Good evening all.
I am new to the forum so please excuse me if I get some of this wrong.
I am building a boxing robot and I need some advice and suggestions on arm sensors and motor controllers, and I'm hoping that some of your robotic gurus can help me out.

I am building a boxing style robot with two robotic arms
I have linear actuators on the arms but they currently operate at full speed in forward or reverse and I would like a bit more finesses in the operation of the arms
The linear actuators are Linco s200 (12 volt 3amp max)
I am loojking for advice on a motor controller that would operate these units at variable speed and forward / reverse
There are three motors so a controller that can operate three motors (or three controllers)

I am also looking for a linear position sensing potentiometer or rotary potentiometere or joystick that can be used to trigger the linear motors
I have an scale model analogue of the robot arms version and movement of the scaled arms is translated into movement of the large arms.
(I am looking for incremental movement not mirror movement)

Does anyone have some suggestions for arm sesnsors and for motor controllor. Any advice would be greatfully accepted
Chris Maca

Hey,

Not quite the sort of thing we typically build here but will do my best to help you out.

3A is pretty low current so you should have no problem driving them. If you want some commercial controllers I would suggest pololu.com. If you want something cheaper you can reprogram RC plane brushless ESCs yourself. Or myself and aaron are reselling them here www.botbitz.com

I am not sure about the small pots. Maybe try and get some control of the robot from manual input first then worry about that.

Steve
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Steven Martin
Twisted Constructions
http://www.botbitz.com

Welcome!

I did some work at my uni with some guys doing mobility assist robots, which can detect and then enhance strength and movement like a real life mecha suit. The biggest problem with linear actuators in this application as i'm sure you're aware is they're SLOW, but very powerful.

The people I was working with used very high cost maxon motors with built in encoder, coupled to a custom made planetary gear reduction. They could detect the location of the joint through the encoder but also did some experiments with soft pots (http://www.spectrasymbol.com/softpot) and a swiper at the top of the joint for absolute position sensing. The beauty of the softpot is it could be wrapped around the radius of the joint.

Can't really help on electronics, really sounds like a highly custom environment but could perhaps be done with a 'dumb' beefy Hbridge being fed signals from a PC or such. Not really my field...

Pneumatics would be a nice cheap way to get rapid movement but then you really lose out on resolution on the movement.

Hi guys, thank you very much for the suggestions, let me provide a bit more information.

In terms of power I am prototyping with linear actuators but I plan to swap these out for hydraulic rams. Hydraulics are stronger, smoother, lighter at the arms abut more expensive. For the prototype the controller will drive the linear actuators, when I swap to hydraulics they will drive variable hydraulic vales.
Steve, Thanks for the suggestion , I will grab one of your controllers and try it out, If it works well I can get a few more. Which one would you suggest, (i'm guessing the ESCheap85?)

In terms of control, I'm going simple at the start, it is essentially a joy stick to control each motor inwards and outwards, but the joy sticks are mounted on the joints of a small control arm. As you move the control arm, the robot arm moves. I don't want absolute or mirror positioning at this stage, I want relative positioning. ie you move the control arm out and the large arm moves out until you pull the small arm back. This way small movements in the control arm can drive a full range of motion in the robot arm.
So what I’m looking for is a stand alone joystick or a linear sensor to sense movements in the control arm elbow or shoulder.
I'm assuming a stand alone joystick shouldn't be too hard to find, but I haven't seen one
If you have any suggestions in this area they would b greatly appreciated

Thanks Chris

Hi Chris,

I can't really offer much in terms of solutions or suggestions right now but I'm just curious; what sort of boxing robot is it? Is it being built to compete against other boxing robots in a contest? If so, would linear actuators and/or hydraulic systems not be too slow for arm movements and such?

We've got a couple of boxing robots over here in the UK that do the rounds at various live robot events and all their actuations are pneumatically powered. It allows for a fast punch that's more akin to something you'd see in boxing, compared to the steady movement of electrics/hydraulics.

Not saying that actuators or hydraulics are bad, but just curious as to why
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Jamie
RogueTwo Robots
www.rogue-two-robots.vze.com

With great power, comes great reliability

Thanks for your reply

The robot is actually more of an exoskeleton than a true boxing robot. Think WallE 6 foot tall or a bobcat with two robotic arms. I describe it as a boxing robot in the first pass because it is a simpler headline and this is one of the end games. In the short term I'm building a
In the large WallE or SpyKee that you sit in and operates as a robotic exoskeleton.

For the prototype strength and finesse are more important than speed. Speed can come in the second stage.

I'm interested in the boxing robots though, do you have a link to them?

Do you have any information on the arm control systems that I can learn from?

What sort of control protocol are you proposing between the master arms and the robot? All our stuff uses R/C tramsmitters that are probably not much use for your robot - have you thought a more sophisticated protocol like I2C or CAN? you need to decide on the control protocol before you choose

You mentioned you wanted the arms to have some strength as well as speed and precision control - I don't think hydraulics will provide enough speed unless you have a really massive and expensive pump. It would probably be just as easy to up-size the electric actautors with custom units.

You probably don't need linear sensors on the control arms. Think of it this way; when you reach out to get something, your arm doesn't change length, you change the angles at your shoulder, elbow and wrist. What you probably need is a rotary encoder or potentiometer at each joint.

Keep in mind that you will need some way of converting the position sense to a control signal that your actuator controllers can understand. If you use Steve's hacked ESCs, you could buy a cheap Hobbyking radio and get 4 channels of control by hacking the joysticks to take your own arm-mounted potentiometers If you want to go with something more sophisticated, you will need an MCU board like an Arduino at the controll end and ESCs that understand one of the serial interface busses.

For control it may be worth looking at something like a Kinect.
http://www.youtube.com/watch?v=g28riwk4krA

RC control is pretty easy most of the time which is why most people use it. And just make everything an RC servo style input. But no reason why you can't use something more sophisticated.

I made a simple interface to RC transmitter just using a micro.

Pictures might help as well..
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Steven Martin
Twisted Constructions
http://www.botbitz.com

Thanks for that Nick, that is realy helpful
I take your point about the rotating potentiometers on the arm, I just need to allow for small angles of movement to translate into motor signals.
For control connections the control arm (and potentiometers) can be hard wired to a motor controller at this point. The first step is not remote control but onboard control (exoskeleton style) so the sesnsors can be hard wired to the motor controller. Step two down the track is a remote control version, but I need to get the finesse and control right first.
I’m thinking that if I use a rotary potentiometer or a hacked joy stick, I can plug this into and ESC and then plug the motor in and movements in the control arm will move the robot arm and give me slow sensitive movements or fast movements up to the limit of the motor speed. I have it working in prototype with simple DPDT rocker switches but it is all on or all of so the finesse is not there. Is my thinking sound or am I missing anything here.
Do you have an suggestions for a motor controller that can take 3 to 5 potentiometer inputs, hard wired in, and drive 3-5 linear motors (3amp max), in a nice simple package?

Your suggestion for a MCU board like an Arduino at the control end and ESCs to drive the motors that understand one of the serial interfaces, is where I was heading.

Am I smarter to go Arduino board and Arduino controllers
Or Pololu and pololu controllers
Or is there a smarter mix and match solution

If your looking at using something similar to a MCU to control your robot make sure you buy one with enough expandability. You need 1 PWM output for each ESC you want to drive. 1 analog input for each potentiometer and 1 digital IO for each encoder.

You might want to look at the Axon or Axon II if you want to go bigger in the future, the Arduino only has 6 PWM ports.