Need Help Building A RC Lawn Mower Using Basic Stamp

[rs14smith]

Hi,

Currently I have a parallax developer board (Boe Bot Kit), and I was trying to learn about micro a little and then try to build a RC lawn mower using the board if it is possible at all.

My RC lawn mower will have 2x 24VDC motors, so I need to build some type of circuit that can handle that much voltage as well.

I'm also new to remote controls using Radio Frequencies to control something, so I'm just looking for advice and support on how to implement this design.

My two motors will be at the back of the lawn mower, and both can either be going forward, backward, or I can live one at a stand by state while the other one moves to make the mower turn right/left.

 

[nickelflippr]

A Vex RC transmitter kit worked for me, it has the sticks for tank drive, or single stick control. Wouldn't pay more than $30 including shipping for **broken link removed**, although they seem more scarce than a couple of years ago. The receiver has the raw rf pulse train available for breakout, and ready for decoding by your Basic Stamp. Plenty of info on the net for these.

You could do it without the Basic Stamp if you wanted too, by using a compatible receiver module (Futaba?) and appropriate ESC's that would handle the 24V motor voltage, and amperage requirements.

 

[rs14smith]

A Vex RC transmitter kit worked for me, it has the sticks for tank drive, or single stick control. Wouldn't pay more than $30 including shipping for **broken link removed**, although they seem more scarce than a couple of years ago. The receiver has the raw rf pulse train available for breakout, and ready for decoding by your Basic Stamp. Plenty of info on the net for these.

You could do it without the Basic Stamp if you wanted too, by using a compatible receiver module (Futaba?) and appropriate ESC's that would handle the 24V motor voltage, and amperage requirements.

Which way do you think will be easier though, using Basic Stamp, or using the compatible receiver module...etc?

I'm better at programming than dealing with a lot of circuitry even though I'm still new to Basic Stamp I've had several program classes (C++ etc..). So yeah, just wondering what route you think I should take, as this will probably be the most complicated part for me to create.

 

[Vizier87]

a cheap PT2262/PT2272 with RF/IR modules chip is good enough actually. It handles the wireless control, and you'll just need to use a H-Bridge IC which handles the motors' power. If you have more details on the motors i.e what is the wattage and so on?

My RC lawn mower will have 2x 24VDC motors, so I need to build some type of circuit that can handle that much voltage as well.

...And since you need to isolate the electronics and motor supply, the electronics can be powered using even a 9V box battery.

 

[rs14smith]

a cheap PT2262/PT2272 with RF/IR modules chip is good enough actually. It handles the wireless control, and you'll just need to use a H-Bridge IC which handles the motors' power. If you have more details on the motors i.e what is the wattage and so on?

...And since you need to isolate the electronics and motor supply, the electronics can be powered using even a 9V box battery.

I think I made a small typo there, as I didn't notice I put 2x 24VDC lol, I meant 2x 12VDC hooked up in series to make 24v since my wheelchair motor is a 24VDC motor, HOWEVER, I decided I may just go with one 12v deep cycle battery as it turns fast enough for me.

So lets just say I'll go with a 12v DC battery.

Motor Info:
24VDC motor
420 Watt
10 Amp
4600 r.p.m.

All that info came from the sticker on the side of the motor as well.

So I was hoping I could find a H-Bridge chip that has all those mosfets built in as I'm still a bit rough building H-Bridges. Do you know where I could find one that could fit my needs in this case?

 

[nickelflippr]

Which way do you think will be easier though, using Basic Stamp, or using the compatible receiver module...etc?

I'm better at programming than dealing with a lot of circuitry even though I'm still new to Basic Stamp I've had several program classes (C++ etc..). So yeah, just wondering what route you think I should take, as this will probably be the most complicated part for me to create.

The easiest route is to go with the a 2-4 channel transmitter/receiver combo and the rc ESC's, but not familiar enough to help with gear selection. People over at rcgroups.com or other rc forum might be a better source.

On the other hand, it's not that hard to decode the Vex receiver signal, and you already have an appropriate h-bridge from the solar tracker project. Get a h-bridge driver to interface between the Stamp and the h-bridge, and you would be in business.

I strongly recommend using a commercial dual stick transmitter, if nothing else but for the ergonomic aspect of the controls, antenna, batteries etc. being all neatly packaged up. Not worth re-inventing that wheel. You can get Chinese tx/rx combo's for under $30.

I have a couple of 24V Invacare motors laying around, and just haven't got around to them.

 

[rs14smith]

On the other hand, it's not that hard to decode the Vex receiver signal, and you already have an appropriate h-bridge from the solar tracker project.

Haha, surprised you still remember that project, yeah, I was going to give that H-Bridge a try later today and see how well the motor performs, and then try to learn more about this RF stuff as that's what's gonna be a huge challenge for me figuring out how that all works.

 

[Vizier87]

actually it ain't all that complex, you'll see.

 

[rs14smith]

actually it ain't all that complex, you'll see.

Great, boosting up my confidence

 

[rs14smith]

Alright, so I took a look at my Solar Tracker circuit which does have the H-Bridge, but also has the comparator, so I thought why not just remove the photo transistors and run some connections from P0 and P1 from my Parallax Board of Education to the same spots the two photo transistors were and send some HIGH/LOW connections to P0/P1......and what do you know, it worked like a charm!

