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View Poll Results: What is your favorite feature of the SD540?
Light Weight 25 20.33%
Low Cost 47 38.21%
Multi-Bank Option 31 25.20%
I do not like this product. 47 38.21%
Multiple Choice Poll. Voters: 123. You may not vote on this poll

 
 
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Unread 25-11-2015, 15:26
philso philso is offline
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Re: SD540 Motor Controller

Quote:
Originally Posted by aldaeron View Post
- Multi Bank Option (Sure we need a bank of controllers for the drive train, but sometimes they need to be placed creatively to get the rest of the bot to work. I can mount them touching each other just fine by myself without the need for the bank. Also there is no air gap between controllers. I like a small air gap, especially if these are the drive train motors that will producing a good deal of heat.)
It would be good if Mindsensors could provide temperature test data covering the 2-bank and 4-bank configurations with all inverters in the bank loaded the same way. Because the individual inverters are right next to each other and the heatsinks rely on convection cooling, the heat coming off one heatsink WILL cause the temperature on the adjacent heat sinks to be higher than if there were "ample space" around individual heatsinks. A simple test of this would be to monitor the heatsink temperature of all 4 heatsinks of a 4-bank controller where only one of the middle ones is loaded and the other 3 are not loaded. The two heatsinks on either side of the loaded inverter will be hotter than ambient.

Temperature test data with the controllers mounted in different orientations would also be helpful to the potential users.


Quote:
Originally Posted by aldaeron View Post
2) Robust screw terminals for a ring type connector or bare wire
Solid wire would be acceptable under the screw head but no one should be using solid wire on a robot. Stranded wire would be risky since it could slip out. Mindsensors can add a clamp plate under the screw head for just pennies to make this safe with bare, stranded wire.



Quote:
Originally Posted by aldaeron View Post
1) Single 16 pin male connector with no cable retention. It is very easy to plug the PWM into the limit switch pins or vice versa. Do I use a standard PWM connector (3x1) and two 2 pin limit switches connectors? Or do I make my own 16 pin custom connectors? How do these stay in during the season (please no more hot glue)? How do I keep the exposed male pins safe (especially from student hands when they are rooting around in the belly pan)? Also I am not sure why connectors are mounted parallel to the mounting face instead on normal to it (this will increase the part footprint quite a bit when it is used).

2) Brake/Coast & Cal under the mounting face. To me this is inexcusable. If I want to change/control the mode or re-cal a controller I have to demount these (by unscrewing them from the bottom - see #3)?! Why not use the spare 8 pins on the connector for these features?
Locating the 16-pin connector and the Brake/Coast & Cal DIP switch to the top surface would increase the footprint of the product. While they are at it, they may as well move the LED's to the top surface so they would not be obscured by the wiring.


Quote:
Originally Posted by aldaeron View Post
3) Lack of thru hole mounting. I can't zip tie these down to something temporarily. Grrrrr.
The blind, threaded mounting holes on the bottom may be a very bad idea. What happens when a screw that is too long is screwed in till it bottoms out and is continued to be driven in? Will it damage the circuit board? Will it cause a short circuit and possibly a fire? Will it push the heatsink off the top?

Making it mandatory to have access to the back side of the mounting surface severely restricts where these can be mounted and remain serviceable. The mounting holes will have to be drilled pretty accurately or nothing will line up. The low-resource teams who are likely to be attracted to this controller will likely find it hard to do this. Mounting ears that one can match-drill from the front side would have been much better.


Quote:
Originally Posted by aldaeron View Post
5) 3D printed case. Other plastic manufacturing methods would make more consistent parts for cheaper and with better properties (at the right manufacturing quantities).
If this product does gain wide acceptance, will Mindsensors be able to manufacture them fast enough? The build period for FRC is very short and not receiving their motor controllers in a timely manner would be (near) fatal for any team.


Mindsensors may want to consider dropping the switching frequency to half of what they are using now. It would cut the switching losses in the transistors in half and should reduce the heatsink temperatures very significantly. It is not clear what benefit the 32kHz switching frequency gives. It may also be beneficial to attach a fan like those used to cool the CPU's in a desktop computer. A modest amount of air flow will increase the heat removal capacity of the heatsink by several times.

As it is, the high heatsink temperatures would make me question the service life of the product. Any electrolytic capacitors used in the controller would live a very short life since they are typically rated for operation in an 85 degrees C environment with some available that are rated for 105 (but they are more expensive and probably physically larger). Mindsensors may also want to check the temperature rating of the plastic they are using for the casing since many are only rated for around 90 degrees C.
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