I have a sabertooth 25a speed controller running two electric wheelchair motors on a rc lawnmower. The system wks well with my AM transmitter/receiver combos and super glitchy (unusable) with the more expensive Futaba 3pm FM tansmitter/receiver. I have good 12v batteries running the thing. So, I don’t think “brown outs” are the problem. I’ve also soldered in 104 ceramic capacitors between both electric wheelchair motor poles. These capacitors helped. I’m still experiencing control jitters with the AM system when I’m more than 30ft away. Still, I can’t get FM to wk at all. Any ideas? Thanks guys.
Are you sure the FM radio doesn’t have a seperate unrelated problem? In other words does it work with servos and no wheelchair motors?
rawdoggy,
What style of antenna are you running?
It should be vertical and as far from the motors as possible.
Those wheelchair motors probably have some pretty big magnets along with a pretty strong magnetic field that could be causing you some of your rf problems.
Just a thought.
Regards,
TCIII
My transmitter and receiver are brand new. It runs both of my rc trucks and my boat beautifully. No interference problems at all. I was wondering if perhaps I had the rc terminals wired incorrectly. The sabertooth manual was a bit fuzzy on this subject (just an unclear photo). I would think the wiring is correct because it wks with the AM system. Here’s how I have it wired now:
-ch.1 and ch.2 positve wires to 5v
-ch.1 and ch.2 negative wires to 0v
-ch.1 signal wire to S1
-ch2 signal wire to S2
Thanks.
I have the antenna running 1.5 ft straight up in a plastic tube. The receiver and antenna are only about 8in. away from the motors. I’ll try moving them farther away tonight. Thanks for the tip.
Its definitely a little odd that you’d have glitches with an FM system and not with a (usually considered to be more reliable) FM system.
First question: Are you running a separate RX pack? If so the 5v conection should be left unconnected. Otherwise it sounds like you are hooked up correctly.
Are the AM and FM transmitters both running the same frequency range? I.E 75MHz?
Definitely move the reciever and antenna as far away from the motors, motor drive and wiring as possible. Especially the wiring.
One thing that sometimes helps is twisting each wire pair together. This will cancel out some of the field, and will be RF quieter than having the wires running separately, or even worse running apart from each other.
I think the biggest question to answer is whether the AM system is on 27mhz or 75mhz.
I’m not using a seperate batt pack for the receiver. Though I’ve certainly tried to. Just to see if it would correct the problem. The AM system that wks is 27mhz and FM system I can’t get working is 75mhz. I’ve been an rc hobbyist for years and I’m just getting into robot building. Needless to say, I’m an amature when it comes to electronics. Though I do have a good grasp on electrical circuitry. Please bear with me.
All rc connections are twisted together. Wiring is correct. The antenna is positioned correctly. I’ve also tried the FM setup and two smaller/matched motors ( really small magnets) supplied with 14.4v to the sabertooth. Still can’t get the FM to wk… Is this a common problem? I’m totally stumped. The FM system wks great with just servos conn. to the receiver. When the transmitter is switched off there is no sign of interferance to the receiver. Everything stays completely still. Maybe it’s an incomatable FM system. It’s the Futaba 3PM/ digital proportional/ 75mhz FM/ 3 channel. I’m using ch 1 for throttle, ch 2 for steering, and the 3rd channel is unused. The transmitter is programmable. But, I’ve wiped it clean. Every adjustment has been fooled with and even zeroed out back to factory default settings. Thanks again for your help… keep the tips comin’ if your not totally frustrated yet.