This is a copy of an email sent to support a few hours ago concerning motor reliability. The videos are not attached to this post… not sure if it is even possible to attach a video.
I order six pairs of motors to use on an experimental spider robot. One pair to replace the very basic and weaker motor that came with the spider kits.
I then tested one of each motor for low load characteristics driving the spider leg gear box. See video. The robot is placed on it’s back so the legs are free of more resistance.
The motors were tested at three voltages, minimum to get the legs to move and keep moving, at 3 Volts, and 6 Volts. I recorded the minimum and maximum currents during operation. Thereby concluding the RM2 being a good choice. The video is showing a range just for keeping records.
I then installed the RM2 motors and tested out performance. The robot walked way too fast at 80% PWM Duty Cycle with 70-1 gear ratio (very rough estimate). So I redesigned the side gear box to reduce the speed by 50%. Which happens to be the maximum reduction in the space provided. I think it will be too slow now, not sure yet.
Yesterday after installing the new gear boxes and testing them out one motor stopped moving in only one direction. With the motor removed and connected to the DC power supply the motor works only in one direction unless I twist it by hand. It also is very slow and the current being drawn about 1 amp and is erratic.
The second video is with the 70 to 1 gear box using RM2 Motors at 40% duty cycle. Note the robot walks forward and backwards.
So my questions
Are these motors designed to work in both directions? I assume yes is the answer.
The motors work in both directions, but it is not abnormal for them to fail after short periods of use. As we describe on the product page, these motors draw a ton of power and have relatively short lifetimes, especially at high voltages. In our testing, we found that these motors can only run continuously at 6 V with no load for about five hours before failing. Operating the motor under load at full power could reduce the motor’s lifetime significantly further. In case it helps, you can see some lifetime testing results for similar motors here.
BTW… the cost is not the issue. It is the time spent designing this motor in only to discover it wont meet the need.
After reading the 130 sized motor report and then re-reading the RM2 motor description it all adds up to a fully informed understanding. This could have been made easy by adding a lifetime expectancy in the motor comparison chart.
These motors are not actually designed to run at voltages greater than 3 Volts for any length of time. And if under load the lifetime is greatly reduced. Basically they are designed for short time operation then discard. I may have to buy a bunch of them to continue the experiments this robot was built for.
Conclusion:
The RM2 description is dishonest by omission. “A hint concerning lifetime is not honesty”
A company of your stature should have included a column in the chart to indicated the actual lifetime of 1.x hours at 7.2 Volts. What would it be for 9 Volts, less than an hour most likely.
Please add expected life time range to the chart so future customers will understand what they are getting. While doing that maybe consider adding clarity to all motor descriptions that are advertised at greater than 3 Volts but will burn out in a short time.
I understand your frustration or disappointment in the motors not having the lifetime you expected, but talking about “dishonesty by omission” is not appropriate when the product has a short description and we say right there that it has a notably short lifetime at higher voltages. This is a branded product we are reselling, and we do not have lifetime data beyond what we already include on the product page. Nevertheless, we have made the lifetime warning more prominent on the product page.
