Placement of RC Equipment
by David Thomson
I'm at the point of installing the RC components in my Hellen Trawler. I have a 2.4Ghz system. Any placement pit falls to watch out for regarding location of receiver, ESC & battery pack in relation to the servo & motor? I'm thinking about electromagnetic interference or is that not an issue with a Spectrum DX6 - 2.4GHz?
#2; Fuse question: Battery pack NiMH 7.7v (8,000mAh); motor 7-14V & .8A draw; ESC 4.8 to 12V, max 40A with BEC 6V and 1amp. There are lots of conflicting opinions on "to fuse or not to fuse" and where to fuse - between battery & ESC and/or ESC & motor. I'm leaning towards not fusing or at the very most a 5amp fuse between the battery and ESC. That should protect against the ESC or motor drawing too much power. But part of me says the ESC would automatically shut down if things got too hot. What's your take? Thanks.
First, congrats for getting this far. Now onto the questions...
1) I don't think you need to worry about interference with the 2.4GHz band. Having said that, it's always good practice to keep power cables separate from control cables. The leads going from the ESC to the motor is especially of concern since it is most definitely a PWM signal (pulsed at moderate frequency) and carries a relatively high current, so the emitted EMF is relatively strong. Overall, I don't perceive interference to be an issue though.
2) Once you've witnessed a Lead Acid Cell short out, you'll be in favor of fusing. I'm aware that's not what you are using, but the power released in any charged cell can be life-changing, if you know what I mean.
Placing the fuse between the ESC and Motor makes no sense to me. I think the theory is that it will protect the ESC from a short downstream. I don't feel comfortable placing anything, other than leads, between the ESC and the motor. Not sure why, it's mostly a hunch. I'd rather fuse between the Battery pack and ESC as you mentioned.
In my mind, the fuse is not primarily there to protect the ESC or radio, but rather to prevent fire and/or explosion and any consequences thereof.
With that in mind, I'd go for a 10-20A fuse. 5A, as you suggested may work, but could possibly blow if you encounter sea weed in the prop or other occasional, but not catastrophic situation. I'm thinking it's better to limp home than to be paralyzed unnecessarily.
I'd stay away from the automotive blade-type fuses. I find them unreliable and with too rough of a tolerance span. Instead, one of the glass types in an inline holder have worked well for me so far. Just make sure the holder and fuse are compatible, and that the lead is of sufficient gauge to handle the current.