So it's cool now that I can control the direction of my wheelchair motor with my computer, however, I have been looking at that VEX Robotics....from eBay you linked me to, and was wondering if I would still need to buy the Parallax Transceiver and mount onto my Parallax Board as I don't see any other way it would be able to control my board remotely?

 

[nickelflippr]

Alright, so I took a look at my Solar Tracker circuit which does have the H-Bridge, but also has the comparator, so I thought why not just remove the photo transistors and run some connections from P0 and P1 from my Parallax Board of Education to the same spots the two photo transistors were and send some HIGH/LOW connections to P0/P1......and what do you know, it worked like a charm!

So it's cool now that I can control the direction of my wheelchair motor with my computer, however, I have been looking at that VEX Robotics....from eBay you linked me to, and was wondering if I would still need to buy the Parallax Transceiver and mount onto my Parallax Board as I don't see any other way it would be able to control my board remotely?

Good deal with the h-bridge, that's more than half the battle won!!!

Not sure what the Parallax transceiver is about? If you went with the Vex Transmitter add on kit, it comes with a receiver and matching crystal to communicate with the transmitter. The receiver would attach to your Parallax board for decoding. Lucky you, the attached pdf gives you all the details including schematic and code for the Stamp module. All that remains is to change the servo signals to a forward/off/backward commands for the motors.

I see some serious mower cookies being laid down in the yard.

 

[rs14smith]

Okay, so it seems I got a little ahead of myself or over confident, and fried like 2 MOSFETs a minute ago.

The first time around, I had a varable DC power supply, which has a max voltage of 15V and 2Amps hooked up to the circuit.

Now that does supply enough current to get my wheel moving (good to test things), but it's not nearly enough for the real deal, as I could stop the wheel from turning with my hand if I wanted to.

The second time around, I hooked up a 12VDC EverStart Lawn and Garden battery up to the circuit which has 275 Cranking Amps and 230 Cold Cranking Amps, and at first the circuit was doing fine, and the wheel was rotating fine. However, when I quickly switched the direction of the wheel, SPARKS WENT FLYING around my MOSFETS.

My guess is when it's changing directions (around the H-Bridge) a ton of current spikes or something before it stables back out? If so, what should I do to prevent this? My schematic is attached as well.

 

[Dragon Tamer]

Yes, that's exactly it. When ever a motor, or any electro-mechanical device, the current will spike. That's why with your solar tracker Q4 was getting so hot when you switched it back and forth so rapidly. In this case the current is a lot more than with that little DC motor for your solar tracker. Try attaching more MOSFETs in parallel with your current ones so they can handle the extreme current. If you're trying to use the solar tracker circuit (the one you posted) for controlling these remote lawn mower motors, you're going to tend to run into some problems.

 

[rs14smith]

Yes, that's exactly it. When ever a motor, or any electro-mechanical device, the current will spike. That's why with your solar tracker Q4 was getting so hot when you switched it back and forth so rapidly. In this case the current is a lot more than with that little DC motor for your solar tracker. Try attaching more MOSFETs in parallel with your current ones so they can handle the extreme current. If you're trying to use the solar tracker circuit (the one you posted) for controlling these remote lawn mower motors, you're going to tend to run into some problems.

Yeah I recall you built a similar circuit. Would yours probably perform okay for this project?

 

[Dragon Tamer]

Mine didn't use MOSFETs (me and FETs hate each other). I would use something like a high power transistor.

 

[rs14smith]

Hmm, would a High Power motor driver like this work out then: **broken link removed** ?

It's been quite tough to find some that support high current, however, I'm sure it's probably far cheaper to build it yourself if I could find a decent schematic

 

[nickelflippr]

Might browse some the mow-bots on the net to see what they are using. The OMSC project is a super heavy duty controller.

 

[rs14smith]

Might browse some the mow-bots on the net to see what they are using. The OMSC project is a super heavy duty controller.

Do you think this circuit here is a better built H-Bridge circuit: Free Schematic Diagram at www.circuitdiagram.net ?

I'll be using IRF3205 (NPN) for my bottom two FETs though instead of IRF3707 (NPN) which they have in the circuit if it indeed is a reliable H-Bridge...

 

[nickelflippr]

Do you think this circuit here is a better built H-Bridge circuit: Free Schematic Diagram at www.circuitdiagram.net ?

I'll be using IRF3205 (NPN) for my bottom two FETs though instead of IRF3707 (NPN) which they have in the circuit if it indeed is a reliable H-Bridge...

High power h-bridges seem to be a real challenge, and generally expensive to build for bullet proof design. I have no experience in that area. The suggestion to use the solar tracker circuit appears to have been a bad one . Adding some code to ramp up/down, braking, and a good size delay before reversing direction would be a big help.

Here is a low cost circuit that has some potential? I may someday try that out for my Invacare wheelchair motors. Would consider bumping the relays to 30A, and adding some high side over current protection to protect against a stall.

Here is an interesting project **broken link removed**.

 

[Dragon Tamer]

The lawnbot400 has a lot of potential. I would follow the example that they set on that website. The smart thing to do is to protect your high power devices with a fan to help dissipate heat. That's what I did in my power supply circuit.

The other thing they did in their design which was really cleaver, was they used a worm gear to drive the wheels. That way they could have a motor with a really low current rating and not over whelm it with torque. That is what I would suggest you do with your design.