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Dagu Wild Thumper

I am thinking about ways to add encoders. What is the shaft diameter of the motors and the diameter of the motors? A picture of the back of the motor or a link to a data sheet would be nice.

John Abshier

Hello, John.

I don’t think there is an easy way to add encoders to the Wild Thumper. The plastic brackets encase the motors and prevent easy access, and the motor shaft does not protrude from the back of the motor. We don’t have a datasheet for the motor, but we will be putting up a picture of the motor soon. The motor diameter is approximately 24 mm and the diameter of the gearbox output shaft is 4 mm.

Also, using encoders on the Wild Thumper is complicated by having six motors. When driving over uneven terrain, it’s very likely that various motors will lose contact with the ground and spin freely, which would make your encoder feedback unreliable.

- Ben

I’ve got another question about the Dagu Wild Thumper: The videos have a background musical track, and it’s hard to tell if there’s any foreground sound in there. I’ve got a possible application for one of these, but one of the requirements is for the whole thing to be as quiet as humanly possible. Can you post anything on the noise level the gear motors generate when the Dagu is in motion? In particular I’m looking at the 75:1 model. Low speed, high torque.

Just in case the motors are too loud, any idea how hard it would be to add some insulation? I could see sticking a neoprene or soft urethane rubber sleeve over the cylindrical part that’s parallel to the wheel’s axis. But the pivot end looks like it’d be tough to add sound insulation to.

It also looks like the chassis is made for tinkering, so it might be possible to add blanketing insulation on the inside, and add some side plates to wrap it around the motors. Let me know if I’m barking up the wrong tree on this.

As far as current draw goes, do you have a figure for how it would do on loose dry sand with a TReX driving the motors?

Thanks,

Tom

Hi Tom.

Just out of curiosity, can you tell us more about the application you want to use it for?

I think the noise level from the Wild Thumper is pretty much what you would expect from an RC car that size. I don’t recall thinking that it was very loud when we ran it, but I also don’t remember being amazed at how quiet it was. Unfortunately, our sample unit isn’t in a state where I can easily run it at the moment. You can help keep the noise down by using a controller with an ultrasonic PWM. The TReX is capable of a PWM frequency of 20 kHz (I believe this is the default setting).

You might be able to add some insulation, but I don’t really have any particular advice I can give you about this.

Similarly, I can’t really say much about what the current draw would be on sand. I think you’d need to make an educated guess that extrapolates from the no-load current of approximately 400 mA per motor at 7.2 V. I don’t think it would be very close to stall, especially if you use the higher gear ratio model.

If you do get one and try it out, we’d love to hear more about your experience with it.

- Ben

I’m looking at using it as a platform for a remotely operated camera. (Hey, seems to be a running theme with me.) The catch with this one is that it’d be used to approach wildlife. A good rule of thumb when photographing wildlife is not to do anything that will alert the animal to your presence. Basically, if they react to your presence at all, you’re already either too close, too loud, or moving too fast. Ideally you want them to have no reaction whatsoever.

I just finished starting one vibration damping project at work, and I’m about to start another one for a different project at home. So I’ve got some ideas rattling around already for how to minimize whatever noise is already coming out of the gear motors. I’ve got an RC car at home I can test some of this on. And yeah, by all means if this pans out and I wind up building this thing off the Dagu, I’ll share my experiences.

Thanks, Ben.

Tom

Sounds interesting. Are you targeting any wildlife in particular?

I have added a couple of pictures of the motor to the Wild Thumper picture gallery. They don’t show the back side of the motor, but it it is just a solid metal plate with no access to the motor shaft.

- Ben

Hey, thanks for the additional pictures. It looks like this project is heating up again, so I’ve got some more questions to run by you:

The picture of the 4WD Thumper with the two simple high powered motor controllers look like each side of the 4WD chassis is wired into one of the two controllers. Put another way, each controller is driving two motors. I’m still looking at the 6WD chassis for this application. The 6WD chassis page says the motors draw 6.6A at stall. If all six motors are stalled (heaven forbid), that’s 19.8A per motor controller, if wired this way. This points toward using a pair of the 18v25 controllers. Did I read this right? And would this be the preferred configuration rather than running with six 18v7 controllers? (I like the idea of fewer controllers, just from the cost standpoint.)

This would be an entirely RC application, no smarts in the thing at all. The idea would be to use a 6Ch radio with one joystick controlling the wheels, the second joystick controlling a pan/tilt camera mount, and one of the two remaining channels operating the shutter on the camera.

Thanks,

Tom

P.S. I’m glad this one is coming back to life. That 6WD chassis looks NICE.

