Low VIN error

Support Motor controllers/drivers and motors
1

Hi,

When I set both my SMC’s to full power from zero power I get a low VIN error. Is this a battery issue in combination with the servo’s or can I configure something? How can I solve this problem?

Roel

2

Hello.

It’s hard to give you much advice with the limited amount of information you have provided so far. For example, what specific product are you using, what is your power source, and what are the specs for your motor? You use the term “servo”, which implies some kind of feedback is in play. Is this the case or are you just trying to drive some DC motors?

I suspect your batteries are either bad or not appropriate for your application and the voltage is dropping below the low-VIN threshold when your motors draw a lot of current (as happens when they stall, change directions, or start from rest). Assuming “SMC” stands for Simple Motor Controller, there are several ways you can reconfigure the controller to deal with this:

  1. Add acceleration limiting so the motor speed ramps up more gradually and the current draw stays lower.
  2. Lower the low VIN shutoff threshold (see documentation for the Advanced tab of the Simple Motor Control Center).
  3. Increase the low VIN timeout (also under the Advanced tab).

Options 2 and 3 could just mask a real problem and could lead to trouble down the road if the voltage drops far enough to brown-out the controller. I suggest you try to understand why the voltage is dropping and take steps to prevent that (get a higher capacity and/or higher voltage battery, limit motor acceleration, add more power capacitance, etc).

- Ben

3

Hi Ben,

Thanks for your answer and sorry for not being clear.

The SMC stands for Simple Motor Controller 18v15. I like to drive 6 DC motors on the Wild Thumper. For 3 DC motors I got one 18v15.

I think the problem is indeed the battery. I got the problem also with another power supply but at a higher difference (end speed - start speed). I will not modify the things in point 2 and 3 cause it can brown out the controller. But please provide me what information about brown out because I don’t know what it is.

Thanks for helping me out here!

Roel

4

A “brown-out” is what happens when the input voltage falls below the minimum voltage required for a microcontroller to operate. If this happens to the microcontroller on the Simple Motor Controller, it will reset. This won’t harm the board, but is probably not desirable for your application. What are you currently using as your power source (type of battery and voltage)?

The motors on the Wild Thumper draw a lot of current. As you draw current from a battery, the voltage will drop, especially if you try to draw more than the battery can comfortably supply. For the Wild Thumper, I suggest you use a six-cell NiMH battery pack with C or sub-C cells, such as this. The higher the capacity, the more current they can typically deliver without the the output voltage dropping significantly. You could also use two LiPo cells, but LiPo batteries aren’t as easy to use (they can blow up if you don’t charge them properly, and they die permanently if you over-discharge them), so make sure you know what you’re doing if you use them.

I still recommend you enable acceleration limiting on the Simple Motor Controller, and if you use LiPo batteries, you should set the low-VIN shutoff so that the controller shuts down before the batteries get over-discharged.

- Ben

5

Hi Ben,

I am using a battery with low mAh, I am going to buy better ones.

Works max acceleration like this:

Current speed 1600
Going to be speed 3200
Max acceleration 800
Going to be speed will be 2400

Please let me know!

Roel

6

Pretty much. The acceleration value is added to your current speed every update period. By default, the update period is 1 ms. So if your acceleration is set to 10 and your update period is 1 ms, it will take 3200/10=320 ms to go from a speed of 0 to a speed of 3200. You can see the effect for yourself by playing around with the values using the Simple Motor Control Center (you don’t even need to have a motor connected, you can just look at the controller variables in the status tab as you drag the slider bar around).

- Ben