Help in deciding the right robotic arm (crustcrawler AX-12A or Lynxmotion AL5D)
Hi all,
I intend to add a robotic arm on my eddie robot. Please help me in deciding which robotic arm to choose. Either the AX-12A from crustcrawler or AL5D from lynxmotion. My main requirement is the possibility of controlling the robotic arm from the main parallax control board. So is there sufficient provision on the main board to connect all the servos of the robotic arm and control it without adding any additional hardware? Can it control both the RC servos and dynamixel 12-A servos? I am not particularly concerned with the esthetics of the robotic arm or its weight lifting capacity but its easy integration into the already existing control board which comes with the eddie robot.
Any suggestions?
Thanks.
I intend to add a robotic arm on my eddie robot. Please help me in deciding which robotic arm to choose. Either the AX-12A from crustcrawler or AL5D from lynxmotion. My main requirement is the possibility of controlling the robotic arm from the main parallax control board. So is there sufficient provision on the main board to connect all the servos of the robotic arm and control it without adding any additional hardware? Can it control both the RC servos and dynamixel 12-A servos? I am not particularly concerned with the esthetics of the robotic arm or its weight lifting capacity but its easy integration into the already existing control board which comes with the eddie robot.
Any suggestions?
Thanks.
Comments
The AX-12A is an upgraded AX-12+. The Propeller can communicate with all seven AX-12A controllers with a single pin. You need to use a couple of resistors on the signal line of the AX-12A. Normal servos each need their own pin to control them. So to control seven normal servos would require seven Propeller I/O pins. Being able to control many AX-12As with a single pin is one of the really nice things about these actuators.
I don't know the details of the Eddie control board, but I'd be very surprised if using AX12-As with it would be a problem.
IIRC the AL5D uses normal hobby servos. This robot arm could probably be used the Eddie board if there are five free I/O pins.
Edit: I just looked at the Eddie board's schematic. It looks like there are 14 I/O pins that could be used to control servos so the AL5D shouldn't be a problem. (Both arms would likely require at least one cog to run the control software in the background.)
Yes I think there are 12 General-Purpose Digital I/Os and 7 Analog I/Os on the eddie control board (Maybe I am counting them wrongly). Actually, I have 10 sensors on-board (7-PING & 3-IR) which occupy 10 I/Os. That's why I am a little worried about interfacing a 5DOF robotic arm with the existing hardware. If I use R/C servos, then I would have to use a separate controller like SSC-32 interfaced with the eddie control board since each r/c servo requires an individual 3-pin connection for power and control signals. Would this interfacing be plug & play? Please advise.
On the other hand if I go with AX-12A or even AX-18A dynamixels, as you said I may have the option to control all the servos in a series-like fashion consuming only one I/O on the eddie control board. Right? If that's true, then this configuration would reduce the complexity of interfacing an additional hardware like SSC32. Actually, I have always played with R/C servos and never had a chance to use the dynamixels that's why I request you to please advise me in the best possible manner.
My interest lies in having a plug & play solution with the least hardware modifications.
Thanks
The Dynamixels have a lot of useful features. I really like the way you can limit the torque they use and being able to read the torque back from the controllers means you can use the servos as input devices. I think you could even use them for haptic feedback (I've tried this with limited success(but I was pretty new to programming the Propeller at the time)). The Dynamixels also have a significant "cool" factor (IMO).
I think it was Ratronic who wrote an object for the AX12 Smart Arm. I modified his object to use with a R/C system (I also modified it so any ID numbers could be used with the servos). I think he has updated his object since he originally wrote it. I haven't tried the updated version yet.
I'd be glad to help you get started using the AX12s. I'm sure I could find the objects I'm referring to if you have trouble finding them yourself.
Edit: Here's Ratronic's forum post about the Smart Arm. I wrote a utility to find the baud(up to 1Mbps) and/or ID of an AX12 if unknown. The utility also lets you change the baud and ID of an AX12 servo. My utility uses a lot of Radtronic's code.
I don't think I posted my R/C controlled Smart Arm code anywhere yet. I'd be glad to find and post it, if anyone is interested in seeing it.
Below is a schematic of the eddie control board:
Please help me in choosing the right option:
1- One way is to interface a "Lynxmotion SSC32" with eddie robot control board to control multiple r/c servos. Is it possible to interface SSC32 with the eddie control board? Any suggestions please?
2- The second option is to use dynamixels and either control them directly from the eddie control board or indirectly by interfacing some additional servo controller with the main board. I have no clue about controlling dynamixels independently or through the propeller so please advise me.
Thanks.
You'll have to do that yourself. There are pros and cons to each approach.
