Darathian
Resolved by Dunning-Kruger!
Since I know some of you have used the Sabertooth and Kangaroo I figured I would ask opinions.
I have decided on the Parralax Arlo base for my next robot chassis. I will use the caster's from parralax.
I will most likely be using the Sabertooth and kangaroo combination for motor controller/PID but I am not decided on this and open to suggestions.
I also find myself in a heated mental debate between the wheel/motor combination from parralax or the Zagros Rex motors and wheels combined with the Sabertooth/Kangaroo.
Item 1:
One of the key items for me is how well the encoders between the two different motor/wheel sets works with the Sabertooth and kangaroo.
Item 2:
The other item floating in my mind is the ground clearance between the two motor/wheel sets. It seems at least to me that the Zagros wheels would provide more ground clearing but since the base plate of the chassis provides stability to the base platform I am not really sure if using the Zagros motors are feasible.
Item 3:
Since I am going to build a body, arms and head on top of the base the torque and weight carrying ability is important.
Item 4:
I need to be able to control both the position and speed of the motors at the same time. For example example I should be able to have to robot move lets say 1 feet at a certain speed.
I know this is kind of an open ended questions but if anyone have used any of these wheel/motor combinations please provide your 2 cents as it relates to the items listed above.
I appreciate any comments or insights you guys can provide.
Hey Tony,
I haven't gotten the 4013's yet, so I don't have any specific version info yet on the version of the 4013 that I purchased. They are only around $0.30 each, so if I got slower ones, it's no big deal to replace.
In looking at the data sheets for these though, at 5v these run at about 5 mhz. At 15v these push the 16mhz range. I have also found some that say they need between 4v and 20v. In any event, I am still going to try this and try to come up with a solution outside of replacing the encoder. The reason for this is that finding the motors without the encoders attached seems to be a difficult thing. They are a specific version of Globe IM-15 motors. I can find them for about $200 each right now without the encoders. The encoders are a little over $40 each. Zagnos sells the motor with encoders for $130.00 each.
From an ease of install situation, it would be far easier to just put a module on the encoder that uses a flip flop.
If I were doing this one time, I think the solution would be to buy the other encoders and replace the ones on the back of the motors. For a larger scale solution, I think the flip flop is better and far easier if these flip flop modules were able to be mass produced. It's much easier to just plug a completed flip flop module into the encoder than to replace the encoders.
The HEF4013B has a typical max clock frequency of 14MHz at 5v although it should in reality be higher than this.
www.nxp.com/documents/data_sheet/HEF4013B.pdf
You got me too looking at changing the encoders themselves, but it seems a minefield (here in the UK) trying to find ones that are available with the right shaft size also they are expensive at over £30 each making it over 60 quid for the two required. You are right, in a one-off robot build that is not a problem, but in volume manufacture the humble 4013 looks like it will save valuable prime-cost. When I get back to working on the ALTAIR locomotion unit I will build the 4013 divider circuits into the actual lead that connects the encoder to the Roo and then heatshrink it all. I am pretty sure that the 4013 should work in this application, and there are also other (high speed) logic families that have D-type flip-flops all pin compatible. Best of luck with this and lets us know how you get on.
BTW Rafiki looks amazing, great job!
Tony
One question for you Tony. Would it matter much if the flip flop were at the motor end vs the roo end of the connection? You got me thinking. Is it better to have the flip flop circuit plugged into the roo or into the encoder directly? This is only an issue when using these motors with a differential drive system. I had thought about making a left and right side version that would connect to the encoder with wires going to the roo. Now I am thinking that a single module that plugged into the roo with both of these (left and right) flip flops on a single board would be better. It would reduce the chance of someone plugging the left module into the right encoder for example.
I will be using a breadboard to prove the concept so there would be wires going to both initially I guess. If the breadboard works then short of some interference caused by the motor or roo, I guess that it really wouldn't matter from a functioning perspective.
From a usability perspective (once I build this in a circuit board config), I will try to make the working prototype connect to the roo directly I think.
I will probably do two separate 4013 leads (left and right), I just think it will be neater. I always colour code all Molex type connections with coloured CD marker pens, so they dont get incorrectly plugged. From a (electrical) noise point of view it would probably be best to have the 4013 board as close to the encoder as possible, also put a decoupling capacitor (100nf) as close to the power in pins (14 and 7) of the 4013 on each of the two IC's.
Tony
Thank you sir. Your insight is always very helpful.
Would you see any reason to include a diode?
Here are my thoughts on this. If I am already building the board, I might as well put in pull up resistors for the signals that are recommended with the encoder. All of this in one nice package would be nice. Also, do you think that this circuit could be powered by the 5v feed from the encoder pins on the roo or should I power it from the 5v out on the back of the roo?
No need for a diode (you would only drop 0.7volts (or 0.3v for a Schottky) from the 5v supply. The 4013 is CMOS so it draws very very little current so can easily be powered from the 5v (feed line from the Roo) to the encoder. Yes the three 2K7 pull-up resistors will need to be added on the encoder side.
Tony