I think using a single motor controller per motor would be overkill and a huge pain to control. Two 18v25 simple motor controllers should totally cover it and will run the coolest, though I think you can get by with two 18v15 controllers. It’s very unlikely that all three motors on a side will stall at once, and if they do, manual control means you can stop trying to drive the chassis, and if you somehow don’t notice, the board’s thermal protection should eventually kick in to protect the driver.

I’d love to hear how your project turns out if you get it up and running! Please ask if you have any further questions, and please let me know if you have any feedback about our new Simple Motor Controllers.

- Ben

Thanks again for your help, Ben. It looks like this project is going to happen soon.

The plan is to go with the 6WD Dagu Wild Thumper, two 18v25 controllers, a single 7.2V NiMH battery for the moment, and an RC Tx/Rx for control. The payload is a Servo City SPT400 and SPG400, likely sunk into the top plate of the Wild Thumper as far as I can to lower the CG, with a camera on top. I believe I have all the weights well inside the limits. The running surface will be dirt and sand, for the most part, so it should play nicely with the tank-style steering on the Wild Thumper.

If any of that raised any red flags, let me know. I’ll happily post details of the build as it goes.

Thanks again!

Tom

No red flags here. I look forward to hearing how it goes!

- Ben

One more question (hey, I’m full of 'em!): This thing is going to be used on a beach, so there’s a good chance of getting wet sand on it. More important, there’s a good chance of getting saltwater on it. It wouldn’t be driven in salt water, but the chances of splashes catching it are pretty high.

I’d like to package all the electronics in a waterproof box. “Waterproof” can also mean “really bad for cooling electronics”. Is it worth building an aluminum heat sink into the waterproof enclosure so I can tie that back to the chassis of the Dagu? I’m thinking of machining a block of aluminum to fit into a hole cut into the enclosure. The block would be epoxied in place with high temperature epoxy. Mounting holes for the 18v25 motor controllers would be drilled and tapped into the block, and they’d be mounted either with heat sink grease (not my favorite) or with heat sink foam (better). Am I going overkill here? Or would it be better to just stick them in the box and check for overheating issues first?

Thanks,

Tom

P.S. I’m more or less considering the drive motors consumables in this case. I don’t think I can weather seal them, and they can be replaced individually in case of water contamination. But the electronics should be sealed.

I suspect the heat sink might be overkill, but I can’t say for sure. In open air at room temperature, the 18v25 can conservatively do a continuous 25 A, and I think you will be well under this, so I expect the drivers to stay relatively cool. My advice would be to try it out in an enclosure first without a heat sink and see what the temperature does for varying loads on the motors (it should be easy to monitor the using the Simple Motor Control Center).

I’m very interested to hear how this chassis and the Simple Motor Controllers perform under these conditions, so please keep us updated on how things go!

- Ben

All the bits are here, and I started the build yesterday. The Wild Thumper went together FAST. I like that platform a LOT. Once I’m done with this build I need to find another reason to build a robot based on it. It’s fun to work with.

I haven’t put the electronics together yet. My plan is to mount everything to a backboard for testing, then mount it all permanently in an enclosure once everything is sorted out. Jury’s still out on the choice of enclosure.

I had a question about populating the Simple Motor Controllers: They’re only ever going to be used in RC mode, so I was only going to populate those headers. As for the power and motor out connectors, the controllers came with screw terminals. Do you think it would be ok to use these at this current draw? Or would it be better to directly solder wires into the holes?

Pictures to come…

Thanks,

Tom

I’m glad to hear your initial experience with the chassis is so positive. The included screw terminals are convenient for making quick, temporary connections, but they are only rated for 15 A, so you will potentially be limiting the, well, potential of the controller if you use them. It seems unlikely that you will ever stall all three motors on the same side of the Wild Thumper simultaneously, so you probably won’t exceed 15 A for any prolonged period of time in this application (you might briefly exceed 20 A if you floor it from rest or abruptly change direction, though you could use the SMC’s built-in acceleration limiting to help prevent such spikes). I think the terminal blocks would be okay for your application, but if you’re at all worried about it, you should just directly solder the wires to the controller.

- Ben

I got everything packaged and running yesterday. (Yes, I’m very very slow on this build. Unfortunately I haven’t had a lot of time to dedicate to it.) I have to say, I’m in love with your Simple Motor Controllers. They’re dead-nuts easy to set up, and the channel mixing was a snap. I had some odd behavior early on: one side of the robot would stop moving if I really goosed the speed. Plugging the SMCs into a computer made troubleshooting extremely easy. One board was racking up error counts, and by looking at the temperatures on the two boards I could see something was seriously screwy. Turns out when I populated the power cables, I got a really tiny solder blob connecting the supply ground to one of the motor outputs. Cleaning that up fixed the problem. That would’ve been a bear to troubleshoot, otherwise. User friendliness on these gets a +++ in my book.

