Hi,
Attached is a photo of my mowbot.
I’m using it to cut the grass in my ditches as they are really steep and dangerous to physically do. The mowbot works great as I did my inaugural cut today. The issue that I noticed is because I’m cutting on a grade and using the motors to counteract the effects of gravity by the time I completed one of my ditches the motors were hot to the touch. I’m looking for suggestions on a cooling system so I don’t burn them out. I’m thinking of putting 24VDC cooling fans in front of each motor possibly tied to a thermal sensor so they’re not running all of the time but I’m concerned about battery usage as I want to keep as much battery capacity for the motors themselves as I have about 300’ of ditches to cut and I don’t want it to be a 4 day job because I need to keep stopping to recharge the batteries.
Any suggestions would be greatly appreciated.
Before you add cooling, you might instead change the cutting method - don’t go up and down the slope, but instead go along it, so the motors are not working against gravity. This will also conserve battery power.
If the motors still get too hot, they might be under-spec’d (they look pretty large… NPC perhaps, but can’t see gearing).
Active cooling - fan. Passive cooling - a bunch of heatsinks with thermal paste.
Be sure to run the motors at their nominal voltage to get max. efficiency.
Hi CBenson.
That is running along the slope and not up and down. There’s a ditch liner installed in the bottom of the ditch which precludes me from being able to run in and out. The issue is my ditches are about a 3:1 slope meaning for every 3 feet of horizontal run there’s 1 foot of vertical drop this equates to about a 18 degree slope. In order to stop the mowbot from trying to dive into the bottom of the ditch I have to counter steer it which is where the constant loading of the motors comes in.
The motors are M1HA/B motors off of a Jet 3 Ultra mobility chair and have a 300lbs capacity. I believe they are about 40 amps per under load. That’s all the information I can get from them.
Yikes - easy to see why the motors are toasty. Note that to correct, you’re likely having to run the rear drive motor which is further down the slope more, which also creates a torque on the system because the front idler wheels are so far away - it’s fighting the weight at a distance. Although not an easy fix at all, installing the drive motors close to the front wheels (perhaps on the sides of the mower section itself) should help significantly with turning since it minimizes the torque effect.
Forced air over custom heat sinks might help, and liquid cooling might entail quite a design challenge. Running them at a 25% duty cycle keeps them cooler, but as you said, it takes a lot longer.
Thanks CBenson,
You’re right that moving the drive wheels to a point closer to the center would provide greater stability but it would also make it impossible to get close to objects to cut the grass properly. Right now the idea is to keep the wheels inside of the diameter of the mower blade in order to reduce trimming.
I’ll have to experiment with some cooling techniques to see if it will help. The motors aren’t smoking but I know that excessive heat will shorten their lives.
Before you start testing, you might create / buy a cheap temperature sensor - you’d place the sensor at the “hottest” part of the motor case and see the actual difference.
That’s a good idea. Thanks.
