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Robot Videos / Robot Costume Contest
« Last post by avgrant on Yesterday at 01:12:21 PM »
Hey guys! I know quite a few people on here have built their own robots, and just wanted to share our little competition with you if you are interested. We'd love to see some Society of Robots submissions!

Thanks, and let me know if you have any questions!
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by Tranq97 on Yesterday at 04:26:22 AM »
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by sdk32285 on October 21, 2014, 02:59:55 PM »
1. Just google "motor brake". Often when you order a motor you can get encoders, brakes, gears, etc.. from the same vendor.

2. For the most part you know the position of your motor from hall sensors or an encoder. And the rate you spin it can change when you start or stop the motor. When you issue a stop command instead of instantly stopping you send the intermediate commands from current speed to 0 based on how fast you want to decelerate. In an extreme case you can imagine commanding the motor to go backwards to reach a desired deceleration rate.

Based on how you are braking or if you have gravity forces on your motor you might also need a shunt regulator in your design.

3. There are a few reasons. The simplest can be to achieve a desired form factor. Another common reason is that certain gear boxes will have a max input speed, so you need another gear box to slow the shaft enough for the second gear box.

Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by Tranq97 on October 21, 2014, 12:52:18 PM »
I've just used the motor sizing calculator on SoR, one of the motors was 16.2 kW but that's just from estimated data.
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by Tranq97 on October 21, 2014, 10:16:58 AM »
Hi, thanks. This isn't for a hobby, I plan to start a business using a theory I have with computer architecture. But more to the point:
1. What types of motor brakes are there available?
2. I will have to build the motor driver myself (long story), the digital side of it isn't a problem, but I need to know what it's physically going to do to the motor (which I will also be building myself) in order to accelerate and decelerate at different rates.
3. I've seen a lot of designs where they increase torque and decrease RPM with many gears, rather than just one small one and one large one. Why is this?

Thanks. It's unbelievably hard to find someone on the internet willing to help.
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by sdk32285 on October 21, 2014, 09:50:30 AM »
Using gearing to get the high torque low RPM you need is the standard way of doing this. Most people do not make a custom motor for this (even though I know of several exceptions to this).

If you get a professional quality motor driver such as an Elmo or a Copley (I have a post on Copley drives that I am releasing in the next few days) you ca configure the acceleration and deceleration rates (it is just a parameter).

The nice thing wit using a bunch of gearing is that it will give you some resistance so there is a good chance you will not need any active braking to slow down. This should not be confused with a motor brake which you might need if you need to hold a position with the motor unpowered (or when stationary to conserve power). Note that motor brakes are typically only to be used when the motor is not in motion and not to slow down.

If you look on the main SOR site (or google it) you can find calculators for determining motor specs required.

Often harmonic drive gears are used for the compact size with good torque and low (or no) backdriving of the motor (which helps hold position).

A downside to professional hardware (motors, gears, controllers, etc..) is that they are often much more expensive than hobby level hardware. If you can find a hobby level digital motor drive it might be able to do the acceleration/deceleration stuff also.
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by Tranq97 on October 20, 2014, 03:35:51 PM »
Large motor, large motor... I'm not talking about one I possess, and I'm not sure how to judge it in kW. Let's just say the nominal dimensions are 150mm/150mm/250mm. That's probably as much as I can give you, sorry.

Now, this thing is going to go at high RPM and low torque, attached to a couple of gears to convert that to low RPM and high torque for the robot's arm. Before, I was trying to design a type of motor which could just run at high torque, low RPM. But, I found that that would hinder it's precision, accuracy and braking mechanisms. So, then I decided to use the gears with a high RPM motor. So, the braking on the arm will have to be virtually instant on the arm (big gear), so I don't know how quickly the motor (small gear) will have to stop to make that happen.

Basically, I'm building the motor and controller myself. The controller I have sorted. But electronic motors have always made me a little confused. With all this back EMF and whatnot. The things I need help with are as follows:
- Calculating motor requirements
- How to build a motor and account for those requirements
- What system can I use to change the acceleration rate?
- What system can I use to change the deceleration rate?
- What system can I use to hold a stationary motor in place?
- How to calculate gear sizes
- Are there any systems which can make the large gear more compact?
I'm 17, I've been interested in robotics for 4 years and it's all been textbooks, internet and college. I haven't had much practical experience at all, and about half of my education hasn't been learning, but rather developing ideas. As for the last point I made, basically I am worried that the large gear will be too big to fit in the robot's arm. So, are there any special gears which have the same effect as a big gear but a more compact? You seem like an expert on robotics, David, so I was wondering if you could give me a hand with these hurdles?
Mechanics and Construction / Re: Questions about robot actuators
« Last post by sdk32285 on October 19, 2014, 04:40:37 PM »
I am not positive why they are not used.

In most of my past projects we have used brushless DC motors with various types of gearing. I think one advantage to this approach is the ease of using your own gearing to modify speeds and torques.

I have used frameless motors before and they are very tricky to get right. You need to be very careful with the mechanical design and assembly to get the rated performance specs of the motor.
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by sdk32285 on October 19, 2014, 04:33:09 PM »

In many digital motor drives you can specify acceleration and deceleration rates.  After that a lot will depend on the type of gearing that you use and how much resistance that puts on your drive motor.

How much braking do you need? What do you consider a "large" motor?
Mechanics and Construction / how to make tiny pistons move
« Last post by amrosik on October 18, 2014, 12:37:18 PM »

I want to know which of the following methods would be best, to make tiny pistons (8mm diameter of the cylinder, max. 6mm diameter of the piston) move. Of course the piston should have a recoil spring. It is important that the system has a quick response time, about 5 Hz should be no problem.

Indirect methods:

1. Using pneumatics and pushing solenoids.
2. Using a pressure reservoir and magnetic valves.

Direct method:

3. using a self made pushing solenoid in that size, with a neodymium magnetic core.


1. A pushing solenoid is attached to a big cylinder with piston (isolated with a rolling membrane (diaphragm) or a bellow), and that is connected with a thin air hose to the tiny   
piston, again using rolling membranes or a bellow.
As the Solenoid is activated, the volume of the system is decreased, therefore the pressure increased, making the tiny piston push with a certain force. I need a force a 6 N.
I calculated that then the pressure should be about 22 Psi, and , given that the Solenoid has a stroke length of 1 centimeter and that the air hose has a inner diameter of 4mm and a length of 2 meters, we need a force of  about 300 Newton for the Solenoid, to create that pressure.
There is no Solenoid that could do that, in fact the best thing that I know creates 20 Newtons for that stroke length.
Can you do something about it, or is that method already checked off?

2. A pressure reservoir of big volume, holding air at about 22 psi is connected to a 3/2-way valve, which is connected with the tiny piston. Turing of the valve connects the piston with the reservoir, turning it of connects it with atmosphere.

Does that work? How to get those valves, working at these pressure levels? The should not be too expensive, because I need 40 of them.

3. I dont know how to wind the cupper wire with that tiny size restriction, to get 6 N out of it.

I will be grateful for any suggestion. Thank you in advance.
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