller is blury but you get the idea.

[crazifunguy]

I've been reading the DIY Narrow Band threed and it has some usefull info there. Im not really limited to narrow band where im located. Broad band is an option but I would like to stick with semi-current technology at the least weight possible. Im gonna set my goal and 2-3gm and pray for the best range possible. I would like to get 800m but I dont think that is possible being this small. synthesized looks cool but can it really be smaller than standard crystal? I've seen a few schematics but I want to pick the best for my application or design 1 with the help of an EE. I'm a ME undergrad. I've seen the 900MHZ stuff and WOW is it small but thats not the way I want to go. Again thanks for the help
~Jasn

[Zlatko]

Hi crazifunguy,

That looks good!!!

I think the FET you linked to may be a bit too small, see if you can get IRLML2502. It should be better for M20 type motors.

Sorry, I cant help you with that FM radio. If you want to test the concept, get a BlueArrow 5ch RX. Hobby-Lobby have them for $30 with crystal
http://www.hobby-lobby.com/receiver.htm

You can take the PPM signal from them and feed it to Koichis PIC that I posted a link to earlier. That PIC will decode throttle and rudder channels, mix them and drive 2 motors through the FETS. This will give you what you need for the 2 main motors .
For elevator, you can stack this
http://babelfish.altavista.com/babelfish/trurl_pagecontent?lp=ja_en&trurl=http%3a%2f%2fwww.oyajin.jp%2f%7etoko%2fpic%2 f0061%2findex.html , just use the elevator FETs and PIC.
The code for above is here
http://www.oyajin.jp/~toko/pic/0037/index.html

Cheers