And you’re right, Ben, about how cool these things run. Even putting it through its paces they never really get warm. I’m not worried about how this will perform in the field.

I’m still trying to get the Servo City pan/tilt head happy, but it’s mounted to the Dagu and everything appears to be working ok. There’s a jitter in the servos that seems to leak over to the SMCs, but when it’s just the Dagu and SMCs running on their own this thing is smooth as smooth can be.

Thanks again for all your input!

Tom

Thanks for the feedback, Tom. I’m glad to hear your project is under way, and I’m really happy that your experience with our SMCs has been so positive!

- Ben

Tom:

I NEED to build one of these 6WD Wild Thumpers. So cool!..
Are you using any kind of receiver besides the TReX dual motor controller? Looks and sounds pretty straight forward as far as the electronics go running only RC control. Could you post or send pictures of your installation? Anything you can send would be useful. So many uses for this platform… I’m thinking bigger tires so it can run upside down.

I would suggest you disassemble the chassis and either paint it or get it anodized to resist the salt corrosion. Salt water loves bare aluminum.

Not sure how we can communicate, not sure if it’s safe to post an email address here and I didn’t see the pictures on the forum you said you were sending so maybe posting pictures is not allowed?.
Thanks
Neil

I’ll try this again. I re-read the thread and noticed you are using two 18V25 controllers. So the question is are you using any kind of RC receiver besides the two 18V25 controllers? Sorry for the brain fade.
Neil

Hello, Neil,

None of our motor controllers have RC receivers built in, so the ones that support RC control require you to connect your own receiver to them. For our Simple Motor Controllers, you can find a detailed explanation of how to do this in the user’s guide.

By the way, if you would rather not post your email address publicly, you can send it to someone in a private message; just click the “PM” button under their name to the right of one of their posts. You are also welcome to add pictures as attachments to your posts.

- Kevin

Sorry for not jumping in on this. I had a family emergency come up that took me out of commission for a while.

Ben is right: I’m using a conventional RC receiver to talk to the two motor controllers. But this is where the fun starts. Ben, I’m hoping you can shed some light on this:

Here’s the setup for the drive train:
Dagu Wild Thumper 6WD rolling chassis, otherwise unmodified
Two 18v25 Simple Motor Controllers, set up to do channel mixing, each driving half the motors on the Dagu
Hitec Laser 6 75MHz RC radio system
Two 7.2V NiMH batteries wired in parallel, directly powering the 18v25 controllers
5V 2.5A regulator, also powered by the NiMH battery pack, providing power to the radio (the reason for this in a sec)

Here’s the rest of the setup, which can be installed or removed as needed:
Servo City pan/tilt head using two HS-7985MG digital servos, driven by the RC radio
Digital camera mounted to the pan/tilt head
Hahnel Inspire 2.4GHz camera control / video feedback system

Now for the problem(s):

The first is that the Servo City pan/tilt unit is not designed to be counterbalanced, so the weight of the camera is basically hanging out in space at some tilt angles. This puts load on the servo, which winds up jittering. The jitter is unacceptably large for photography, so I’m looking into a solution for this.

The second is that when I did a range test on this, with or without the whole pan/tilt head assembly, it failed beyond about twenty feet. The motor controllers appeared to enter an error state (I have not verified this through the USB interface), which then clears several seconds later. The further away I get with the transmitter, the worse it gets.

I tried putting a different radio on the system, a 2.4GHz system I use for a different photography project. It worked like a charm. Gobs of range, super clean steering, even good control of the pan/tilt head at several hundred feet. Perfect! Except that the 2.4GHz radio system interferes with the 2.4GHz video system.

The use of the Hahnel Inspire is a design requirement, so I can’t just swap it out for a 900MHz system. I need to make this work with the Hahnel Inspire handling the camera control and video feedback.

I’m guessing there’s some sort of radio interference between the 75MHz system and the drive system. I haven’t opened up the Dagu drive units to see if they have any filtering across the motor leads. (Ben, if you have an easy answer to this one I’d prefer not to have to open the thing up just to find out.) Other than that, is there anything I can do that would get rid of the radio interference that’s killing my range on the 75MHz radio?

I still haven’t figured out to do about the pan/tilt head jittering on the 75MHz radio when it’s under load. That’s my project for the day. It doesn’t jitter nearly as bad on the 2.4GHz radio, so I have to think it’s a problem with the radio rather than the servos. But I don’t have anything to back that up.

Thanks,

Tom