I think that stronger servos that can rotate farther than the current ones would be really helpful for joints and arms. Any thoughts?
A HS motor would be stronger than a servo, although i do have to question why one would use servos on arms as they have plastic internal gears, making them quite weak. The amount the motor rotates could then be limited by a potentiometer and some programming from anywhere between 0 to 250 degrees.
Servos in my opinion have limited use, in all our years our team only has had about 3 mechanisms that used them.
Servos powerfull enough for arms without any external gear reduction would be expensive, large, and the Cortex wouldn’t be able to handle that much power.
As for having continuos rotation servos, that would be similar to a 393 with integrated shaft encoder.
A 393 with a potentiometer is also essentially a servo motor as well, however you can gear it up as much as you’d like unlike a servo with a set gear ratio.
Although a servo motor can be very handy if it were as strong as a 393 geared down and still as small as it is now, and with metal gears so no clutches will be needed anymorem but for vex to make this let alone finding one in a hobby shop is not going to happen.
Yeah, i see what you both mean. But I like the metal servo gears idea. that would be useful.(cough-review-board-look-at-this-cough)
You would have to prove why it would be useful, as both thedarry and Stanley have made good points as to why there doesn’t need to be a HS servo.
i just wanted an arm bot…
nah. It was just an idea.
Dang it. I wasted a thread.
I think alternative internal motor gearing is what you want. If we could have 30 or 50 rpm gears, building lifts would be much much easier. I believe people mentioned this in the discussion thread of turbo gears.
Ex: building a rotational scissor slower that 1:7 will require external gearing and shafts that will potentially be twisted, for teams that do not have or would not use high strength shafts.
A servo is just a motor with feedback.
A 393 with potentiometer feedback into a well tuned PID closed loop control system… is a servo.
This sounds like a good idea for the VEX CAD Engineering Online Challenge!
We used quarter scale servos on our Block Party FTC bots. Very handy and best of all keep their positions between autonomous and driver control modes. You can buy metal gear servos too.
This season we’re permitted to use any servos provided the sum of rated stall current for all servos connected to a single servo controller doesn’t exceed 5A. So technically larger than quarter scale servos are now permitted (here’s your Super Servo!)
As others have already mentioned 393 + feedback = servo. Although 100rpm is a pretty fast “servo”.
Check out http://servocity.com/
It’s all relative, the motors I’m currently working with (day job) used in a servo application have an output shaft speed of 2200rpm, admittedly there is further gear reduction in the form of a ball screw, but I can control that to within 2 degrees (1 encoder count, however, the current encoder is low resolution, accuracy should improve when I get final parts).
The only problem with low rpm internal gears in a 393 motor case is that they are too weak. Turbo gears may have a higher rpm output, but they are actually less likely to shear or break a tooth than 160rpm and lower gear sets. This is because with a greater gear reduction the smaller the driving gear of each compound gearset and is easier to shear. In addition higher amounts of rotational torque also creates more force on the gear teeth, particularily to shock loads because it becomes harder to backdrive them.
This is why I think that high torque gear sets with output RPM lower than 100 won’t be made by vex, that is for the 393 motor case. If there were a different motor design, that did not use a motor that drew more current but instead just a greater gear reduction using a planetary gearset(like lego powerfunctions) or something very efficient at achieving a high gear ratio in a compact space I could see 50 or 10 rpm motors coming out, that would make things so much easier.
On another note it does away some of the challenge to building a robot by not having to build well designed gear boxes and allocating space for them so its half and half.
You know what I mean In the context of high school robotics programs “servo” akin to a small black box with a shaft sticking out.
I used to work with 0.5MW vector controlled 3 phase motors, which technically could be called servos depending on the application
I actually wish we had a decent servo as well, there’s plenty of applications where having everything self contained would be helpful.