Hi…
I’ve been working on my RC lawnmower for about 6 months now. Build is almost complete, just testing electronics. I have a Sabertooth 2x60 that I tested 6 mns ago when I bought it. I use a Spektrum DX6e. I connected the Sabertooh to a couple of small brushed motors connected I had around before I got my wheeelchair motors. It worked great. I was getting ready to test with the wheelchair now motors but suddenly my Sabertooth seems to have quit.
I don’t have anything other than power (24VDC) wired to it, and the receiver’s 2 channels (right stick, channels 2+3). The Sabertooth outputs 5VDC to the receiver OK, and occasionally the fan comes on. But there is no output to either motor terminals and for some reason NONE of the LEDs light up—not the Status LED, not the Cells LED and not the Error LED.
I know in my initial testing 6 mns ago I shorted it once when the battery wires touched the heat sink (silly design, I now have tape across here). But it still worked after that. Yet now, 6 mns later, I can’t get a status LED to light.
Did I fry it? Should there be a status LED of some sort on when battery power is connected? Or is this a communication issue with my receiver? I would have though at least the Status LED would power on.
@CalgaryPT Honestly good question, so some preliminary questions, with special attention to point 3:
- Can you spot anything on the board which appears fried? It can be as small as a surface mount resistor or the main chip itself. Look for burn marks anywhere and everywhere. Many components are under the heat sink which is unfortunate, but try your best.
- If not, you disconnected everything and re-tried with the smaller motors?
- If you tried and it doesn’t work, double-check the setup again just in case - oversights like reconnecting cables the wrong way happen to the best of us. Note that the Sabertooth PROVIDES 5V on the red pin, so if you powered your receiver from a separate source and didn’t disconnect this pin, you’d have two power supplies on the same line (not good).
- Might seem evident, but double-check the voltage of the main battery, and the batteries in the transmitter just in case
- Check that the DIP switches are pushed to the sides properly (nothing’s “in the middle”) and the settings correspond to your setup.
- The board has built-in protection, so it should have shut off if there was too much current draw.
So, if it still doesn’t work after all of this, the problem as you said might be an ESD discharge which fried something within the main chip.
Await your update .
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Thanks for responding. I did in fact order a new board from you via Amazon, and am awaiting it now.
- Nothing looks fried. Went over it with a magnifying glass and I see nothing. Again, the 5VDC output works and is powering my receiver. Occasionally the fan works. No fried or burn marks I can see, but as you point out the good stuff is sealed down under.
- Haven’t tried this but I will. However, I can’t even get a status light with just the power connected. (I used a power supply @24VDC to test and then tried a 12V 35AH AGM battery).
- The two harnesses from the receiver to the Sabertooth both have their red wires cut (now), so I don’t think this is the problem. (Having said this I know I originally didn’t cut these when I first got the Sabertooth, but then remedied it). It seemed to work fine after this mistake 6 mns ago. I was new to RC and it took a few days to understand this.
- Did check with a Fluke VOM, both when using the power supply for testing as well as the AGM battery. Also, the fact that I am getting a regulated 5VDC @ the receiver output tells me I am in fact getting correct input voltage.
- I haven’t changed the DIP switches since my initial setup. They are 1 (DOWN); 2,3,4 (UP); 5 (DOWN); 6 (UP).
- I don’t see that I could have drawn too much current as I haven’t yet tested them on my 250W wheelchair motors. The only thing I had them connected to were two small brushed 12V motors used for power car windows (for testing purposes). I was able to get everything hooked up using these 6 mns. ago and was happy to see them operating differentially from the right joystick on my DX6E. So I put the Sabertooth away until I finished the build and was getting ready to test a few days ago.
So I messed up twice: once with the 5VDC output when I first got it (had power from the receiver as well until I figured out my mistake), then with the ESD across the heat sink (hate that design). However, it’s weird that it worked so well even after both these mistakes when testing on the small motors, and now not at all. I would have expected the failure immediately after the ESD.
Oh well, live and learn. It’s been a fun build for 6 mns., and I learned tons. I even had a linear actuator working to adjust the lawn mower deck height at one point. But I bailed on that idea because the geometry of the setup made for such a long wheelbase it defeated the purpose of differential steering.
The new board should be here in a few days. As expensive of a mistake this has been, it’s been the only big one so far, and everything else is also ready. It’s also -38C in Calgary today…so I’ve got some time before I’ll be mowing any lawns.
Thanks for the suggestions.
As you’re well aware, we all make mistakes - some more expensive than others and sometimes even the most knowledgeable people still trip up or encounter “act of god” situations. A blade of grass might end up more conductive than others, get itself lodged somewhere and cause a short circuit. The best designs are the ones where the creator persisted despite obstacles like that (grated they do make the wallet a bit lighter). Looking forward to seeing the robot in action! Instead of scrapping the board, consider gently removing the heat sink to see if you can spot anything. Dimension Engineering is an excellent company to deal with and although RobotShop can’t approve an RMA if it’s due to customer’s actions, they might have some options, so it’s worth reaching out to them just in case (they really appreciate honesty): [email protected]
You’re right. It’s all about persistence. I got into this because I do metalwork for a hobby and knew I could handle that part easily. I understand electronics pretty well and build lot of my own circuits; but the RC side was a real learning experience. So I am almost there… I basically looked at a upkit kit available online but just bought the motors and modified a design I liked so I could utilize my hydraulic punch to make the frame. I’m playing with some Arduino failsafe such as a flex strip that shuts things down if an obstacle is contacted. Lots of fun.
I will remove the heatsink and investigate further and see if repairable so I have a spare. In the end, it’s all the cost of education right?
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Ah HA!
Took the board apart…RIP:
P.S. I did email Dimension to see if I can get the SMD’s to try to repair. We will see…
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If they cannot send you the component, perhaps its specs so you can order it from Digikey?
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I emailed them as you suggested and was shocked that they offered to repair it for free. They issued me an RMA number and I popped it in the mail yesterday. I couldn’t believe it. What a great company; you don’t see that anymore. Thanks. Now I will have a spare it looks like 
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