Super Slow Robot Recommendation -newbie

Robotics and electronics discussion Mechanical design and actuators
1

Good day to everybody :slight_smile:

I apologise in advance if this or similar post has been already answered but I wasn’t able to find it. Also, I am a complete beginner :open_mouth: and even I tried to read and understand some blogs I think still many things are not clear.

I would like to ask any experienced person about a recommendation. I would like to build a robot with a normal digital camera (Ricoh 250grams) on the top using .Net Gadgeteer (I am c# developer) which moves very slowly and smoothly, I will say how slow in a moment :slight_smile:

…This robot is not going on Mars :slight_smile: ha ha

I am looking for all parts I would need and found “Dagu Wild Thumper 4WD All-Terrain Chassis” which I really love as I could use it also out door :slight_smile:

Just to get lesson on this, if the wheels are 120mm in diameter (circumference=37.6cm?) and 75:1 steel gearboxes on the motors is used:

  1. what would be the theoretical maximum and minimum speed? Please, could the calculation be provided so I could learn/understand?
    1a) well the website says max speed is 3km/hour how did they calculated this speed?

  2. If I would like to move my robot with a speed
    a) 10meters/hour
    b) 10-20meters/hour
    c) 5-10meters/hour
    How could I achieve this task? If I am calculating right in case of a) I would need some motor with a speed of: 10 meters = 1000 cm / 37.6cm = 26.59 / 60 minutes = 0.44rpm? (2.77mm/second)

  3. Does Pololu sell such a slow motors which would be compatible with “Dagu Wild Thumper 4WD All-Terrain Chassis” or do I need a gear box to achieve this?

  4. I am just guessing, if I used .Net Gadgeteer I could also program that motor switches on/off every few seconds so I could move the robot super slowly but wouldn’t be movement jerky?

  5. Can the batteries last 1-3 hours moving this robot?

  6. To go to the next level :slight_smile: Can I get any nice Pan and Tilt platform/tower from Pololu I could use on the top of the chassis for my camera? I would like again slow motion movement maybe 360degrees/hour. Can you recommend such a platform or motors?

Really, really, thank you very much for your time on this, I might have more question later but these are kind of foundation I would like to understand.

Regards, Vaclav Elias.

2

Hello, Vaclav.

  1. The maximum speed depends on what voltage you drive the motor at. The motor’s RPM depends on the drive voltage and the load on the motor. You can get an upper bound by assuming you can rotate at the free-run RPM. The upper bound of the speed would be the free-run RPM * the wheel circumference. Of course the wheel and ground adds load, so you won’t be able to reach that speed. The minimum speed depends on how you control the motor. You can go almost arbitrarily slowly by having the motor off for long periods of time. If you want to go slowly more smoothly, you can try to add closed-loop control with motor current sense or encoders. Unfortunately, it is not easy to theoretically determine how slow or how smooth you can make it. 1a) Someone measured the speed.
  2. Your calculations here are correct.
  3. The slowest Dagu Wild Thumper configuration is the 75:1 gear ratio motors. It is not easy to change the motors from the ones that are installed. We sell compatible higher-gear ratio motors that would help you go more slowly.
  4. Yes, in general, you could use a microcontroller along with a motor driver/controller to only turn the motors on intermittently. Yes, it would be jerky.
  5. That depends on what batteries you use and how much power you draw from them.
  6. We do not sell any pan tilt products.

- Ryan

3

Thank you Ryan for your reply :slight_smile:

All clear but would like to elaborate my point 3). You mentioned that it is not easy to change the motors from ones that are installed. Isn’t it just a question to unscrew whatever is holding current 75:1 gear motors and replaced it with e.g. 499:1 gear motors? Or the motor holders are sealed and we cannot manipulate with those motors coz we could damage those holders or chassis? If I am right the dimension of motors is the same but 499:1 is a bit longer (4mm) would that be a problem?

Thank you for your help :slight_smile:

Regards, Vaso.

4

The motors are not screwed in, they are press-fit/clamped into a plastic housing and are kind of hard to dislodge. You will also have to do some rewiring, because the motors are wired through a hole in the pipe. Yes, some of the motors are a bit longer. The longer motors (including the ones with encoders) should still work, but they will stick out of the motor housing pipe.

- Ryan