I think the biggest con to the AX-12 arm is the price.
Either method would likely take only one Propeller I/O pin. Either method would work with the Eddie board.
If it were me, I wouldn't use the SSC32 (mainly since I haven't ever used it and I'd feel more comfortable using a second Propeller); I'd use a QuickStart of some other Propeller board to control the servos. The QuickStart can control 32 servos without additional hardware, but it would be a lot easier to use if you limited the number of servos to 28 (so as to not interfere with P28 - P31 used on bootup).
Parallax sells a Propeller board for controlling servos. I think it has connections for 16 servos. I'm pretty sure the same code used by this board could also be used on other Propeller boards.
As I mentioned previously, there are several examples of using AX-12 servos with the Propeller (the code for AX-12+ servos will work fine with AX-12A servos). You could certainly control all the AX-12A servos from a single I/O pin on the Eddie board.
I hope some other forum members chime in with their opinions so u.asif can get a second (or more) opinion(s).
So, if I go with the AX-12A configuration, I may just need to connect all the servos in a series-like fashion dedicating a single I/O out of the 12 Digitial I/Os on the eddie control board, right? Then, it should be just a matter of modifying the eddie's firmware to include an appropriate code to realize an independent control of all the connected servos. No additional hardware or interfacing should be required, right? Furthermore, if I plan to add a pan/tilt system, I should again choose to use dynamixels with it rather than r/c servos so as to occupy minimum number of I/Os on the eddie control board.
Finally, what do you suggest in comparing AX-12A with AX-18A. The price difference is significant but does that correspond to significant performance difference as well? What do you suggest. I generally have no finance-related constraints for the moment.
Thanks
Edit: Please also guide me in preparing the right shopping list for a 5-axis arm to interface with the eddie control board. Here is what I have compiled so far:
1 - Hardware Kit (349$)
2- AX-12A/18A servos (7 for the arm)
3- AX-12A/18A Dual Gripper Full Kit
I assume no additional hardware/software should be required for interfacing/powering with the eddie control board. Please advise.
It had been a while since I'd looked at Crustcrawler's arms and Robotis servos. Those AX-18A servos look like they are a lot faster than the AX-12As. I just don't see the added speed (and some added torque) as being worth the much higher price. In general, I try to slow down the motion of my arm a bit because the AX-12+ servos move a bit too fast to use it accurately. There might be applications where the AX-18A servos would be worth the extra cost, but I don't think a robot arm is one of those applications.
I don't see a problem with your shopping list. Depending on how much shipping costs it might be cheaper to order the hardware and the servos seperately. It looks like their 6-pack of AX-12A servos is a better price than buying them as part of the "Basic Kit".
I think wtih the Dual Gripper Kit, you'll need one additional servo since you can use one from the original gripper.
If I had some extra money to spend on this arm, I'd be tempted to buy six AX-12A servos (you'll still get the good 6-pack price) and two AX-18A servos. As I mentioned previously, my SmartArm had a hard time picking up an empty soda can. It might be fun to see if the AX-18A's provide a significant advantage with either the gripper or some other joint of the arm. I don't think using only AX-12A servos (8 of them) would be a bad choice either.
The AX-12As can pull almost a full Amp of current each. I think this might be too much to draw directly from the Eddie board (except from the motor ports). I think you should be able to power the servos directly from the Eddie's battery.
The hardware connection for the robot arm should be relatively simple to make. I'm pretty sure I could help you out wth this part. Getting the robot arm to work with the Eddie software will be a much greater challenge. I've looked at the Eddie control board's software a little, and it looks like it was purposely made to be easy to add features. I haven't looked at the PC software at all.
I think you'll want to use one of the "Additional I/O" ports to use with the robot arm because I'm afraid the 4.7K resistors on the other I/O ports may present a problem when communicating with the Dynamixel servos (I'm not sure they would). IIRC the data line to the AX-12As needs to be pulled high to 5V(through a 10K(or so) resistor). The 4.7K resistors would create a voltage divider on the data line (probably not a good idea).
If you use AX-12A servos for your pan/tilt system, these could use the same data bus as the robot arm.
No, I don't have a video of my arm in action. I rigged up my arm with my RC gear before I started making videos of projects.
Right now my arm is detached from the base because I had planned to add it to the my TRex600 for the Expo's aerial robotics contest (back when we were going to drop things). I still wonder about adding an arm to my ELEV-8 so I can use it to . . . rescue cats from trees pick apples from the high branches of our apple tree.
As I mentioned earlier, my arm had a hard time picking up an empty soda can. I think with a gripper shaped to match the item it is going to pick up, it would perform a lot better than it has in the past.