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Spindle
04-19-2005, 06:54 PM
Hey,

I am building an inverted pendulum robot for my final project. Luckily our team has the EDU MINI RC Robot Controller. I am using that as the brains of my project. The problem is that I need to power two dc motors. Here is the specs on the motor I am running if it helps.

1. Voltage Operating Range: 3~9VDC
2. Nominal Voltage: 6V constant
3. No-Load Speed: 160 16rpm
4. No-Load Current: Approx.140mA
5. Rated Speed: Approx.180rpm
6. Rated Current: Approx. 900mA
7. Rated Torque: Approx. 1.2kg-cm
8. Output Power: Approx. 2Watt
9. At Max. Effciency: Approx. 45%
10.Stall Torque: Approx. 5.2kg-cm 11. Motor Speed: 5000 50rpm
12. Gear Ratio: 31:1
13. Shaft Brush: Sintered oiled bronze
14. Gear Material: Steel/Bronz hobbing gears
15. Max. allowable moment Torque : 18 kg-cm
16. Temperature Range: -10C ~ 60C
17. Relative Humidity: 20% to 85%RH
18. Insulatiion Strength: 20MΩ, 500VDC
19. Dielectric Strength: AC250V, 60Sec. Min.
20. Connector: JST PHR-2

I want to use the PWM outs to control this motor the problem of course is that this has to run through a speed controller and I don't have access to anymore Victor 884s and I also believe they wound's work because they draw too much power and are for higher power motors. Is there an Electronic Speed Control/Speed Controller out there I could use that would work with the input of the EDU MINI RC Robot Controller which output would work accordingly for my motors. I have searched for RC hobbie speed controllers for planes and the like but I don't know if this is the same because its a different PWM signal or has low hertz. Any help is appreciated! Thanks guys this is such a great community.

-Spindle

sanddrag
04-19-2005, 07:02 PM
You might want to look around on www.parallax.com and www.robotmarketplace.com

Max Lobovsky
04-19-2005, 07:12 PM
It's only 1 amp and its the approximately the correct voltage so I wonder if you could drive it directly from the pwm? I don't really know the properties of the pwm signal, but if it goes from a duty cycle of ~0% - ~100%, it might just cut it. If not, I am pretty sure that the RC world does use the same pwm signal. I wish I could say for sure, but if you could find some rc speed controller to test it on, I would.

Spindle
04-19-2005, 07:30 PM
Yeah I checked out www.robotmarketplace.com . I am not sure of the robot controller would work. I looked at http://robotcombat.com/marketplace_speedcontrollers.html specifically this model, Ant 150 Dual 5A Robot Controller with 15A AUX channel Now it says that the input for the speed controller is taken from the RC Reciever output. Now the big question is, is the EDU RC Mini Controller Board's PWM Outs the same as the RC Reciever outs. In short if I hook this up to the Left and Right motor along with the battey and pwm cables this shouldl work right? Plus there is an AUX line just in case I use it for something :) Thanks for the help guys/gals!

sanddrag
04-19-2005, 08:22 PM
If I remember correctly (which I may not but I think I do) RC receivers send out (and the speed controls like to receive) pulses approximately every 20ms varying in length from 1.0-2.0 ms each with a 1.5ms pulse being neutral. If that is approximately what the PWM command on the EDU RC does than you should be okay.

Another option for speed controllers would be to use two cheap (single) ones made for RC cars.

Spindle
04-19-2005, 10:01 PM
Ok thanks I'll try it! :)

Andy A.
04-20-2005, 12:46 AM
The Edubot controller (at least the old pbasic version, and likely the newer C based board) outputs a PWM signal that is compatible with most hobby speed controllers. Likewise, most R/C systems made for model car use can drive a Victor with out any additional electronics (not true for many R/C systems used for aircraft).

So the Edubot controller will drive a typical R/C speed controller. Whether or not that will work at for you is harder to say. If you're willing to run the motor off a standard RC pack (7.2 volts) then there shouldn't be a problem. It will probably work with 6 volts. Although it seems to me that your current draws are so low that a full sized hobby speed controller may be overkill.

Also, make sure that if you choose to use a hobby speed controller, you get one that is capable of reverse.

