Hi, I am working on a project that involves me needing to remotely control the throttle on a lawnmower engine using a twist grip throttle. I understand that I will need a servo to move the butterfly and alter the throttle, then a receiver to pick up the signal from my transmitter and a battery to power them. I have a twist grip throttle from an electric bike so it's fully electronic, this is the thing that is confusing the hell out of me right now, How on earth do I turn my twist grip throttle into an rc transmitter?! Any help, both large and small would be greatly appreciated, George

why not simply use a standard transmitter, or are you saying that you want to control the motor via a radio signal in like something like a go-cart where you will be riding the item you wish to control

I need to control it with a twist grip throttle for ease of use, it is unfortunate as obviously a standard transmitter would be desirable. thanks

You still haven't given too much away as to what you are actually trying to do, so its hard to suggest ways that may work.

Twist grips such as those used on motorcycles etc use cable to operate the throttle. You would need to change this for a potentiometer and then use an alternative to the pot used inside a standard transmitter.

Failing that, you could design your own radio transmitter that use a microchip to convert an analogue voltage produced by the pot in to a digital value, which then uses this value to set the pulse width of the signal you want to send to the receiver. This PPM signal is then modulated using whatever frequncies are legal in your country and transmitted to the receiver.

Depending on your level of expertise, you can either scratch build the controller, or source ready made items like an FM transmitter, etc..

Please remember that you can not do this legally on 72 or 75 Mhz, legal only for "Flying Models" and "Non-Flying Models" respectively. You can only do so on 27 Mhz (Radio Control Devices) and 49 MHz, which is limited to 100 milliwatts of power but ample for your application.
Look at converting one of Radio Shack's toys, they are on the latter frequencies.
In addition to being ilegal on 72 or 75, you could cause interference and serious damage to very expensive models and/or people.

In the UK its 35 mhz for flying and 27 & 40 mhz for surface

Eitherway, Eloy raises some very good points, plus you should make sure you have enough public liability insurance just in case your project causes such damage and or injury

thank you for your help guys, as for the frequency I will certainly make sure I follow the law on that one. The twist grip throttle does not use a bowden cable, it is from an electric bike and is fully electronic, it has a metal strip inside that is in contact with a point and moves along it when twisted (not a very good explanation I know!!) and output is in 3 wires. I will post pictures tonight, thanks again for your help

Originally Posted by Malc C

In the UK its 35 mhz for flying and 27 & 40 mhz for surface

Eitherway, Eloy raises some very good points, plus you should make sure you have enough public liability insurance just in case your project causes such damage and or injury

Strictly 27MHz is for just about anything, including aircraft and Bluetooth type mice and keybaords..

Originally Posted by vintage1

Strictly 27MHz is for just about anything, including aircraft and Bluetooth type mice and keybaords..

I still have a 27MHz AM Futaba M series setup that I use to fly with, channeled on brown,(26.995) In the 30 years I've had it all I have ever needed to do was change the cells every 5 years, never had a glitch or a crash. Seems to have REAL transistors in it

here are 2 photos of the twist grip throttle, one shows the output of 3 wires and the other shows the mechanism (metal plate inside moves with grip). I hope this will help explain the device and allow someone to suggest a method of essentialy using it as a transmitter. Many thanks for your ongoing support

I would guess some sort of pot. Red and Black to + and gnd, White to wiper. Check with Multimeter. If 5K it would be easy to wire in a standard TX.

ok, cool, how would I go about testing it with a multimeter as it is obviously not part of a circuit? probably a stupid question.....! cheers

Not wanting to step on your toes, but your questions lead me to believe that you should look for some local help. You obviously don't have the foggiest idea how these things work, and if you have to consult an online forum for every step you take things are bound to get tedious.

As for your latest question: set the multimeter to Ohms and measure the resistance between the red and the black lead. If it is 5 k you are lucky and can use the grip as direct input to a standrad transmitter, replacing one of the pots of the sticks.

At the same time you can check for which connetction of the multimeter the reading changes with position of the throttle grip. If Mike's assumption is right (very likely), thats white to black and white to red; black to red being constant. The lead that's involved in each combination that gives varying resistance is the one connected to the wiper, i.e. the one carrying the input signal to the Tx.

You are right MarcusN I really dont have the foggiest idea about building my own rc project, I am an engineer at heart and have delayed this part of the project's electronics until now, but I had to ask someone and there dont seem to be very many people who are accessible for advice in my area so I thought the forum would be a good place to seek help. I really don't want to be irritating and I do very much appreciate all the help I have been given. I will test the pot with a multimeter, thanks

I think the point Markus is trying to make is that if you have little or no understanding of how a simple pot works then what hope do you have if you need to troubleshoot your project when it has problems. Its not a case of asking on forums or local contacts, basic electronics guides, how to's and general "how things work" can be found on the net, and a few hours research might help you undrstan how these things work

Just to help, if you don't have access to a meter, often the value of the pot is marked on the can. I would susspect that the value may be 10K or 100K.