elchulono1

Hi,

I'm currently building a robotic arm to attach to my RC that'll use two servos to pick up a beer can. I wanted help regarding crystals and my transmitter. OK here it goes:

I have an RC with a transmitter and receiver with a 75.670 MHz crystal. I have bought two servos and a receiver with a set of 75.430 MHz crystals.

I want to know if I can use a center-toggle switch to connect both crystals to the transmitter and be able to use it to control both receivers: one for the car and the other for the two servos. All I'd have to do would be to flip the switch to the desired crystal.

IS THIS POSSIBLE? Would I have any problems? Please let me know what I need to do.

Thank you for your time,
DJ

mr.rc-cam

That sort of hack is expected to cause problems. The loading on the xtal will change due to the stray wire & switch capacitance. The oscillator's nominal frequency would be affected and it could push the signal into non-comformance (FCC-wise).

BTW, in the USA such modifications are not allowed by end-users. Per FCC part 95 regs. It would be much better to just set up all your Rx's on the same R/C channel.

staggerwing

My Feedback: (5)

Depends on the transmitter. First of all, you will void the transmitters warranty. Second, the lead length and switch may affect how the crystals work. Why not just get a crystal for your second receiver that matches your transmitter? Seems like the cheapest and easiest way to go.

ghendrix01

My Feedback: (1)

Are you modifying a RC car, i.e. adding the robotic arm to the car. If so you should get a 4ch tx and rx on the 75MHz band.

Reguardless of the legal and tuning problems with changing the crystal with a switch, you will also have problems with unexpected servo motion when you switch the crystal. Just like when you turn off the tx without first turning off the rx. To see what I mean, just cycle the transmitter off and on with the rx left on.

George

elchulono1

Thank you all for your replies. I have managed to get the crystals working after burning up a transmitter. All seems to work fine. Now I was wondering about the legal issues. Why is it illegal to use two crystals with a toggle switch on one tx? What kind of consequences are there?

Thanks again,
DJ

amcross

My Feedback: (2)

DJ, it is illegal to change your transmitters frequency without proper tuning. there are pages and pages of discussion here about it if you'd like to do a search and read them. The right way to do what you are doing is a single transmitter with a single proper crystal, with 4+ channels to operate everything you need.