I would recommend against trying to run a motor right from the PWM header. The switching frequencies are different and trying to draw that much current from the controller strikes me as likely to cause problems. Certainly, the pwm outputs were not meant to drive anything larger then a servo, and those have their own circuitry to actually control speed and position.

-Andy A.

seanwitte
04-20-2005, 08:18 AM
It's only 1 amp and its the approximately the correct voltage so I wonder if you could drive it directly from the pwm? I don't really know the properties of the pwm signal, but if it goes from a duty cycle of ~0% - ~100%, it might just cut it. If not, I am pretty sure that the RC world does use the same pwm signal. I wish I could say for sure, but if you could find some rc speed controller to test it on, I would.

No, this won't work. The PWM signal output from the RC is encoded with the direction and magnitude, which is decoded by the ESC to drive the motor. The frequency of the output to the motor is around 20kHz with variable duty cycle.

I think the mini-RC can output a 20kHz square wave, but you would need an external H-bridge to drive the motor. By controlling the duty cycle of the output you control the speed of the motor. A full bridge would have one input for the direction and another for the speed. For a small motor this would be an inexpensive option assuming you can figure out how to configure the PWM outputs on the RC.

Gdeaver
04-20-2005, 02:29 PM
If you can do a little breadboard wiring and reprogram the pwm port you might want to take a look at the SN754410 DC motor drive chip. It can control 2 motors. 2 inputs control the direction and the enable line can control speed by driving it with a fixed frequency PWM. Vary the duty to control power. You'll have to modify the default code to change the hardware PWM for the frequency and then add code to change the duty.
This app note is for basic but gives an example.http://kronosrobotics.com/an101/DAN101.shtml The same chip can controll stepper motors too. It could also drive Fets for higher power.There are also chips that can generate the PWM and monitor current for curent limiting. They are harder to implement. Note the warning about the 10000K resisters inline on the inputs. This chip is not isolated and if it fails there could be drive voltage on the inputs. The resistors povide some protection.

Spindle
04-22-2005, 07:18 PM
Ok I am a bit confused, I am am going to get this product Dual 5Amp Speed Controller - Carbide SOZDSCR2.3 at http://robotcombat.com/marketplace_soz.html will it work. I know it can control up to two motors independatly and it will hook up to my motor, battery, and pwm outputs from the EDU RC. My question is that I am running a 7.2volt battery of course and my dc motors are rated for 3-9 volts. I want to run the motors at 7.2 volts. Will the voltage be truncated down to 5volts or will the DC motors ends up getting the 7.2 volts from the battery. I need to know before I make the purchase.

seanwitte
04-22-2005, 09:09 PM
Ok I am a bit confused, I am am going to get this product Dual 5Amp Speed Controller - Carbide SOZDSCR2.3 at http://robotcombat.com/marketplace_soz.html will it work. I know it can control up to two motors independatly and it will hook up to my motor, battery, and pwm outputs from the EDU RC. My question is that I am running a 7.2volt battery of course and my dc motors are rated for 3-9 volts. I want to run the motors at 7.2 volts. Will the voltage be truncated down to 5volts or will the DC motors ends up getting the 7.2 volts from the battery. I need to know before I make the purchase.

It should work, but you will need to do two things:

1. Build a wiring harness to split the battery into two leads in parallel. One goes to the ESC and the other to the robot controller.

2. Read the manual and disable the BEC on the speed control.

Spindle
04-23-2005, 02:45 AM
Would I just have to splice the battery wires having one go to the ESC and the other to the EDU RC or is that in series? If you have a link to a wiring harness similar or a diagram that would be much appreciated. :) Also for the BEC I know its on the ESC but is it also on the EDU RC? Does 7.2 volts come out of the EDU RC PWM Outs or is it 5.0 volts. I needs to be 7.2. Thanks again!

seanwitte
04-23-2005, 09:18 AM
I would order a few male and female battery connectors from IFI. Cut two red wires and join them at one end. Do the same with the black. The ends you joined together will go into a female connector that will mate to the battery. One of the free pairs gets a male connector and plugs into the rc, the other goes into the terminal block on the ESC.

Now you have power going to the ESC so you need just the signal. The ESC will be powered from the battery. If you cannot disable the BEC on the ESC then the best thing to do would be to get a servo extension and disconnect the red lead. The rc only needs to supply signal and ground, not sure how it would react to the BEC input.