Not in the context of FRC, but can a Rev Neo be run (by a Spark Max) at 24V without any ill effects? Anyone done it? If not, any recommendations on a similar or more poweful motor/esc combo that can do 24V?
Sure. Make sure you’re using current limiting, but it’ll be fine.
Some degree of caution is appropriate with what you are proposing.
The operating Voltage range is 5 to 24 Volts, with an absolute maximum of 30 Volts.
When it comes to the NEO, it is rated for 12 Volts. Recommend that you contact REV to discuss your idea. Operating the motor from a 24 Volts source will be capable of operating the NEO at twice it’s intended speed.
How are you creating the 24V source?
If two batteries in series, you will likely exceed 24 Volts.
Motors transfer energy from the electrical source to the mechanical load.
When starting a mechanism, the energy transfer is from the electrical source to the load. When stopping a mechanism, the energy transfer is from the load to the electrical source. When stopping, the DC supply bus will typically exceed it’s normal value.
FRC systems typically have ~17.5 Volts of margin (assuming 12.5 Volt battery). Your operating point will start with 6 Volts of margin.
Recommend that you exercise caution with this idea.
2 Likes
You copying my scooter idea?
This is a custom robot build, where I’d like a little more power. 24V source will be two 12V batteries in series, so, perhaps 26 Volts max. Can anyone confirm having run Neos at this voltage? @Greg_Needel will this work okay?
CIMs will run happily at nominal 24v. Grab some old Talon SRs, 883’s, or Jaguars for controls. I hear @troy_dietz has Jaguars to sell…
1 Like
As @p_h_argo correctly mentioned the maximum operating voltage is 24V for the SPARK MAX. In other words, continuous operation is not guaranteed above this voltage. For example, at higher voltages, some of the internal regulators are dissipating more heat. If the circumstances are right, this can cause a thermal shutdown. Please note that when running at 24V, you are also much closer to the 30V absolute maximum. Exceeding 30V, even momentarily, can permanently damage the SPARK MAX.
Regarding the NEO at 24V, this will technically work, but the NEO will be running at twice the rated speed which can have a significant impact on the lifespan of the motor.
1 Like
This is something I was not aware of. Have you actually done it? Any pictures or specs on what they were driving? How is the thermal performance at 24V ?
If put under significant load the will get burning you hot in about 3-5 minutes from a cold start. 1 CIM 8:1 reduction to an 8 inch wheel gets to ~20mph in about 300 feet running off 24V with no amp limiting or voltage control with a system mass of ~190lbs.
I calculate a CIM speed of 6700rpm at the end.
Assuming an average speed of 2/3 the end speed, this will take a little over 15s. Average acceleration is a bit under 2 ft/s².
I get a final kinetic energy of 2550 lb-ft. Assuming the time calculated above, that’s an average power of 166 lb-ft/s, or 0.22 Hp or 226W. That’s about 2/3 of max power for 12V or likely 1/6 max power for 24V.
I take it that you really did just have one drive CIM, likely on a center-mount wheel, or possibly with wheels on both side driven by the same CIM?
I think you’re still a little under-geared. Cut your own dinner-plate sprocket, since I think you’re already at the max vex size?
Any pics for the thread? I don’t think I remembered to take any at Madtown
@sanddrag , I remember reading on chief years ago that they were rated for 24v in their original trailer lift application but don’t have a sauce right now. I’ll see if I can get search to spit something out later if it’s a slow day at work…
This is the new one however. 1800W BLDC China motor and controller, geared 2.7:1 wheel free speed should be 1667 RPM on a 7.5 inch wheel(~37 mph). It has been clocked at 29 mph.
The one I mentioned was a single CIM with a 4:1 gear set and ~4:1 chain reduction run at 24V. I don’t have any real data about it other than it’s top speed, voltage, and that the furthest I drove it in one shot was 3 miles and it was beginning to toast the motor.
1 Like
Motor controllers get rated at twice the motor voltage because under hard deceleration the motor can actually dump back twice the voltage it is being drive at; a 12V motor can dump 24V back to the controller when jammed. Motor controllers design for this with protection circuitry that can dump the excess voltage. With the 30V maximum rating on the Spark Max, any motor over 15V has the potential to damage the Spark Max. If you don’t have rapid deceleration under 100% of your operating conditions (especially fault conditions), you might be able to run a higher voltage motor. Otherwise you need to add additional protection on the outputs of the Spark Max and this isn’t trivial.
2 Likes
I don’t think this is accurate - otherwise, a lot of speed controllers used in FRC that are rated for a max of 12-15V would routinely be damaged by FRC teams.
Correct. There is usually a 2:1 ratio between ‘rated for’ voltage and ‘absolute maximum’ voltage. Read your data sheet carefully.
The 12-15V rating would the the Nominal Operating Voltage. As @JohnD stated, the manufacturer of the motor controller should be giving an Absolute Maximum Voltage rating that should be about double the Nominal Operating Voltage rating.
The Absolute Maximum Voltage rating would be based on the Absolute Maximum Voltage rating of the devices used in the motor controller. The Absolute Maximum Voltage rating of the controller should be lower than the Absolute Maximum Voltage rating of the devices to allow some margin. The amount of margin for a particular controller design is dependent on the priorities of the designer and are not easily known by the user.
Thus, running the motor controllers much above half of their Absolute Maximum Voltage rating is going to be risky and the results observed in one application with one particular motor controller will not be applicable to a different motor controller or application.
This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.