A far too ambitious rc throttle project, I need help!!

[confusedamateur]

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

[Malc C]

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

[confusedamateur]

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

[Malc C]

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..

[EloyM]

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.

[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

[confusedamateur]

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

[vintage1]

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..

[andrew b]

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 :D

[confusedamateur]

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

http://i198.photobucket.com/albums/aa296/georgesp/DSC_0191-1.jpg
http://i198.photobucket.com/albums/aa296/georgesp/DSC_0193.jpg

[MikeDD]

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.

[confusedamateur]

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

[MarkusN]

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.

[confusedamateur]

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

[Malc C]

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.

[Endurance]

Why not just try wiring it into your transmitter like MikeDD suggested?

[confusedamateur]

There is nothing marked on the throttle to indicate resistance. Took it to a mechanic friend and we tested the wires:

Black to red - 2.2k constantly

black to red - no change

white to black - first it seemed to change when twisted but then we couldn't get it to do it again and it seemed constant on 13.46M

white to red - 1.5M

This stumped him slightly and I wonder if any of you can work out what's going on. much appreciated

[Dan Baldwin]

If it's just a pot, either it is bad, or the connection between the meter and the pot was bad when you made the last two tests. It's possible that there are some electronics built into the throttle, and the readings are correct, but it doesn't seem likely.

Dan

[MikeDD]

Possibly a rotary encoder circuit then, though would seem to be a bit overkill.
I assume this electric bike had proprtional throttle and not just off, slow, fast?

[red-panda]

Since I have a spare electric bicycle throttle, I took it apart to see how it works. The active bit turns out to be a hall effect device, sensing a moving, and presumably magnetic, strip. This means that the three wires coming out of the controller are + and - volts, and a voltage proportional to throttle position. This voltage will depend on the supply voltge, and the spec of the sensor. Common sense says that you could probably test this by applying around 5v. to the red and black, and measuring the output on the white wire, but this assumes the manufacturer has used standard colour codes. If you can dismantle your throttle further, there may be a part number on the hall device, so you could check its specs via the manufacturers data sheet.

Hope this helps

Chris

[confusedamateur]

Chris, Thanks so much for confirming the nature of the device. I will try and track down the data sheet and test it with a battery. My preliminary investigations suggest that most run on 5V. I suspect this makes it slightly more complicated to use as a transmitter!? I suppose it cannot just be connected to a transmitter to replace a pot, due to it not being a pot. Is there some way anybody knows to get around this? any further input is greatly appreciated

[MarkusN]

It might still work like a pot, if output impedance of the throttle and input impedance of the sensing circuit of the transmitter are right (i.e. the current that the transmitter draws does not bog down the hall sensor's output). Basically the wiper of a pot also just outputs a voltage that is proportional to position, so not much different from what the Hall sensor would deliver. The question is the range of voltage being output, though. You may need some adapter cirquitry to overcome this.

[MatC]

A simple pot wouldn't make much sense for most automotive applications - pot output is relatively high (and variable) impedence, so very subject to noise. Chances are it's something active like red-panda suggested.
Hopefully it's power in and signal out - If the sig out is a voltage you might still be good to go to a standard transmitter. If it's PWM or something else, you'll have a bit more work to do.

[confusedamateur]

Hi Guys, thanks for your continued input. Still no word from the Chinese manufacturers of the device.... I bought myself my very own multimeter!! and have tested the throttle using a 9V battery:

black to white- resting-1.12V
fully twisted-7.51V

red to white- 7.83V
fully twisted-pretty variable but i think it was aroung 2.68V

I dont know if this allows anybody to suggest a way to plug it into my transmitter?
I own a battery pack, servo, receiver and an Ace RC 'Jaguar' 2ch AM 27 mhz transmitter. Many thanks again for your help.

[MatC]

black to white looks promising, but if you're testing that with a multimeter you won't know if that's a variable DC level or a PWM signal being averaged by the multimeter. Like others have said, I think you're biting off more than you can chew here, but if you want to progress, you need to understand the following:
- Nature of the output signal (ideally put it into an oscilloscope)
- Nature of the transmitter input signal (probably a voltage instead of the pot)
- How to convert between the two.

[Malc C]

Its not a perfect answer, but if you download one of the free windows based oscilloscope programs and use your soundcard to check the outputs. This will atleast show you if the output is a PWM signal or a voltage level.

My guess (assuming that we've all agreed its not a pot) is that its some hall effect device that either sends a voltage out or a PWM out that is proportional to the distance between the device and its trigger (magnet etc).

IMO this is one project I would give up on.. even with a fair bit of experience of electronics.

[confusedamateur]

I have decided to attach a bowden cable to the actual control stick and use a motorcycle twist grip to push/pull the control stick, I am much happier using this simpler, less electronic method!! Thank you all for your patient replies