Im currently building a remote control snow plow, yes it sounds crazy, but very cool. Right now im trying to figure out a way to lift the plow up and down. I have an actuator from an electric wheelchair. my issue is how do i hook it up to the servo so it can be remote opperated!
Thank you for your help!!
I am sure you mean servo output…
There are some “make a big servo out of a motor” style kits out there but I am unsure if there are any that will work with your actuator. Let’s pretend there is not one and we will have to make our own.
The first issue is the feedback pot. Inside of most servos, there is a pot that reads the position of the servo. This information is sent to the little brain inside of the servo. You would need a similar system on your actuator. The good news is that there may already be a linear pot of some kind inside the actuator. If the actuator does not contain any kind of feedback pot, you will have to fashon your own. This is going to take some MacGyvering, but somehow, you need a change in resistance as the actuator moves in and out.
Assuming you figured that out…
This pot (or whatever is reading the postion of the actuator) will go into your microcontroller --most likely into an ADC (analog) input. Now your micro controller knows where the actuator is. Next, you need to “read” the signal coming from the receiver (this is the signal that would normally go to a servo). Most micro controllers have a “pulse in” command of some kind that can do this. The “commands” going to a servo are actually little “pulses” and how long each pulse is, determines the servos position. In our case, the microcontroller is going to read these pulses so we can know where to put the actuator.
So far, we can read the position of the actuator, and we can read what position we want to be in (from the reciever to the microcontroller)…
Next, the microcontroller needs to actually turn the motor (in the actuator) on and off (fwd and rev) to put it in the position we want. You will need a motor driver for this. Assuming the actuator tilted the seat or raised the passenger on the old wheel chair, it is probably a pretty hefty motor and thus, will need a pretty hefty driver. First, see what the actuator is connected to on the chair --There is a posibility that the actuator has its own “stand alone” driver. If not, you will need to determine the current draw of the actuator (either by reading it on some kind of ID plate on the motor) or by measuring the current under load (with a meter). Simply buy a motor driver big enough to handle it.
From there, it is just a matter of running the actuator from one end to the other and noting the values coming out of the pot. When you know what value is being read by the ADC at each end of the stroke, it is just a little math to figure out all the positions in between.
Now, you just have to do the math to get from the “pulse in” readings from the RX and translate them to what should come out of the pot at that position. The microcontroller fires up the motor driver and keeps an eye on the pot. If the receiver says, “put the actuator in the middle” the microcontroller turns on the motor on the actuator until the pot reads that it is indeed, in the middle.
This may sound complicated, but if you break this problem down to individual steps, i.e. at first, just try to read something from the receiver, you can figure this guy out.
Good luck
do you need the full range
Do you need the full range of height control or only an “up” and “down” direction?
In the last case it will be much easier to make. It can be that easy as a servohorn pressing 2 switches.
see below on this page: http://vfranco.blogspot.com/2011_03_01_archive.html
