Does anyone need a hand servo controller
I had a robot project where I wanted to build a small hand using a servo. The problem was that once the hand had the object, the servo must stop so that it doesn't break. So I just got done programming a m.c. today so that it can sense the pressure and stop the servo from moving more. The chip can be polled (serial) and it will send back the servo position, pressure and other data. The chip can be sent data so that it can set up a low and high limit on the hand servo as well as at what pressure to stop the servo at. The other 7 servo ports are just normal ports that can be stepped 10 us at a time to 2.29 ms.
If anyone could use one for their robot project, let me know. You will have to cover my cost for the chip and s/h.
PS
If anyone would like to trade a PCB layout design for 5 chips; let me know. I hate doing PCB layouts.
Al
If anyone could use one for their robot project, let me know. You will have to cover my cost for the chip and s/h.
PS
If anyone would like to trade a PCB layout design for 5 chips; let me know. I hate doing PCB layouts.
Al
Comments
Servos work in a much different way than steppers. The chip is only good for servos. Fifteen would cover it if you live in the US. Outside the US, I would have to look up the shipping cost.
Al,
I'm trying to figure out how you can sense position and pressure of the servo.
Are you monitoring the current drawn by the servo to determine the pressure/torque? Do you need to hack the servo in order to measure its position or pressure?
Beau came up with a method to sense a servo's position by limiting and monitoring the current to a servo.
When you say the chip will send back the position of the servo is this the actual position or is this the position of the last command from the uC?
I've seen your cool robot with arm picking up a glass vase here. I'd be very interested in seeing your force sensing servo in action (and to learn how it works).
BTW, Are you aware the Propeller can easily control 28 servos (32 if you have a way of disconnecting them during bootup) with 1us resolution?
I have designed boards that controls 16 servos & I'll be interested to take this on since I've recently just completed a project. Do you have the schematics done?
If you are good with the 5 chip payment; I can have a schematics by Wed. Let me know if that is good with you.
Thanks,
Al
Are you monitoring the current drawn by the servo to determine the pressure/torque?
Yes
Do you need to hack the servo in order to measure its position or pressure?
No
Beau came up with a method to sense a servo's position by limiting and monitoring the current to a servo.
I would not use the word "limit" I use a 2.2 ohm resistor to monitor the current.
When you say the chip will send back the position of the servo is this the actual position or is this the position of the last command from the uC?
It only gives the position for the servo hand port. Yes it is the actual position. I do this in part by making the servo move just a little bit slower than it normal speed. Once the uC gives the command open or close hand; no other command has to be give. The chip does the rest. You can use the position data to give you an idea of how big the object is. You can use the pressure data to tell if the object is still in the hand or if it was droped. The chip will also let you move the servo at 4 speeds the last being the normal speed.
BTW, Are you aware the Propeller can easily control 28 servos (32 if you have a way of disconnecting them during bootup) with 1us resolution?
I'm really not looking to learn yet another M.C. family. I programmed the chip so that up to 5 chips can be wired to one serial port. So that would give me control of up to 40 servos. I know I should never say never but I am never going to use 40 servos on any project. For any project I have planned, I never even going to use 8 servos. I don't think a normal servo can sense a 1us change. Anyway, that why I did what I did.
Al
Wasn't aware Duane was interested but if he is, it would be better for him to do it as he is in the States. I'm half-way around the globe & the shipping charges might be more than the 5 chips, I think. But if no ones taking the offer, I'll be interested & you can hold on to that 5 chips & pay me some other day (maybe help send as payment to another person in the States on my behalf?). I'd figure, but I might be wrong, that this will be a few hours job? (less than 50 components, a few ICs, 2L board?)
As far as I know, Duane is NOT interested in doing the PCB layout design. He just wants to know a little bit about how it works.
Yes. I can send the chips to someone else in the US when you need me to. I don't do a login much but I read the General Forum & Robotics Forum. So you can tell me there to read my message.
There will be two IC, one will be 20 pins and the other 14 pins. If you don't count the male headers for the servos as a component; there will be about 20 components. BTW there is no rush on the layout design. You can do it between other project if you want.
Thanks,
Al
Sounds good. Then no problem, I'll take on this board layout. Things I'll need:
1. Part# for each component (to ensure I have the library, if not, I'll create the footprint). If it is a normal connector with no part#, then I'll need to know its pitch between its thru-holes & what diameter for the thru-hole. Since its for servo, I presume 3-pin or 4-pin std 2.54mm pitch?
2. Board dimensions (preferably in mm)
3. Layers, I reckon 2?
4. Board thickness? 1.6mm (to be stated in Gerber for fab house)
5. FR4?
And, sure, I'll just do this during my spare time between projects. (still have 1 job I'm still working on at the moment).
I left you a PM in your box.
Thanks,
Al
You can keep your 5 PICs but I'll look into this whenever I have some spare time ...
That's alright, I'll do it myself.
Al