Let's Make Robots!

TRex Jr Motor Driver and FA 130 motors

http://www.pololu.com/catalog/product/767/specs

http://www.pololu.com/file/0J11/fa_130ra.pdf

 

I just got these products and I am trying to build an RC controlled robot. I have the TRex Jr controller and the Tamiya dual gear box with FA 130 motors. I hooked the TRex up to my reciever and configured it. I did a test with the LEDs and everything seemed to be working fine and I was getting a 5 V signal out of both motor outputs. When I hook up the FA 130 motors (with .1 uF capactiors across the leads) the drive LEDs flicker and the motors make a high pitched noise and do not turn. When I hook the motors directly up to a power source they turn normally. I realize the FA 130 motors are designed for 3 V operation but I was under the impression they would work fine with a 5V input and just have a shorter lifetime. 

 I am clueless as to why my motors aren't working. I know these motors have high current draw but the TRex Jr is supposed to be able to supply 2.5A to each motor which is above stall current for these motors. Does anyone have any suggestions? 

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What kind of receiver? The motor driver is not exactly "RC ready"... You need to be giving it some serial data to work with.

I am using a spektrum AR6200 that came with my transmitter. I know it is not the ideal for robotics but from what I read it should work. It just doesn't have all the fail safes necessary for a competition like battlebots. According to the manual it seems RC ready. How can you give it serial data when it has a jumper to select either RC or serial mode? I thought it was to be operated as either RC or serial. When I had hooked it up without any motors all the LEDs were working properly(not flickering) based on how i moved the control stick. That is why I figured it was an issue with my motors or how they were interacting with the board. 

Do your motors run when you lift them up off the ground, assuming you have wheels on them? What about if you start them turning with your finger? 

The motors are probably drawing too much current. Try putting the motors in parallel with the leds and sticking a bigger capacitor in there for when the motor starts up.

I have em hooked up without any wheels at the moment .. just the motor because I wanted to verify that it turns under no load. I'll have to see what capacitors I have lying around. How much bigger do you think would be needed?

 I thought it might be a current issue after I had read some about them on this site, but was confused since supposedly the TRex can supply 2.5 A  which is above the motors stall current.

Have you tried hooking up the reciever to a servo to see what sort of motion you are getting out of it. It may be that it's just not getting a high enough signal. I used to make motors do that high pitch sound with my rc setup when I would give it just enough throttle to get the juice flowing, but not enough to make it turn.

Have you gone through and calibrated the board yet?

Are you using a fresh set of batteries for the motors? are you using a rechargable batter?

can you connect the battery direct to the motor and verify that it turns?

Do you have an image of how the setup looks. That might help with this.

 

I don't have any servos around at the moment so I am not able to do that. I just started into robotics and most of my stuff is currently on order. These were the first parts to arrive. I calibrated the board and I am using a 9V battery to power the board at the moment. I might try going to a 6V NiMh I have lying around.

The motors turned being independently powered.

Also, no images yet sorry.

Edit: Actually, I think the battery might be my problem. I didn't even think about looking up how much current a 9V could source and I doubt it is enough to drive these motors. I will check that now. 

Hehe, 9V batteries are notoriously unreliable under heavy load - internally they're usually made from 6 x 1.5V AAAA cells, which gives them a relatively low maximum current. This of course results in poor performance when a load tries to draw a large current from a 9V, such as with your motors =)

hrmm...the manual says you can manually calibrate the device, have you tried that as well?

not sure what else to try at the moment.

Yes it was calibrated. I got it running by using my NiMh. I feel stupid for not thinking about the current sourcing of the 9V battery to start out with. Luckily I had a 6V NiMh that is working with the motors. Live and learn.
Extremely common mistake Devarsi, I remember wondering why all my 9V powered devices kept dying too. If you look at professional products that use 9V batteries you'll notice they all have low power consumption, such as smoke alarms, RC transmitters, radios, etc.